Fabric based strain and temperature sensors

Abstract

Fabric-based sensors having at least a first electrode and second electrode printed with particle free conductive metal inks and having a coating electrically connecting the electrodes. When a strain sensor is designed, the coating includes a conductive elastomer, wherein the electrical resistance of the strain sensor increases as applied strain increases. When a temperature sensor is designed, the coating includes a temperature dependent resistive coating, wherein the electrical resistance of the temperature sensor decreases as applied strain increases. Textiles having combinations of strain and temperature sensors may be designed for medical, athletic, and industrial uses, among others.

Description

FABRIC BASED STRAIN AND TEMPERATURE SENSORSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U.S.C. § 119(e) of prior U.S. Provisional Application Serial No. 63 / 459,447, filed April 14, 2023, titled “Compression Garments Comprising Strain and Temperature Sensors,” U.S. Provisional Application Serial No. 63 / 459,401, filed April 14, 2023, titled “Fabric Based Temperature Sensing Device,” and U.S. Provisional Application Serial No. 63 / 459,393, filed April 14, 2023, titled “Fabric Based Strain Sensing Device,” the entire contents of which are incorporated herein.TECHNICAL FIELD

[0002] This invention pertains generally to textiles and e-textiles having conductive patterns printed thereon useful as strain and temperature sensing devices, and combinations thereof.BACKGROUND

[0003] Printed electronics is one of the fastest growing technologies in the world, providing integration of complex electronic functionality into a wide range of products. For example, the current interest in flexible electronics such as electronic textiles or “e-textiles” has led to the development of a wide range of newly designed electronic elements and devices. Such devices are typically formed using conductive yams, such as metal composite embroidery yams, or knitted sensing fabrics having copper, nickel, and tungsten wire elements, such as textile-wrapped, enameled wire. E-textiles have also been formed using webs of continuous core-shell nanofibers having a conductive shell that can be attached to or embedded in a variety of objects for directional monitoring of static or dynamic changes in mechanical deformation and pressure.

[0004] While certain of these solutions provide flexible electronic elements, each describes the use of conductive strands of material that are woven to form the conductive element in the flexible substrate and thus may require significant retooling of the manufacturing process to form the devices. Conductive inks comprising particles or metal flakes have also been used, but these perform poorly when the flexible substrate undergoes normal stresses, such as bending and stretching. Accordingly, there is still need in the art for flexible electronic elements that are integral with the textile and methods of forming those elements. SUMMARY

[0005] Described herein are strain sensors that may be incorporated into flexible textiles, where the electrical resistance of the sensor increases as applied strain increases, e.g., stretch of the textile. The strain sensors may comprise at least one sensor trace printed using a conductive elastomeric ink, and first and second electrodes printed using molecular inks and forming electrical contacts with the sensor trace. Strain sensing arrays are also disclosed, wherein a first array of spaced apart strain sensors is positioned orthogonal to a second array of spaced apart strain sensors.

[0006] The present disclosure further provides temperature sensors that may be incorporated into a flexible textile. The temperature sensors may comprise at least a first electrode spaced apart from a second electrode, wherein both the first and second electrodes are printed using a molecular ink of the presentdisclosure. A temperature dependent resistive coating is printed over the first and second electrodes and electrically connects the electrodes, where the electrical resistance of the sensor decreases as the temperature increases.

[0007] The temperature and / or strain sensitivity range for individual sensors may be controlled by at least the separation distance between the printed electrodes and the electrical resistivity of the coating that electrically connects the electrodes, i.e., conductive elastomer ink of the strain sensor or temperature dependent resistive coating of the temperature sensor, which may be tuned by inclusion of various amounts of conductive carbon in the form of powder or nanotubes.

[0008] The strain and / or temperature sensors may further comprise, individually or in combination, a control circuitry, a transceiver, and a controller, wherein the control circuitry is configured to carry the electrical signal to the transceiver and communicate a registered strain, temperature, or change in resistance indicative of a change in strain or temperature, respectively, to the controller.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Aspects, features, benefits, and advantages of the embodiments herein will be apparent with regard to the following description, appended claims, and accompanying drawings. In the following figures, like numerals represent like features in the various views. It is to be noted that features and components in these drawings, illustrating the views of embodiments of the present disclosure, unless stated to be otherwise, are not necessarily drawn to scale.

[0010] FIG. 1 illustrates a schematic diagram of a strain sensor design according to aspects of the present disclosure.

[0011] FIG. 2 illustrates a schematic diagram of a strain sensor array formed by a plurality of equally spaced parallel strain sensors according to aspects of the present disclosure.

[0012] FIG. 3A illustrates a schematic diagram of a strain sensor construct comprising two strain sensor arrays, layer A and C, oriented orthogonally and optionally separated by an electrical isolation layer B according to aspects of the present disclosure.

[0013] FIG. 3B illustrates the strain sensor construct of FIG. 3A positioned over a compressible substrate D and optionally covered by a surface layer E according to aspects of the present disclosure.

[0014] FIG. 4A illustrates a schematic diagram of a strain sensor construct, and FIG. 4B illustrates a close-up view of the contact regions at one end of each sensor in the sensor array for connection to a controller according to aspects of the present disclosure.

[0015] FIG. 5 illustrates a schematic diagram of a change in strain (elongation) resulting from a force applied to a strain sensor construct of the present disclosure.

[0016] FIG. 6 illustrates a contour plot showing the change in resistance with applied pressure on a strain sensor construct of the present disclosure when it is positioned over a compressible substrate.

[0017] FIG. 7 illustrates a three-dimensional representation of the strain deformation of the strain sensor construct of FIG. 6.

[0018] FIGS. 8A-C show graphs of resistance versus strain for strain sensors of the present disclosure.

[0019] FIG. 9 shows a picture of a flexible electronic temperature sensor design having interdigitated electrodes printed on a flexible textile substrate using the molecular inks and methods of the present disclosure.

[0020] FIGS. 10 show a graph of resistance versus temperature for a temperature sensor printed on a flexible textile substrate with molecular inks and methods of the present disclosure.

[0021] FIG. 11 shows a picture of a combination strain and temperature sensor design printed on a stretchable substrate with molecular inks and methods of the present disclosure.

[0022] FIG. 12 shows a graph of the change in resistance with increased strain (stretch) for a conductive trace printed on a textile using molecular inks and methods of the present disclosure.

[0023] FIG. 13A shows a picture of a flexible electronic proximity sensor printed using inks and methods of the present disclosure.

[0024] FIG. 13B shows a schematic diagram of an exemplary 5-trace heater element according to the present disclosure, wherein the numbered blocks are test locations for resistance measurements.

[0025] FIGS. 14A-14C show graphs demonstrating the linearity of temperature increase with power increase (FIG. 14A), and the lack of resistance drift over time or temperature (FIGS. 14B and 14C, respectively) for 5-trace heaters formed according to aspects of the present disclosure.

[0026] FIGS. 15A-15H illustrate schematic diagrams of cross-sections of force sensors of the present disclosure.

[0027] FIGS. 16A and 16B illustrate top views of an electrode layer of a force sensor of the present disclosure showing a spacer frame and spacer dots, respectively, for maintaining the gap between the electrode layer and a conductive layer.

[0028] FIGS. 17 and 18 illustrate electrical signaling, i.e., a change in the resistance, from a sensor to a transceiver in electrical communication with a controller according to aspects of the present disclosure, wherein FIG. 18 shows a configuration when the sensor is positioned on a substrate, optionally including a heater printed according to aspects of the present disclosure.

[0029] FIGS. 19A and 19B are graphs showing the electrical resistance as a function of normal force exerted on the sensor elements of a force sensor as configured in FIG. 15B printed with low or high resistivity carbon ink, respectively.DETAILED DESCRIPTION

[0030] In the following description, the present disclosure is set forth in the context of various alternative embodiments and implementations involving e-textiles comprising sensors, such as strain sensors and temperature sensors. The present disclosure further provides various implementations of these sensors with other electronic elements and e-textiles, such as resistive heaters, lights, force sensors, optical sensors, humidity sensors, proximity sensors, and the like. While the following description discloses numerous exemplary embodiments, the scope of the present disclosure is not limited to the described embodiments but also encompasses combinations and / or modifications of the described embodiments.

[0031] FABRIC BASED STRAIN SENSORS AND SENSOR ARRAYS

[0032] The present disclosure provides strain sensors that comprise a sensor trace printed with a conductive elastomeric ink and sensor electrodes printed with molecular inks. The present disclosure further provides arrays of strain sensors, such as a plurality of equally spaced, parallel strain sensors, and a sensor construct formed by positioned a first sensor array orthogonal to a second sensor array. The strain sensors, sensor arrays, and sensor constructs may be printed onto stretchable substrates to manufacture devices useful for specific applications. One advantage of stretchable textile materials is that the strain sensor(s) can readily conform to the body shape. For example, strain sensors printed on stretchable fabrics according to the present disclosure may find use as bandages and garments, such as compression garments. These strain sensors may be useful for applications such as detection of body swelling in post-operative patients, back stress monitoring for pain prevention, monitoring sleeping position, lack of movement in bed ridden patients (e.g., detect periods of inactivity to reduce likelihood of bed sores), and evaluation of sitting positions.

[0033] Moreover, the conductive elastomeric and molecular inks of the present disclosure, and methods for depositing those inks on flexible substrates such as textiles to form conductive traces allow for a wide range of sensor sizes and configurations. As such, the strain sensors, sensor arrays, and sensor constructs disclosed herein can be incorporated into motion recognition fabric which in turn can be used to make motion recognition clothing for monitoring body motion training for sports which involve complex upper body motion (such as golf, basketball, tennis, baseball), for health monitoring, such as respiration rate during activities (change in strain caused by inhaling and exhaling), for range of movement monitoring during rehabilitation after replacement surgeries, for monitoring movements and contractions of limbs and muscles for health monitoring, including spine and back movements, for monitoring muscle contraction such as during exercise, for monitoring Parkinson's tremors and seizures, in shoe inserts for identifying positions of high strain, and the like.

[0034] The strain sensors, sensor arrays, and sensor constructs disclosed herein may also find use in the evaluation of furniture fitness and comfort, e.g., chairs, couches. They may find uses in monitoring of structural conditions, such as for inflatable habitats and parachutes, and for continuous monitoring of strain and load to detect, diagnose, and locate damage in real time.

[0035] With specific reference to FIG. 1, a strain sensor may comprise at least first and second sensor electrodes, such as a first electrode spaced apart from a second electrode and both printed using any of the molecular inks disclosed herein. The sensor electrodes may be printed to form lines or bars, or interdigitated electrodes (see e.g., FIG. 16A), such as via inkjet printing. For example, the electrodes may have a width of 0.05cm to 2.5cm, such as 0.1cm, or 0.2cm, or 0.3cm, or 0.4cm, or 0.5cm, or 0.6cm, or 0.7cm, or 0.8cm, or 0.9cm, or 1.0cm, or 1.2cm, or 1.4cm, or 1.6m, or 1.8cm, or 2.0cm, or 2.2cm, or 2.4cm, or even 2.5cm. Any upper and lower width may be combined to define a range of widths of the printed electrodes. For example, the electrodes may be 0.0. 1 to 1.0 cm, and the like.

[0036] Any of the metals of the molecular ink compositions disclosed herein are possible and within the scope of the present disclosure.

[0037] Formed over at least an end region of each of the first and second electrode and along the region therebetween, i.e., forming a connection between the spaced apart first and second electrode as shown in FIG. 1, is a sensortrace printed using a conductive elastomeric ink. Alternatively, the sensortrace may be positioned substantially over the electrodes, such as over interdigitated electrodes (see e.g., FIG. 16A). The sensortrace may be printed on fabric and electrode areas using a conductive elastomeric ink via any of the printing methods disclosed herein with the exception of methods using a nozzle, e.g., ink jet printing. Particularly useful printing methods include at least screen printing or stencil methods.

[0038] The sensor traces may be printed to form lines or bars. For example, the conductive sensor traces may have a width of at least 0.5mm up to several cm, such as up to 5cm. The sensor traces may have a width of at least 1mm, or at least 2mm, or 3mm, or 4mm, or 5mm, or 6mm, or 7mm, or 8mm, or 9mm, or 10mm, or 15mm, or 20mm, or 25mm, or 30mm, or 35mm, or 40mm, or 45mm. The sensor traces may have a width of less than 50mm, such as less than 45mm, or 40mm, or 35mm, or 30mm, or 25mm, or 20mm, or 15mm, or 10mm, or 9mm, or 8mm, or 7mm, or 6mm, or 5mm, or 4mm, or 3mm, or even 2mm. Any upper and lower width may be combined to define a range of widths of the printed sensor trace. For example, the sensor trace may be 1mm to 25 mm, and the like.

[0039] The conductive elastomer ink may comprise a silicone or polyurethane elastomer-based ink containing conductive carbon in the form of powder or nanotubes. The resistivity of the elastomer may be tuned to provide a specific range of sensitivity for the strain sensor. For example, the sensitivity of an exemplary strain sensor may be tuned by modifying the composition of the conductive elastomer, such as by inclusion of varied amounts of the conductive carbon (see Examples Al -A3).

[0040] As the substrate comprising the strain sensor is stretched, the sensor trace spanning the region between the first and second electrode also stretches, increasing the electrical resistivity of the conductive elastomeric ink, i.e., the electrical resistance of the sensor increases as applied strain increases (FIGS. 8A-8C). This change in electrical resistance may be communicated via the first and second electrode to a control circuitry. Of note, the molecular inks used to print the electrodes will conformally coat fibers of the textile and demonstrate little to no change in resistivity upon stretching of the textile (see FIG. 12 and Example B). Thus, the electrodes that register the change in resistivity of the sensor trace (i.e., change in resistivity of the conductive elastomeric ink upon stretching) provide a consistent contact point during various stretch motions.

[0041] Further, standard leads used for electrical connections, e.g., wired electrodes, are generally unable to make sufficient contact with the conductive elastomeric ink of the sensor traces. In general, the electrodes are printed on the textile before the sensor trace is printed. As such, the molecular inks of the electrodes conformally coat fibers of the textile and the conductive elastomeric ink of the sensor trace then penetrates the weave of the textile, thus forming a solid electrical connection between the electrode and the sensortrace.

[0042] The strain sensors disclosed herein may further comprise a control circuitry, wherein at least one signal path may connect the at least first and second printed electrodes to the control circuitry. Signal paths may comprise conductive traces printed using the molecular inks and methods disclosedherein. Alternatively, the signal paths may comprise conventional conductive wires connected to the electrodes.

[0043] The strain sensors disclosed herein may further comprise a communications device (transceiver) and a controller. The control circuitry may have wired or wireless communications circuitry for supporting communications between the transceiver and external electronic devices, such as an output of strain sensor measurements readable on an external, connectable device like a computer, phone, tablet or otherwise . The external electronic device may be a computer, cellular telephone, a head-mounted device, a display, a gaming unit, a set-top box, a system including two or more of these devices, or other electronic equipment, and may include software to translate the signal received from the strain sensor. In certain implementations, the signals from the strain sensor may be used to control other electronic devices, such as heaters, lights, and the like.

[0044] The present disclosure further provides strain sensor arrays. As shown in FIG. 2, a plurality of spaced apart, parallel strain sensors may be printed on a stretchable textile, such as a two-way or fourway stretch fabric. As described above, each strain sensor may comprise at least first and second sensor electrodes, such as a first electrode spaced apart from a second electrode and both printed using any of the molecular inks disclosed herein. Formed over at least an end region of each of the first and second electrode and along the region therebetween, i.e., forming a connection between the spaced apart first and second electrode as shown in FIG. 1, is a sensor trace printed using a conductive elastomeric ink. As shown in FIG. 2, signal paths (“conductive fabric”) may extend from the electrodes of each strain sensor in the senor array to a controller.

[0045] The strain sensors in the sensor array may be equally spaced apart, such as 0.25 cm to 15 cm apart. For example, each strain sensor in the sensor array may be spaced at least 0.25 cm from an adjacent parallel strain sensor, such as at least 0.5 cm, or 1 cm, or 2 cm, or 3 cm, or 4 cm, or 5 cm, or 6 cm, or 7 cm, or 8 cm, or 9 cm, or 10 cm, or 11 cm, or 12 cm, or 13 cm, or 14 cm from an adjacent parallel strain sensor. Each strain sensor in the sensor array may be spaced not more than 15 cm from an adjacent parallel strain sensor, such as less than 14 cm, or 13 cm, or 12 cm, or 11 cm, or 10 cm, or 9 cm, or 8 cm, or 7 cm, or 6 cm, or 5 cm, or 4 cm, or 3 cm, or 2 cm, or 1 cm from an adjacent parallel strain sensor. Any combination of upper and lower spacing limits is within the scope of the present disclosure. For example, each strain sensor in the sensor array may be space from 0.5 to 10 cm from an adjacent parallel strain sensor, such as from 1 to 8 cm, or 2 to 7 cm, or 3 to 6 cm.

[0046] An array construct comprising two fabric layers, each having a plurality of equally spaced, parallel sensors forming a positioning grid, is also disclosed. With reference to FIG. 3A, the sensor array of a first fabric layer (A) may be positioned orthogonal to a sensor array on a second fabric layer (C) to form an array construct or sensor construct. In some implementations, the two fabric layers may be electrically isolated by an intervening fabric layer (B). The plurality of fabric-based strain sensors on each layer are arranged in arrays having a series of electrode pairs spaced apart each having a conductive elastomeric ink electrically connecting the electrodes, wherein the electrical resistance of the sensorincreases as applied strain increases. As indicated hereinabove, the electrode pairs are printed using the molecular inks disclosed herein.

[0047] As shown in FIG. 3B, when placed over or joined to a compressible substrate (D), force applied to the sensor construct will deform individual strain sensors as the construct conforms to the source of the force (i.e., is stretched). The compressible substrate may be any known in the art, such as foams, elastomeric polymers, and the like. The compressible substrate may be part of a chair seat and / or back, sofa seat and / or back, or other piece of furniture. The compressible substrate may be part of an article of clothing, such as an insole of a shoe. The compressible substrate may be part of a car seat and / or back. The compressible substrate may be part of a mat used to detect body position and pressure points, such as positioned on a hospital bed.

[0048] With reference to FIG. 4A, a strain sensor construct 10 may include a first plurality of equally spaced, parallel sensors and a second plurality of equally spaced, parallel sensors oriented orthogonal to the first plurality, i.e., forming a positioning grid. As shown in FIG. 4B, at ends of the sensor trace (2, 4) are sensor electrodes (8). Each sensor electrode may be connected to a control circuitry via a signal path 9. When a force is applied to the strain sensor array 10, changes in resistance of the strain sensors at crossover points 6 are indicative of the strain at that point. The electrical resistance data collected from each strain sensor in the sensor construct may be used to create a 3-D strain or deformation map, such as shown in FIG. 5. Exemplary strain maps showing strain at the multiple crossover points of the sensor array area are shown in FIGS. 6 and 7 (see Examples B3 and B4).

[0049] FABRIC BASED TEMPERATURE SENSORS

[0050] The present disclosure also provides temperature sensors. The temperature sensors may be printed onto flexible substrates to manufacture devices useful for specific applications. The molecular inks of the present disclosure, and methods for depositing those inks on flexible substrates such as textiles to form highly conductive traces having little to no ink bleed allow for a wide range of sensor sizes and configurations.

[0051] One advantage of fabricating the sensor using flexible textile materials is that the sensor can readily conform to the body shape. For example, such sensors may be useful for applications such as to monitor body temperature near the healing areas in post-operative patients. The size, construction, and materials used for the device will allow the strain sensor to be custom printed for a wide range of other applications, such as skin compatible temperature sensors for wearable applications, where hard sensors are not conformable to the human body and difficult to integrate in clothing. As another example, the disclosed temperature sensors can be integrated in newborn baby clothing to monitor body temperature, or into a sock to monitor diabetes foot status. In diabetes, foot temperature is a critical factor that needs to be constantly measured. The temperature sensor can be integrated into protective gear for firefighting, sports, the mining industry to monitor the temperature of the human body to avoid heat related illness, and the like.

[0052] The presently disclosed temperature sensors may also find use for monitoring temperatures in extremely thin spaces, or in soft objects such as a vehicle seat, sofa, and the like without limiting any aspect of comfort. Further, because the temperature sensors can be produced in large sizes, orin arrays of sensors, it can measure the average temperature of large surfaces. For example, the disclosed temperature sensors can be used to measure the average temperature of the air flowing through an HVAC duct.

[0053] With specific reference to FIG. 9, a temperature sensor may comprise at least a first electrode spaced apart from a second electrode and both printed using any of the molecular inks disclosed herein. The electrodes may be printed to form bars or interdigitated electrodes, such as via inkjet printing. For example, the electrodes may have a width of 0.05cm to 2.5cm, such as 0.1cm, or 0.2cm, or 0.3cm, or 0.4cm, or 0.5cm, or 0.6cm, or 0.7cm, or 0.8cm, or 0.9cm, or 1.0cm, or 1.2cm, or 1.4cm, or 1.6m, or 1.8cm, or 2.0cm, or 2.2cm, or 2.4cm, or even 2.5cm. Any upper and lower width may be combined to define a range of widths of the printed electrodes. For example, the electrodes may be 0.0. 1 to 1.0 cm, and the like.

[0054] Any of the metals of the molecular ink compositions disclosed herein are possible and within the scope of the present disclosure.

[0055] Formed over at least an end region of the first and second electrode and along the region therebetween, i.e., forming a connection between the spaced apart first and second electrode, is a temperature dependent resistive coating. The temperature dependent resistive coating may comprise conductive carbon nanotubes dispersed in an elastomeric binder, such as a silicone or polyurethane elastomer.

[0056] The temperature dependent resistive coating may be printed to form lines or bars. For example, the temperature dependent resistive coating may have a width of at least 0.5mm up to several cm, such as up to 5cm. The sensor traces may have a width of at least 1mm, or at least 2mm, or 3mm, or 4mm, or 5mm, or 6mm, or 7mm, or 8mm, or 9mm, or 10mm, or 15mm, or 20mm, or 25mm, or 30mm, or 35mm, or 40mm, or 45mm. The sensor traces may have a width of less than 50mm, such as less than 45mm, or 40mm, or 35mm, or 30mm, or 25mm, or 20mm, or 15mm, or 10mm, or 9mm, or 8mm, or 7mm, or 6mm, or 5mm, or 4mm, or 3mm, or even 2mm. Any upper and lower width may be combined to define a range of widths of the printed sensor trace. For example, the sensor trace may be 1mm to 25 mm, and the like.

[0057] Alternatively, the temperature dependent resistive coating may be positioned substantially over the electrodes, such as over the interdigitated electrodes shown in FIG. 9. The temperature dependent resistive coating may be printed on fabric and electrode areas using any of the printing methods disclosed herein with the exception of methods using a nozzle, i.e., ink jet printing. Particularly useful printing methods include at least screen printing or stencil methods.

[0058] The temperature dependent resistive coating may comprise carbon nanotubes, such as single wall or multiwall carbon nanotubes. The nanotubes may be functionalized to improve dispersibility in the coating, such as by carboxylic acid functional groups. The resistivity of the temperature dependent resistive coating, and thus the sensitivity to temperature changes, may be tuned to provide a specific range of sensitivity for the temperature sensor. For example, the sensitivity of an exemplary temperature sensor may be tuned by modifying the composition of the temperature dependent resistive coating, such as by inclusion of varied amounts of the conductive carbon nanotubes.

[0059] Thus, the temperature sensors disclosed herein comprise at least first and second printed electrodes and a temperature dependent resistive coating electrically connecting the electrodes. The temperature dependent resistive coating may comprise a binder and carbon nanotubes, such as single wall or multiwall carbon nanotubes wherein the nanotubes may optionally be functionalized such as via carboxylic acid functional groups.

[0060] As the substrate comprising the temperature sensor is heated, the temperature dependent resistive coating spanning the region between the first and second electrode experiences an increase in temperature, decreasing the electrical resistivity of the temperature dependent resistive coating, i.e., the electrical resistance of the sensor decreases as applied temperature increases (FIG. 10). This change in electrical resistance may be communicated via the first and second electrode to a control circuitry. Accordingly, the temperature sensors disclosed herein may further comprise a control circuitry, wherein at least one signal path may connect the at least first and second printed electrodes to the control circuitry. Signal paths may comprise conductive traces printed using the molecular inks and methods disclosed herein.

[0061] To restrict stretching of the flexible textile, such as when the temperature sensor is printed on the same stretchable textile as a strain sensor as part of an e-textile, the temperature sensor may further comprise a polymeric film that is bonded or heat laminated over the sensor trace, or a non-extensible textile that is laminated or sewn over the sensor trace. Alternatively, the temperature sensor may be printed onto a non-extensible textile and may be integrated into a larger e-textile comprising a stretchable fabric. Exemplary polymeric films include any of film that may be laminate via heat or an adhesive, such as at least polyethylene and polyvinylchloride.

[0062] The temperature sensors disclosed herein may further comprise a communications device (transceiver) and a controller The control circuitry may have wired or wireless communications circuitry for supporting communications between the transceiver and external electronic devices, such as an output of temperature sensor measurements readable on an external, connectable device like a computer, phone, tablet or otherwise. The external electronic device may be a computer, cellular telephone, a head-mounted device, a display, a gaming unit, a set-top box, a system including two or more of these devices, or other electronic equipment, and may include software to translate the signal received from the strain sensor.

[0063] FLEXIBLE RESISTIVE HEATERS

[0064] The present disclosure also relates to textiles comprising resistive heaters that can efficiently deliver warmth in a variety of conditions, including extreme or harsh conditions. Resistive heaters operate by passing electric current through a resistor, which converts the electric energy to thermal energy. The present disclosure provides flexible resistive heaters comprising a flexible substrate having at least one conductive pattern printed thereon with any of the molecular inks disclosed herein, wherein the conductive pattern is configured to carry a current and generate heat.

[0065] The resistive heater may further comprise at least one bus printed with the same molecular ink as the conductive trace, or another of the molecular inks disclosed herein, wherein the at least one bus is electrically connected to the at least one conductive pattern and configured to provide connection to apower source. Alternatively, buses may be included as wired components or contacts, wherein such components may be surface mounted (e.g., mounted with conductive epoxy).

[0066] The conductive pattern and / or bus may be over-coated with a protective coating, such as any of those discussed hereinabove. An exemplary protective dielectric coating composition is disclosed in U.S. Pat. Application Publication No. US 2020 / 0283653.

[0067] Power may be supplied to the bus from a power source. The power source may be a battery pack capable of supplying the necessary voltage and current to drive the heater. For example, a 24V DC battery with 4 Amp of current capability can be used. The power source may be an electrical outlet, such as a wall outlet. The power source may be a 5-15 V electric system of an automobile. The voltage of the power source can be higher or lower than the voltage supplied to the conductive traces and buses, such as using a DC-DC converter to step the voltage down or up to achieve the desired voltage.

[0068] The power source may be controlled by a heater controller (e.g., microcontroller circuit), such as to turn power on or off, or to modulate the power to the bus (and conductive pattern). In some cases, the heater controller draws power from a separate power source, or from the same power source. As such, the power source may supply the required voltage and current to run the heater controller.

[0069] The heater controller may control the functions of the heater, control the heater power supply, provide safety monitoring (e.g., sensors, sensing traces), provide status regarding aspects of the resistive heater, such as status of the power source, (e.g., battery status such as voltage, temperature, etc.; heater resistance; heater current draw; conductive bus voltage drop, etc.), and status of the heater to the user (e.g., heater on, heater level, heater temperature). Exemplary status presented to the user may include power on / off and power level via illumination of indicator lights, which indicate status of a resistive heater.

[0070] The resistive heater may carry a relatively large current through the bus to deliver current to the conductive pattern. If a conductive pattern or bus were to be compromised such as a crack or tear, the current flowing through the remaining part of the pattern or bus might develop a hot spot. To mitigate this potentially hazardous condition, sensing traces can be added to the resistive heater. For example, a sensing trace printed using any of the molecular inks disclosed herein can be connected to either or both buses, or at a point along the conductive pattern, and may be configured to generate a signal indicative of an electrical characteristic of the bus. The sensing trace (s) may measure the voltage at the connection point with the bus, wherein a voltage drop greater than a predetermined level would be indicative of a compromised conductive pattern or bus. The voltage drop can be measured by any sensing circuit, such as an analog -to-digital converter using a microcontroller, a comparator, or the like. A signal indicating bus or conductive pattern integrity error may change the operation of the resistive heater, for example, to power off the heater.

[0071] Resistive heaters may find application as wearable heaters or heating elements for use in clothing, or resistive heating elements in the automotive industry (e.g., seat heaters, electric car heaters) or aerospace industry (e.g., printed on flexible substrate attached to a plane wing, printed directly on materials of the plane wing, etc.), and others. In one example, at least the conductive pattern of the resistive heater is printed directly on a textile, such as the underside of a car seat cover. Alternatively, the resistive heater maybe printed on a flexible substrate, such as the conductive pattern printed on a flexible polymer film that is positioned underneath the material of the seat cover, or under both the seat material and a foam cushion material. When printed on a flexible polymer substrate, the resistive heater may be laminated, adhered, or bonded to another textile, such as to a bottom side of the material of a seat, or to a foam layer of the cushion of a seat.

[0072] An exemplary 5-trace heater is shown in FIG. 13B. These heaters may be placed in series, or parallel. Resistance measurements taken at various points along the traces, as shown by the numbered blocks in FIG. 13B, were found to vary linearly with respect to trace length. In fact, the calculated and measured resistance values at each point were found to be very close (i.e., resistance measured with an alligator clip ground connection and manual tip probe). Similar results were observed for 7-trace heaters. Left-to-right and right-to-left resistance measurements were conducted to investigate print / process-related resistance variations. When normalized for trace length, the measured resistance from 5-trace and 7-trace heaters showed remarkable correlation with the predicted resistance.

[0073] An advantage of the presently disclosed resistive heaters is that they are flexible, thin, and heat / cool rapidly. Heating is initiated almost immediately after current is provided to the resistive heater. The upper temperature limit may be limited based on the total voltage supplied to the printed trace, wherein an upper set point was found to have little effect on the heating rate (i.e., heating to 65°C and 85°C occurs at the same rate). The temperature increases linearly with power until an equilibrium is reached (see FIG. 14A, about 2 watts of power and 100°F). Moreover, the resistance is not observed to drift with time (FIG. 14B) or temperature (FIG. 14C) for resistive heaters printed using the inks and methods of the present disclosure. Such results are observed uniformly from trace to trace, showing an overall deviation of only 3 Q.

[0074] Thus, the resistive heaters may be configured to carry a power density of greater than 400 watts / m2. For example, the resistive heaters of the present disclosure may be capable of carrying a power density of at least 600 watts / m2, such as at least 800 watts / m2, or at least 1,000 watts / m2, at least 1,500 watts / m2, at least 5,000 watts / m2, or even at least 10,000 watts / m2.

[0075] Alternatively, the resistive heaters may be configured to carry a power density of less than 400 watts / m2, such as less than 350 watts / m2, or less than 300 watts / m2, or less than 200 watts / m2, or even less than 100 watts / m2. The resistive heaters may be configured to carry a power density of at least 10 watts / m2.

[0076] When connected to a 5-15 volt electrical system, such as that of an automobile, the at least one conductive pattern may be configured to have a resistance of 1-30 ohms, and / or to generate 10-1,500 watts / m2at -40°C to 60°C, and / or to carry a power density of at least 400 watts / m2, such as up to 1,500 watts / m2, and / or heat at a rate of about 0.1°C / second to about l°C / second. A thermal output from the resistive heaters will depend on various design factors, such as the metal or alloy or combination of metals and / or metal alloys in the molecular ink, a width of the conductive trace, a thickness of the conductive trace, the resistance of the trace, and any other components in the ink composition (e.g., other conductive polymers, etc.), and thus may be tuned to fit the specific application. Moreover, thermal output may alsobe modulated by selection of the power source, overall size of the conductive pattern), and selection of the substrate material. Depending on the material used as a substrate, i.e., type of textile or polymeric material, the resistive heaters formed with the molecular inks and methods disclosed herein may reach a temperature in the range of 25°C - 200°C.

[0077] One approach to improve the electrical and thermal performance of metal-based resistive heaters is to incorporate other conductive materials, such as a second metal complex. One exemplary second metal complex useful in a silver molecular ink is a copper complex, such as an amine copper carboxylate formed according to the present disclosure (see US 2022 / 0306888, the entire contents of which are incorporated herein).

[0078] Another approach to improve the electrical and thermal performance of silver-based resistive heaters such as carbon nanotubes (CNTs), graphene, graphite, metal oxides, and conducting polymers, as fillers. The blending of such conductive filler materials with conductive metals affords a conductive composite with average electrical and thermal conductivity features. More importantly, the composite is expected to exhibit improved film integrity, conformal fabric coating during printing, and lower heater fabrication cost. Since silver is the most conductive metal, the silver-based composites may exhibit reduced electrical resistance with higher heater performance in terms of the maximum heater temperature. Moreover, such composite inks may provide more uniform thermal distribution compared to devices printed with pristine silver films, mainly due to improved interconnection as the conducting polymers fill any voids or cracks.

[0079] Thus, use of these additional conductive filler materials may maintain or even improve the flexibility of the final printed substrate, such as textile fabrics and sheets, and may improve the conformal coating of individual fibers in the textile substrate in much the same manner as particle-free silver inks.

[0080] FLEXIBLE FORCE SENSORS

[0081] The present disclosure also relates to textiles having printed thereon force sensing elements forming a force sensing device comprising at least one electrode layer separated from at least one conductive layer by a gap distance. The at least one electrode layer may comprise at least one electrode printed using the molecular ink on a first flexible substrate. The at least one electrode layer may comprise first and second electrodes that are interdigitally printed on the flexible substrate using the molecular ink. The at least one conductive layer may comprise a conductive trace or region (also referred to herein as a conductive strip) on a second flexible substrate that is printed with any of the molecular inks disclosed herein, a resistive carbon-based ink, a conductive paint, indium tin oxide (ITO), or a combination thereof, or may comprise any of apoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a carbon nanotube-based thin film (CNT), a carbon-loaded thermoplastic polymer, carbon-loaded silicone, carbon- loaded polymeric foil, velostat, or any combination thereof.

[0082] With reference to FIG. 15A, the first flexible substrate 102 may comprise first and second electrodes printed thereon (106a and 106b, respectively). Moreover, the first and second substrate (102 and 108, respectively) may be arranged so that the first and second electrode (106a, 106b) on the first substrate 102 directly oppose a printed conductive region 110 on the second substrate 108 and is separated therefromby a gap 112 formed between these two substrate layers, which provides the piezoresistive property of the sensor. A separation distance may be maintained by a textile that bridges the distance between the conductive layer and the electrode layer. An exemplary textile material includes a mesh fabric or net fabric.

[0083] The separation or gap 112 may also be maintained by embossing one of the substrate layers outside of the region containing the printed electrode(s) and conductive region. The separation may be maintained by a spacer material that frames an open region (frame 107), such as shown in FIG. 16A, wherein the open region comprises all or a portion of the electrode (106a, b on substrate 102) and / or conductive region. Exemplary spacer materials include any of the flexible polymer fdms disclosed herein or an adhesive. The separation may be maintained by dots, such as spacer beads (109; FIG. 16B). The dots or spacer beads may be held in place with adhesives, may be melted into place (i.e., brief exposure to heat), may be printed onto one of the layers of the pressure sensor, such as the electrode layer and / or the conductive region. Any combination of methods and materials disclosed herein to maintain separation between the various substrate layers, and thus the distance between the electrode and conductive regions, is possible and within the scope of the present invention. Selection of the elements and specific design consideration regarding spacing and size of the elements may depend on the size of the force sensor, i.e., printed electrodes, and the selection of the substrates, e.g., highly flexible substrates may benefit from additional separation elements to maintain the preferred separation distance between the substrate layers.

[0084] The separation between the various substrate layers, i.e., the gap, may be used to maintain a “no contact” distance between the electrode(s) and the conductive layer, such that compression of the force sensor (compression of the various layers of the force sensor so that they touch) will bring the substrate layers into contact and reduce the electrical resistivity of the force sensor. Exemplary separation distances may be at least 1 micron, such as at least 10 microns, or at least 20 microns, or at least 40 microns, or at least 60 microns, or at least 80 microns, or at least 100 microns, or even at least 150 microns. An exemplary separation distance maintained by a separation frame formed by a PET polymer film is about 180 microns (-0.18 mm).

[0085] Each of the printed conductive region and the first and second electrodes may be printed using a molecular ink, such as any of the molecular inks disclosed herein. For example, when a particle- free silver ink is used to print the conductive region and the first and second electrodes on a non-woven fabric, the resistance drops proportionately with an amount of applied force.

[0086] FIG. 15B depicts another configuration for a force sensor of the present disclosure. The conductive layer on the second flexible substrate may be printed with a conductive carbon-based ink. As shown in FIG. 19A, when the conductive layer is printed with a low resistivity carbon ink, the force required to generate a proportionate signal is much lower than when the electrically conductive layer is printed with a high resistivity carbon ink, as shown in FIG. 19B.

[0087] Additional configurations of force sensing devices according to aspects of the present disclosure are shown in FIGS. 15C and 15D, wherein the conductive layer and first and second electrodes occupy a full thickness of the flexible substrate. That is, layers 104 and 110 that are shown in FIG. 15A tooccupy only a portion of the thickness of the substrates may occupy a full thickness of the substrate, such as shown in FIGS. 15C and 15D.

[0088] As shown in FIG. 15E, the force sensing device may comprise two electrically conductive layers (110a, 110b), wherein a first electrically conductive layer is printed on the second flexible substrate with a particle-free conductive metal ink, and a second electrically conductive later is printed on a third flexible substrate 114 with a carbon ink. The various layers may be arranged to provide two separation regions or gaps as shown in FIG. 23A (e.g., two airgaps, 112a, 112b as shown, such as separation provided by a mesh fabric, frame, embossed region, dots, etc.).

[0089] The force sensing device may comprise a conductive layer and / or electrode layer printed on a textile, wherein the printed electrically conductive material comprises a range of between ten percent and one hundred percent of the thickness of the textile substrate. The force sensing device may comprise an electrode layer printed on a textile substrate, wherein the printed electrodes are printed equidistant from one another.

[0090] As shown in FIGS. 15A-15D, a force sensing device may comprise two layers of substrate (e.g., fabric), one conductive layer and one electrode layer, wherein the electrically conductive material on the conductive layer faces the printed electrodes on the electrode layer. The conductive layer and electrode layer may both be printed with a particle-free conductive metal ink (e.g., particle-free silver ink), as shown in FIGS. 15A and 15C. The conductive layer may be printed with a resistive carbon ink where the electrode layer may be printed with the particle-free conductive metal ink, as seen in FIG. 15B and 15D. Alternatively, a force sensing device may comprise two layers of conductive metal ink printed on a substrate, such as fabric, and one electrode layer, wherein a conductive layer printed with piezoresistive carbon ink lays between a conductive layer printed with a particle-free conductive metal ink and an electrode layer printed with a particle-free conductive metal ink (See FIG. 15E).

[0091] A force sensor configured as shown in FIG. 15E may have a range of electrical resistance of from 100 to 10,000 Q when met with up to 45 pounds of force.

[0092] The various layers of the force sensor, such as electrode layer and the conductive layer, may be bonded by a hot melt bonding film, pressure sensitive bonding film, pressure sensitive adhesive, or by sewing, such as outside of the region comprising the first and second electrodes. For example, any of the hot melt bonding film, pressure sensitive bonding film, or pressure sensitive adhesive may be used to form a frame that maintains the separation distance of the gap and may also function to bond the layers of the force sensor together.

[0093] As a force is applied to the force sensor, the at least one electrode and conductive layer are brought into closer proximity, thus reducing the electrical resistivity of the force sensor. This change in electrical resistivity may be communicated with a control circuitry. Accordingly, the force sensing devices disclosed herein may further comprise a control circuitry, a communications device (transceiver), and a controller, wherein at least one signal path may connect the at least one printed electrode to the control circuitry.

[0094] Accordingly, compression of the flexible substrate initiates an electrical signal, i.e., a change in the resistance, which travels to a transceiver in electrical communication with a controller (see FIG. 17, sensor would be the force sensor in this example) . The control circuitry may have wired or wireless communications circuitry for supporting communications between the transceiver and external electronic devices, such as an output of force sensor measurements readable on an external, connectable device like a computer, phone, tablet or otherwise . The external electronic device may be a computer, cellular telephone, a head-mounted device, a display, a gaming unit, a set-top box, a system including two or more of these devices, or other electronic equipment, and may include software to translate the signal received from the force sensing device.

[0095] Accordingly, the force sensing device may comprise a textile having at least one conductive trace printed thereon, wherein at least a portion of the at least one conductive trace is overcoated with a protective dielectric coating. The at least one conductive pattern may exhibit an ink bleed of less than 0.5mm, and a resistance of less than 10 Q / D. The particle free conductive trace may comprise two or more layers of the molecular ink.

[0096] The conductive layer and electrode layer may each be printed directly onto a flexible substrate. Accordingly, the electrode layer may comprise first and second electrodes interdigitally printed on a flexible substrate using a particle-free conductive metal ink, and the conductive layer may be printed on a flexible polymer film (FIG. 15G) or glassine paper (FIG. 15H) using a conductive carbon-based ink.

[0097] While various examples of the present force sensors are described as including one or more conductive layers printed with any of the molecular inks disclosed herein, or with a carbon-based ink, other conductive materials may be used and are within the scope of the present invention. For example, the at least one conductive layer may be printed with the presently disclosed molecular ink, a resistive carbonbased ink, a conductive paint, indium tin oxide (ITO), or a combination thereof, or may comprise any of a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a carbon nanotube-based thin film (CNT), a carbon-loaded thermoplastic polymer, carbon-loaded silicone, carbon-loaded polymeric foil, velostat, or any combination thereof, wherein specific selection of the material may provide different force resistance responses.

[0098] The force sensors disclosed herein include use of a particle-free conductive metal ink that conformally coats the fibers of the flexible substrate, thus providing excellent flexibility for the force sensors on the present disclosure. As such, the at least one electrode printed with these inks may demonstrate a resistance of less than 10 Q / D.

[0099] Moreover, the methods used to print the particle-free conductive metal inks provides conductive traces having an ink bleed of less than 0.6 mm, such as less than 0.5 mm, or less than 0.4 mm, or less than 0.3 mm, or even less than 0.2 mm. As such, these force sensors may be designed to be very small and may be positionable in a wide range of flexible electronics.

[0100] Exemplary uses of the present disclosure include: devices for measuring or controlling force, devices for sensing / measuring impact, measuring blood pressure and similar diagnostics, measuring muscular strength, seat or bed occupant detection, electrical switches, robot feedback / control, tactilesensing / signaling, tactile feedback, monitoring patient respiration, bed / body pressure (bed sore prevention), bandage pressure monitor, pressure from foot or shoe monitoring, or sensor arrays for force mapping.

[0101] For example, the flexible force sensor may be printed on a flexible substrate or textile that will be configured as a cover for a car seat. As such, the flexible force sensor may sense whether a person is seated in that particular seat, i.e., by compression of the conductive and electrode layers of the force sensor, and may adjust certain systems of the car or bed accordingly. For example, when included in a car seat, the force sensor may enable the air bag system, activate or deactivate heaters within a seat or cabin lights, adjust the position of the seat or driver and passenger side mirrors, and the like. Such signals may be sent along a control circuitry to other systems.

[0102] The flexible force sensor may be set to detect particular weights or forces, such as of a weight of a passenger or driver when positioned in the car seat. For example, the sensor may be calibrated to detect when a person or object is under the requisite weight associated with airbag deployment and adjust the car’s system accordingly. Multiple sensors may be used in a seat back to determine a height and / or weight of a person in the car seat, and may pre-adjust systems of the car automatically, e.g., seat position, mirror positions, and the like. A combination of sensors may be used to determine characteristics of a specific individual (passenger or driver), and systems of the car may be set to correspond to that individual (passenger or driver recognition) so that later entry to the car may reset those systems to correspond to that individual’s preferences.

[0103] COMBINATIONS OF THE DISCLOSED TEXTILES

[0104] The present disclosure also relates to textiles comprising combinations of the disclosed electronic elements, i.e., temperature, strain, and force sensor, heaters, etc. While specific example combinations are detailed below, other combinations are possible and within the scope of the present disclosure.

[0105] Strain or force sensors and temperature sensors

[0106] Textiles comprising a combination of a strain or force sensor and a temperature sensor, as disclosed herein, may find use in healthcare, such as for wound dressings. For example, a bandage sized and configured to cover a wound on a patient may detect inflammation in the area of the wound via the strain or force sensor, such as when an inflamed area of the wound pushes against the bandage. When a strain sensor is included, this may stretch the sensor trace causes the electrical resistivity of the conductive elastomer ink connecting the at least first and second electrodes to increase. Alternatively, when a force sensor is included, this may bring the at least one electrode and conductive layer into closer proximity, thus reducing the electrical resistivity of the force sensor.

[0107] The bandage may further detect a possible infection in the wound or surrounding area, such as via the temperature sensor registering an increased temperature. The size, construction, and materials used for these sensors allow such bandages to be custom printed, i.e., specific to a patient and patient wound size and location.

[0108] The disclosed force-temperature and strain-temperature sensors may also find use in car seats, such as to detect the temperature of various regions of the seat at points contacted by a person, whereinconnection to a control circuitry may provide control of external or additional electronic elements, e.g., heating elements such as disclosed herein, cooling elements (fans, adjust a thermostat, etc.), and the like.

[0109] An exemplary combination strain-temperature sensor is shown in FIG. 11, wherein a first electrode and a second electrode separated therefrom are printed on a four-way stretch fabric using the molecular inks disclosed herein. The first and second electrodes are electrically connected via a conductive elastomeric ink to form a strain sensor. A third electrode may be printed using the molecular inks disclosed herein and may be separated from each of the first and second electrodes. The third electrode may be electrically connected to one of the first or second electrodes via a temperature dependent resistive coating to form a temperature sensor. Alternatively, the strain sensor and temperature sensor may be positioned in close proximity on the substrate, but may not share an electrode, i.e., each sensor electrically connects a separate pair of electrodes.

[0110] Force or strain sensor controlled resistive heater

[0111] It is well known nowadays to equip automotive vehicles with comfort related functional components such as heaters for seating area heating, backrest heating, arm-rest heating, steering wheel heating, gearshift lever heating, or heating of other interior surface areas, additional lighting, and positional controls for the seating area, headrest, and even steering wheel. Seat heaters, for example, use electrode elements arranged in the vehicle in close vicinity to the occupant within the passenger compartment. Usually these electrode elements, such as seat heating mats, are arranged into the seating surface of the occupant seat in contact with or proximate to the occupant, such as in the seat surface area, the seat backrest, an armrest, and / or the steering wheel or gearshift lever. In order to hide the electrode elements for the occupant, the electrode elements are normally arranged below a seat trim, below a covering, or below other surfaces delimiting the vehicle passenger compartment.

[0112] These electronic elements should not impair the comfort of the passenger, i.e., it is important that the electrode elements cannot be sensed below the trim or covering by the passenger. Moreover, such electrode elements would also need to be highly flexible and, especially if integrated into a surface such as a seating surface of a vehicle seat, highly permeable to air and humidity.

[0113] The presently disclosed molecular and conductive elastomeric inks and methods for printing these inks to form electronic elements offer the flexibility and manufacturing ease needed to provide e-textiles. For example, the molecular inks, when deposited and cured, do not affect fabric feel and flexibility. Accordingly, the present disclosure provides force sensors, strain sensors, resistive heaters, and combinations of such elements, which may be incorporated into common items, such as chair seats and back for heating (e.g., car seat), etc.

[0114] Specifically, and with reference to FIG. 18, the present disclosure provides a device comprising force sensitive resistors or strain sensors in addition to one or more resistive heaters. These two components may be combined to provide a device for sensor control of a resistive heater, wherein the device generally comprises at least one heating layer including a resistive heater, such as any of the resistive heaters disclosed herein, at least one sensing element including a force or strain sensor, such as any of the force orstrain sensors disclosed herein, and electronic elements configured relay power to the resistive heater and sense contact with the force or strain sensor.

[0115] The device may further include a controller configured to receive electrical signals from the various sensing element(s), and responsive of these signals, send control signals to the resistive heater. In this way, individual forces on the sensing element(s) may provide feedback to the controller that may provide fine-tuned control of the heating element(s). For example, should a user manually turn on a heater but not be positioned in the seat, the controller may register the signals from the individual force or strain sensors (or lack thereof) and turn the heater off, such as via communication with a heater controller (see FIG. 18) Should a user shift in a seat so that contact is no longer made with a back portion of the seat, as sensed by at least one of the force or strain sensors, the controller may turn off the heater in the back portion of the seat. Such control may provide means to conserve battery use, an aspect that is especially relevant in electric vehicles, wherein the motor is powered by a battery.

[0116] Additional flexible printed electronic elements and combinations thereof

[0117] The present disclosure is also directed to additional electronic elements or components printed on flexible substrates, such as textiles (e-textiles) or polymeric films having printed thereon at least one conductive trace or pattern using inks and / or methods disclosed herein. The traces may terminate in contact pads or connectors for connection to a current, such as a power supply or battery. Various hardware elements may be connected to portions of the trace or pattern to form electric devices. As such, the conductive patterns on the flexible substrates may be formed as a trace or pattern that may provide a sensor (e.g., optical, thermal, humidity, gas, acceleration, and proximity), a conductor, an electrode, a circuit, an interconnect, a light, an antenna, a resistive heating element, a switch, a transparent conductive element, a battery, or any combination thereof. An exemplary flexible electronic comprising a proximity sensor according to the present disclosure is shown in FIG. 13A. Such a proximity sensor 34 may be included, for example, in an automobile, wherein the conductive traces of the proximity sensor may be printed on an underside of the textile of a headrest of a car seat and may be configured to detect motion, such as the motion of a person’s hand. The sensor may be configured to activate or deactivate motors upon detection of specific motions, such as activate motors that raise or lower the head rest (e.g., swipe up to move the headrest upward and swipe down to move the headrest down). The proximity sensor may be included, for example, in a bed, wherein the conductive traces of the proximity sensor may be configured to detect the motion of a person’s hand. The sensor may be configured to activate or deactivate motors upon detection of specific motions, such as activate motors that raise or lower portions of the bed. The sensor may be configured to turn on a heater positioned within the bed.

[0118] Further electronic components, such as lights, may be included in the e-textiles, or controlled by other elements configured as e-textiles. For example, lights may be electrically connected by conductive traces printed using inks and methods of the present disclosure or may comprise traditional wired connections. These lights may be controlled by proximity sensors, such as shown in FIG. 13A and discussed hereinabove, and / or by capacitive touch sensors printed using the inks and methods of the presentdisclosure, and / or by communications from a controller connected to a strain or force sensor, such as any of those described hereinabove.

[0119] Further exemplary flexible electronics may include, for example, a directional compass, one or more gyroscopes, one or more accelerometers, and fiber optics. The sensors employed in such flexible electronics may be used to monitor parameters of a user wearing the flexible electronic device. Such parameters may include heart rate, respiration rate, skin temperature, and body position and movement. Moreover, flexible electronics may be used to measure a user's full-body biomechanics such as joint angles, angular velocity, angular acceleration, and range of motion.

[0120] These flexible electronics are found to have greatly improved wear performance, e.g., bendability, washability, strain resistance, etc., over flexible electronics formed using the inks and methods of the prior art. For example, the resistance of the conductive traces formed using the inks and methods of the present disclosure may increase only slightly after multiple wash cycles, such as by less than 50% after 50 washes, or less than 30% after 50 washes, or less than 15% after 50 washes, or less than 70% after 100 washes, or less than 60% after 100 washes, or less than 40% after 100 washes, or less than 30% after 100 washes, or less than 20% after 100 washes, wherein a wash cycle is defined as in according to AATCC 61- 2013 (laundering).

[0121] The flexible electronics may be abrasion resistant (up to 500 cycles by standard ASTM testing methods) and may be sweat resistant (moisture resistant).

[0122] The flexible electronics may be strain resistant. For example, knit e-textiles may be stretched by up to 50%, or up to 100%, without connection loss, generally showing a small increase in conductivity with an increase in stretching of the textile substrate (see FIG. 10 and examples).

[0123] While specific embodiments of the disclosure have been described in detail, it should be appreciated by those skilled in the art that various modifications and alternations and applications could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements, systems, apparatuses, and methods disclosed are meant to be illustrative only and not limiting as to the scope of the disclosure.

[0124] FLEXIBLE SUBSTRATES

[0125] The electronic elements disclosed herein, e.g., strain sensors, sensor arrays, sensor constructs, temperature sensors, for sensors, etc., of the present disclosure may be printed on any of the flexible substrates disclosed herein. For example, the flexible substrate may be a knit, woven, or non-woven substrate or textile. The textile may be made of polyester, polyamides, spandex, nylon, Evolon®, elastane, cotton, cellulose, silk, wood, linen, wool, leather, or blends thereof. According to certain aspects, the strain sensors, sensor arrays, and sensor constructs, may be printed using stencil, screen, or ink jet printing, or combinations thereof on a two-way or four-way stretchable fabric. Exemplary two-way or four-way stretch fabrics include polyester-spandex blend, or a nylon-elastane blend (e.g., 61-39 or 85-15).

[0126] CONDUCTIVE INKS

[0127] (Al Conductive elastomeric inks

[0128] A conductive elastomeric ink was prepared from a mixture of an elastomeric binder and a conductive carbon. Exemplary elastomeric binders include polyurethanes, silicone rubbers, and the like. As a specific example, a 2-part, low viscosity liquid silicone rubber may be mixed with a conductive carbon. The conductive carbon may a carbon black powder, such as a carbon black having moderate surface area (e.g., 45-65 m2 / g). The conductive carbon may be added to either or both parts of the 2-part, low viscosity liquid silicone rubber to a final of 5 to 20 pph. For example, the conductive carbon may be added to the elastomer (2-part, low viscosity liquid silicone rubber) in an amount of at least 5pph, or 6pph, or 7pph, or 8pph, or 9pph, or lOpph, or l lpph, or 12pph, or 13pph, or 14pph, or 15pph, or 16pph, or 77pph. The conductive carbon may be added to the elastomer (2-part, low viscosity liquid silicone rubber) in an amount of up to 20pph, such as up to 19pph, or 18pph, or 17pph, or 16pph, or 15pph, or 14pph, or 13pph, or 12pph, or 1 Ipph, or lOpph, or 9pph, or 8pph. Any combination of upper and lower addition amounts of the carbon black may define a range such as, for example, the conductive carbon may be added to the elastomer at 8 to 14 pph, or 9 to 13pph, etc.

[0129] The conductive carbon and liquid silicone rubber are ground together, such as via a high shear mixing blade, until a uniform paste is formed. The conductive elastomeric ink may then be stencil printed over the electrodes as illustrated in FIG. 1, and oven cured at 90°C for 10 minutes to produce an elastomeric resistive sensor. For example, the conductive elastomeric ink may be oven cured at temperatures of at least ambient, such as at least 30°C, or 40°C, or 60°C, or 80°C, or 100°C, or 120°C. The conductive elastomeric ink may be oven cured at temperatures of up to 250°C , such as up to 230°C, or 220°C, or 200°C, or 180°C, or 150°C, or 100°C. Any combination of upper and lower addition amounts may define a range for curing the ink.

[0130] (B) Temperature dependent resistive coating

[0131] A temperature sensitive resistive coating was prepared from as a dispersion of carbon nanotubes in an elastomeric binder. Exemplary elastomeric binders include polyurethanes, silicone rubbers, and the like. As a specific example, a 2-part, low viscosity liquid silicone rubber may be mixed with the carbon nanotubes. The carbon nanotubes may be single wall or multi wall, they may be dispersed in the binder with addition of aqueous or organic solvents, and they may be functionalized to improve dispersion. For example, the carbon nanotubes may comprise carboxylic acid functional groups on the surface.

[0132] The carbon nanotubes may be added to either or both parts of the 2-part, low viscosity liquid silicone rubber to a final of 0.1 to 5pph. For example, the carbon nanotubes may be added to the elastomer (2-part, low viscosity liquid silicone rubber) in an amount of at least O. lpph, or 0.25pph, or 0.5pph, or 0.75pph, or l.Opph, or 1.5pph, or 2.0pph, or 2.5pph, or 3.0pph, or 3.5pph, or 4.0pph, or 4.5pph. The carbon nanotubes may be added to the elastomer (2-part, low viscosity liquid silicone rubber) in an amount of up to 5pph, such as up to 4.5pph, or 4.0pph, or 3.5pph, or 3.0pph, or 2.5pph, or 2.0pph, or 1.5pph, or 1.Opph, or 0.75pph, or 0.5pph, or 0.25pph. Any combination of upper and lower addition amounts of the carbon nanotubes may define a range such as, for example, the carbon nanotubes may be added to the elastomer at 0.2 to 2 pph, or 0.5 to 1.5pph, etc.

[0133] The carbon nanotubes and liquid silicone rubber are ground, such as via a high shear mixing blade, until a uniform paste is formed. The temperature sensitive resistive coating may then be stencil printed over the electrodes as illustrated in FIG. 9, and oven cured at 90°C for 10 minutes to produce an elastomeric resistive sensor. For example, the temperature sensitive resistive coating may be oven cured at temperatures of at least ambient, such as at least 30°C, or 40°C, or 60°C, or 80°C, or 100°C, or 120°C. The temperature sensitive resistive coating may be oven cured at temperatures of up to 250°C , such as up to 230°C, or 220°C, or 200°C, or 180°C, or 150°C, or 100°C. Any combination of upper and lower addition amounts may define a range for curing the ink.

[0134] (C) Molecular inks

[0135] The molecular inks of the present disclosure include a particle-free metal complex composition comprising at least one metal complex dissolved in at least one solvent. Such particle-free metal complex compositions and molecular inks have been described in US Patent Application Publication No. 2019 / 0249026 and 2020 / 0369061.

[0136] The metal complex can be mononuclear, dinuclear, trinuclear, and higher. For example, the metal complex may be a neutral metal complex comprising at least one metal, at least one first ligand, and at least one second ligand. The metal complex may be as described in US Patent Application Publications 2011 / 0111138, 2013 / 0236656, and 2020 / 0369061. The metal complex may comprise a first metal complex having at least one first metal, and a second metal complex having at least one second metal. The metal complex may be as described in any of US Patent Nos. 9,487,669; 9,920,212; 10,738,211; and 11,118,078.

[0137] For example, a neutral metal complex may be formed by first forming a complex between the metal (M) and the second ligand (U2), such as by reacting a metal, metal salt, or metal oxide with the second ligand. The metal-second ligand complex may then be reacted with an excess of the first ligand (U) to form the neutral metal complex. The stoichiometric reaction ratio between the first ligand and the metal- second ligand complex can be, for example, at least 10: 1, such as at least 13: 1, or at least 15: 1, or at least 20: 1. When formulated in this way, the reaction mixture remains substantially or totally free of particles and progresses to completion forming a metal complex having stoichiometric amounts of the first and second ligands and the metal.

[0138] The excess, unreacted first ligand may be removed to provide the metal complex having stoichiometric amounts of the metal, first ligand, and second ligand (i.e., free of unliganded first ligand). For example, the excess, unreacted first ligand may be removed by vacuum evaporation of the complex and may include one or more wash steps with an appropriate solvent, to yield a final dry powder having stoichiometric amounts of the metal, first ligand, and second ligand. For silver metal complexes, this powder is typically white.

[0139] The resulting purified metal complexes are substantially or totally free of particles (particle -free) including nanoparticles and microparticles and are highly soluble in various solvents. This differs greatly from prior art complexes that do not include stoichiometric amounts of the metal, first ligand, and second ligand and / or may include residual unliganded first ligand, and accordingly generally includeparticles such as nanoparticles and / or microparticles (see additional discussion in the Examples). Printing of these prior art nanoparticle inks on certain textiles has demonstrated that they often do not penetrate into the textile, but rather pool on top of the textile, which may be observed by scanning electron microscopy images, and thus do not form conductive traces. The molecular inks of the present disclosure are capable of conformally coating fibers of a textile substrate and form highly conductive traces.

[0140] The molecular inks may optionally further include at least one conductive filler material. Exemplary filler materials include at least conductive polymers, metal oxides, and carbon-based materials, such as carbon nanotubes (CNTs), graphene, and graphite. The conductive filler material can be preferentially selected from commercially available conductive polymers or carbon-based materials. Possible conducting filler materials include carbon black, graphite, polypyrrole (PPy), poly[3,4- ethylenedioxythiophene] (PEDOT), polyacetylene, polythiophene (PT), graphene, polyphenylene, CNTs, polyaniline (PANI), and polyphenylene ethylene.

[0141] Among the different types of conductive polymers that have been applied to textiles, PANI, PT and PPy provide high electrical conductivity and simple processing. PPy and PANI, in particular, provide excellent stability under environmental conditions, good conductivity, ease of fabrication onto flexible substrates such as fabrics, simple synthesis methods, and corrosion resistance. A general concern around the use of certain polymeric fillers in the presently disclosed molecular inks is poor mechanical properties. However, in those instances such concerns can be mitigated by incorporating polymer additives and binders such as nitrocellulose, which is characterized by its thermoplastic behavior, fast solvent evaporation, good compatibility with a wide range of materials, excellent processability and good mechanical properties. Thus, the molecular inks comprising a conductive filler may optionally comprise an additional binder material.

[0142] The molecular inks may optionally comprise one or more surfactants. The surfactants may comprise anionic, cationic, nonionic, or amphoteric surfactants, which may be present in the amount of 0.001-5 wt. %, such as 0.001-3 wt. %, or 0.01-2 wt. %, or not more than 0.1 wt. %, such as 0.001-0.1 wt.%, based on the total weight of the ink. Exemplary surfactants may be those useful to reduce the surface tension of the molecular inks, such as silicone-based surfactants (i.e., silyl surfactant). Exemplary surfactants of particular use include polydimethyl siloxanes and modified polydimethyl siloxanes, e.g.. polyether- modified polydimethylsiloxane.

[0143] The molecular inks may be formulated by dissolving the at least one purified metal complex, i.e., complex that is free of any unreacted first ligand, in a hydrocarbon solvent to form the particle-free metal complex composition, and adding any optional components, such as the conductive filler(s), surfactant(s), additional solvents, and binder material(s). Alternatively, the molecular inks may be formulated by dissolving the at least one purified metal complex, i.e., complex that is free of any unreacted first ligand, and any optional components, such as the conductive filler(s), surfactant(s), and any binder material(s), in an organic solvent system such as a hydrocarbon solvent system.

[0144] The molecular inks may be formulated by dissolving the at least one purified metal complex, i.e., complex that is free of any unreacted first ligand, in at least one polar protic solvent to formthe particle-free metal complex composition, and adding any optional components, such as the conductive fdler(s), surfactant(s), additional solvents, and binder material(s). Alternatively, the molecular inks may be formulated by dissolving the at least one purified metal complex, i.e., complex that is free of any unreacted first ligand, and any optional components, such as the conductive filler(s), surfactant(s), and any binder material(s), in at least one polar protic solvent.

[0145] Examples of polar protic solvents include water, linear or branched alcohols, amines, amino alcohols, and hydroxyl-terminated polyols including glycols. The polar protic solvent may also be, for example, ethylene and higher glycols, as well as alcohols. Particular examples of polar protic solvents include water, methanol, ethanol, n-propanol, isopropanol, n-butanol, acetic acid, formic acid, and ammonia. The polar protic solvent may comprise, for example, water and at least one amine solvent. The amine solvent may have a molecular weight of, for example, about 200 g / mol or less, or about 100 g / mol or less. The amine solvent may be, for example, at least one monodentate amine, at least one bidentate amine, and / or at least one polydentate amine. The amine solvent may be, for example, at least one primary amine or at least one secondary amine. In one embodiment, the amine solvent may comprise at least one alkyl group bonded to at least one primary or secondary amine. The amine solvent may comprise at least two primary or secondary amine groups connected by a linear or branched alkyl group. The amine solvent may comprise at least two linear or branched alkyl groups connected by at least one secondary amine. Advantages of the amine solvent include, for example, improved solubility and thus higher possible concentrations of the metal complex in the solvent, as well as lower decomposition temperatures for the metal complex.

[0146] The molecular inks can be prepared by mechanical mixing of the at least one polar protic solvent(s) and the at least one metal complex (e.g., an amine silver carboxylate, an amine copper carboxylate), and any of the optional components, such as the conductive fillers, surfactants, and any binders.

[0147] When included, the conductive filler can be blended with the particle-free metal complex, such as a particle-free silver precursor, in various weight ratios. Exemplary weight ratios include 50:50 metal complex : conductive filler, such as 60:40 metal complex : conductive filler, or 70:30 metal complex : conductive filler, or 80:20 metal complex : conductive filler, or 90: 10 metal complex : conductive filler, or even 99: 1 metal complex : conductive filler, and other ratios in-between.

[0148] As indicated, the molecular inks may comprise at least one conductive polymer. According to specific aspects, the ink may comprise a mixture of polypyrrole (PPy) and polyaniline (PANI). Formation of interpenetrated PANI / PPy networks play a decisive role in enhancing the conductive polymer film integrity and offer good film conformality during printing.

[0149] Certain conducting organic polymers are known to be excellent hosts for metal nanoparticles where cured nanoparticles may be embedded in the polymer matrix. In the past, PANI- or PPy-coated textiles have been used as substrates for a second coating with another conductive polymer such as PEDOT, PPy or PANI. In this case, such precoated textiles can be used to seed surfaces for silver printing which afford reduced temperature curing. In fact, the PPy-aided silver metalation can yield silver particleswith different shapes and sizes in the nanometer and micrometer range. In addition to tuning the particle size of cured silver, the low temperature used for curing silver-printed textiles may not decompose the conductive fdlers or seed layer.

[0150] The present inventors have recognized the potential of PPy to reduce amine silver carboxylates to metallic silver and use this potential as a new route to lower temperature curing of particle- free silver inks. Thus, the blending of conductive fdlers in the molecular inks can enhance the performance of flexible electronic elements printed using such inks through improved mechanical, thermal, electrical, and other processing properties. The blending approach can minimize fabrication cost and promote easy process scale-up and commercialization by enabling sheet-to-sheet and roll-to-roll processing.

[0151] An exemplary molecular ink according to the present disclosure may comprise 10-40wt% of the at least one conductive fdler material mixed with a metal complex at any of the above indicated ratios, 2-10wt% of alcohol or amine, 2-15wt% of glycol, 10-25wt% of a conductive fdler solubilizer, and 40-70wt% of water. An exemplary fdler solubilizer includes at least N-methyl -2 -pyrrolidone.

[0152] To enhance the textile coating homogeneity, multiple printing cycles can be repeated from 1 to 20, as necessary. The printed textile can be cured or dried in between prints to avoid textile saturation. The resistance of the coated textile is optimally within 0.01 - 500 / n, such as 0.01 - 300 / n, or even 0.01 - 100 / n based on the fdm thickness and printed textile.

[0153] The viscosity of hydrogen bonding solvents is inherently greater than non-hydrogen bonding solvents such as hydrocarbons. Further the elevated solvent boiling points (due to energetically greater intermolecular forces) and polar ink nature render them capable and competent systems for the formation of thin fdms and structures of greater quality than strictly hydrocarbon or aromatic hydrocarbon delivery systems due to slower controlled drying times, surface tensions, and surface wetting properties. Thus, mixed solvent systems can provide superior application, solubility, and performance for the presently disclosed molecular inks.

[0154] The molecular inks of the present disclosure may be formulated to include hydrogels and / or polymers, such as polyacrylic acids, having lower molecular weights, and which may function as viscosity modifiers. For example, the compositions may include up to 5 wt.% of a hydrogel and / or polymer, such as up to 4 wt.%, or up to 3 wt.%, or up to 2 wt.%, or up to 1 wt.%, or up to 0.5 wt.%, or up to 0.1 wt.%, or up to 0.05 wt.%. The compositions may include hydrogels and / or polymers at from 0.01 wt.% to 5 wt.%, such as 0.01 wt.% to 4 wt.%, or 0.01 wt.% to 3 wt.%, or 0.01 wt.% to 2 wt.%, or 0.01 wt.% to 1 wt.%. The polymer may be a conductive polymer, such as any of the polyacetylenes, polyanilines, polyphenylenes, polypyrenes, polypyrroles, polythiophenes, etc. known in the art.

[0155] The metal complexes described herein may have a solubility in at least one polar protic solvent at 25° C of at least 50 mg / ml, or at least 100 mg / ml, or at least 150 mg / ml, or at least 200 mg / ml, or at least 250 mg / ml, or at least 300 mg / ml, or at least 400 mg / ml, or at least 500 mg / ml, or at least 1,000 mg / ml, or at least 1,500 mg / ml, or even or at least 2,000 mg / ml.

[0156] The amount of organic solvent in the molecular inks disclosed herein can be, for example, less than 30 wt. %, less than 20 wt. %, less than 10 wt. %, less than 5 wt. %, less than 3 wt. %, less than 1wt. %, less than 0.1 wt. % or less than 0.01 wt. %. The molecular ink formulations may be substantially or totally free of organic solvent.

[0157] The viscosity of the ink formulations measured at 25°C can be, for example, about 800 cps or less, about 500 cps or less, about 250 cps or less, or about 100 cps or less. According to certain other aspects, the viscosity of the ink formulations measured at 25°C can be, for example, about 50 cps or less, 40 cps or less, 30 cps or less, 25 cps or less, 20 cps or less, or even 10 cps or less. According to yet other aspects, the ink formulations have a viscosity of about 2 cps to about 20 cps, or about 2 cps to about 15 cps, or about 2 cps to about 10 cps.

[0158] The viscosity of the ink formulations measured at 25°C can be, for example, about 800 cps or more, such as about 1500 cps or more, about 2,500 cps or more, about 5,000 cps or more, or even about 10,000 cps or more.

[0159] The molecular inks can be formulated for a total metal complex concentration of 3 g / ml to 0.1 g / ml, 2 g / ml to 0.1 g / ml, such as 1.5 g / ml to 0. 1 g / ml, or 1 g / ml to 0.1 g / ml, or 2 g / ml to 0.4 g / ml, or 1.5 g / ml to 0.4 g / ml. The molecular inks can be formulated for a pH in the range of 7 to 12. The molecular inks can be formulated for a viscosity of at least 2cP such as at least 5cP, or at least lOcP.

[0160] Analysis of the molecular ink formulations, in either of the organic or polar protic solvent systems, has shown that the amounts of the metal, and first and second ligands, in the ink solutions are stoichiometric (see Examples).

[0161] The molecular ink formulations may be substantially or totally free of particles, microparticles, and nanoparticles, and metal particles, such as metal microparticles and metal nanoparticles. In particular, the molecular ink formulations comprising the metal complex may be substantially or totally free of nanoparticles and / or metal nanoparticles before deposition or printing, and during deposition or printing. The molecular ink may be substantially or totally free of particles, including nanoparticles and / or metal nanoparticles, after deposition but before reduction to metal (e.g., before curing). For example, the level of nanoparticles can be less than 1 wt. %, less than 0.1 wt. %, or less than 0.01 wt. %, or less than 0.001 wt. %. The level of metal nanoparticles can be less than 1 wt. %, less than 0. 1 wt. %, or less than 0.01 wt. %, or less than 0.001 wt. %. One can examine the composition for particles using methods known in the art including, for example, SEM and TEM, spectroscopy including UV-Vis, dynamic light scattering, plasmon resonance, and the like. Nanoparticles can have diameters of, for example, 1 nm to 500 nm, or 1 nm to 100 nm. Microparticles can have diameters of, for example, 0.5 pm to 500 pm, or 1 pm to 100 pm.

[0162] Upon cure, the ink forms a continuous conductive trace on the substrate, e.g., flexible substrate, and may include metal nanoparticles formed in situ during cure (see FIGS. 8A-8B). The metal nanoparticles may have diameters of l-500nM, such as 5-100nM, or 10-50nM, or even 20-40nM (see FIG. 8C).

[0163] dl Metal complex of the molecular inks

[0164] The metal complex may comprise a metal useful for forming electrically conducting lines, particularly those metals used in the semiconductor and electronics industries. Exemplary metals include at least silver, gold, copper, platinum, ruthenium, nickel, cobalt, palladium, zinc, iron, tin, indium, and alloys thereof. The metal complexes may comprise a single metal center or two metal centers.

[0165] For example, the metal complex may be a neutral metal complex comprising at least one metal, at least one first ligand, and at least one second ligand. The first ligand may be adapted to volatilize when heated without formation of a solid product. For example, the first ligand may volatize upon heating at a temperature of, for example, 250°C or less, or 200°C or less, or 150°C or less. Heating can be done in the presence or absence of oxygen. The first ligand may be a reductant for the metal. The first ligand may be in neutral state, such as neither an anion nor a cation.

[0166] The first ligand may be a monodentate ligand, or a polydentate ligand including, for example, a bidentate or a tridentate ligand. The first ligand may be a thioether, such as tetrahydrothiophene, a phosphine, or an amine compound. In certain examples, the first ligand may be a thioether, such as a thioether having the formula R1-S-R2, wherein Ri and R2 may be independently selected from C1-C3 alkyl or may form a saturated heterocyclic compound with the sulfur. Exemplary thioethers include at least dimethyl sulfide, diethyl sulfide, dipropyl sulfide, diisopropyl sulfide, ethyl methyl sulfide, and tetrahydrothiophene .

[0167] In certain examples, the first ligand may comprise an amine compound having at least two primary amine groups. Primary amines are stronger reducing agents than alcohols and can form homogenous solutions with polar protic solvents. Moreover, the first ligand may comprise two primary amine end groups and no secondary amine group, or one primary amine end group and one secondary amine end group. In this latter example, the secondary amine end group may be substituted with a linear alkane or a polar group, such as a hydroxy or alkoxy. In yet another example, the first ligand may comprise two primary amine end groups and one secondary amine group. The first ligand may be an amine including an alkyl amine. The alkyl groups can be linear, branched, or cyclic. Bridging alkylene can be used to link multiple nitrogen together. In the amine, the number of carbon atoms can be, for example, 15 or less, or 10 or less, or 5 or less. In particular examples, the first ligand is ethylenediamine, 1,2-diaminopropane, 1,3- diaminopropane, diaminocyclohexane, or diethyl ethylenediamine.

[0168] The molecular weight of the first ligand, may be, for example, about 1,000 g / mol or less, or about 500 g / mol or less, or about 250 g / mol or less.

[0169] The second ligand is different from the first ligand and may also volatilize upon heating the metal complex. For example, the second ligand may release carbon dioxide, as well as volatile small organic molecules. The second ligand may be adapted to volatilize when heated without formation of a solid product. The second ligand may volatize upon heating at a temperature of, for example, 250°C or less, or 200°C or less, or 150°C or less. Heating can be done in the presence or absence of oxygen. The second ligand can be anionic. The second ligand may be self-reducing.

[0170] The second ligand may be a carboxylate. The carboxylate may comprise a linear, branched, or cyclic alkyl group. In one embodiment, the second ligand does not comprise an aromatic group. Thesecond ligand may be an amide represented by — N(H) — C(O) — R, wherein R is a linear, branched, or cyclic alkyl group, with 10 or fewer carbon atoms, 8 or fewer carbon atoms, 6 or fewer carbon atoms, or 5 or fewer carbon atoms. The second ligand can also be an N-containing bidentate chelator. In particular examples, the second ligand may be isobutyrate, oxalate, malonate, fumarate, maleate, formate, glycolate, lactate, citrate, or tartrate.

[0171] The molecular weight of the second ligand, including the carboxylate, may be, for example, about 1,000 g / mol or less, or about 500 g / mol or less, or about 250 g / mol, or about 150 g / mol or less or less.

[0172] The second ligand may be a halide such as fluoride, chloride, bromide, iodide, or astatide.

[0173] Thus, the metal complex may comprise at least one metal, at least one first ligand, and at least one second ligand, wherein the metal may be silver, gold, platinum, or copper. Exemplary first ligands include amines and sulfur containing compounds, and exemplary second ligands include carboxylic acids, dicarboxylic acids, tricarboxylic acids, and halides. Exemplary solvents include one or more polar protic solvents, such as at least two polar protic solvents selected from the group comprising at least water, alcohols, amines, amino alcohols, polyols, and combinations thereof.

[0174] According to certain other aspects, the metal complex may comprise at least one first metal complex having at least one first metal, at least one second metal complex having at least one second metal, at least one third metal complex having at least one third metal, and so forth, wherein each metal complex may comprise stoichiometric amounts of a metal and first and second ligands. For example, the metal complex may comprise two neutral metal complexes formed as detailed above (i.e., having stoichiometric amounts of a metal and first and second ligands).

[0175] According to certain other aspects of the present disclosure, the metal complex may be configured to provide a metal alloy (e.g., after curing in the textile substrate). The metal complex may comprise at least one first metal complex, wherein the first metal complex comprises a first metal and at least one first ligand and at least one second ligand, different from the first ligand; and at least one second metal complex, which is different from the first metal complex, and comprises a second metal and at least one first ligand and at least one second ligand, different from the first ligand, for the second metal; and at least one solvent. The (i) the selection of the amount of the first metal complex and the amount of the second metal complex, (ii) the selection of the first ligands and the selection of the second ligands for the first and second metals, and (iii) the selection of the solvent may be adapted to provide a homogeneous composition.

[0176] According to yet other aspects, the metal complex may comprise at least one first metal complex having at least one first metal in an oxidation state of (I) or (II), and at least two ligands, wherein at least one first ligand is an amine and at least one second ligand is a carboxylate anion; at least one second metal complex, which is different from the first metal complex, wherein the second metal complex is a neutral complex comprising at least one second metal in an oxidation state of (I) or (II), and at least two ligands, wherein at least one first ligand is a sulfur compound and at least one second ligand is the carboxylate anion of the first metal complex.

[0177] According to certain other aspects of the present disclosure, the metal complex may comprise at least one first metal complex, wherein the first metal complex is a neutral, dissymmetrical complex comprising at least one first metal in an oxidation state of (I) or (II), and at least two ligands, wherein at least one first ligand is an amine and at least one second ligand is a carboxylate anion; at least one second metal complex, which is different from the first metal complex, wherein the second metal complex is a neutral, dissymmetrical complex comprising at least one second metal in an oxidation state of (I) or (II), and at least two ligands, wherein at least one first ligand is sulfur compound and at least one second ligand is the carboxylate anion of the first metal complex; at least one organic solvent, and wherein the atomic percent of the first metal is about 20% to about 80% and the atomic percent of the second metal is about 20% to about 80% relative to the total metal content.

[0178] Exemplary metals for use in these metal alloys include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg. In particular, coinage metals can be used including silver, gold, and copper. Precious metals can be used including gold, iridium, osmium, palladium, platinum, rhodium, ruthenium, and silver. In other preferred embodiments, platinum, nickel, cobalt, and palladium can be used. Still further, lead, iron, tin, ruthenium, rhodium, iridium, zinc, and aluminum can be used. Other metals and elements can be used as known in the art.

[0179] The first metal complex is a silver, gold, copper, platinum, nickel, iridium, or rhodium complex. For example, the first metal complex may be a silver complex. The second metal complex is a silver, gold, copper, platinum, nickel, iridium, or rhodium complex. For example, the second metal complex may be a gold complex. Examples of binary combinations of metals to form binary alloys include at least Ag-Au, Pt-Rh, Au-Cu, Zn-Cu, Pt-Cu, Ni-Al, Cu-Al, Pt-Ni, and Pt-Ir.

[0180] The metal complexes of the metal alloy can comprise a plurality of ligands including two or more ligands, or just two ligands. There can be, for example, a first ligand and a second ligand, different from each other. The first ligand can provide sigma electron donation, or dative bonding. The first ligand can be in a neutral state, not an anion or cation. Examples of the first ligand include amines, oxygencontaining ligands, and sulfur-containing ligands including oxygenated ethers and thioethers, including cyclic thioethers. Asymmetrical or symmetrical amines can be used. The amines can comprise, for example, at least two primary or secondary amine groups. Monodentate ligands can be used. Polydentate or multidentate ligands can be used. Alkylamino ligands can be used.

[0181] The second ligand can be different from the first ligand and can volatilize upon heating the metal complex. For example, it can release carbon dioxide, as well as volatile small organic molecules such as propene, in some embodiments. The second ligand can be a chelator with minimum number of atoms that can bear an anionic charge and provide a neutral complex. The second ligand can be anionic. For example, the second ligand can be a carboxylate, including a carboxylate comprising a small alkyl group. The number of carbon atoms in the alkyl group can be, for example, ten or less, or eight or less, or five or less. The molecular weight of the second ligand can be, for example, about 1,000 g / mol or less, or about 250 g / mol or less, or about 150 g / mole or less.

[0182] The metal complexes of the present disclosure can be substantially or totally free of particles, including nanoparticles and microparticles, when in the dried state (powder) or when formulated as an ink in at least one solvent (i.e., particle-free composition comprising the metal complex and at least one solvent).

[0183] (ii) Curing the molecular inks

[0184] Once the disclosed molecular ink formulations have been printed onto a flexible substrate, at either ambient temperatures or elevated temperatures, they may be cured to form the conductive pattern (i.e., converted to a metallic structure). Curing can include heating the printed substrate, and / or irradiating the printed substrate. In certain examples, the printed substrate may be cured by heating to a temperature of 200°C or less, such as 150°C or less, or 100°C or less, for a time period of less than 60 minutes, such as less than 30 minutes, or less than 15 minutes. In a particular example, the printed substrate is heated to 140°C for 10 minutes, or exposed to infrared radiation for 10 minutes, to form a conductive pattern with a resistance of less than 1 Q / n.

[0185] Sheet resistance values for knit, woven, and nonwoven textiles, wherein the substrate was heated or not during deposition of the molecular inks (i.e., printed on the textile at ambient temperatures and cured; or printed on the textile at elevated temperatures and cured) were evaluated. The lowest sheet resistance was found for conductive traces on woven polyester, wherein the textile was at ambient or elevated temperatures during printing, while both the knit and nonwoven textiles benefited from printing on a heated substrate.

[0186] In certain examples, the conductive trace on the textile substrate may be additionally, or alternatively, cured by exposure to pulsed light, such as by photonic curing, wherein the number of pulses ranges from 2 to 20. Alternatively, or in addition, curing may include irradiating the conductive trace on the textile substrate, such as by exposure to infrared radiation.

[0187] (Hi) Protective coatings on the molecular inks

[0188] The conductive traces formed using the molecular inks disclosed herein may be coated with a protective coating, such as a dielectric coating. For example, all or a portion of a trace may be coated with an aqueous dielectric polymer solution. Exemplary polymer solutions include at least acrylic and polyurethane polymers.

[0189] The protective coating can be deposited by painting, spraying, or printing (e.g., inkjet printing). The viscosity of the polymeric solutions can be adjusted for the specific textile and deposition method by dilution with appropriate solvents and solvent mixtures. Such coatings may be cured by heat treatment, evaporation of solvents, irradiation (e.g., UV treatment), or any combination thereof. An exemplary coating includes an acrylic-based coating that is printed over the conductive trace and is cured by heating the textile to 160°C or less, such as 150°C or less for 30 minutes or less, such as 20 minutes or less.

[0190] The composition may be printed by inkjet, gravure, flexographic, or screen-printing techniques, wherein the viscosity of the ink is adjusted for the specific technique, e.g., the viscositymeasured at 25°C may be 2 to 40 centipoise for inkjet printing, or 100 to 400 centipoise for flexographic printing, or 50 to 300 centipoise for gravure printing.

[0191] An exemplary protective dielectric coating composition is disclosed in in U.S. Pat. Application Publication No. US 2020 / 0283653, which includes an aqueous binder, an inorganic nanoparticle having a particle size of less than 250nm, and one or more polar protic solvents. The aqueous binder may be a polyvinyl alcohol, a hydroxy cellulose, a hydrogel, or a combination thereof. The inorganic nanoparticle may be SiC>2 nanoparticles, AI2O3 nanoparticles, TiO? nanoparticles, ZrC>2 nanoparticles, nanoclay, or a combination thereof. The inorganic nanoparticle may be a colloidal particle. The inorganic nanoparticle may have a particle size of less than lOOnm, or even less than 50nm. Accordingly, an exemplary protective dielectric coating composition may comprise 2-15 wt.% of an aqueous binder, 1-5 wt.% of a colloidal silica having a particle size of less than lOOnm, and an aqueous solvent, wherein the composition has a viscosity measured at 25°C of 2 to 400 centipoise.

[0192] The coatings may be cured via heat, such as by exposure to 250°C or less for 30 minutes or less, or photonic curing. The dielectric coating composition may be dried before curing.

[0193] Additional conductive coatings may be provided over contact regions, such as at the contact points or pads of a trace. Such coatings may include conductive polymers and may provide conductive contact with the printed trace while also protecting the trace from abrasion and / or during wash cycles.

[0194] PRINTING AND DEPOSITION METHODS OF THE CONDUCTIVE INKS

[0195] Deposition of Molecular inks

[0196] Methods known in the art can be used to deposit the presently disclosed molecular inks including, for example, pipetting, inkjet printing, lithography or offset printing, gravure or gravure offset printing, flexographic printing, microdispersion direct write printing, screen printing or rotary screen process printing, offset printing, stencil printing, drop casting, slot die, roll-to-roll, stamping, roll coating, spray coating, flow coating, extrusion printing, and aerosol delivery such as spraying or pneumatic or ultrasonic aerosol jet printing. One can adapt the ink formulation and the substrate with the deposition method.

[0197] The disclosed molecular inks may be deposited by direct printing methods such as pipetting, stencil printing, rolling, spraying, or inkjet printing. In certain examples, the molecular inks are deposited using inkjet printing.

[0198] The disclosed molecular inks may be printed directly onto a surface of the flexible substrate, e.g., surface of a woven or non-woven textile or polymeric fdm.

[0199] Certain flexible substrates may benefit from pre-treating. For example, for textile substrates, pre-treatment such as prewashing the textile and optionally treating by oxygen plasma, corona, and / or chemical etch (e.g., acidic, caustic). Accordingly, the molecular inks of the present disclosure may be printed on the textile substrate after it has been pretreated by oxygen plasma, corona, and / or chemical etch.

[0200] Certain flexible substrates may benefit from addition of a coating. For example, cellulose based substrates such as paper and / or cotton textiles may need a coating to reduce ink bleed and enhance conductivity of traces formed thereon. That is, the cellulose or cotton-based substrates may be coated with a transparent layer, such as a polyurethane coating prior to printing the conductive pattern.

[0201] One can adapt the viscosity of the disclosed molecular inks to the deposition method. For example, viscosity can be adapted for inkjet printing. Viscosity of the ink formulations measured at 25°C can be, for example, about 500 cps or less, such as 200 cps or less, or 50 cps or less, or even 25 cps or less. Viscosity of the ink formulations measured at 25°C can be, for example, at least 50 cps. Viscosity of the ink formulations measured at 25°C can be, for example, about 50 cps or less, such as about 25 cps or less. According to certain other aspects, the viscosity of the ink formulations measured at 25°C can be, for example, about 2 cps to about 20 cps, or about 2 cps to about 10 cps. Viscosity of the ink formulations may be tuned through selective ratios of polar protic solvents (e.g., ratio of water to amine).

[0202] Alternatively, the viscosity of the disclosed molecular inks can be formulated, for example, to be greater than 15 cps, or 20 cps, or even 25 cps, such as by addition of binders, resins, or other additives or solids that may thicken or increase the viscosity of the ink formulation. For example, one can adapt the concentration of dissolved solids in the ink to about 2,000 mg / ml, or 1,500 mg / ml or less, about 1,000 mg / ml or less, about 500 mg / mL or less, about 250 mg / mL or less, about 100 mg / mL or less, about 50 mg / mL or less, or about 10 mg / mL or less.

[0203] Additives may also be included to adapt the wetting properties of the disclosed molecular inks. Additives such as, for example, surfactants, dispersants, colorant (e.g., dye), and / or binders can be used to control one or more ink properties as desired. For example, a hydrophilic binder may aid in wetting certain textiles, and thus may aid in providing a conductive trace that conformally coats the textile fibers (i.e., improve conductivity of the conductive trace). For example, the molecular ink formulations may include up to 10 wt.% of one or more additives, such as up to 8 wt.%, or up to 6 wt.%, or up to 4 wt.%, or up to 2 wt.%, or up to 1 wt.%, or up to 0. 1 wt.%, or up to 0.05 wt.%. The compositions may include additives at from 0.001 wt.% to 5 wt.%, such as 0.001 wt.% to 4 wt.%, or 0.001 wt.% to 3 wt.%, or 0.001 wt.% to 2 wt.%, 0.001 wt.% to 1 wt.%, or 0.001 wt.% to 0. 1 wt.%, based on the weight of the ink formulation.

[0204] According to certain aspects, molecular ink formulations of the present disclosure may be substantially or totally free of additives such as surfactants, dispersants, colorant (e.g., dye), and / or binders.

[0205] Nozzles used for inkjet or aerosol jet printing of the molecular inks can have diameters, for example, of less than 1000 micrometers, or even less than 80000 micrometers, or even less than 500 micrometers. The absence of particulates can help with prevention of nozzle clogging.

[0206] The molecular inks may be printed on flexible or stretchable substrates at ambient conditions, such as at standard room temperatures and pressures.

[0207] The flexible substrate may be heated before and / or during deposition of the ink. For example, the flexible substrate may be heated to temperatures of 40°C to 90°C. An exemplary inkjet printer may include a heated platen and a nozzle assembly. In use, the molecular inks of the present disclosure may be loaded to the printer so that droplets of the ink may be deposited. The platen may be heated totemperatures of at least 30°C, such as at least 35°C, or at least 40°C, or at least 45°C, or at least 50°C, or at least 55°C. The platen may be heated to temperatures of up to 90°C, such as up to 85°C, or up to 80°C, or up to 75°C, or up to 70°C, or up to 65°C, or up to 60°C, or up to 55°C. Any upper and lower temperature may be combined to define a temperature range for heating the platen during printing, such as 30°C to 90°C during printing, or 40°C to 80°C, and the like.

[0208] Thus, according to certain methods of the present disclosure, the molecular inks may be deposited on a substrate such as a textile that is heated at low temperatures during deposition, followed by a curing step that converts the metal complex in the ink formulation to a metallic structure, wherein the curing step may be by any of the curing steps detailed herein.

[0209] According to certain other methods of the present disclosure, the disclosed molecular inks may be deposited on a substrate such as a textile at ambient temperatures (and pressures), followed by a curing step that converts the metal complex in the ink formulation to a metallic structure, wherein the curing step may comprise any of the curing steps detailed herein.

[0210] Deposition of conductive elastomeric inks and temperature dependent resistive coatings

[0211] Methods known in the art can be used to deposit the presently disclosed elastomeric inks and resistive coatings including, for example, pipetting, lithography or offset printing, gravure or gravure offset printing, screen printing or rotary screen process printing, offset printing, stencil printing, drop casting, slot die, roll-to-roll, stamping, roll coating, flow coating, and extrusion printing. One can adapt the ink formulation and the substrate with the deposition method.

[0212] According to preferred aspects, the disclosed elastomeric inks and resistive coatings may be deposited by direct printing methods such as stencil printing, or screen printing.

[0213] ASPECTS OF THE INVENTION

[0214] The invention provided in the present disclosure includes strain sensors, temperature sensors, force sensors, resistive heaters, and combinations thereof, formed by printing conductive inks on a flexible substrate, such as a stretchable textile. Also provided in this disclosure are the conductive inks, i.e., molecular inks, conductive elastomeric inks, and temperature dependent resistive coatings, and methods for printing the inks on textiles and other flexible substrates to form conductive and resistive traces, coatings, and patterns (used interchangeably and referred to herein as “conductive traces”). Further, conductive traces patterned to form other flexible electronic elements such as proximity sensors, communication devices, and the like are also disclosed.

[0215] A novel and unique aspect of the presently disclosed molecular inks used to form the conductive traces is that they are particle-free compositions of stoichiometric metal complexes dissolved in a solvent. This affords printing of traces that are narrow and may be precisely deposited. When printed on a woven or non-woven textile substrate, these molecular inks conformally coat fibers of the flexible substrate, and are resistant to degradation by the standard strains and forces exerted upon such substrates, e.g., bending, stretching, twisting, washing, abrasion, etc. As such, the molecular inks and electronic elements formed using the methods of the present disclosure provide dramatic improvements over those disclosed in the prior art.

[0216] Aspect 1: An e-textile comprising a flexible strain sensor, the flexible strain sensor comprising a first electrode printed with a molecular ink, a second electrode printed with the molecular ink, the second electrode spaced apart from the first electrode, and a sensor trace printed with an elastomeric conductive ink, wherein the sensor trace covers at least an end portion of each of the first and second electrode and extends along the region therebetween, wherein the first and second electrodes and the sensor trace are printed on a stretchable textile, and wherein the flexible strain sensor is configured to initiate an electrical signal upon deformation of the sensor trace.

[0217] Aspect 2: An e-textile comprising a flexible strain sensor array, the flexible strain sensor array comprising a plurality of equally spaced, parallel strain sensors according to aspect 1 printed on a stretchable textile.

[0218] Aspect 3: An e-textile comprising a strain sensor construct, the strain sensor construct comprising a first strain sensor array according to aspect 2 printed on a first stretchable textile; and a second strain sensor array according to aspect 2 printed on a second stretchable textile, wherein the first and second strain sensor arrays are positioned so that the plurality of equally spaced, parallel strain sensors of the first strain sensor array are orthogonal to the plurality of equally spaced, parallel strain sensors of the second strain sensor array.

[0219] Aspect 4: The e-textile according to aspect 3, further comprising a stretchable substrate positioned between the first and second stretchable textiles; and a compressible substrate positioned below the second stretchable textile.

[0220] Aspect 5 : The e-textile according to any of the aforementioned aspects, further comprising a control circuitry connected to the first and second electrodes, a transceiver, and a controller, wherein the control circuitry is configured to carry the electrical signal to the transceiver and communicate a registered change in resistance to the controller.

[0221] Aspect 6: The e-textile according to aspects 2 or 3, further comprising a control circuitry comprising signal leads connected to the first and second electrodes of each of the strain sensors in the strain sensor array, wherein the control circuitry is also connected to a transceiver and a controller and is configured to carry electrical signals from each of the strain sensors in the strain sensor array to the transceiver and communicate a registered change in resistance for each of the strain sensors to the controller.

[0222] Aspect 7: The e-textile according to aspect 5 or 6, wherein the control circuitry comprises conductive traces printed with the molecular ink.

[0223] Aspect 8: The e-textile according to any of the aforementioned aspects, wherein the particle-free metal complex composition comprises: at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent, wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

[0224] Aspect 9: The e-textile according to any of the aforementioned aspects, wherein the conductive elastomeric ink comprises 5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

[0225] Aspect 10: The e-textile according to any of the aforementioned aspects, wherein the stretchable textile is a two-way or four-way stretch fabric.

[0226] Aspect 11: The e-textile according to any of the aforementioned aspects, wherein the stretchable textile comprises polyester, polyamide, a polyether-polyurea copolymer, nylon, and blends thereof.

[0227] Aspect 12: The e-textile according to aspect 10, wherein the two-way or four-way stretch fabric comprises a polyester / polyether-polyurea copolymer blend or a nylon / polyether-polyurea copolymer blend.

[0228] Aspect 13: The e-textile according to any of the aforementioned aspects, wherein the molecular ink conformally coats fibers of the stretchable textile, and the conductive elastomeric ink penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

[0229] Aspect 14: An e-textile comprising a temperature sensor comprising a first electrode printed with a molecular ink, a second electrode printed with the molecular ink, the second electrode spaced apart from the first electrode, and a sensor trace printed with a temperature sensitive resistive coating, wherein the sensor trace covers at least an end portion of each of the first and second electrode and extends along the region therebetween, wherein the first and second electrodes and the sensor trace are printed on a textile, wherein the molecular ink comprises a particle-free metal complex composition and a solvent, and wherein the temperature sensor is configured to initiate an electrical signal upon a change in temperature at the sensor trace.

[0230] Aspect 15: The e-textile according to aspect 14, further comprising: a control circuitry connected to the first and second electrodes, a transceiver, and a controller, wherein the control circuitry is configured to carry the electrical signal to the transceiver and communicate a registered change in resistance to the controller.

[0231] Aspect 16: The e-textile according to aspect 15, wherein the control circuitry comprises conductive traces printed with the molecular ink.

[0232] Aspect 17: The e-textile according to any one of aspects 14 to 16, wherein the particle-free metal complex composition comprises at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent, wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

[0233] Aspect 18: The e-textile according to any one of aspects 14 to 17, wherein the temperature sensitive resistive coating comprises a dispersion of carbon nanotubes in a low viscosity liquid silicone rubber, wherein the carbon nanotubes are included at 0.2 to 5pph, or 0.5 to 4pph, or 1 to 3pph, or 1 to 2pph.

[0234] Aspect 19: The e-textile according to any one of aspects 14 to 18, further comprising: a polymeric film was heat laminated over the sensor trace to restrict stretching of the flexible textile.

[0235] Aspect 20: The e-textile according to any one of aspects 14 to 19, wherein the molecular ink conformally coats fibers of the stretchable textile, and the temperature sensitive resistive coating penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

[0236] Aspect 21: An e-textile comprising: a strain sensor construct according to any one of aspects 3 to 13, and at least one temperature sensor according to any one of aspects 14 to 20.

[0237] Aspect 22: The e-textile according to aspect 21 , wherein the at least one temperature sensor is printed on one of the first or second flexible textiles of the strain sensor array, or wherein the at least one temperature sensor is printed on the stretchable substrate that is sandwiched between the first and second flexible textiles.

[0238] Aspect 23: The e-textile according to aspects 21 or 22, wherein the at least one temperature sensor comprises a polymeric film was heat laminated over the sensor trace thereof to restrict stretching of the flexible textile or the stretchable substrate.

[0239] Aspect 24: An e-textile comprising one or more of: a strain sensor construct according to any one of aspects 3 to 13, a temperature sensor according to any one of aspects 14 to 20, a force sensor according to the present disclosure, or a resistive heater according to the present disclosure.

[0240] DEFINITIONSAND ABBREVIA TIONS

[0241] Various aspects of the conductive elastomeric inks, molecular inks, traces printed using those inks, and printed electronic elements and devices disclosed herein may be illustrated by describing components that are coupled, attached, and / or joined. As used herein, the terms “coupled,” “attached,” and / or “joined” are interchangeably used to indicate either a direct connection between two components or, where appropriate, an indirect connection to one another through intervening or intermediate components. In contrast, when a component is referred to as being "directly coupled", “directly attached,” and / or “directly joined” to another component, there are no intervening elements shown in said examples.

[0242] Various aspects of the conductive elastomeric inks, molecular inks, traces printed using those inks, and printed electronic elements and devices disclosed herein may be described and illustrated with reference to one or more exemplary implementations. As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other variations of the devices, systems, or methods disclosed herein. "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. In addition, the word “comprising” as used herein means “including, but not limited to.”

[0243] Relative terms such as “lower” or “bottom” and “upper” or “top” may be used herein to describe one element’s relationship to another element illustrated in the drawings. It will be understood that relative terms are intended to encompass different orientations of the elements and / or devices disclosed herein in addition to the orientation depicted in the drawings. By way of example, if aspects of a strain sensor shown in the drawings are turned over, elements described as being on the “bottom” side of the otherelements would then be oriented on the “top” side of the other elements as shown in the relevant drawing. The term “bottom” can therefore encompass both an orientation of “bottom” and “top” depending on the particular orientation of the drawing.

[0244] It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. For example, although reference is made to “a” textile, “an” ink, and “the” sensor, one or more of any of these components and / or any other components described herein can be used.

[0245] Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0246] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0247] “Substantially free,” as used herein, is understood to mean inclusive of only trace amounts of a constituent. “Trace amounts” are those quantitative levels of a constituent that are barely detectable and provide no benefit to the functional properties of the subject composition, process, or articles formed therefrom. For example, a trace amount may constitute 1.0 wt.%, 0.5 wt.%, 0.1 wt.%, 0.05 wt.%, or even 0.01 wt.% of a component of any of the particle-free ink formulations disclosed herein. “Totally free,” as used herein, is understood to mean completely free of a constituent.

[0248] The terms flexible substrate and textile substrate are used interchangeably throughout the specification and may be understood to mean any woven or non-woven, organic or synthetic substrate unless specifically indicated otherwise. Moreover, when a fiber is referred to, it may be part of a woven or non-woven flexible substrate unless specifically indicated otherwise.

[0249] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.EXAMPLES

[0250] Example A: Production of a molecular ink

[0251] Exemplary molecular inks comprising silver complexes comprising a carboxylate second ligand (e.g., silver carboxylate) may be formed by reaction of a metal oxide or metal-acetate and a carboxylic acid in a reaction that affords analytically pure compounds and proceeds in quantitative yields.

[0252] As example, silver acetate was reacted with a carboxylic acid (isobutyrate and cyclopropate). The elemental analysis of the two silver complexes were C, 24.59; H, 3.72 and C, 24.68; H,2.56 for the isobutyrate and cyclopropate, respectively. Theoretical values are C, 24.64; H, 3.62 and C, 24.90; H, 2.61 for the isobutyrate and cyclopropate, respectively.

[0253] The metal-second ligand salt was then reacted with an excess of the first ligand to form the metal complex. In a typical preparation, silver isobutyrate was prepared as described above, and placed in a 25 mL one-neck 14 / 20 round bottom flask containing a Teflon coated magnetic stir bar. To this was added 13 eq. ethylenediamine (amounts as shown in Table 1 below). The reaction proceeded for 2 h at room temperature with stirring, filtered to remove any particulates, and the unreacted ethylenediamine was removed by rotary evaporation at 40°C to yield a white powder. Additional wash steps can be included. The isolated metal complex - ethylenediamine silver isobutyrate - was then dissolved to at least 100 mg / ml in a mixture of polar protic solvents (water, propylene glycol, and isopropanol) to form a molecular ink that is clear (see Table 2).Table 1Table 2

[0254] Example B: Strain resistance of molecular inks

[0255] Woven fabrics were printed using the molecular inks of the present disclosure and subjected to strain resistance measurements. Shown in FIG. 12 are results for electromechanical stretch testing under various amounts of stretching. The molecular ink and printing methods of the present disclosure provide conductive traces that are little affected by increased strain until the breakpoint of the textile (i.e., textile rips into two pieces). As shown in FIG. 12, the resistance of such a conductive trace does not increase under various amounts of stretching (0% to 230%) . This unusual behavior is demonstrated by a very slight increase in the average spot temperature of the trace (as measured using FLIR; data not shown), where the spot temperature correlates to the amount of heat generated when electrons flow through a stretched conductive fabric; the higher the temperature, the more heated generated by the flowing electrons.

[0256] Bendability of the printed traces was also evaluated, and only a small loss of conductivity (< 10%) was observed for bending of a conductive trace printed on woven textiles using the molecular inks and methods of the present disclosure (10,000 x bends in the trace; tested according to ASTM D522 - Mandel Bend Test). Nonwoven textiles showed reduced performance after 1,300 bends, which is likely a function of breakdown of the textile and not the conductive trace.

[0257] Example C: Fabric based strain sensors

[0258] Example Cl - Single Strain Sensor

[0259] Sensor electrodes were printed on 4-way stretch polyester / Spandex blend with a molecular ink (particle free silver ink of Example A) using a Model IP410 inkjet printer equipped with a Konica Minolta KM512 printhead. The printing platen was set at 75°C. After printing, oven curing was done for 25 minutes at 140°C.

[0260] A resistive ink (i.e., conductive elastomeric ink) was prepared from a 2-part, low viscosity liquid silicone rubber and conductive carbon. The carbon (10 pph) and liquid silicone rubber were ground until a uniform paste was formed. The resistive ink was stencil printed over the electrodes as illustrated in FIG. 1. Oven curing at 90° for 10 minutes produced an elastomeric resistive sensor. Resistivity of the conductive elastomeric ink was 8.700 ohms / square, and the gauge factor was 38.6. The gauge factor is a measure of strain sensitivity. The electrical resistance of the sensor is shown to increase as applied strain increases (FIG. 8 A)

[0261] Example C2

[0262] Sensor electrodes were printed on 4-way stretch nylon / Elastane (61 / 39) blend with a particle free silver ink using a Model IP410 inkjet printer equipped with a Konica Minolta KM512 printhead. The printing platen was set at 75°C. After printing, oven curing was done for 25 minutes at 140°C.

[0263] A resistive ink was prepared from a 2-part, low viscosity liquid silicone rubber and conductive carbon. The carbon (11 pph) and liquid silicone rubber were ground until a uniform paste was formed. The resistive ink was stencil printed over the electrodes as shown in the sketch. Oven curing at 90° for 10 minutes produced an elastomeric resistive sensor. Resistivity of the conductive elastomeric ink was 1600 ohms / square and the gauge factor was 8.1. The electrical resistance of the sensor is shown to increase as applied strain increases (FIG. 8B)

[0264] Example C3

[0265] Sensor electrodes were printed on 4-way stretch nylon / Elastane (85 / 15) blend with a particle free silver ink using a Model IP410 inkjet printer equipped with a Konica Minolta KM512 printhead. The printing platen was set at 75°C. After printing, oven curing was done for 25 minutes at 140°C.

[0266] A resistive ink was prepared from a 2-part, low viscosity liquid silicone rubber and conductive carbon. The carbon (12 pph) and liquid silicone rubber were ground until a uniform paste was formed. The resistive ink was stencil printed over the electrodes as shown in the sketch. Oven curing at 90° for 10 minutes produced an elastomeric resistive sensor. Resistivity of the conductive elastomer ink was 975 ohms / square and the gauge factor was 5.3. The electrical resistance of the sensor is shown to increase as applied strain increases (FIG. 8C)

[0267] Example D: Fabric based strain sensor array

[0268] Example DI

[0269] Four pairs of sensor electrodes were printed on 4-way stretch polyester / Spandex blend using a molecular ink comprising silver. After printing, oven curing was done for 25 minutes at 140°C.

[0270] A resistive ink was prepared from a 2-part, low viscosity liquid silicone rubber and conductive carbon. The carbon (10 PPH) and liquid silicone rubber were mixed with a high shear mixing blade until a uniform paste was formed. The resistive ink was stencil printed, electrically connecting thepairs of silver electrodes to form an array of 4 parallel, 4 mm x 225 mm sensors, spaced 50 mm apart. Oven curing at 90° for 10 minutes produced an elastomeric resistive sensor. Resistivity of the conductive elastomer ink was 1000 ohms / square. A second array was prepared in the same manner. The two unidirectional arrays were oriented orthogonally to form a bidirectional mapping array.

[0271] Example D2

[0272] The sensor array of Example D 1 was sandwiched between a top layer of fabric (top layer, E of FIG. 3B) and a compressible substrate layer (D of FIG. 3B). Initial resistance measurements were made for each of the 8 sensors using a multimeter, then a 7 lb. weight (3 -inch x 4-inch x 2-inch) was placed on the top layer, i.e., over the sensor array. Resistances were again measured and the percent difference for each sensor was calculated. An average resistance was calculated for each position of the 4 X 4 array construct, shown in Table 3.Table 3

[0273] Example D3

[0274] Eleven pairs of electrodes were printed on 2-way stretch knit fabric blend using a particle free silver ink with a Model IP410 inkjet printer equipped with a Konica Minolta KM512 printhead. After printing, oven curing was done for 25 minutes at 140°C.

[0275] A resistive ink was prepared from a 2-part, low viscosity liquid silicone rubber and conductive carbon. The carbon (12PPH) and liquid silicone rubber were combined using high shear mixing until a uniform paste was formed. The resistive ink was stencil printed to form linear strain sensors electrically connecting the electrode pairs as shown in Figure 1. Oven curing at 90° for 10 minutes produced an elastomeric resistive 11 -sensor array for a first layer of the construct. Resistivity of conductive elastomer ink was 975 ohms / square.

[0276] The second layer of the array construct was fabricated in the same manner to produce a 6- sensor array. The two layers were stacked with sensors oriented orthogonally to form a 6 x 11 array construct.

[0277] Example D4

[0278] The sensor array construct of Example D3 was placed between a cover layer of textile and a compressible substrate, i.e., polyurethane foam. Initial resistance measurements were made for each of the 17-sensors using a multimeter, then two 10 lb. spherical weights were placed on the sensor array. Resistances were again measured and the percent difference for each sensor was calculated. An average resistance was calculated for each position of the 6 X 11 array construct, shown in Table 4 (6 horizontalsensors: A-F, and 11 vertical sensors: 1-11). These data are displayed as a contour plot, FIG. 6, and as a 3- D plot showing strain deformation of the sensor array on the substrate, FIG. 7.Table 4

[0279] Example E: Fabric based temperature sensors

[0280] Interdigitated sensor electrodes were printed on 4-way stretch polyester / Spandex blend using a particle free silver ink using a Model IP410 inkjet printer equipped with a Konica Minolta KM512 printhead. The printing platen was set at 75°C. After printing, oven curing was done for 25 minutes at 140°C.

[0281] A temperature sensitive resistive ink coating was applied to the fabric bridging the electrodes. The ink was an aqueous carboxylic acid functional multiwall carbon nanotube dispersion. Oven drying for 30 minutes at 100°C produced a conformal coating with good adhesion and flexibility. After drying, a 3 -mil polyethylene film was heat laminated over the sensor area as a protective layer and to reduce stretching of the temperature sensor during use. The change in resistance with temperature is -3662 ohms / °C. The electrical resistance of the sensor is shown to decrease linearly as temperature increases (FIG. 10)

Claims

CLAIMSWhat is claimed is:

1. A flexible strain sensor comprising: a first electrode printed with a molecular ink; a second electrode printed with the molecular ink, the second electrode spaced apart from the first electrode; and a sensor trace printed with an elastomeric conductive ink, wherein the sensor trace covers at least an end portion of each of the first and second electrode and extends along the region therebetween, wherein the first and second electrodes and the sensor trace are printed on a stretchable textile, wherein the molecular ink comprises a particle-free metal complex composition and a solvent, and wherein the flexible strain sensor is configured to initiate an electrical signal upon deformation of the sensor trace.

2. The strain sensor according to Claim 1, further comprising: a control circuitry connected to the first and second electrodes, a transceiver, and a controller, wherein the control circuitry is configured to carry the electrical signal to the transceiver and communicate a registered change in resistance to the controller.

3. The strain sensor of Claim 2, wherein the control circuitry comprises conductive traces printed with the molecular ink.

4. The strain sensor according to Claim 1, wherein the particle-free metal complex composition comprises: at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent, wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

5. The strain sensor according to Claim 1, wherein the conductive elastomeric ink comprises 5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

6. The strain sensor according to Claim 4, wherein the conductive elastomeric ink comprises 5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

7. The strain sensor according to Claim 1, wherein the stretchable textile is a two-way or four-way stretch fabric.

8. The strain sensor according to Claim 7, wherein the stretchable textile comprises polyester, polyamide, a polyether-polyurea copolymer, nylon, and blends thereof.

9. The strain sensor according to Claim 7, wherein the two-way or four-way stretch fabric comprises a polyester / polyether-polyurea copolymer blend or a nylon / polyether-polyurea copolymer blend.

10. The strain sensor according to Claim 1, wherein the molecular ink conformally coats fibers of the stretchable textile, and the conductive elastomeric ink penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

11. A strain sensor array comprising: a plurality of equally spaced, parallel strain sensors according to claim 1 printed on a stretchable textile.

12. The strain sensor array according to Claim 11, further comprising: a control circuitry comprising signal leads connected to the first and second electrodes of each of the strain sensors in the strain sensor array, wherein the control circuitry is also connected to a transceiver and a controller and is configured to carry electrical signals from each of the strain sensors in the strain sensor array to the transceiver and communicate a registered change in resistance for each of the strain sensors to the controller.

13. The strain sensor array according to Claim 12, wherein the control circuitry comprises conductive traces printed with the molecular ink.

14. The strain sensor array according to Claim 11, wherein the particle-free metal complex composition comprises: at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent, wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

15. The strain sensor array according to Claim 11, wherein the conductive elastomeric ink comprises5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

16. The strain sensor array according to Claim 14, wherein the conductive elastomeric ink comprises5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

17. The strain sensor array according to Claim 11, wherein the stretchable textile is a two-way or four- way stretch fabric.

18. The strain sensor array according to Claim 17, wherein the stretchable textile comprises polyester, polyamide, a polyether-polyurea copolymer, nylon, and blends thereof.

19. The strain sensor array according to Claim 17, wherein the two-way or four-way stretch fabric comprises a polyester / polyether-polyurea copolymer blend or a nylon / polyether-polyurea copolymer blend.

20. The strain sensor array according to Claim 11, wherein the molecular ink conformally coats fibers of the stretchable textile, and the conductive elastomeric ink penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

21. A strain sensor construct comprising : a first strain sensor array according to claim 10 printed on a first stretchable textile; and a second strain sensor array according to claim 10 printed on a second stretchable textile, wherein the first and second strain sensor arrays are positioned so that the plurality of equally spaced, parallel strain sensors of the first strain sensor array are orthogonal to the plurality of equally spaced, parallel strain sensors of the second strain sensor array.

22. The strain sensor construct according to Claim 21, further comprising a stretchable substrate positioned between the first and second stretchable textiles; and a compressible substrate positioned below the second stretchable textile.

23. The strain sensor construct according to Claim 21, further comprising: a control circuitry comprising signal leads connected to the first and second electrodes of each of the strain sensors in the first and second strain sensor arrays, wherein the control circuitry is also connected to a transceiver and a controller and is configured to carry electrical signals from each of the strain sensors in the first and second strain sensor arrays to the transceiver and communicate a registered change in resistance for each of the strain sensors to the controller.

24. The strain sensor construct according to Claim 23, wherein the control circuitry comprises conductive traces printed with the molecular ink.

25. The strain sensor construct according to Claim 21, wherein the particle-free metal complex composition comprises: at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent,wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

26. The strain sensor construct according to Claim 21, wherein the conductive elastomeric ink comprises 5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 15pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

27. The strain sensor construct according to Claim 26, wherein the conductive elastomeric ink comprises 5 to 20 pph carbon black in a low viscosity liquid silicone rubber, such as 5 to 1 pph, or 7.5 to 15pph, or 9 to 13pph carbon black in a low viscosity liquid silicone rubber.

28. The strain sensor construct according to Claim 26, wherein the stretchable textile is a two-way or four- way stretch fabric.

29. The strain sensor construct according to Claim 28, wherein the stretchable textile comprises polyester, polyamide, a polyether-polyurea copolymer, nylon, and blends thereof.

30. The strain sensor construct according to Claim 28, wherein the two-way or four-way stretch fabric comprises a polyester / polyether-polyurea copolymer blend or a nylon / polyether-polyurea copolymer blend.

31. The strain sensor construct according to Claim 21 , wherein the molecular ink conformally coats fibers of the stretchable textile, and the conductive elastomeric ink penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

32. A temperature sensor comprising: a first electrode printed with a molecular ink; a second electrode printed with the molecular ink, the second electrode spaced apart from the first electrode; and a sensor trace printed with a temperature sensitive resistive coating, wherein the sensor trace covers at least an end portion of each of the first and second electrode and extends along the region therebetween, wherein the first and second electrodes and the sensor trace are printed on a textile, wherein the molecular ink comprises a particle-free metal complex composition and a solvent, and wherein the temperature sensor is configured to initiate an electrical signal upon a change in temperature at the sensor trace.

33. The temperature sensor according to Claim 32, further comprising: a control circuitry connected to the first and second electrodes, a transceiver, and a controller, wherein the control circuitry is configured to carry the electrical signal to the transceiver and communicate a registered change in resistance to the controller.

34. The temperature sensor of Claim 33, wherein the control circuitry comprises conductive traces printed with the molecular ink.

35. The temperature sensor according to Claim 32, wherein the particle-free metal complex composition comprises:at least one metal complex comprising: at least one metal, at least one first ligand that is a sigma donor to the metal and volatilizes upon heating the metal complex, and at least one second ligand that is different from the first ligand and volatilizes upon heating the metal complex, wherein the metal complex has a solubility measured at 25°C of at least 250 mg / ml in the solvent, wherein the at least one metal, the at least one first ligand, and the at least one second ligand are provided in stoichiometric amounts in the conductive ink.

36. The temperature sensor according to Claim 32, wherein the temperature sensitive resistive coating comprises a dispersion of carbon nanotubes in a low viscosity liquid silicone rubber, wherein the carbon nanotubes are included at 0.2 to 5pph, or 0.5 to 4pph, or 1 to 3pph, or 1 to 2pph.

37. The temperature sensor according to Claim 35, wherein the temperature sensitive resistive coating comprises an aqueous carboxylic acid functional multiwall carbon nanotube dispersion.

38. The temperature sensor according to Claim 32, further comprising: a polymeric film was heat laminated over the sensor trace to restrict stretching of the flexible textile.

39. The temperature sensor according to Claim 32, wherein the molecular ink conformally coats fibers of the stretchable textile, and the temperature sensitive resistive coating penetrates the weave of the textile at least in the region of overlap on the first and second electrodes.

40. An electronic textile comprising: a strain sensor construct according to Claim 21 ; and at least one temperature sensor according to Claim 32.

41. The electronic textile according to Claim 40, wherein the at least one temperature sensor is printed on one of the first or second flexible textiles of the strain sensor array, or wherein the at least one temperature sensor is printed on the stretchable substrate that is sandwiched between the first and second flexible textiles.

42. The electronic textile according to Claim 41, wherein the at least one temperature sensor comprises a polymeric film was heat laminated over the sensor trace thereof to restrict stretching of the flexible textile or the stretchable substrate.

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