A bistable deformable tactile responsive material and device

Abstract

A deformable electroactive polymer membrane including a layer of a bistable electroactive polymer layer comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature; a deformable electrode layer comprising a pattern of heating elements each comprising a network of nanowires and / or a network of carbon nanotubes patterned into a conductive trace on the polymer layer; and an elastomer penetrating into pores in the network.

Description

A BISTABLE DEFORMABLE TACTILE RESPONSIVE MATERIAL AND DEVICECROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. Section 1 19(e) of:

[0002] U.S. Provisional Application No. 63 / 568,839, filed March 22, 2024, byQibing Pei, Jinsung Kim, and Hyeon Ji Hong, entitled “A BISTABLE DEFORMABLE TACTILE RESPONSIVE MATERIAL AND DEVICE;’ (30794.0509USP1): and

[0003] U.S. Provisional Application No. 63 / 737,919, filed December 23, 2024, by Qibing Pei, Jinsung Kim, and Hyeon Ji Hong, entitled “ A BISTABLE DEFORMABLE TACTILE RESPONSIVE MATERIAL AND DEVICE,” (30794.0509USP2);

[0004] both of which applications are incorporated by reference herein.FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0005] This invention was made with government support under EY030246 awarded by the National Institutes of Health. The government has certain rights in the invention.BACKGROUND OF THE INVENTION

[0006] Soft actuators offer the opportunity for drug deliver}', medical surgery,[1,2]designs for actively deformable apparel / 31soft human-machine interactions,141and refreshable Braille display / 51The essential components for building a soft actuator include the nature of the soft material as a body and the mechanism used to actuate this soft material / 6’7’81The soft actuator material should be flexible, stretchable as well as reliable, fast, repeatable, and dynamically stable under deformation. It converts an input stimulus into a useful mechanical output. To build the soft actuators, smart materials and structures such as shape memoryalloys,191dielectric elastomers,110 111ionic polymer-metal composites,1121fibers / 13,141hydrogels / 151phase-changes / 51and magnetic responsive materials116 171have been used. Particularly, phase-change materials (PCMs) can change their state when triggered by heat. Their mechanism can be thermal expansion / contraction (e.g., wax-based materials), liquid-to-solid state transformation (e.g., silicone polymer elastomers[61), an ordered-to-disordered phase transformation (e.g., liquid crystalline elastomers1111), and thermal transition from the amorphous-to-crystalline state thermal transition (e.g., shape memory polymers). Phase-change polymers containing crystallizable side chains have been shown to combine shape memory with dielectric elastomer actuation.13’181These bistable electroactive polymers (BSEPs) are promising for large-strain rigid-to- rigid actuation; however, their operation entails a highly stretchable Joule heating electrode (JHE) to administrate the temperature change.

[0007] Carbon nanotubes (CNTs) / 191carbon fibers,1201graphene / 211MXene / 221metallic nanomaterials / 19’231liquid metals / 241and conducting polymers have all been reported to fabricate stretchable JHEs / 25’261High electrical conductivity is required for low-voltage Joule heating. However, achieving highly reversible deformability with preserved low resistance at all strains is difficult / 271Carbonbased nanomaterials and conductive polymers have medium conductivities[281which push the input voltage to > 10 V, thereby limiting the application scope of the resulting soft actuators. Metallic nanomaterials have high electrical conductivity but lose their conductive network at high strains and have inferior thermal and oxidation stability / 291Liquid metal electrodes with low thicknesses can be used for low-power processing systems, but their fabrication is complicated and high stability over time is challenging to obtain / 241SUMMARY OF THE INVENTION

[0008] Tactile interactive interface is demanded in virtual surgery' training in medical technology', haptic controller of virtual reality headsets in entertainment, andtele-manipulation in robotic controls. People with visual impairment also rely on tactile communication to read. An illustrative embodiment of the invention provides a deformable electroactive polymer membrane capable of producing large diaphragm deformation and an architecture to produce a plurality of tactile pixels. The polymer membrane comprises (1) a bitable electroactive polymer layer having a large elastic modulus on the order of 10-100 MPa at ambient temperature to support finger pressing force, but it turns into a soft rubbery state on the order 100 kPa modulus or less when heated to allow for large-strain deformation, (2) a deformable electrode layer consisting of a hybrid network of carbon nanotubes and (e.g., silver) nanowires to obtain low surface resistance, largestrain deformability, and thermal stability’, and (3) an elastomer penetrating in the hybrid network to protect the nanowires and nanotubes during deformation.BRIEF DESCRIPTION OF DRAWINGS

[0009] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0010] Referring now to the drawings in which like reference numbers represent corresponding parts throughout:

[0011] Fig. 1. Schematic of the fabrication process of stretchable JHE electrodes. (Middle row) Optical images and (Bottom row) side view of the above schematic, i) The WPU deposition on a BSEP membrane mounted on an air chamber, ii) Prestraining the membrane by pneumatic pressure, iii) Spray-coating CNTs / AgNWs / CNTs hybrid electrode layers and a WPU top layer, iv) Subsequent release of the membrane, resulting in the formation of wrinkles on its surface, v) Patterning the electrode layers employing a laser engraver (scale bars: 600 pm).

[0012] Fig. 2. Hybrid electrodes on the BSEP membrane used in the Braille system. Scanning electron microscopy images of the layered a, bottom CNTs b, AgNWspositioned atop the bottom CNTs, and c, top CNTs (scale bars: 300 nm). Optical microscopy images of wrinkles formed during the pre-straining and releasing stages, including d, enlarged image of the ‘‘legs” area (scale bars: 30 pm), di, entire dot area encompassing both the “legs” and “body” regions (scale bars: 100 pm), dii, enlarged view of the “body” area (scale bars: 30 pm). Scanning electron microscopy images of the wrinkled hybrid electrode under different area expansion stages e, 0% area expansion ei, 30% area expansion, and eii, 70% area expansion (scale bars: 3.5 pm), f, Schematic illustration of a locally actuated JHE and fi, charge transport mechanisms within a co-network system comprising a CNTs / AgNWs / CNTs hybrid structure.

[0013] Fig. 3. Design and architecture of a Braille display system, a, An exploded- view schematic of a pneumatic actuator-based Braille display featuring a 1 x 10 cell configuration, b, A cross-sectional view delineating the operational mechanism of the device, with a depiction of 2 pixels, i) The initial state with all pixels in a relaxed position, ii) Actuation of the pixels through the application of Joule heating and air pressure, iii) The fixation of the actuated state of the pixels at ambient temperature, iv) The return of pixels to a relaxed state, c. An illustration of the operational mechanism of the BSEP membrane to be used in Braille display, highlighting its ability to transition between soft and rigid states through heating and cooling, d, i) U.S. standard dimension of a single cell, including yellow copper contacts on a PCB. Dimensions and spacing of the pixels correspond to the standard U.S. Braille, ii) FEA results of the Joule heating of a serpentine patterned electrode.

[0014] Fig. 4. Joule heating and electromechanical performance of the electrodes used in the Braille display system, a, Resistance change of the CNTs / AgNWs / CNTs hybrid electrodes with different initial resistances (Rl= 2.2 k , R2= 3.4 k . R3= 4.1 k ) over six actuation-relaxation cycles (left axis). The curve of area strain applied during the actuation cyclic test, with a peak strain of 90% (indicated by red circles) and 0% in the relaxed state (indicated by the black square) (right axis).b, Resistance change under different area strains during actuation, including 30%, 50%, 80%, and 100%. c, Joule heating temperature change of the electrodes with various initial resistance (Rl= 2.2 kQ. R2= 3.4 k , R3= 4.1 k ), with Tt representing the phase transition temperature of the BSEP membrane, d. Joule heating temperature change in response to actuation area strains of 30%, 50%, 80%, and 100%. e, Resistance and temperature change of the electrode during repeated actuation and relaxation tests under the same applied voltage of 7.7 V. f. Transient temperature rise of the electrode with 3.0 kQ during Joule heating curves at different applied voltage of 7, 9, and 11 V. g, Transient temperature curve of a Braille dots during Joule heating voltage activation and deactivation at various applied voltages of 6, 8, 10 and 12 V. h, Transient temperature curve during specified actuation cycles to 80% area strain, with a heating voltage of 10 V. i, Transient temperature curve of the top, middle, and bottom dots within a 3 x 2 cell (see Fig. 3d).

[0015] Fig. 5. Demonstration of the letters ucla smrl' in Braille with the CNTs / AgNWs / CNTs hybrid JHEs. a, IR thermal image of the Braille dots heated above the transition temperature of the BSEP membrane by 1stJoule heating at 10 V. b, Optical image of the heated dots actuated by an air pressure of 9 - 10 kPa. Activated dots are marked with white dashed circles, c, Braille pins raised as a result of the actuated BSEP diaphragms, d, Braille pins that remained raised even after the heating voltage and the pump were turned off. e, Braille pins at the relaxed state after 2ndJoule heating with no pneumatic pressure applied.

[0016] Fig. 6. Chemical structure of monomers and photoinitiators employed for BSEP synthesis. Octadecyl acrylate (OA) and urethane diacrylate (UDA) are the primary domains in phase-changing polymer networks. Typical composition of the prepolymer solution contains 80 parts OA, 20 parts UDA, 1.5 parts TMPTA, 0.5 parts DMPA, and 0.25 parts BP, 10 parts acry lic acid.

[0017] Fig. 7. Mechanical Properties of the BSEP membrane, (a) The storage modulus versus temperature profile of the BSEP membrane, (b) The stress-strain curve of the BSEP membrane at 50°C, tested at a stretching rate of 0.1 mm / s.

[0018] Fig. 8. Optical microscopic images of a BSEP membrane (diaphragm architecture) during a 200,000-cycle actuation test. Applying pneumatic pressure between 10 and 12 kPa induced a 100% area strain, equivalent to Braille dots measuring 0.7 to 0.8 mm in height. A complete actuation cycle took 2 seconds to actuate (switching on the dot) and 1 second to relax (switching off the dot).

[0019] Fig. 9. Photographs for the effect of the solvent treatment, (a) Freshly sprayed WPU and (b) after spraying IPA and subsequent drying of the solvent, (scale bar : 300 nm (second row), l / r m (third row))

[0020] Fig. 10. Thickness measurement using Atomic Force Microscopy (AFM). A deposition of 0.6 ml of a 0.3wt% WPU solution was sprayed onto the glass substrate and allowed to dry for 10 minutes. Subsequently, the dried film thickness was measured in tapping mode AFM.

[0021] Fig. 11. Adhesion test to assess bonding of the nanomaterials by the WPU layer, (a) Before the Kapton tape was laminated, (b) after the tape was laminated, (c) after peeling off of the tape, and (d) average resistance change of the CNTs / AgNWs / CNTs hybrid electrode embedded in specified polymers before and after tape peeling test. The Kapton tape has a peeling strength of 46oz / in. CPP is a dielectric elastomer formulated from CN990, propoxylated neopentyl glycol diacrylate, poly propylene glycol acrylate, and acrylic acid. The tape-peeling test started by measuring the initial resistance of the electrodes embedded in four different matrices, BSEP, PUA, CPP, and WPU. Afterward, the Kapton tape was tightly laminated onto each sample without any air bubbles. The resistance was measured again after peeling off the tape from each sample.

[0022] Fig. 12. 3D Finite Element Analysis (FEA) for the stress (a), out of plane displacement (b), and strain of the electrode (c). under pneumatic pressure. In (a), the stress over the active area varies from 0 to 1.97E8 N / m2, F(10)=18000 Pa,contour: first principal stress (N / m2), and Max / Min Surface: first principal stress (N / m2).The center of the patterned electrode experienced the highest stress, consistent with the experimental results showing the vulnerability of the center lines to breakage. In (b), the applied pressure resulted in a maximum film actuation of 0.6 mm at the center, F(10)=18000 Pa Surface: Displacement magnitude (mm) , Max / Min Volume: displacement (mm). Discrepancies between simulated and experimental pressures arose from simulation boundary limitations. In simulation, a distinct modulus difference between the heated and non-heated areas is applied, whereas in reality, the heating gradually diffuses along the boun ary. Also, simulated nanomaterial thickness exceeded practical limits, suggesting that achieving the same strain in reality w ould require less pneumatic pressure. Fig. 12 (c) shows a maximum strain change of 1.65 over the active area. The simulation utilized a solid mechanics model with pressure sweeping from 0 to 18 kPa . Material parameters used in the simulation were as follows: CNT (E: 1E9 Pa, v: 0.35, p: 1.3 kg / m3), BSEP matrix layer (E:7E5 Pa, v : 0.49, p:1.5 kg / m3. t: lOOp m ). In (c), . F(10)=18000 Pa, contour: first principal strain (1), and Max / Min Volume: first principal strain (1).

[0023] Fig. 13. Hybrid structure of Joule heating electrodes. The heating electrodes comprise a hybrid network of two CNT layers sandwiching an AgNWs layer (CNTs / AgNWs / CNTs). Each CNT and AgNW layers were sprayed layer by layer from each solution. This hybrid system has higher electrical conductivity than homogenous CNT or AgNW films, enabling a thinner conductive layer. Also, it has a higher thermal stability' by improving the high contact resistance issue at AgNW junctions.

[0024] Fig. 14. Scanning electron microscopy image for a silver nanowire. Its width is about 41 nm . (scale bar: 200 nm )

[0025] Fig. 15. The sheet resistance of the CNTs / AgNWs / CNTs electrodes as a function of the ratio between AgNWs and CNTs. The concentration of AgNW solution was fixed at 0.01wt% with 3.5 ml for spraying. Also, 2 ml and 3 ml of0.035wt% CNT solution were sprayed for 1: 2 and 1 :3 ratio samples, respectively. For the homo CNT electrode, a 15 ml volume was used. Homo AgNWs electrode has a substantial deviation in sheet resistance, ranging from 420fl / sq to 6.8 kfl / sq within a substrate, possibly due to non-conductive voids among the nanowires. W In contrast, homo CNT electrodes demonstrate the highest uniformity with the minimal deviation. Employing the hybrid electrodes with AgNWs and CNTs reduces the variation of the sheet resistance. A higher AgNW : CNT ratio (1:3) enhances sheet resistance uniformity compared to a 1:2 ratio. Hybrid electrodes exhibit even lower resistance than homo AgNW electrodes because the CNTs effectively connect the junctions of silver nanowires, allowing more current paths.

[0026] Fig. 16. A sheet resistance of the electrodes as a function of AgNW concentration from 0.01wt% to 0.04wt%. Higher AgNWs solution concentration leads to increase in sheet resistance variation. Conversely, reducing the AgNWs concentration and increasing the number of spraying paths significantly improve the variation. The ratio between AgNWs and CNTs was fixed at 1:2. The total amount of the used AgNWs volume was also fixed at 0.33 mg .

[0027] Fig. 17. IR thermal image of the Joule heating electrodes showing different heating uniformity with different concentration of AgNWs and the ratio between CNTs and AgNWs. 9 V was applied to all three samples for Joule heating. The same size of heating electrodes was used for each condition and the electrode area is indicated with white dot line, (a) 0.8 ml of 0.04wt% AgNWs was sprayed, followed by 3.0 ml of 0.035wt% CNTs. (b) 1.7 ml of 0.02 wt % AgNWs was sprayed, followed by 2.0 ml of 0.035wt% CNTs. (c) 3.4 ml of 0.01wt%AgNWs was sprayed, followed by 2.0 ml of 0.035wt%CNTs. All films showed 1.5kfl / sq of sheet resistance.

[0028] Fig. 18. Transmittance spectrum of the hybrid structured electrodes with AgNWs and CNTs (sample 1 -5) and homogenous CNTs electrode (sample 6). Samples 1 to 5 have increasing amount of CNTs / AgNWs with sheet resistances of58kfl / sq, 28kfl / sq, 2kfl / sq, 0.7 kfl / sq, 0.5kfl / sq, respectively. The sheet resistance of Sample 6 is l.Skfl / sq.

[0029] Fig. 19. Optical microscopic images of (a) pre-strained state, (b) relaxed (wrinkled) state, and (c) a single dot showing its leg and body areas. The dot diameter is approximately 1.5 mm . Pre-strain ranged from 80 to 100% area strain, correlating with an actuation height of 0.6 to 0.7 mm . In (b) and (c), wrinkled surface scattered more light compared to flat surface in microscopic images.

[0030] Fig. 20. Optical Microscopy images of the wrinkled electrodes after patterning, (a) Entire serpentine-shaped active area, with a boundary between prestrained and non-pre-strain regions, (b) An enlarged centerline, showing a 200 / 1 m width with wrinkles along the line, (c) An enlarged image of a serpentine turn. (All scale bars: 200g m ).

[0031] Fig. 21. Optical Microscopy images of a uniaxial stretching test, (a) Before stretching, (b) after 50% stretching the entire electrode film, and (c) an enlarged image (scale bar: 200g m ). The serpentine-patterned electrode underwent uniaxial deformability testing. Prior to stretching, the dark-colored serpentine pattern is the pre-strained area (Fig. a). After 50% uniaxial stretching (equivalent to 125% area strain in biaxial), Fig. (b) and (c) revealed no micro-cracks across the pattern. The ability of the wrinkles to stretch in the strain direction absorbed the strain energy, preventing cracks initiation and propagation, averting conduction loss. The electrode's relatively low thickness facilitated the unwrinkled bus line to remain free from cracks, unlike the thicker geometry, which exhibited cracking (see Fig. SI 6).

[0032] Fig. 22. Optical Microscopy images of a uniaxial stretching test of the JHE electrode, (a) Before stretching and (b) after 30% stretching in the vertical direction (scale bar: 200g m ). Note that only the active area with the serpentine structure has wrinkled structure. After a 30% stretch of the entire electrode film, the bus line area develops multiple cracks. I2-3]Fig. 23. Layout of the PCB for independent control of the dots. Electrical inputs to the dots are supplied via the contacts points marked in gold color. The shared ground is marked in orange. Spacings are in mm .

[0033] Fig. 24. Finite Element Analysis (FEA) results of current density distribution in (a) serpentine-shaped and (b) spiral-shaped electrodes. The color bar indicates current density as a Joule heating performance. The conductance between the ground and terminal point is 0.049 S for the serpentine pattern and 0.028 S for the spiral pattern, determined based on the surface area and length. The serpentine pattern has surface area of 1.25 mm2and length of 5.34 mm . The spiral pattern has surface area of 1.03 mm2and length of 6.42 mm . The serpentine structure displays uniform current flow with around 2.5 X 104mA / mm2. In contrast, the spiral pattern showed low current density at its circular center around1.5 X 104mA / mm2, represented in blue. This results in a 46% difference in resistance, followed by the equation R = p ). The 'extremely fine' mesh was used for accurate steady-state electric conduction, utilizing an isotropic electrical conductivity of SWCNT ( 10,000 S / m ) and a 12 V potential difference between the ground and terminal points. The stationary form of the partial differential equation for electric currents: V • J = Q] N, where J = oE (J: current density, <7 : conductivity, E : electric field) E = — VV (V: electric potential)

[0034] Fig. 25. Design of the electrode with a serpentine pattern. Optimized serpentine pattern design for uniform Joule heating and minimized resistance. Point-to-point resistance increases with distance from the bottom contact point on the bus line. The top two contact points have higher resistance than the middle and bottom two contact points. The serpentine pattern width is adjusted to compensate for resistance across all six contact points.

[0035] Fig. 26. Diagram for the measurement of Joule heating (circles) and actuation (triangles). A set up is designed for resistance and temperature measurement. Using the Keithley and an IR camera, voltage 1 and 2 supply Joule heating andpumping, respectively, following the cycles outlined in Fig. 30 (a). The red indicates the "start" points, and the blue indicates the "end" points.

[0036] Fig. 27. Electromechanical and thermal performance of the Braille system, (a) and (c) show the normalized resistance and temperature change of BSEP membranes with different initial resistances, (b) and (d) illustrate the normalized resistance and temperature change of the BSEP membrane under varied actuated area strains from 30% to 100%.

[0037] Fig. 28. Normalized resistance and temperature in lifetime cyclic test (see Fig. 4 e for absolute values).

[0038] Fig. 29. (a) Temperature and pressure profiles during actuation cycles. The circle is for the Joule heating temperature and the triangle is for the pressure. Red color indicates "On" and blue color indicates "Off . Joule heating at 9 V for 2 - second, followed by applying 8 kPa pneumatic pressure for 2-second to actuate the softened film. A subsequent 2-second relaxation occurs by halting both the Joule heating and pressure input. This cycle was employed for the lifetime cyclic test, (b) A pin displacement profile measured by a laser displacement sensor, showing a height range of approximately 0.55 — 0.60 mm. Actuations span 0.8 — 1.0 seconds (between black and blue dash lines), while relaxation spans 0.3 — 0.5 seconds (between blue and red dash lines).

[0039] Fig. 30. The calculation for the power consumption and power efficiency for Joule heating on active area, (a) Optical microscopy image for the serpentine patterned electrode and (b) circuitry diagram for its resistance in the electrode. Fig. (a) show s the optical image of the patterned electrode with all contact points marked from A to G. To calculate the power consumption and efficiency, the power consumed on each active line and bus line needs to be calculated. As shown in Fig. (b), the resistance between point A and the other points is in series. Resistance between each line, top (FG1, FG2), middle (DEI, DE2) and bottom (BC1. BC2) is in parallel. By using the measured values, the resistance between point A and all other points ( RAC, RAE, RAC) and resistance on the bus line (RAB, BD> RDF the Rparallelin Fig. (b) is calculated as O.Skfl. With the voltage drop on each line ( Ubottom, Umiddle, Utop), the power consumed on the active areas is 0. 142 W out of 0. 155 W of the total power consumption. Hence, the power efficiency for Joule heating on active area is more than 91.6%. The calculation was based on 9 V of operating voltage.

[0040] Fig. 31 shows Table SI. Deformable joule heating electrodes made of polymer nanocomposites and used in a soft actuator system.

[0041] Fig. 32. Schematic illustrating a method of making a Joule heating electrode.

[0042] Fig. 33. Flow chart illustrating a method of making a device.DETAILED DESCRIPTION OF THE INVENTION

[0043] In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0044] Technical Description

[0045] The present disclosure describes (referring to Fig. 1 as an example) a deformable electroactive polymer membrane 100, comprising a layer of a bistable electroactive polymer layer 102 having a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature (e.g.. but not limited to, 30 degrees Celsius); a deformable electrode layer 104 comprising a pattern of heating elements 108 each comprising and / or formed by a network of nanowires on the polymer layer; and an elastomer 106 penetrating into pores in the network. In one or more embodiments, the deformable electroactive polymer comprises the deformable electrode layer formed on a surface area of a combination of the elastomer andthe polymer layer after application and subsequent release of a strain or prestretching or actuation force increasing the area (e.g., by up to 100% (e.g., actuation force in direction of actuation during operation).

[0046] electrode layer comprises at least a layer of the metal nanowires and a layer of the CNTs or a layer of the metal nanowires sandwiched between a first layer of the carbon nanotubes and a second layer of the carbon nanotubes.

[0047] As illustrated in Fig. 2, the electrode layer 104 comprises at least a layer 206 of the metal nanowires 200 and a layer 208 of the CNTs 202. For example, the layer 206 of the metal nanowires can be sandwiched between a first layer 208 of the carbon nanotubes and a second layer 208 of the carbon nanotubes as illustrated in Fig. 13. The deformable electrode layer 104 is patterned into a conductive trace 220 to Joule heat an area covered by the trace, e.g., wherein the conductive trace is patterned into a shape that is serpentine or radial, and / or the conductive trace has a width in a range between 10 micrometers and 200 micrometers.

[0048] Fig. 1 further illustrates the deformable electroactive polymer membrane comprises a pre-strain characterized by formation of an electrode layer, comprising the nano wires and the carbon nanotubes, on a substrate 110 comprising a first layer 112 of the elastomer on the polymer layer during application of a force F deforming 114 the substrate by at least a portion of an amplitude 116 of an actuation in a direction 118 of the actuation (as shown in Fig. 1 (iii)) and subsequent patterning 122 of the electrode layer (as shown in Fig. l(v)) after release of the force and optionally after deposition of a second layer 120 of the elastomer on the electrode layer and then the release of the force, wherein the actuation is the actuation during operation of the electroactive polymer membrane in a device (e.g., fluidic device as illustratedin Fig. 3). Thus, the electrode layer is formed on a wrinkled surface 130 of the elastomer formed after the release of the force.

[0049] Fig. 3 illustrates an exemplary implantation in a device 300, comprising a fluidic device 302 for applying fluidic pressure; the deformable electroactive polymer layer 102, 304 on the fluidic device; a haptic or tactile display 306 above the deformable electroactive layer comprising a plurality of holes 310, each of the holes operably coupled to a pin 308 so that the pin can move up and down through its respective one of the holes in response to physical contact from a different one of the protrusions 150 in the electroactive polymer layer actuated by the selective heating of one of the heating elements 122 comprising the electrode layer 104 in thermal contact with the deformable electrode layer during a presence of the pressure. A circuit 312 is provided and operable to apply a voltage (e.g.. less than 10 V) to pass current to the heating elements so as to heat the polymer layer above the transition temperature, thereby deforming selected areas of the polymer layer into the protrusions that are sized / dimensioned to be spatially differentiated by haptic sensing, e.g., using fingertips. .

[0050] Fig. 3 illustrates the device further comprises an adhesive layer 350 adhering edges of the polymer membrane to an underside of the haptic or tactile display 306.

[0051] 2. Manufacture and Characterization of an example embodiment

[0052] 2.1. BSEP membrane as reversible variable stiffness material

[0053] BSEP was synthesized from a precursor containing octadecyl acry late (OA), urethane diacrylate (UDA), and other compounds as shown in Fig. 6. The octadecyl side chains in the BSEP crystallized at room temperature leading to a high Young’s modulus. They melt above a transition temperature, leading to a modulus reduction by ~103. UDA is a long chain difunctional acrylate that forms a crosslinked network structure with OA and thus improves the toughness andelongation at the break of the membrane.

[0032] To tune the phase transition temperature and modulus change, the composition of all chemicals used in the prepolymer solution of BSEP was formulated to contain 80 weight parts of OA, and 20 parts of UDA. A short chain crosslinker, trimethylolpropane triacrylate (TMPTA), was added at 1.5 parts to increase the tensile strength of the BSEP at the softened state.

[0033] In addition, 0.5 parts of dimethoxy phenyl-acetophenone (DMPA), and 0.25 parts of benzophenone (BP) were added as photoinitiators in the prepolymer solution. 10 parts of acrylic acid (AA) were added to introduce a reversible crosslinking system and to improve the toughness.[3]

[0054] Dynamic mechanical analysis of the BSEP shows a sharp stiffness change from ~102MPa in the rigid state to tens of kPa in the soft state (Fig. 7a). The modulus change of three orders of magnitude was reversible. The transition temperature of the BSEP was designed to be approximately 45 - 47 °C so that the required Joule heating energy for the stiffness transition can be reduced while the membrane remains stiff at average environmental temperature and human body temperatures. Fig. 7b shows the stress-strain curve of the BSEP membrane at 50 °C. Its elongation at break was at 320% linear strain. The normal tensile strength was 2 MPa, corresponding to a true tensile strength of ~8 MPa, indicative of high toughness to resist tearing or crack formation at high strains. Fig. 8 shows the result of the durability7test of the BSEP membrane, ft endured more than 200.000 actuation cycles without any sign of failure.

[0055] 2.2 Stretchable Joule heating electrodes

[0056] To selectively soften local areas of a BSEP membrane, a JHE was applied to the membrane surface as illustrated in Fig. 1. The first step (i) of the process was to attach the BSEP membrane to an air chamber, followed by spray-coating of 0.3 wt% waterborne polyurethane (WPU) solution on the BSEP membrane. The hydrophilic nature of WPU enhances the bonding of CNTs and AgNWs compared to the bare BSEP surface with low surface energy. The sprayed WPU had a ratherrough surface (Fig. 9a). To smoothen the surface and improve the adhesion, isopropanol alcohol (IP A) was sprayed to wet and dissolve the WPU to allow the polymer to spread out to form a smoother surface (Fig. 9b). The roughness value from atomic force microscopy measurement changed from 2.84 nm to 0.71 nm. WPU was also sprayed as a top layer over the CNTs / AgNWs / CNTs hybrid layers to penetrate the porous networks of CNTs and AgNWs and form a strong bond with the lower WPU layer. This WPU top layer was -120 nm thick (Fig. 10), which was greater than the total thickness of the hybrid layers and thus could completely embed the conductive network. To evaluate the adhesion between the nanomaterials and the WPU matrix, a tape-peeling test was performed (Fig. 11). The WPU matrix strongly bonded the hy brid electrode lay ers to the BSEP substrate. Peeling of the strong Kapton tape did not remove the conductive nanomaterials from the surface. The electrode resistance increased by 7.6% after peeling. It indicates that the nanomaterials have a strong bond with the WPU matrix.

[0057] Conventional methods for pre-stretching soft films often involve an additional rigid frame, which requires manual handling of the delicate films, transferring films between different substrates, and complex adhesion requirements between the film and the frame.1341These methods rarely provide reliable and uniform relaxation. The optical microscopy images in Fig. 1 (ii) demonstrate the prestrained dome on the diaphragm with a 1.5 mm diameter. In our OPS approach, air pressure was used to strain and relax the membrane in a diaphragm fashion. The same air chamber for the operation of the active BSEP membrane was used for pre-stretching of the membrane in the OPS process, which can facilitate prestraining process by eliminating the need for additional pre-straining substrates, for laminating and delaminating samples on different substrates, and for transferring samples between different substrates. The finite element analysis (FEA) data shows that the top center area on the actuated membrane had higher stress and strain than the peripheral area (Fig. 12). Therefore, unlike theconventional pre-straining methods with the same pre-strain over the entire membrane area / 351the OPS method can afford localized pre-straining specific to each area. Not only can this pre-straining method provide local areas with their required pre-straining %. but it can also match the pre-straining direction with the actual actuation direction, which might help minimize the movement of the nanomaterials during actuation. Although the percentage of pre-straining may be changed as the application needs, the BSEP membrane in this work was prestrained to approximately 90%, which was slightly greater than what was required for the targeted actuation height of 0.5 mm.

[0058] In step (iii) of Fig. 1, after the membrane was cooled to the ambient temperature, layers of CNTs, AgNWs, and CNTs were successively deposited on top of the WPU layer. The top WPU layer was deposited on the pre-strained area (active area) of the electrode to cover and embed the conductive nanomaterials. After the membrane relaxation, wrinkles were formed (iv), and the relaxed areas became opaque showing light scattering from the buckled structure, as shown in Fig. l(iv). To enhance the stretchability of the electrode, the wrinkled active area was patterned into a serpentine trace using laser engraving. Finally, the membrane was gently peeled off the chamber as a free-standing membrane.

[0059] The resistance of the electrode active area could be adjusted by spray coating different amounts of CNTs and AgNWs. Although lower resistance led to faster heating and lower driving voltage, it should be compromised for stretchability.[36,37]As the thickness of the CNTs and AgNWs increased, the risk of crack formation near the bus lines could increase. The minimum thickness of the electrode layer was identified by adopting a hybrid layer of CNTs / AgNWs / CNTs (Fig. 13). The concentration of the AgNW solution was optimized to 0.01 wt% to make a uniform resistance over the coating substrate. The width and length of the AgNW are about 41 nm and 15 - 25 / im (Fig. 14). The concentration of the CNT solution w as optimized to be 0.03 wt%. The w eight ratio of AgNWs to CNTs in the sandwich electrode affected the sheet resistance asshown in Fig. 15. At the ratio of 1:3, the hybrid electrode had lower sheet resistance than the homogeneous AgNWs electrode (0.489 kQ / sq for CNTs / AgNWs / CNTs versus 2.32 kQ / sq for AgNWs). Also, the concentration of AgNWs impacted on the uniformity of the sheet resistance (Fig. 16) and 0.01 wt% showed lower variation in the sheet resistance than 0.02 wt% and 0.04 wt%. The optimized ratio and concentration condition showed the most uniform Joule heating as shown in Fig. 17.

[0060] Fig. 2 shows the scanning electron microscopy (SEM) images of the electrode active layer. The deposition of CNTs on a WPU layer improved the uniformity of the nanotubes on the BSEP membrane (Fig. 2a). The AgNWs deposition on the CNT layer was also more uniform than direct deposition on BSEP which has a hydrophobic surface (Fig. 2b). The image shows the nanowires coarsely laid on the CNTs layer. The sparsely interconnected AgNW networks were next covered by the densely packed CNTs as shown in Fig. 2c. The diameter of the nanowires was approximately 40 nm, whereas the diameter of CNTs was about 0.8 - 2.0 nm. These surface morphologies demonstrated that CNTs bridged the AgNWs network. The CNT layers in the hybrid electrode can be thinner than JHEs using CNTs alone owing to the much higher conductivity of the silver nanowires than CNTs. As shown in Fig. 18, hybrid electrodes had more than 90% transparency whereas the CNT electrodes had approximately 80% transparency, indicating lower thickness of the conductive layers in hybrid electrodes.

[0061] The hybrid electrode could address the conventional local overheating issues at the inter-nanowire contact points in the AgNW network aforementioned in Fig.2f illustrates a locally actuated JHE. Charge transport occurred in a serpentine-patterned network when the electrode was heated and the BSEP membrane was actuated. The densely distributed CNT network enabled electrons to travel without clogging at the silver nanowire-nanowire junctions, which could reduce the local overheating.

[0062] As indicated above, the embedded hybrid electrode membranes underwent a pre-stretching process to induce wrinkle formation (Fig. 2d). This approach leveraged the modulus disparity between the upper nanomaterial layer and the lower layer of WPU on the compliant BSEP layer. To ensure uniform Joule heating voltage requirements during both actuation and relaxation phases, the introduced w rinkles served to maintain the operational voltage irrespective of the initial state of a pneumatic actuator. Figs. 19 and 20 provide visual representations of the pre-strained state of the membrane, taking on a dome-like configuration, and the resulting wrinkled structure follow ing the release of pre-strain within the electrode layers and the matrix. The dome structure gives rise to tw o distinct types of w rinkles: ‘leg'’ and “body” wrinkles (Fig. 2d (i) and Fig. 19(c)). Leg-shaped wrinkles manifested near the dome’s periphery, predominantly oriented radially (Fig. 2d). They exhibited a regular pattern characterized by a wavelength of approximately 15 pm. Conversely, the central region of the active area underwent wrinkling with biaxial strain, featuring densely packed wrinkles with wavelengths of 5 - 10 pm (Fig. 2d (ii)). These induced wrinkles facilitated deformation by unfolding, without subjecting the nanowires and nanotube networks to stretching.

[0063] Fig. 2e illustrates the status of the wrinkles before and after expansion. Initially, wrinkles exhibited distinct buckling patterns with a wavelength of 5 - 10 pm, arising from an approximate 80 - 90% pre-strain. Nanowires were also distributed along the wrinkle surfaces. Upon subjecting the sample to a 30% area expansion (Fig. 2e (i)), the wrinkles experienced slight flattening, resulting in reduced peak heights compared to their pristine state. At 70% strain, the surface was almost completely flattened (Fig. 2e (ii)). Figs 21 and 22 show7the effect of the wrinkled structure in uniaxial stretching tests, wherein a 50% uniaxial stretching of the electrodes, equivalent to 125% area strain in a biaxial deformation with 50% strain in all directions, did not yield significant elongation in the hybrid electrode network.

[0064] These three strategies synergistically can enhance the stretchability of the JHE, making their expanded state beyond the reported deformable JHEs.1261which are mostly only bendable and will lose their function under high strain deformations. Table SI in Fig. 31 presents a comparative overview of our newly developed stretchable electrode in conjunction with existing literature, particularly those that can be concurrently applied to soft actuation systems.

[0065] 2.3 Architecture design for multi-cell refreshable Braille (MCRB)

[0066] The deformable JHE was applied to design an electronic Braille (e-Braille). A letter, number, or character in Braille was represented by a specific pattern of raised dots (a k.a. pixels) in a 3 x 2 array called a cell. E-Braille devices have been proposed using piezoelectric bimorphs.[38,39]shape memory polymers,[40’46,471volume change materials,[41,42]fluidic elastomer actuator arrays,

[0043] and diverse dielectric elastomer actuators1441(DEAs). However, these prior approaches have been constrained by their bulky structures, sluggish response times, and / or limited blocking forces. For instance, the manufacturing of fluidic elastomer actuator arrays requires numerous valves, one for each pixel, limiting the feasibility of packing multi-cells in a compact structure. DEAs demand high voltage operation, potentially posing physical and psychological risks to users.[441Stretchable heaterbased e-Braille cells recently reported had low pixel resolution and high driving voltages.[5,45]

[0067] Fig. 3a illustrates an MCRB display incorporating the stretchable electrodes fabricated in this study. The assembled structure had external dimensions of 70 mm x 150 mm x 10 mm and accommodated 60 pixels in 10 cells. The device comprised a BSEP membrane with the JHE, a printed circuit board (PCB) control panel, adhesive layers, and 3D-pnnted pneumatic chambers and pins. The active BSEP membrane was laminated between the PCB and a rigid cover. The JHE electrode was patterned to define the individual dot areas. The PCB delivered electrical voltage to each of the electrode areas. Fig. 23 shows the layout of theelectrical contacts. A miniature pump provided global pneumatic pressure and expanded the Joule heated electrode areas in the BSEP membranes. The sequence of an actuation cycle was shown in Fig. 3b. A dot (left in Fig. 3b-i) started from its relaxed position and was Joule heated above 48 °C. The softened area of the BSEP membrane was pneumatically actuated under the applied pneumatic pressure, forming a hemispherical shape that raised the corresponding pin out of the plane (Fig. 3b-ii). Upon cooling, the membrane stiffened, while the actuated area remained expanded to maintain the pin at the elevated height (Fig. 3b-iii). To revert the pin to its original state, the dot area was heated again, allowing the membrane to relax and the pin to return to its initial position (Fig. 3b-iv). The actuation can be repeated, such that the MCRM displays refreshable texts. The MCRM structure was 10 mm thick, the pins measured 1.5 mm in diameter, the dot-to-dot pitch was 2.5 mm. and the cell-to-cell pitch was 6.5 mm. in accordance with standard Braille dimensions.1291

[0068] The MCRB design exploits the large stiffness change of the BSEP in a narrow temperature range (Fig. 3c). At room temperature, the BSEP membrane behaved as a rigid plastic capable of providing a blocking force exceeding 50 g, despite having a thickness of merely 120 pm.[5]It met the requisite blocking force criterion of 15 g for Braille devices, thereby providing enough resistance for users to stably scan and read the Braille.1481After the transition to the soft state, a low pneumatic pressure of approximately 8 kPa can expand the membrane up to approximately 90% area strain, resulting in a raised height of 0.6 mm. The expanded BSEP membrane raised the pin. This low pressure was optimized based on the thickness of the membrane and the target actuation height.

[0069] The hybrid network electrode was patterned into a serpentine trace in each Braille dot area for uniform heating. From a geometrical perspective, the serpentine pattern exhibits low mechanical impedance on electrodes and facilitates efficient Joule heating.[49’5°1 Fig. 3d-i shows the dimension of the dot pattern designed to conform to the U.S. standard dimensions for Braille devices. Theheating patterns were simulated by finite element analysis (FEA) of the current density distribution. The electrical current was confined within the winding path of the electrode, resulting in uniform Joule heating along the electrode length. In comparison with the popular spiral pattern often used for Joule heating, the serpentine pattern had a higher conductance of 0.049 S (Fig. 24).

[0070] Within each Braille cell, the 6 terminal points (b, c, d in Fig. 25) had different distances from the ground point (a). Fig. 3 d-ii shows the FEA results of the heating distribution in the serpentine traces. To compensate for the finite resistance on the bus line, the width of the trace was calculated to be between 0.20 and 0.24 mm, ensuring that the resistances in the 6 serpentine traces were identical. Consequently, the 6 dots obtained approximately the same Joule heating temperature under a constant voltage applied between the terminal points and the ground (FEA details are included in Method SI).

[0071] 2.4. Performance of the heating electrodes in the MCRB display

[0072] The operation of the MCRB required the JHE to maintain its resistance in both relaxed and expanded states, allowing for a consistent voltage to heat the BSEP membrane during expansion and recovery. The resistance changes of the electrodes were monitored during actuation cycles using a setup that supplies two voltages, one for the Joule heating and the second for the pneumatic pump (Fig. 26). The temperature change was recorded using an infrared camera. Fig. 4a and Fig. 27 show the resistance evolution of three different serpentine traces with initial resistance of 2.2 kQ, 3.4 kQ, and 4. 1 kQ (Rl, R2 and R3, respectively), indicating different hybrid layer thicknesses, during repeated actuation between 0 and 90% area strains. The measured resistance change between the relaxed and actuated states was 0.1 kQ, 0.5 k , 0.0 kQ for Rl, R2, and R3, respectively. Other than a slight increase in the initial few cycles, the resistances remained stable. Applying area strain levels below 90% similarly resulted in consistently low resistance change (Fig. 4b). However, at 100% strain, there was anapproximate 22% increase in resistance, rising from 5.0 kQ in the relaxed state to 6. 1 k in the actuated state. This abnormally large resistance increase was likely caused by excessive deformation beyond the pre-strain level used in the fabrication of the hybrid layers in the electrode. It also confirms the efficacy of the OPS method forming a conductive layer on the wrinkled surface of the BSEP membrane. Note that 58% area strain is the requirement to obtain the 0.5 mm height raise.

[0073] The Joule heating stability of the CNTs / AgNWs / CNTs hybrid electrodes is further monitored via temperatures. Fig. 4c shows the measured temperatures at the relaxed and actuated state (90% strain) of the three electrodes (Rl, R2 and R3) at 9 V. The temperatures were fairly stable, staying between 65 - 68 °C, well above the phase transition temperature of 46 °C. When subjected to different actuation strains, electrodes still maintained each initial temperature of 63, 65, and 68 °C until the end of the actuation at 30%, 50%, and 80% area strains, respectively (Fig. 4d). Applying 100% area strain resulted in a 2 °C drop in the actuated state, but the sample returned to the initial temperature of 60 °C after relaxation.

[0074] To assess the lifetime of the JHE, repeated actuation to 0.5 - 0.6 mm height with a pneumatic pressure of approximately 8 kPa was performed at 7.7 V (Fig. 4e). The resistance of the electrode increased from 2.2 k to 3.3 kQ after 20,000 actuation cycles (Fig. 28). At the constant voltage of 7.7 V, the temperature generated from Joule heating gradually decreased from 66 °C to 54 °C after 20.000 cycles. The final temperature remained higher than the transition temperature of the membrane.

[0075] The speed of Joule heating plays a key role in determining the refreshing rate of the MCRB.[51’52]Fig. 4f displays the temperature evolution of the electrode within Braille dots at 7, 9, and 11 V. It took 1.2, 0.6, and 0.4 s to reach the phase transition temperature of 46 °C at 7, 9, and 11 V, respectively. As shown in Figs 29(a) and (b). the pneumatic pressure could expand the membrane within 1 s, andthe membrane stiffened within 1 s as it was cooled below 40 °C. The laser displacement sensor showed that the actual pins were displaced within 1 s and released back to their original state within 0.5 s. Therefore, the total refreshing rate was less than 1.5 s. Based on the 9 V of operating voltage, the power consumption of one electrode is calculated as 0.155 W and Joule heating efficiency on the active area is calculated as 91.6% (Fig. 30).

[0076] Fig. 4g shows the temperature beyond the initial rise at constant voltages.Following the initial rapid rise, the temperature reached an equilibrium value, and remained constant for 5 min until the driving voltage was removed from the electrode at the relaxed state. This result confirmed the heating stability of the JHE in MCRB. Fig. 4h shows the temperature profiles in the 1st, 10th, 100th. and 500thactuation cycles at 80% area strain with an applied voltage of 10 V. There was no significant temperature change after 500 actuation cycles. Each temperature point was measured after the membrane returned to its relaxed state. Fig. 4i shows a comparable Joule heating among the dots within a unit cell. With resistance finely tuned by electrode pattern design depicted in Fig. 25, every dot within a cell reached the phase transition temperature in 0.5 s when subjected at 9 V. This consistent response at the cell level ensured uniformity across the entire MCRB display array.

[0077] 2.5. Demonstration of an MCRB display

[0078] Fig. 5 illustrates a 1 X 10 cell array MCRB. The hybrid JHEs on a BSEP membrane with serpentine pixel patterns were laminated onto the PCB board such that the contact points on the electrode overlapped with the copper contacts on the PCB. The assembly was sealed within an air chamber connected to a pneumatic micropump with specific dimensions. The testing of Joule heating was initiated by applying 10 V to selected dots via the PCB. The pixels subjected to the voltage were heated to temperatures exceeding 60 °C. Fig. 5a displays the IR image of the 1 x 10 Braille cell array corresponding to ‘ucla smrl’ in Braille language. Thetemperature rise was uniform among all the activated pixels. Fig. 5b shows the top-view optical image of the array under pneumatic pressure of approximately 9 - 10 kPa. The actuation height of the heated dots was measured to be around 0.6 mm, corresponding to an area strain of 81.3%. A 3D-printed top cover (dimensions: 70 mm X 150 mm X 0.7 mm) with pins, aligned with the through holes, was placed over the BSEP membrane and screw-tightened with the pneumatic chamber beneath the PCB board. The positions of the pins and the serpentine traces were vertically aligned. Fig. 5c depicts the array with pins over the actuated BSEP dots, causing them to be raised. Even after the heating voltage was removed, the dots remained elevated. After turning off the pump, the position was maintained as well (Fig. 5d). When the BSEP membrane returned to ambient temperature, and the pump was turned off. the raised pins remained their elevated state and could support up to 50 g of force. The contents were erased when the JHE was reheated without the pump pressure. Then the pins returned to their lowered state, completing the refresh cycle of the Braille display (Fig. 5e).

[0079] Advantages and Improvements

[0080] A stretchable, pattemable, and low-voltage operating JHE has been developed using CNTs / AgNWs / CNTs hybrid layers. The on-site pre-stretching (OPS) approach was effective in creating Joule heaters locally at the active areas of the BSEP membrane. The incorporation of a buckled structure and serpentine patterning of the hybrid layers ensured a strain-invariant stretchability. Moreover, embedding the CNTs / AgNWs / CNTs electrode within a WPU matrix enhanced its adhesion to the substrate and allowed for reversible stretchability of the electrode. The Joule heaters exhibited consistent performance with the same voltage at both actuated and relaxed states, enduring more than 20,000 actuation cycles. By using the localized Joule heating of individual dots in combination with globally applied pneumatic pressure, a 1 x 10 Braille cell array was demonstrated.

[0081] 4. Experimental Section

[0082] CNTs, AgNWs, and WPU solution 8 mg P3 SWCNT functionalized with carboxylic groups (Carbon Solution Inc) was dispersed into 2 ml deionized (DI) water and 18 ml ethanol (EtOH). The solution was bath-sonicated for 120 min, then centrifuged at 9000 rpm for 18 min. The supernatant CNT solution was used for spraying. A 1 ml of 1 wt% diluted AgNW solution (Kechuang Inc) was diluted with 9 ml of isopropyl alcohol (IP A). The mixture was agitated to ensure homogeneity. The solution was centrifuged at 5500 rpm for 10 min to facilitate the removal of the supernatant. Subsequently, 10 ml of EtOH was added to make a 0. 1 wt% AgNW solution with agitation. The solution underwent filtration and further dilution to attain the requisite concentration for the experiment. A 35 wt% diluted water-borne polyurethane (WPU, Bond Poly mers International) was further diluted by IPA to yield a 0.3 wt% solution. Stirring for 1 hour ensured uniformity in the resulting solution. The prepared solutions detailed above were utilized for subsequent experimental procedures.

[0083] Preparation ofBSEP membranes: BSEP synthesis involved the use of octadecyl acrylate (OA, Aldrich, Mw 324.54) for crystallization at room temperature and urethane diacrylate (UDA, Sartomer) to enhance elongation at the break. The final prepolymer composition for BSEP is comprised of 80 weight parts OA, 20 parts UDA, 10 parts acrylic acid (AA, Aldrich), 1.5 parts trimethylolpropane triacrylate (TMPTA, Aldrich), 0.5 parts dimethoxy phenylacetophenone (DMPA, Aldrich), and 0.25 parts of the benzophenone (BP, Aldrich). The prepolymer solution was injected between two slide glasses, using a spacer thickness of 120 pm.

[0084] Laser Cutting and Engraving: The hybrid electrodes underw ent laser engraving using an engraver (Epilog FiberMark Model 8000) to create a serpentine pattern, with parameter adjustments based on material layer thicknesses. Additional membrane components such as adhesion layer 2, WPU deposition face masks, and gold sputtering substrates were produced using a lasercutter (Epilog Zing Model 10000). Laser settings were fine-tuned according to specific material properties.

[0085] Finite Element Analysis (FEA): COMSOL software facilitated FEA to model Joule heating uniformity and current density distribution across various patterns. A description of material properties, boundary conditions, and equations were described in each simulation result and detailed under Method 1.

[0086] Characterization'. Optical images were acquired using an optical microscope (TFProbe, SP200MS) at varying magnification. Membrane thicknesses were determined using a surface profiler (Veeco Dektak 8 Profilometer) and an AFM (Bruker Dimension FastScan SPM). The mechanical properties of the materials were characterized by using Dynamic Mechanical Analysis (DMA, TA Instruments RSAIII). An IR camera and Kiethley conductivity device were used to measure changes in temperature and resistance during the actuation. Dynamic temperature sweep tests were performed by ramping the temperature at a rate of 2 °C / min and a frequency of 1 Hz, spanning from 25 to 60 °C. Samples measuring 8 mm in width and 120 pm in thickness were analyzed using DMA, utilizing an 8 mm gap between thin membrane grips. Stress-strain curves of the BSEP membrane were measured at 50 °C with a strain rate of 0. 1 mm / s. The structure of hybrid electrodes and the evolution of wrinkle expansion under varying applied strains were observed and confirmed using SEM (ZEISS Supra 40VP). Transmittance measurements for comparison between hybrid and homogeneous electrodes were measured by UV-vis spectrophotometer (Shimadzu). The evaluation of actuation performance involved monitoring changes in resistance using a Keithley 2400 analyzer and tracking temperature variations through a thermal IR camera (ICT Inc, 9320P).

[0087] Method SI. FEA for heating distribution in the serpentine pattern. The electrical conductivity, thermal conductivity, and density of SWCNT in the model were 10000 S / m, 1000 W / mK, and 1.5 kg / m3. respectively. A 9V voltage was applied for Joule heating between the ground ( 6 copper contacts) and the terminal(copper contact on the bus line). Utilizing Joule's first law ( P = 12R, where P is the power converted from electrical energy to thermal energy, I is the current, and R is the resistance), heating primarily occurred on the serpentine active area. To improve Joule heating efficiency, a thin layer of Au was deposited on the bus line to maintain low electrical resistance and avoid excessive heating. Also, the width of the top, middle, and bottom serpentine patterns was varied ( 0.24,0.22, and 0.20 mm , respectively) to account for resistance difference due to the varying distance between the ground and contact points.

[0088] Fabrication of the stretchable Joule heating electrode.

[0089] Fig. 32 illustrates a method of fabricating a stretchable Joule heating electrode, comprising:(a) stretching the polymer film to achieve an area strain of 125% in-plane at an elevated temperature,(b) performing oxygen plasma treatment on the stretched film to enhance surface wettability.(c) depositing CNT layer via air-spraying onto the pre-stretched film,(d) depositing a waterborne polyurethane (WPU) layer via spraying on top of the CNT layer to enhance mechanical stability ,(e) relaxing the polymer film at an elevated temperature back to its original size to induce surface wrinkling, and(f) patterning the CNT layer into serpentine conductive traces using laser ablation.Fig. 33 illustrates a method of making a device, comprising the following steps. Block 3300 represents deforming and / or pre stretching a (e.g.. bistable electroactive) polymer film, the (e.g., bistable electroactive) polymer layer comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature, to achieve a stretched film, e.g., comprising an in plane area strain of at least 125% of the strain in the unstretched bistable electroactivepolymer film, wherein the stretching is at an elevated temperature above the transition temperature.Block 3302 represents depositing an electrode layer comprising the carbon nanotubes onto the stretched film. The step can optionally comprise performing oxygen plasma treatment prior to the deposition on the stretched film to enhance surface wettability of carbon nanotubes.Block 3304 represents depositing an elastomer on the CNT layer, the elastomer permeating and / or penetrating between the carbon nanotubes to form a composite layer comprising the elastomer and the carbon nanotubes, wherein the composite layer is on top of the stretched film.Block 3306 represents relaxing (releasing the force / stretching / strain in) the polymer film, e.g., at the elevated temperature back to its original size to induce surface wrinkling of the polymer film.Block 3308 represents patterning the composite layer comprising the elastomer and carbon nanotubes into conductive traces (e.g., serpentine conductive traces using laser ablation) to form the electrode comprising the patterned composite layer on the (e.g., bistable electroactive) polymer film.Block 3310 represents optionally assembling the electrode in a device, e.g., an electrode, a haptic device or tactile display.

[0090] Device and Method Embodiments

[0091] Illustrative embodiments include, but are not limited to, the following (referring to Figs. 1-33).

[0092] A deformable electroactive polymer membrane 100, comprising:

[0093] a polymer layer 102 having a modulus change by 2 to 4 (e.g., 2 < modulus change < 4) orders of magnitude from more than 10 MPa of elastic modulus below 30 °C to less than 100 kPa above 50 °C, wherein the modulus change is reversible;

[0094] a deformable electrode layer 104 on the polymer layer, wherein the deformable electrode layer comprises a network of metal (e.g., silver) nanowires 200 electrically connected to a network of carbon nanotubes (CNTs) 202 and / or a network formed by metal (e.g.. silver) nanowires 200 (e.g., AgNWs) and carbon nanotubes (CNTs) 202; and

[0095] an elastomer 106 contacting or penetrating (e.g., into pores) in the network.

[0096] 2. The deformable electroactive polymer membrane of clause 1, wherein the electrode layer comprises at least a layer 206 of the metal nanowires 200 and a layer 208 of the CNTs 202 or a layer of the metal nanowires sandwiched between a first layer of the carbon nanotubes and a second layer of the carbon nanotubes.

[0097] 3. The deformable electroactive polymer membrane of clause 1 or2, wherein the deformable electroactive polymer membrane comprises a prestrain characterized by formation of an electrode layer, comprising the nano wires and the carbon nanotubes, on a substrate 110 comprising a first layer 112 of the elastomer on the polymer layer during application of a force F deforming 114 the substrate by at least a portion of an amplitude of an actuation in a direction of the actuation and subsequent patterning of the electrode layer after release of the force or after deposition of a second layer of the elastomer on the electrode layer and then the release of the force, wherein the actuation is the actuation during operation of the electroactive polymer membrane in a device.

[0098] 4. The deformable electroactive polymer of any of the clauses 1-3, wherein the electrode layer is formed on a wrinkled surface 130 of the elastomer.

[0099] 5. The deformable electroactive polymer of any of the clauses 1 -4, wherein the deformable electrode layer is formed on a surface area of a combination of the elastomer and the polymer layer after application andsubsequent release of a strain or prestretching or actuation force increasing the area by up to 100% (e.g., actuation force in direction of actuation during operation).

[0100] 6. The deformable electroactive polymer of any of the clauses 1-4, wherein the polymer layer comprises a bistable electroactive polymer.

[0101] 7. The deformable electroactive polymer of any of the clauses 1-6, wherein the polymer layer is formed from a combination of octadecyl acry late (OA). urethane diacrylate (UDA), trimethylolpropane triacrylate, dimethoxy phenyl-acetophenone, and a photoinitiator such as benzophenone.

[0102] 8. The deformable electroactive polymer of any of the clauses 1-7 polymerized from a prepolymer solution comprising at least 70 wt. % of the OA, at least 15 wt.% of the UDA, and less than 1 wt% each of the trimethylolpropane triacrylate, dimethoxy phenyl-acetophenone, and benzophenone.

[0103] 9. The deformable electroactive polymer of any of the clauses 1-8 wherein the elastomer comprises waterborne polyurethane (WPU), silicone elastomer, and / or soft (not waterborne) polyurethane.

[0104] 10. The deformable electroactive polymer of any of the clauses 1-9, wherein the electrode layer has a thickness less than 200 nm, the elastomer has a thickness 100-1000 nm, and the polymer layer has a thickness of 10-1000 micrometers, the nano wires have a diameter of less than 100 nm and a length of at least 1 micron, and the carbon nanotubes have a diameter of less than 20 nm and a length of at least 0. 1 micron.

[0105] 11. The deformable electroactive polymer membrane of any of the clauses 1-10, wherein the deformable electrode layer is patterned into a conductive trace to Joule heat an area covered by the trace, and:

[0106] (a) the conductive trace is patterned into a shape that is serpentine or radial, and / or

[0107] (b) the conductive trace has a width in a range between 10 micrometers and 200 micrometers, and / or

[0108] (c) the deformable electrode layer is patterned by laser engraving.

[0109] 12. A method of fabricating the deformable electroactive polymer membrane of any of the clauses, comprising:

[0110] (a) prestretching the polymer layer at an elevated temperature above a phase transition temperature (e g,, but not limited to. above 30 degrees Celsius) that converts the polymer layer from a rigid crystalline state to a soft amorphous state,

[0111] (b) depositing the deformable electrode layer on the prestretched polymer layer,

[0112] (c) depositing the elastomer comprising an elastomer material on the deformable electrode layer.

[0113] (d) relaxing the polymer layer at the elevated temperature, and

[0114] (e) patterning the deformable electrode layer into a conductive trace.

[0115] 13. A method of fabricating the deformable electroactive polymer membrane of any of the clauses 1-12, comprising:

[0116] (a) deforming selected areas of the polymer layer at an elevated temperature above a phase transition temperature (e.g., but not limited to 30 degrees Celsius) that converts the polymer layer from a rigid crystalline state to a soft amorphous state,

[0117] (b) depositing the deformable electrode layer on the deformed selected areas,

[0118] (c) depositing the elastomer comprising an elastomer material on the deformable electrode layer,

[0119] (d) relaxing the deformed areas of the polymer layer at the elevated temperature, and

[0120] (e) patterning the deformable electrode layer into a conductive trace.

[0121] 14. The method of clause 12 or 13, wherein the elastomer material is a water borne polyurethane.

[0122] 15. The method of any of the clauses 12-14, wherein the elastomer material is deposited on the deformable electrode layer by spraying.

[0123] 16. The deformable electroactive polymer membrane of any of the clauses 1-11 manufactured by the method of any of the clauses 1-11.

[0124] 17. The deformable electroactive polymer membrane of any of the clauses 1-16, wherein the polymer has an elastic modulus greater than 20 MPa below 35 °C and less than 50 kPa above 45 °C.

[0125] 18. A refreshable tactile display unit 301, comprising:

[0126] (a) the deformable electroactive polymer membrane of any of the clauses 1-11;

[0127] (b) a fluidic pressure source to deform the deformable electroactive polymer membrane;

[0128] (c) a pressure chamber 302 connected to a fluidic pressure source; and

[0129] (d) a cover membrane 306 comprising one or more through holes 310.

[0130] 19. The refreshable tactile display unit of clause 18, further comprising a pin 306 placed in each of the through holes and supported by the deformable electroactive polymer membrane.

[0131] 20. The refreshable tactile display unit of clause 18 or 19, wherein the pressure chamber and / or the cover membrane is stiff.

[0132] 21. The refreshable tactile display unit of any of the clauses 18-20, wherein the pressure chamber and / or the cover membrane is flexible.

[0133] 22. The refreshable tactile display unit of any of the clauses 18-21, wherein the fluidic pressure source is a pneumatic source.

[0134] 23. A tactile display unit, comprising:

[0135] (a) the deformable electroactive polymer membrane of any of the clauses 1-22;

[0136] (b) an electrical power source to supply a voltage to the deformable electrode layer to induce Joule heating.

[0137] 24. A tactile display unit, comprising:

[0138] (a) the deformable electroactive polymer membrane of any of the clauses 1 -22; and

[0139] (b) a printed circuit board 310 or circuit to provide electrical voltage to a plurality of areas on the deformable electroactive polymer membrane.

[0140] 25. The unit of clause 23 or 24 combined with the unit of any of the clauses 18-22.

[0141] 26. A deformable electroactive polymer membrane, comprising:

[0142] a layer 102 of a bistable electroactive polymer characterized by having and / or comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature (e.g., having a modulus change by 2 to 4 (e.g., 2 < modulus change < 4) orders of magnitude from more than 10 MPa of elastic modulus below 30 °C to less than 100 kPa above 50 °C, wherein the modulus change is reversible);

[0143] a deformable electrode layer 104 comprising a pattern of heating elements each comprising a network of nanowires 200 and / or a network of carbon nanotubes 202 patterned into a conductive trace 220 on the polymer layer; and

[0144] an elastomer penetrating into pores in the network.

[0145] 27. The membrane of clause 26 comprising the deformable electroactive membrane of any of the clauses 1-11.

[0146] 28. A device 301 comprising the membrane 102 of clause 26 or 27, further comprising a circuit 310 operable to apply a voltage less than 10 V to pass current to the heating elements so as to heat the polymer layer above the transition temperature, thereby deforming selected areas of the polymer layer into protrusions 150 that can be differentiated by haptic sensing using fingertips. .

[0147] 29. The device of clause 26, further comprising a plurality of pixels, each of the pixels (e.g., pins 306) actuated and / or defined by a different one of the protrusions 150 deformed by heating of a different one of the heating elements.

[0148] 30. The device of any of the clauses 26-29, wherein the protrusions ion the pixels are actuatable to indicate information using Braille.

[0149] 31. The device of any of the clauses 26-29, further comprising

[0150] a fluidic device for applying fluidic pressure:

[0151] the deformable electroactive polymer layer on the fluidic device:

[0152] a haptic or tactile display above the deformable electroactive layer comprising a plurality of holes, each of the holes for insertion of a pin that can move up and down through its respective one of the holes in response to physical contact from a different one of the protrusions in the deformable electroactive polymer layer actuated by the selective heating of one of the heating elements in a contact with the deformable electroactive polymer layer.

[0153] 32. The device of clause 29, further comprising an adhesive layer adhering edges of the polymer membrane to an underside of the haptic or tactile display.

[0154] 33. The device of any of the clauses 1-32, wherein the elastomer and polymer layer comprise dielectric elastomers or polymers as described in

[0062] -

[0064] of the references section, including those listed on pages 20-26 or Table 2 in

[0064] or in Section 2. DIELECTRIC ELASTOMER MATERIALS of

[0063] (e.g. VHB elastomers, polyacrylate with Diels Alder bonds, bistable electroactive polymers).

[0155] 34. The deformable electroactive polymer of any of the clauses 1-33, wherein the polymer layer is formed from Hexadecyl acrylate and tetradecyl acrylate in combination with OA., e.g., wherein these smaller acrylates can low er the transition temperature from rigid to soft state.

[0156] 35. The electroactive polymer or device of any of the clauses wherein the metal nanowires comprise or consist of metal nanowires.

[0157] 36. A method of fabricating a stretchable Joule heating electrode, comprising:(a) stretching a bistable electroactive polymer film, the bistable electroactive polymer layer comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature, to achieve a stretched film comprising an in plane area strain increased by 20%- 200%, wherein the stretching is at an elevated temperature above the transition temperature;(b) performing a treatment (e.g. oxygen plasma or chemical treatment) on the stretched film to enhance surface wettability of carbon nanotubes.(c) depositing a CNT layer comprising the carbon nanotubes onto the stretched film.(d) depositing an elastomer on the CNT layer, the elastomer permeating and / or penetrating between the carbon nanotubes to form a composite layer comprising the elastomer and the carbon nanotubes, wherein the composite layer is on top of the stretched film,(e) relaxing the polymer film at the elevated temperature back to its original size to induce surface wrinkling of the polymer film, and(f) patterning the composite layer comprising the elastomer and carbon nanotubes into conductive traces (e.g., serpentine conductive traces using laser ablation).

[0158] 37. The membrane or device of any of the clauses 1-11 or 17-35 manufactured using the method of clause 36.

[0159] 38. A stretchable Joule heating electrode, comprising:

[0160] a bistable electroactive polymer layer exhibiting a phase transition between a rigid crystalline state and an amorphous elastic and / or soft state above a transition temperature; and

[0161] an electrode layer attached to a wrinkled surface of the bistable electroactive polymer layer, the electrode layer comprising an elastomer incombination with carbon nanotubes and the wrinkled surface formed by depositing the electrode layer on the bistable electroactive polymer layer when stretched to an in plane area strain increased by 20%-200% and then subsequently releasing the strain to revert to an unstretched state.

[0162] 39. The electrode of clause 38, wherein the electrode layer is patterned with a conductive trace on the wrinkled surface.

[0163] 40. The electrode of clause 38 or 39 manufactured using the method of clause 12, 13, or 36.

[0164] 41. The method, device, display, electrode, or membrane of any of the clauses 1 -40, wherein the stretching, deforming, pre-straining of the polymer layer (e.g., bistable electroactive polymer) comprises applying a strain to the polymer layer in a range of 20%-200%, e.g., 20% < strain < 200% with preferred strains between 75%-150%. e.g., 75% < strain < 150%.

[0165] 42. The method, device, display, electrode, or membrane of any of the clauses 1-41, wherein the stretching, deforming, pre-straining of the polymer layer (e.g.. bistable electroactive polymer) comprises applying a force / the strain to increase or expand the in-plane area of the polymer layer by 20%-200% of the original (e.g., unstretched / unstrained / pre-force) area, e.g., 20% < increase < 200%.

[0166] 42. The method, device, display, electrode, or membrane of any of the clauses 1-42, wherein the stretching, deforming, pre-straining of the polymer layer (e.g., bistable electroactive polymer) comprises applying a force / the strain to increase or expand the in-plane area of the polymer layer by 75%-150% of the original (e.g., unstretched / unstrained / pre-force) area, e.g., 75% < increase < 150%.

[0167] 42. The method, device, display, electrode, or membrane of any of the clauses 1 -42, wherein the stretching, deforming, pre-straining of the polymer layer (e.g., bistable electroactive polymer) comprises applying a force / the strain to increase or expand the in-plane area of the polymer layer byless than 125% (e.g., 40%) or more than 125% of the original (e.g., unstretched / unstrained / pre-force) area.

[0168] 43. The method, device, display, electrode, or membrane of any of the clauses 1-42 wherein the electrode layer or deformable electrode layer comprises or consists of or consists essentially of carbon nanotubes.

[0169] 44. The method, device, display, electrode, or membrane of any of the clauses 1-43 wherein the electrode layer comprises or consists of carbon nanotubes alone without metal or silver nanowires that cause degradation of the electrode upon repeated heating cycles.

[0170] 45. The method, device, electrode or membrane of any of the clauses 1-44, wherein the stretching, deforming, pre-straining of the polymer layer (e.g., bistable electroactive polymer) comprises applying force such that the polymer layer has an area strain of 75% < area strain < 150% or 20% < area strain < 200 %, wherein area strain is 100 x(change in area in units) / (original area in units).

[0171] 46. The method, device, electrode, or membrane of any of the clauses 1-45, wherein the elastomer comprises or is waterborne polyurethane (WPU), silicone elastomer, soft (not waterborne) polyurethane, or acrylate.

[0172] Further Device and Method Embodiments

[0173] 1 ; A deformable electroactive polymer membrane comprising a polymer layer 102 having a modulus change by 2 to 4 orders of magnitude from more than 10 MPa of elastic modulus below 30°C to less than 100 kPa above SOT, wherein this modulus change is reversible; and a deformable electrode layer 104 (on the polymer layer) comprising a network formed by silver nanowires 200 (AgNWs) and carbon nanotubes (CNTs) 202; and an elastomer 106 penetrating in the network.

[0174] 2. The deformable electrode layer of clause 1 comprising at least a layer of AgNWs and a layer of CNTs

[0175] 3. The deformable electrode layer of clause 1 or 2 patterned into a conductive trace to Joule heat an area covered by the trace:(a) shape of the pattern is serpentine or radial,(b) the conductive trace has a width in the range between 10 micrometers and 200 micrometers, or(c) patterning is done by laser engraving

[0176] 4. Fabrication of the deformable electroactive polymer membrane of any of the clauses 1-3, comprising(a) stretching the polymer layer at an elevated temperature,(b) depositing the deformable electrode layer on the prestretched polymer layer,(c) depositing an elastomer material on the electrode layer,(d) relaxing the polymer layer at an elevated temperature, and(e) patterning the electrode layer to have a conductive trace

[0177] 5. Fabrication of the deformable electroactive polymer membrane of any of the clauses 1-3, comprising(a) deforming selected areas of the polymer layer at an elevated temperature,(b) depositing the deformable electrode layer,(c) depositing an elastomer material on the electrode layer,(d) relaxing the deformed areas of the polymer layer at an elevated temperature, and(e) patterning the electrode layer into a conductive trace.

[0178] 6. The deformable electroactive polymer of any of the clauses 1-5 wherein the elastomer material is a water borne polyurethane.

[0179] 7. The deformable electroactive polymer of any of the clauses 1-6 wherein the elastomer material is deposited on the electrode layer by spraying.

[0180] 8. The polymer layer of any of the clauses having an elastic modulus greater than 20 MPa below 35°C and less than 50 kPa above 45°C.

[0181] 9. A refreshable tactile display unit comprising: a) a deformable electroactive polymer membrane of any of the clauses 1-8; b) a fluidic pressure to deform the polymer membrane;c) a pressure chamber connected to a fluidic pressure source; e) a cover membrane comprising one or more through holes;

[0182] 10. The refreshable tactile display unit of clause 9, further comprising a pin placed in each hole and supported by the deformable electroactive polymer membrane

[0183] 11. The refreshable tactile display unit of clause 9 or 10, wherein the pressure chamber and / or the cover membrane is stiff.

[0184] 12. The refreshable tactile display unit of any of the clauses 9-11 , wherein the pressure chamber and / or the cover membrane is flexible /

[0185] 13. The refreshable tactile display unit of any of the clauses 9-12 , wherein the fluidic pressure is pneumatic.

[0186] 14. A tactile display unit comprising:(a) a deformable electroactive polymer membrane of any of the clauses 1-13;(b) an electrical power source to supply a voltage to the deformable electrode layer to induce Joule heating

[0187] 15. A tactile display unit comprising(a) a deformable electroactive polymer membrane of any of the clauses 1-14; and(b) a printed circuit board to provide electrical voltage to a plurality of areas on the deformable electroactive polymer membrane.ReferencesThe following references are incorporated by reference herein(1) Dang, T.; Annaswamy, T. M.; Srinivasan, M. A. Development and Evaluation of an Epidural Injection Simulator with Force Feedback for Medical Training. Stud. Health Technol. Inf. 2001, 81, 97-102.(2) Langrana, N. A.; Burdea, G ; Lange, K.; Gomez, D ; Deshpande,S. Dynamic Force Feedback in a Virtual Knee Palpation. Artif. Intell. Med. 1994, 6, 321-333.(3) Vining, D. J.; Liu, K.; Choplin, R. H.; Haponik, E. F. Virtual Bronchoscopy. Chest 1996, 109, 549-553.(4) Maisto, M.; Pacchierotti, C.; Chinello, F.; Salvietti, G.; De Luca,A.; Pratichizzo, D. Evaluation of Wearable Haptic Systems for the Fingers in Augmented Reality Applications. IEEE Trans. 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SPIE 11587, Electroactive Polymer Actuators and Devices (EAPAD) XXIII, 1158700 (22 March 2021); doi: 10.1117 / 12.2584039(66) Refreshable Tactile Display Based on a Bistable Electroactive Polymer and a Stretchable Serpentine Joule Heating Electrode Yu Qiu. Zhiyun Lu. and Qibing Pei* ACS Appl. Mater. Interfaces 2018, 10, 24807-24815http: / / pubs.acs.org / action / showCitFormats?doi=10.1021 / acsami.8b0 7020 / (67) S. Pillai. J. Wang, Y. Wang, M. Sk. A. Prakoso, C. Park, Sci. Rep. 2016. 6, 1.(68) J. Park, W. Hyun, S. Mun, Y. Park, O. O. Park. ACS Appl. Mater. Interfaces 2018, 10, 7371.(69) A. Abdelhalim. A. Abdellah, G. Scarpa, P. Lugli. Carbon 2013, 61, 72.(70} R. Zhou, P. Li, Z. Fan, D. Du and J. Ouyang. Journal of Materials Chemistry C, 2017. 5, 1544.(71) H. Kim, S. Lee and H. Kim, Sci. Rep., 2019, 9, 1511(72) N. Anusak, J. Virtanen, V. Kangas, V. Promarak and P. Yotprayoonsak, Thin Solid Films, 2022, 750, 139201.(73) Y. Qiu, Z. Lu and Q. Pei, ACS Appl Mater Interfaces, 2018, 10, 24807.(74) J. C. Shanshan Yao, Zheng Cui and Yong Zhu, Nanoscale 2017, 9, 3797.(75) S. Hong, H. Lee, J. Lee, J. Kwon, S. Han, Y. D. Suh, H. Cho, J. Shin, J. Yeo and S. H. Ko, Adv. Mater, 2015, 27, 4744.(76) Further information on one or more embodiments described herein can be found in Deformable Joule Heating Electrode Based on Hybrid Layers of Silver Nanowires and Carbon Nanotubes and its Application in a Refreshable Multi-Cell Braille Display, by Jinsung Kim, Zhixin Xie, Zihang Peng, HyeonJi Hong, Shaghayegh Shajari. Yuxuan Guo, Hanxiang Wu, Yuan Meng, Roshan Plamthottam, Yuan Zhu, Yu Qiu. Huiying Wang, Alex Cheng. Qibing Pei, https: / / doi.org / 10.1002 / adfm.202400023. Volume34. Issue33August 14, 2024.(77) Dual-Stimuli -Responsive Polymer Composite with Ultrawide Tunable Stiffness Range Triggered by Water and Temperature, Yu Qiu,l Erm Askounis,! Fangyi Guan, Zihang Peng, Weikun Xiao, and Qibing Pei ACS Appl. Polym. Mater. 2020. 2, 2008-2015 (78) PCT international patent publication No. WO 2020013902 entitled Refreshable tactile display using bistable electroactive polymer and deformable serpentine electrodeConclusionThis concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Il is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A deformable electroactive polymer membrane, comprising: a polymer layer having a modulus change by 2 to 4 orders of magnitude from more than 10 MPa of elastic modulus below 30 °C to less than 100 kPa above 50 °C, wherein the modulus change is reversible; a deformable electrode layer on the polymer layer, wherein the deformable electrode layer comprises a network of carbon nanotubes (CNTs); and an elastomer penetrating into pores in the network .

2. The deformable electroactive polymer membrane of claim 1, wherein the electrode layer comprises at least a layer of metal nanowires connected to the layer of CNTs or a layer of the metal nanowires sandwiched between a first layer of the carbon nanotubes and a second layer of the carbon nanotubes.

3. The deformable electroactive polymer membrane of claim 1, wherein the deformable electroactive polymer membrane comprises a pre-strain or has been pre-strained as characterized by formation of an electrode layer, comprising the nanowires and the carbon nanotubes, on a substrate comprising a first layer of the elastomer on polymer layer during application of a force deforming the substrate by at least a portion of an amplitude of an actuation in a direction of the actuation and subsequent patterning of the electrode layer after release of the force or after deposition of a second layer of the elastomer on the electrode layer and then the release of the force, wherein the actuation is the actuation during operation of the electroactive polymer membrane in a device.

4. The deformable electroactive polymer of claim 1 wherein the electrode layer is formed on a wrinkled surface of the elastomer.

5. The deformable electroactive polymer of any of the claims 1-4, wherein the deformable electrode layer is formed on a surface area of a combination of the elastomer and the polymer layer after application and subsequent release of a strain or prestretching or actuation force increasing the area by up to 100% (e.g., actuation force in direction of actuation during operation).

6. The deformable electroactive polymer of claim 1, wherein the polymer layer comprises a bistable electroactive polymer.

7. The deformable electroactive polymer of claim 1, wherein the polymer layer is formed from a combination of octadecyl acry late (OA), urethane diacrylate (UDA). trimethylolpropane triacrylate, dimethoxy phenyl-acetophenone, and a photoinitiator such as benzophenone.

8. The deformable electroactive polymer of claim 1 polymerized from a prepolymer solution comprising at least 70 wt. % of the OA, at least 15 wt.% of the UDA, and less than 1 wt% each of the trimethylolpropane triacrylate, dimethoxy phenyl-acetophenone, and benzophenone.

9. The deformable electroactive polymer of claim 1 wherein the elastomer comprises waterborne polyurethane (WPU), silicone elastomer, and soft (not waterborne) polyurethane.

10. The deformable electroactive polymer of claim 1 , wherein the electrode layer has a thickness less than 200 nm, the elastomer has a thickness 100- 1000 nm. and the polymer layer has a thickness of 10-1000 micrometers, the nanowires have a diameter of less than 100 nm and a length of at least 1 micron, and the carbon nanotubes have a diameter of less than 20 nm and a length of at least 0. 1 micron.

11. The deformable electroactive polymer membrane of claim 1, wherein the deformable electrode layer is patterned into a conductive trace to Joule heat an area covered by the trace, and:(a) the conductive trace is patterned into a shape that is serpentine or radial, and / or(b) the conductive trace has a width in a range between 10 micrometers and 200 micrometers, and / or(c) the deformable electrode layer is patterned by laser engraving.

12. A method of fabricating the deformable electroactive polymer membrane; comprising:(a) prestretching a polymer layer at an elevated temperature above a phase transition temperature that converts the polymer layer from a rigid crystalline state to a soft amorphous state,(b) depositing a deformable electrode layer on the prestretched polymer layer,(c) depositing an elastomer comprising an elastomer material on the deformable electrode layer,(d) relaxing the polymer layer at the elevated temperature, and(e) patterning the deformable electrode layer into a conductive trace, wherein: the polymer layer has a modulus change by 2 to 4 orders of magnitude from more than 10 MPa of elastic modulus below 30 °C to less than 100 kPa above 50 °C, wherein the modulus change is reversible; the deformable electrode layer comprises a network of metal nanowires electrically connected to a network of carbon nanotubes (CNTs).

13. A method of fabricating the deformable electroactive polymer membrane, comprising:(a) deforming selected areas of a polymer layer at an elevated temperature above a phase transition temperature that converts the polymer layer from a rigid crystalline state to a soft amorphous state,(b) depositing a deformable electrode layer on the deformed selected areas,(c) depositing the elastomer comprising an elastomer material on the deformable electrode layer,(d) relaxing the deformed areas of the polymer layer at the elevated temperature, and(e) patterning the deformable electrode layer into a conductive trace, wherein: the polymer layer has a modulus change by 2 to 4 orders of magnitude from more than 10 MPa of elastic modulus below 30 °C to less than 100 kPa above 50 °C, wherein the modulus change is reversible; and the deformable electrode layer comprises a network of metal nanowires electrically connected to a network of carbon nanotubes (CNTs).

14. The method of claim 12 or 13, wherein the elastomer material is a water borne polyurethane.

15. The method of any of the claims 12 or 13, wherein the elastomer material is deposited on the deformable electrode layer by spraying.

16. The deformable electroactive polymer membrane of claim 1 manufactured by the method of claim 12 or 13.

17. The deformable electroactive polymer membrane of claim 1, wherein the polymer has an elastic modulus greater than 20 MPa below 35 °C and less than 50 kPa above 45 °C.

18. A refreshable tactile display unit, comprising:(a) the deformable electroactive polymer membrane of any of the claims 1-11;(b) a fluidic pressure source to deform the deformable electroactive polymer membrane;(c) a pressure chamber connected to a fluidic pressure source; and(d) a cover membrane comprising one or more through holes.

19. The refreshable tactile display unit of claim 18, further comprising a pin placed in each of the through holes and supported by the deformable electroactive polymer membrane.

20. The refreshable tactile display unit of claim 18 or 19, wherein the pressure chamber and / or the cover membrane is stiff.

21. The refreshable tactile display unit of claim 18, wherein the pressure chamber and / or the cover membrane is flexible.

22. The refreshable tactile display unit of claim 18, wherein the fluidic pressure source is a pneumatic source.

23. A tactile display unit, comprising:(a) the deformable electroactive polymer membrane of claim 1;(b) an electrical power source to supply a voltage to the deformable electrode layer to induce Joule heating.

24. A tactile display unit, comprising:(a) the deformable electroactive polymer membrane of claim 1; and(b) a printed circuit board or circuit to provide electrical voltage to a plurality of areas on the deformable electroactive polymer membrane.

25. The unit of claim 23 or 24 combined with the unit of claim 18.

26. A deformable electroactive polymer membrane, comprising: a layer of a bistable electroactive polymer layer comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature; a deformable electrode layer comprising a pattern of heating elements each comprising a network of nanowires and / or a network of carbon nanotubes patterned into a conductive trace on the polymer layer; and an elastomer penetrating into pores in the network.

27. The membrane of claim 26 comprising the deformable electroactive membrane of any of claim 1.

28. A device comprising the membrane of claim 26 or 27, further comprising a circuit operable to apply a voltage less than 10 V to pass current to the heating elements so as to heat the polymer layer above the transition temperature, thereby deforming selected areas of the polymer layer into protrusions that can be differentiated by haptic sensing using fingertips. .

29. The device of claim 26. further comprising a plurality of pixels, each of the pixels actuated by a different one of the protrusions deformed by heating of a different one of the heating elements.

30. The device of claim 26. wherein the protrusions ion the pixels are actuatable to indicate information using Braille.

31. The device of claim 26, further comprising a fluidic device for applying fluidic pressure;the deformable electroactive polymer layer on the fluidic device; a haptic or tactile display above the deformable electroactive layer comprising a plurality of holes, each of the holes comprising a pin that can move up and down through its respective one of the holes in response to physical contact from a different one of the protrusions actuated by the selective heating of one of the heating elements in a pressure of the pressure.

32. The device of claim 31. further comprising an adhesive layer adhering edges of the polymer membrane to an underside of the haptic or tactile display.

33. The device of claim 1, wherein the elastomer and polymer layer comprise dielectric elastomers or polymers as described in [62]-[64] of the references section, including those listed on pages 20-26 or Table 2 in [64] or in Section 2. DIELECTRIC ELASTOMER MATERIALS of [63],34. The deformable electroactive polymer of claim 1, wherein the polymer layer is formed from Hexadecyl acrylate and tetradecyl acrylate in combination with OA., wherein these smaller acrylates can lower the transition temperature from rigid to soft state.

35. A method of fabricating a stretchable Joule heating electrode, comprising:(g) stretching a bistable electroactive polymer film, the bistable electroactive polymer layer comprising a phase transition between a rigid crystalline state and an amorphous elastic or soft state above a transition temperature, to achieve a stretched film comprising an in plane area strain increased by 20%- 200%, wherein the stretching is at an elevated temperature above the transition temperature;(h) performing a treatment on the stretched film to enhance surface wettability of carbon nanotubes,(i) depositing a CNT layer comprising the carbon nanotubes onto the stretched film,(j) depositing an elastomer on the CNT layer, the elastomer permeating and / or penetrating between the carbon nanotubes to form a composite layer comprising the elastomer and the carbon nanotubes, wherein the composite layer is on top of the stretched film,(k) relaxing the polymer film at the elevated temperature back to its original size to induce surface wrinkling of the polymer film, and(l) patterning the composite layer comprising the elastomer and carbon nanotubes into conductive traces (e.g., serpentine conductive traces using laser ablation).

35. A stretchable Joule heating electrode, comprising: a bistable electroactive polymer layer exhibiting a phase transition between a rigid crystalline state and an amorphous elastic and / or soft state above a transition temperature; and an electrode layer attached to a wrinkled surface of the bistable electroactive polymer layer, the electrode layer comprising an elastomer in combination with carbon nanotubes and the wrinkled surface formed by depositing the electrode layer on the bistable electroactive polymer layer when stretched to an in plane area strain increased by 20%-200% and then subsequently releasing the strain to revert to an unstretched state.

36. The electrode of claim 35, wherein the electrode layer is patterned with a conductive trace on the wrinkled surface.

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