Multidirectional flexible sensor and preparation method thereof

Abstract

The invention provides a multidirectional flexible sensor and a preparation method, the multidirectional flexible sensor comprises a plurality of conductive paths and a plurality of flexible substrates, the conductive paths continuously extend in a first direction, the diameter of the conductive paths gradually increases in a second direction, and the second direction and the first direction are inclined at a certain angle; the plurality of conductive paths are radially dispersed, a certain gap is formed between the adjacent conductive paths, the diameter of the gap is gradually increased along the second direction, the flexible substrate is filled in the gap, and the flexible substrate and the conductive paths are adhered to form the sensor with the orientation gradient. The multidirectional flexible sensor provided by the invention has a microcosmic orientation gradient structure, has an excellent multidirectional sensing function, and can respond to mechanical stimulation in different directions and generate different resistance changes. And meanwhile, the flexible matrix material is filled in the gaps between the conductive paths, so that the flexibility and environmental adaptability of the material are further enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible multi-directional sensors, and in particular to a multi-directional flexible sensor and a preparation method thereof. Background Art

[0002] With the rapid development of smart devices and wearable technology, flexible sensors, as an important component of information acquisition, have gradually become a research hotspot for the new generation of sensor technology. Traditional rigid sensors, such as those made of metal or semiconductor materials, cannot adapt to the complex morphology of flexible surfaces such as human skin due to their high stiffness, poor flexibility, and limited strain range. Therefore, flexible sensors are widely used in smart wearables, health monitoring, robot control, and human-computer interaction due to their advantages such as lightness, softness, small size, and good biocompatibility.

[0003] However, in practical applications, mechanical stimuli (such as pressure, tension, shear force, etc.) often act on the sensor at the same time, and their mutual coupling makes the sensor response complicated. Existing multi-directional sensors face certain challenges in identifying the direction and motion mode of the applied load, mainly due to the isotropic properties of their structure and materials, which leads to similar sensor responses under forces in different directions, making it difficult to effectively distinguish multiple mechanical stimulation modes.

[0004] To solve this problem, researchers have proposed multi-directional flexible sensors based on anisotropic design, which decouple multiple stimulation modes by designing special material structures and sensor arrays. However, these methods often involve complex preparation processes and cumbersome assembly processes, which limits their development in lightweight, functional and large-scale applications. Although integrated molding technologies such as 3D printing have been developed to prepare multi-directional sensors, multiple circuits still need to be assembled. There is an urgent need for a new and simple preparation method that can realize the spatial distribution of mechanical stimulation and deformation pattern recognition through a single circuit, so as to promote the widespread application of flexible sensors in health monitoring, intelligent auxiliary equipment and other fields. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a multi-directional flexible sensor and a preparation method, which has a microscopic orientation gradient structure and excellent multi-directional sensing function, has strong flexibility, adaptability and versatility, and can be widely used in smart wearables, health monitoring, human-computer interaction and other fields.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A multi-directional flexible sensor, comprising:

[0008] A plurality of conductive paths, wherein the conductive paths extend continuously in a first direction, the diameter of the conductive paths gradually increases along a second direction, the second direction is inclined at a certain angle to the first direction, the plurality of conductive paths are radially spread out, and there is a certain gap between adjacent conductive paths, and the gap gradually increases in diameter along the second direction;

[0009] A flexible substrate is filled in the gap, and the flexible substrate is bonded to the conductive path to form a sensor with an orientation gradient.

[0010] Furthermore, the conductive path is any one or a combination of a lamellar, columnar, or porous structure, the conductive path includes a conductive substance, the conductive substance includes any one or a combination of carbon materials, conductive polymers, ionic liquids, metals, and metal ions, and the flexible matrix includes any one or a combination of hydrogels, aerogels, oil gels, rubbers, and plastics.

[0011] Furthermore, the orientation gradient is any one of spacing, size, and material gradient or a combination of several of them.

[0012] Furthermore, the size gradient includes any one of pore size and particle size or a combination of the two.

[0013] Furthermore, the material gradient includes any one of a concentration gradient and a cross-linking density gradient or a combination of the two, wherein

[0014] The concentration gradient is generated by layer-by-layer printing or gradient cross-linking of materials of different concentrations.

[0015] Furthermore, the conductive wire paths at the two side parts have a certain angle with the conductive wire path at the middle part, and the angle between the conductive wire paths at the outer side and the conductive wire path at the middle part is larger.

[0016] A method for preparing a multi-directional flexible sensor comprises the following steps:

[0017] Prepare conductive material slurry and flexible matrix slurry in a certain proportion;

[0018] Cryoprinting: Make the cold source reach the set temperature, fill the configured conductive material slurry into the extruder, extrude the conductive material slurry toward the cold source through the extruder, and at the same time make the cold source and the extruder move relative to each other in the first direction. During the relative movement of the cold source and the extruder, the conductive material slurry that first contacts the cold source will quickly freeze into ice crystals and grow upward. During the growth of the ice crystals, the solutes in the conductive material slurry will be squeezed on both sides of the ice crystals to form a conductive path growing in the second direction. The diameter of the ice crystals and the conductive path increases in the direction away from the cold source.

[0019] Remove ice crystals formed during freezing;

[0020] The flexible matrix is ​​filled into the position of the original ice crystals, and the flexible matrix is ​​combined with the conductive path under certain temperature conditions.

[0021] Furthermore, when the extruder extrude the conductive material slurry toward the cold source, extrusion freezing printing is used, and the freezing rate and the cold source moving rate are matched with the viscosity of the conductive material slurry.

[0022] Furthermore, the preparation method includes a mold method and a mold-free method, wherein:

[0023] A mold method is used to set a mold on the cold source. The mold is composed of one or more materials with different thermal conductivity to adjust the local freezing orientation and rate. The conductive material slurry is extruded into the mold on the cold source through an extruder, or

[0024] The mold-free method does not require a mold during the freezing printing process. The contact interface between the conductive material slurry and the cold source is a line or a surface, and a certain geometric shape is formed before the conductive material slurry is completely radially dispersed.

[0025] Furthermore, the cold source is a point / surface or a combination of the two in space. The growth pattern of ice crystals is controlled by adjusting the position and cooling rate of the cold source. The radial growth of ice crystals causes the ice crystals to squeeze the conductive path along the first direction to form a uniform and continuous conductive path.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] The present invention provides a multi-directional flexible sensor with a thickness gradient, a spacing gradient and / or an orientation gradient, so that the sensor can achieve anisotropic response on a microstructure. The multi-directional sensing capability is obtained by analyzing the change amplitude and waveform, which simplifies the design and manufacturing process of the sensor. It can effectively detect various mechanical stimuli such as compression, stretching, bending, etc., and identify different deformation directions of different stimuli.

[0028] The preparation method provided by the present invention has high flexibility and adaptability, and can adjust the characteristics of the conductive path and the flexible matrix material according to different application requirements. Through the configuration of particles with different particle sizes, mold selection, freezing source control and layered design, sensors that meet specific requirements can be customized. This variability and adaptability make the present invention widely applicable to the fields of smart wearables, health monitoring, human-computer interaction, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1A schematic diagram of the decomposition structure of a multi-directional flexible sensor provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of thickness and spacing of a multi-directional flexible sensor provided by an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of a process for preparing a multi-directional flexible sensor provided in Example 2 of the present invention;

[0033] Figure 4a The resistance change curve of the orientation gradient multi-directional flexible sensor prepared in Example 3 of the present invention under 20% compressive strain and 20% tensile strain;

[0034] Figure 4b The resistance change curve of the orientation gradient multi-directional flexible sensor prepared in Example 3 of the present invention under 45° torsional strain to the left / right;

[0035] Figure 4c The resistance change curve of the orientation gradient multi-directional flexible sensor prepared in Example 3 of the present invention under 45° upward / downward bending strain;

[0036] Figure 4d The resistance change curve of the orientation gradient multi-directional flexible sensor prepared in Example 3 of the present invention under 45° bending strain to the left / right;

[0037] Figure 5 Schematic diagram of a multi-directional flexible sensor with particle size orientation gradient provided in Example 4 of the present invention;

[0038] Figure 6 A schematic diagram of a layered orientation gradient multi-directional flexible sensor provided in Example 5 of the present invention;

[0039] Figure 7 Schematic diagram of a concentration gradient multi-directional flexible sensor provided in an embodiment of the present invention.

[0040] In the figure: 11, conductive path; 12, conductive path formed by deposition of particles of different sizes; 21, flexible substrate; 31, first layered material; 32, second layered material; 41, high thermal conductivity mold; 42, low thermal conductivity mold; 43, cold source. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In the description of the embodiments of the present invention, unless otherwise specified, “ / ” means or. For example, A / B can mean A or B. The “and / or” in the text is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present invention, “multiple” refers to two or more than two.

[0043] In some processes described in the embodiments of the present invention, multiple operations or steps appearing in a specific order are included, but it should be understood that these operations or steps may not be executed in the order in which they appear in the embodiments of the present invention or may be executed in parallel, and the sequence numbers of the operations are only used to distinguish different operations, and the sequence numbers themselves do not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed in sequence or in parallel, and these operations or steps may be combined.

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0045] Example 1

[0046] Embodiment 1 provides a multi-directional flexible sensor, such as Figure 1 FIG. 1 is a schematic diagram of a multi-directional flexible sensor decomposition structure provided by an embodiment of the present invention. The multi-directional flexible sensor includes:

[0047] A plurality of conductive paths 11, wherein the conductive paths 11 extend continuously in a first direction, the diameter of the conductive paths 11 gradually increases along a second direction, the second direction is inclined at a certain angle to the first direction, the plurality of conductive paths 11 are radially dispersed, and there is a certain gap between adjacent conductive paths 11 and / or inside the conductive paths 11, and the spacing gradually increases along the second direction;

[0048] The flexible substrate 21 is filled in the gap, and the flexible substrate 21 is bonded to the conductive path 11 to form a sensor with an orientation gradient, which has an anisotropic response to external mechanical stimulation.

[0049] This embodiment provides a multi-directional flexible sensor, in which the conductive path 11 has a cross-sectional orientation gradient along a first direction, and the flexible substrate 21 is distributed in the gaps between the conductive paths 11 to improve flexibility and stress response capabilities. When the multi-directional flexible sensor is deformed, the distance between adjacent conductive paths 11 or the distance between conductive materials within a single conductive path 11 changes, resulting in a corresponding change in resistance.

[0050] Specifically, when a certain part of the multi-directional flexible sensor is subjected to tensile strain, the flexible substrate corresponding to the part drives the conductive materials on the conductive path 11 to move away from each other, the original conductive path 11 is interrupted, and the overall resistance increases; conversely, when a certain part of the multi-directional flexible sensor is subjected to compressive stress, the flexible substrate corresponding to the part drives the conductive materials on the conductive path 11 to move closer to each other, constructing more conductive paths 11, and the overall resistance decreases.

[0051] like Figure 2 As shown, the conductive paths 11 inside the multi-directional flexible sensor are radially distributed, and have a thickness gradient and a spacing gradient along the second direction. The thickness refers to the width of a single conductive path 11 in the cross section, the spacing refers to the distance between adjacent conductive paths 11 in the cross section, and the orientation gradient refers to the gradient of the former two due to the change in position.

[0052] In this embodiment, the multi-directional flexible sensor is usually generated by cryoprinting, so the first direction is the printing direction, so that the multi-directional flexible sensor has a continuous microscopic conductive path 11 in the longitudinal section, and the second direction is the growth direction of the conductive path 11. The conductive path 11 is combined with the flexible substrate to make the multi-directional flexible sensor have an orientation gradient in the cross section.

[0053] In this embodiment, the conductive path 11 is any one of a laminar, columnar, and porous structure or a combination of several of them.

[0054] Preferably, the lamellar and columnar structures can be obtained by adjusting the concentration of the printing slurry. When the concentration is less than 1%, the material presents a columnar microscopic conductive path after the freezing process, and when the concentration is in the range of 1-20%, the material presents a lamellar microscopic conductive path after the freezing process. For the printing slurry that is highly viscous after dissolution, when the concentration is too high, a larger extrusion device needs to be used.

[0055] In this embodiment, the conductive path 11 includes a conductive material, and the conductive material includes any one or a combination of carbon materials, conductive polymers, ionic liquids, metals, and metal ions.

[0056] In this embodiment, the flexible substrate 21 includes any one or a combination of hydrogel, aerogel, oil gel, rubber, and plastic. By setting a flexible base, it can be combined with the conductive path 11 through microscopic interaction to enhance the mechanical properties and stability. These filling materials not only enhance the mechanical flexibility of the sensor, but also improve its adaptability on complex morphological surfaces, especially when applied on human skin or other flexible electronic devices, it can provide good fit and comfort.

[0057] In this embodiment, the flexible substrate 21 can be combined with the conductive path 11 through microscopic interaction to further enhance the mechanical properties and stability. The combination mode is any one or a combination of covalent bond, ionic bond, metal bond, hydrogen bond, and van der Waals force.

[0058] In this embodiment, the orientation gradient is any one of spacing, size, and material gradient or a combination of several of them.

[0059] In this embodiment, the size gradient includes any one of pore size and particle size or a combination of the two. In the size gradient, particles of different particle sizes can be assembled into a conductive material. After filling the flexible substrate, if the particles are etched away, the original particle positions become holes, and the particle size is converted into the pore size. The strategy for generating a porous structure is not only the etching method, but also the foaming method, the 3D printing method, and the template method.

[0060] Preferably, the pore size gradient can be obtained by pre-sedimentation and etching or foaming method. The pre-sedimentation time is controlled between 5 seconds and 1 hour.

[0061] In this embodiment, different pore sizes can be obtained through different pore gradient preparation strategies. The pore size generated by the template method is 10-200 μm, the pore size generated by the foaming method is 10-2000 μm, and the 3D printing method can generate a macro porous structure with a pore size of 0.5-10 mm.

[0062] In this embodiment, the material gradient includes any one of a concentration gradient and a cross-linking density gradient or a combination of the two. Specifically, the orientation gradient can be achieved through a layered design of different materials, and the layered design is achieved by printing solutions of different monomer or cross-linking agent concentrations layer by layer. The layer height of the layered printing is controlled at 200-2000μm, and a printing interval can be set between two adjacent layers to ensure that the lower layer is fully pre-cooled, so that the upper and lower layers have better interface fusion, thereby improving the mechanical and electrical properties of the sensor. The printing interval is 1 second to 5 minutes, and the higher the number of layers, the longer the printing interval.

[0063] Preferably, when preparing a sensor with a concentration gradient, the monomer concentration can be gradually increased from 10% in the bottom layer to 30% in the top layer, and the height of each layer is 500 μm. When the number of printed layers is 2, the printing interval can be set to 3 seconds; when the number of printed layers is 5, the printing interval can be set to 1 minute; when the number of printed layers increases to 10, the printing interval is extended to 3 minutes.

[0064] By controlling the gradient distribution of light, temperature or cross-linking agent, the degree of cross-linking can be controlled, thereby forming an oriented structure with gradient characteristics. The light intensity field can be achieved through a parallel light source, so that the light is irradiated at a specific angle, and the light intensity is higher near the light source, resulting in a higher cross-linking density. The temperature field setting can be achieved by placing a cold source and a heat source. The cold source can be a semiconductor refrigeration sheet or a low-temperature liquid such as liquid carbon dioxide, liquid nitrogen, or ice water contact, and the heat source can be an electric heating plate or a laser.

[0065] Preferably, in the cross-linking step, an electric heating plate is used for heating, and the temperature is gradually reduced from 100° C. at the bottom layer to 50° C. at the top layer, thereby forming a temperature gradient, which in turn affects the cross-linking density.

[0066] The layered design can adjust the physical and chemical properties of each layer according to actual needs, and optimize the performance of the sensor by adjusting the conductivity, flexibility or mechanical strength of different layers. In addition, the gradient cross-linking method can accurately control the structure of the conductive path 11, so that the sensor can produce different responses when subjected to forces in multiple directions.

[0067] In this embodiment, the concentration gradient is generated by layer-by-layer printing or gradient cross-linking of materials with different concentrations, such as Figure 7 FIG. 1 is a schematic diagram of a concentration gradient multi-directional flexible sensor provided by the present invention.

[0068] In this embodiment, the plurality of conductive paths are arranged axially symmetrically, and the conductive paths on both sides have a certain angle with the conductive paths in the middle, and the angle between the conductive paths on the outer sides and the conductive paths 11 in the middle is larger. When there is an angle, when bending in different directions, some parts of the conductive paths 11 may be close to each other and other parts may be partially far away. Figure 1 As shown, when the multi-directional flexible sensor bends downward, the distance between the tops of several conductive paths 11 increases to cause the resistance at the top to increase, and the distance between the bottoms of several conductive paths 11 decreases to cause the resistance at the bottom to decrease; when the multi-directional flexible sensor bends upward, the distance between the bottoms of several conductive paths 11 increases to cause the resistance at the bottom to increase, and the distance between the tops of several conductive paths 11 decreases to cause the resistance at the top to decrease, thereby enhancing the anisotropy, and the larger the angle between the outer wire path and the conductive path 11 in the middle part, the more obvious the anisotropy will be.

[0069] Example 2

[0070] Embodiment 2 provides a method for preparing a multi-directional flexible sensor, such as Figure 3 As shown, the following steps are included:

[0071] Step S1: preparing a conductive material slurry and a flexible substrate slurry in a certain proportion;

[0072] Step S2: freezing printing: making the cold source 43 reach the set temperature, filling the configured conductive material slurry into the extruder, extruding the conductive material slurry toward the cold source 43 through the extruder and moving the cold source 43 toward the first direction at the same time, during the movement of the cold source 43, the conductive material slurry that first contacts the cold source 43 will quickly freeze into ice crystals and grow in a direction away from the cold source 43, during the growth of the ice crystals, the solutes in the conductive material slurry will be squeezed on both sides of the ice crystals to form a conductive path 11 growing along the second direction, and the diameters of the ice crystals and the conductive path 11 will gradually increase in the direction away from the cold source 43;

[0073] Step S3: removing ice crystals generated during the freezing process;

[0074] Step S4: Fill the flexible matrix slurry into the position of the original ice crystals, and combine the flexible matrix 21 with the conductive path 11 under certain temperature conditions. Through step S4, the flexible matrix 21 material is introduced between adjacent conductive paths 11 and / or inside the conductive path 11 to replace the original ice crystal positions, thereby improving the flexibility and deformability of the material.

[0075] In this embodiment, in step S1, the conductive material slurry and the flexible matrix slurry are configured in a certain ratio, and the viscosity of the conductive material slurry and the flexible matrix slurry ranges from 500cP to 5000cP. When the viscosity is low, the conductive material slurry will gather into droplets after extrusion, rather than a uniform straight line; when the viscosity is high, since this method is based on an extruder, the slurry with excessive viscosity will be difficult to extrude due to insufficient extruder power. In this embodiment, mechanical stirring, ultrasound, centrifugation, etc. are used to evenly disperse the solutes in the conductive material slurry and the flexible matrix slurry, and the viscosity of the conductive material slurry and the flexible matrix slurry should be adapted to the power of the extrusion equipment to which it belongs.

[0076] In this embodiment, in step S1, the conductive path 11 is made of a solution prepared by particles of different particle sizes. Before printing, a pre-sedimentation method can be used to obtain a particle size gradient, and the pre-sedimentation time is 5 seconds to 1 hour. By designing the particle size gradient, the resistance characteristics of the conductive path 11 in different regions are controlled, which helps to improve the sensitivity and multi-directional response capability of the sensor.

[0077] In this embodiment, the orientation gradient is generated because when the temperature field is a point or a surface and conducts from the bottom, the radial temperature gradient will form a corresponding (i.e., radial) ice crystal growth direction on the circular contour of the cross section, forming a conductive path with an orientation gradient on the cross section. Due to the axial symmetry of the temperature field, the conductive gradient in the cross-sectional direction is also symmetrical along the symmetry axis, and there is a difference in the orientation of the lamellar structure in the conductive paths on both sides.

[0078] In this embodiment, in step S2, the temperature of the cold source 43 is set to -100°C-0°C to ensure that the conductive material slurry contacting the cold source 43 will quickly freeze into ice crystals and grow away from the cold source 43. The flexible substrate 21 is in the gap between two adjacent conductive paths 11, and this gap is a gap generated by ice as a template. And, when the conductive path 11 is a porous material, it can also be filled in the gap of the conductive material. For example, in the orientation gradient of the pore size composition, the flexible substrate 21 can be filled in the micropores.

[0079] In step S2 of this embodiment, extrusion freezing printing is used when the extruder extrude the conductive material slurry toward the cold source 43, and the freezing rate and the moving rate of the cold source 43 are matched with the viscosity of the conductive material slurry.

[0080] In step S3 of this embodiment, freeze drying, ice melting complexation, supercritical drying, room temperature drying, etc. are used to remove ice crystals generated during the freezing process. The positions of the original ice crystals are replaced by air or liquid, and the microstructure and orientation inside the sample are retained.

[0081] In step S4 of this embodiment, the flexible substrate 21 is combined with the conductive path 11 by immersion, negative pressure immersion, etc., wherein negative pressure immersion is suitable for high-viscosity fillers, and the immersion method is suitable for low-viscosity materials. The flexible substrate 21 is combined with the conductive path 11 under certain temperature conditions to improve the flexibility and environmental adaptability of the sensor.

[0082] In this embodiment, in step S2, the preparation method includes a mold method and a mold-free method to form different sensors, wherein:

[0083] There is a mold method, in which a mold is set on the cold source 43, and the mold is composed of one or more materials with different thermal conductivity to adjust the local freezing orientation and rate, and the conductive material slurry is extruded into the mold on the cold source 43 by an extruder, or

[0084] In the mold-free method, no mold is required in the freezing printing process, and the contact interface between the conductive material slurry and the cold source 43 is a line or a surface, forming a certain geometric shape before the conductive material slurry is completely radially dispersed.

[0085] Among them, the microstructure generated by the mold method has orientation gradient differences, and the number of different orientations is greater than or equal to 1.

[0086] In this embodiment, the mold method can use dual printing nozzles to print layer by layer, and the generated structure has 4 different micro-orientation gradient units, and stresses from 4 different directions in the plane can be detected.

[0087] In this embodiment, the mold is composed of one or more materials with different thermal conductivity, and the mold shape is any one or a combination of rectangle, star, triangle, circle. By adjusting the thermal conductivity and shape of the mold, the local freezing orientation and rate are adjusted, so as to accurately control the growth mode of ice crystals and further realize the regulation of microstructure.

[0088] In this embodiment, the thermal conductivity difference is obtained by any one or a combination of the material surface structure, thickness, density, thermal conductivity, roughness, and wettability.

[0089] In this embodiment, the cold source 43 in the freezing process can be a point / surface or a combination of the two in space. By adjusting the position of the cold source 43 and the cooling rate, the growth mode of ice crystals can be controlled. The radial growth of ice crystals helps to squeeze the material along the printing direction to form a uniform and continuous conductive path 11. In the specific implementation of this embodiment, the cold source 43 is a cold stage.

[0090] In this embodiment, no mold is used in the freezing printing process, and the contact interface between the printing slurry and the cold source 43 is a line or a surface, forming a certain geometric shape before being fully spread out.

[0091] In this embodiment, both the mold-based method and the mold-free method are adapted to the spacing, size, material gradient design and preparation method thereof.

[0092] Several specific embodiments are given below to illustrate in detail a multi-directional flexible sensor and a preparation method provided by the present invention.

[0093] Example 3

[0094] Embodiment 3 discloses a method for preparing a multi-directional flexible sensor, which specifically includes:

[0095] Step S1: preparing a conductive material slurry, preparing a 30 mg / mL sodium carboxymethyl cellulose solution, adding multi-walled carbon nanotubes (length 10-20 μm, diameter 5-10 nm) after the solution is fully dissolved, the weight ratio of multi-walled carbon nanotubes to sodium carboxymethyl cellulose is 1:3, and the conductive material slurry is fully stirred for 24 hours for use; preparing a flexible matrix slurry, using water and dimethyl sulfoxide as solvents, and preparing 20 g of the solvent in a solvent ratio of 2:3, then adding 2 g of polyvinyl alcohol to the solvent and stirring at 90° C. for 2 hours until fully dissolved to form a hydrogel solution;

[0096] Step S2: extrusion and freezing of the conductive material slurry, the extrusion rate of the extruder is set to 2 mL / min, the moving rate of the cold source 43 is set to 9 m / min, and the temperature of the cold source 43 is set to -70°C;

[0097] Step S3: ice crystal removal, using the ice melting complexation method, which can preserve the internal microstructure in a short time, the frozen sample is placed in a 2wt% copper nitrate ethanol solution at -20°C for 2 hours;

[0098] Step S4: Soak the sample after ice melting and complexation in the hydrogel solution prepared in step S1 for 2 hours and then place it at -20°C to complete a freeze-thaw cycle.

[0099] During the freezing printing process, the conductive material slurry that first contacts the cold source 43 is quickly frozen, forming a cold source 43 in surface contact and freezing upward, forming a radial microscopic orientation gradient. At the bottom closer to the cold source 43, due to the lower temperature, the ice crystals grow faster, the ice crystal diameter is smaller, and the faster growth rate also forms a more obvious radial orientation. At the top of the principle cold source 43, due to the lower thermal conductivity of the conductive material slurry, the ice crystals grow slower and form a larger diameter. At the same time, the ice crystals tend to be more parallel, and the orientation changes, so there is an orientation gradient from the bottom to the top. After the flexible substrate 21 replaces the original ice crystal position, different ice crystal diameters generate different conductive path 11 gaps, with a gradient composed of thickness, spacing, and orientation.

[0100] from Figure 4(a)-Figure 4(d) It can be seen that the multi-directional flexible sensor provided in Example 1 of the present invention can effectively identify multiple deformation modes of stretching, compression, torsion, bending, and bending deformation in different directions. Stretching and compression correspond to different resistance change trends, respectively. Compared with compression, stretching can produce greater deformation and corresponding resistance change. When the sensor is twisted to the left and right, similar to stretching, tensile stress is applied to the internal conductive path 11, resulting in an increase in the overall resistance. In addition to distinguishing it from stretching by changing the amplitude, stretching and torsion correspond to different microscopic conductive change mechanisms, so they can be distinguished by their changing waveforms. When the sensor is subjected to bending strain, due to its internal orientation gradient, it responds to different trends of change corresponding to the same deformation mode. When bending upward, the sensor resistance decreases, and when bending downward, the overall resistance increases. When bending left and right, due to the axial symmetry of the cold source 43, the same resistance change trend is responded, which can be distinguished from bending up and down by changing the amplitude and waveform.

[0101] Example 4

[0102] Embodiment 4 discloses a method for preparing a multi-directional flexible sensor, which specifically includes:

[0103] Step S1: prepare a conductive material slurry, prepare a 10 mg / mL sodium carboxymethyl cellulose solution, the solvent is polyethylene glycol (PEG200) and an aqueous solution, the mass ratio of the two is 4:1, and after the solution is fully dissolved, add gold nanoparticles and stir for 24 hours until the particles are completely dispersed; prepare a flexible substrate 21, use polydimethylsiloxane (PDMS) as the flexible substrate 21, the ratio of A liquid to B liquid is 10:1, and the curing condition is heating at 90°C for 1 hour.

[0104] Figure 5 Schematic diagram of a multi-directional flexible sensor with a particle size orientation gradient provided in Example 4 of the present invention, wherein a conductive path 12 formed by the deposition of particles of different sizes naturally settles to form a gradient structure, and the particle size gradually decreases from bottom to top. Large particles can provide high conductivity, and small particles can provide higher sensitivity, which helps to enhance the anisotropic response capability of the sensor.

[0105] Step S2: Extrusion and freezing of conductive material slurry. Before printing, the particles are pre-precipitated for 30 seconds to obtain a particle size gradient, the extrusion rate of the extruder is set to 1 mL / min, the moving rate of the cold source 43 is set to 15 m / min, and the temperature of the cold source 43 is set to -50°C; the flexible matrix 21 (21) is evenly dispersed in the gaps between the particles and the sheets, which improves the mechanical properties and ensures the stability of the structure under cyclic stress.

[0106] Step S3: Removal of ice crystals, using freeze drying method, placing the frozen sample into a freeze dryer, and drying at -40°C and 30 mtorr for 48 hours to obtain aerogel.

[0107] Step S4: Use a low-temperature negative pressure immersion method to allow PDMS to enter the gaps in the aerogel, and solidify it overnight to obtain the final sensor. The curing conditions are 60° C. for 2 hours.

[0108] Example 5

[0109] Embodiment 5 discloses a method for preparing a multi-directional flexible sensor, which specifically includes:

[0110] Step S1: prepare a conductive material slurry, prepare a 20 mg / mL polyvinyl alcohol solution, add graphene oxide powder after the solution is fully dissolved, and make the ratio of graphene oxide to polyvinyl alcohol be 10:1 or 5:1 respectively; prepare a flexible substrate 21, use polyacrylamide / NN-methylenebisacrylamide hydrogel (AM / MBAA) as the flexible substrate slurry, the photoinitiator is PI-1733, and the concentrations are 15% (w / v) AM, 3‰ (w / v) MBAA, and 4% (v / v) PI-1173, respectively, and the curing conditions are ultraviolet light irradiation at room temperature for 3 minutes.

[0111] Step S2: Extrusion and freezing of the conductive material slurry, the extrusion rate of the extruder is set to 2 mL / min, the platform moving rate of the cold source 43 is set to 9 m / min, and the temperature of the cold source 43 is set to -70°C.

[0112] Figure 6 Schematic diagram of a layered orientation gradient multi-directional flexible sensor provided in Example 5 of the present invention, wherein the first layered material 31 and the second layered material 32 are generated by printing in batches, and a cold source 43 is provided by a cold source 43 to form an orientation gradient structure in the cross section. This layered design can accurately adjust the physical properties of the conductive path 11. A PDMS wedge mold (high thermal conductivity mold 42) is set at the bottom to generate an orientation gradient structure inside the material. The copper mold molds (high thermal conductivity mold 41) on both sides can generate a microscopic orientation in a vertical direction different from the bottom orientation at the top of the material, further enhancing the anisotropy of the sensor.

[0113] Step S3: Removal of ice crystals, using freeze drying method, placing the frozen sample into a freeze dryer, and drying at -40°C and 30 mtorr for 48 hours to obtain aerogel.

[0114] Step S4: Use a low-temperature negative pressure immersion method to make the AM / MBAA hydrogel enter the gap between the aerogels, and solidify it overnight to obtain the final sensor. The curing conditions are 60° C. for 2 hours.

[0115] This embodiment can customize the sensing performance of each area by freezing conductive material slurries with different conductive material concentrations in different regions and layers. The molds composed of different thermal conductivities can regulate the growth orientation of ice crystals during the freezing process, and then regulate the orientation of the conductive channels and the final anisotropic sensing capability. In this embodiment 3, the wedge-shaped, low thermal conductivity mold at the bottom can generate a conductive path with a lamellar structure arranged perpendicular to the freezing platform, and the paired, high thermal conductivity molds at the top can generate a conductive path with a porous structure, thereby further enhancing the difference between the upper and lower layers of materials. At the same time, there are various anisotropies in mechanical properties at both the bottom and the top. This difference enables the material to withstand stress in different directions, thereby improving the overall mechanical stability of the sensor.

[0116] In summary, the present invention provides a multi-directional flexible sensor and a preparation method thereof. A flexible sensor with a microscopic orientation gradient structure is prepared using a simple preparation process, and has excellent multi-directional sensing function. The microscopic orientation gradient structure is composed of a microscopic conductive path 11, which presents an orientation gradient in the cross section and has a continuous microscopic conductive path 11 in the longitudinal section, which can respond to mechanical stimulation in different directions and produce different resistance changes. At the same time, the flexible matrix 21 material is filled in the gaps between the conductive paths 11, further enhancing the flexibility and environmental adaptability of the material. The preparation method includes generating a conductive path 11 with an orientation gradient through a freezing process, further removing ice crystals in the freezing process, and replacing the ice crystal gaps with a flexible matrix 21 material. The sensor realizes multi-directional sensing function through a single circuit, can effectively detect various mechanical stimuli such as compression, stretching, bending, etc., and is widely used in smart wearables, health monitoring, human-computer interaction and other fields.

[0117] It should be noted that the serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0118] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper" and "lower" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0119] It should be noted that, in the present invention, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0120] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features invented herein.

Claims

1. A multi-directional flexible sensor, characterized in that: include: A plurality of conductive paths, wherein the conductive paths extend continuously in a first direction, the diameter of the conductive paths gradually increases along a second direction, the second direction is inclined at a certain angle to the first direction, the plurality of conductive paths are radially spread out, and there is a certain gap between adjacent conductive paths, and the gap gradually increases in diameter along the second direction; A flexible substrate is filled in the gap, and the flexible substrate is bonded to the conductive path to form a sensor with an orientation gradient.

2. The multi-directional flexible sensor according to claim 1, characterized in that: The conductive path is any one or a combination of a layer, a columnar, or a porous structure. The conductive path includes a conductive substance, and the conductive substance includes any one or a combination of carbon materials, conductive polymers, ionic liquids, metals, and metal ions. The flexible matrix includes any one or a combination of hydrogels, aerogels, oil gels, rubbers, and plastics.

3. The multi-directional flexible sensor according to claim 1, characterized in that: The orientation gradient is any one of spacing, size, and material gradient or a combination of several of them.

4. The multi-directional flexible sensor according to claim 1, characterized in that: The size gradient includes any one of pore size and particle size or a combination of the two.

5. The multi-directional flexible sensor according to claim 1, characterized in that: The material gradient includes any one of a concentration gradient and a cross-linking density gradient or a combination of the two, wherein The concentration gradient is generated by layer-by-layer printing or gradient cross-linking of materials of different concentrations.

6. The multi-directional flexible sensor according to claim 1, characterized in that: The conductive path at the two side parts has a certain angle with the conductive path at the middle part, and the angle between the conductive path at the outer side and the conductive path at the middle part is larger.

7. A method for preparing a multi-directional flexible sensor, characterized in that: The following steps are involved: Prepare conductive material slurry and flexible matrix slurry in a certain proportion; Cryoprinting: Make the cold source reach the set temperature, fill the configured conductive material slurry into the extruder, extrude the conductive material slurry toward the cold source through the extruder, and at the same time make the cold source and the extruder move relative to each other in the first direction. During the relative movement of the cold source and the extruder, the conductive material slurry that first contacts the cold source will quickly freeze into ice crystals and grow upward. During the growth of the ice crystals, the solutes in the conductive material slurry will be squeezed on both sides of the ice crystals to form a conductive path growing in the second direction. The diameter of the ice crystals and the conductive path increases in the direction away from the cold source. Remove ice crystals formed during freezing; The flexible matrix is ​​filled into the position of the original ice crystals, and the flexible matrix is ​​combined with the conductive path under certain temperature conditions.

8. The method for preparing the multi-directional flexible sensor according to claim 7, characterized in that: Extrusion freezing printing is used when the extruder extrude the conductive material slurry toward the cold source, and the freezing rate and the cold source moving rate are matched with the viscosity of the conductive material slurry.

9. The method for preparing a multi-directional flexible sensor according to claim 7, characterized in that: The preparation method includes a mold method and a mold-free method, wherein: A mold method is used to set a mold on the cold source. The mold is composed of one or more materials with different thermal conductivity to adjust the local freezing orientation and rate. The conductive material slurry is extruded into the mold on the cold source through an extruder, or The mold-free method does not require a mold during the freezing printing process. The contact interface between the conductive material slurry and the cold source is a line or a surface, and a certain geometric shape is formed before the conductive material slurry is completely radially dispersed.

10. The method for preparing the multi-directional flexible sensor according to claim 7, characterized in that: The cold source is a point / surface or a combination of the two in space. The growth mode of ice crystals is controlled by adjusting the position and cooling rate of the cold source. The radial growth of ice crystals causes the ice crystals to squeeze the conductive path along the first direction to form a uniform and continuous conductive path.

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