Programmable flexible thermal response driver and preparation method thereof

Abstract

The invention discloses a programmable flexible thermal response driver and a preparation method thereof. The driver comprises a flexible substrate, a deformation restraint layer and an electric heating driving layer which are arranged in a stacked mode. The flexible substrate has a relatively high thermal expansion coefficient; the deformation restraint layer has a small thermal expansion coefficient and is used for restraining the thermal expansion direction of the substrate. The electrothermal driving layer can generate heat energy through the Joule heating effect. The key point lies in that the electrothermal driving layer forms an array by a plurality of independently controlled heating units, the specific units are selectively heated through programming, and a controllable temperature field can be generated on the surface of the driver, so that complicated two-dimensional programmable morphologies such as local bulges, recesses or waveforms are driven to be generated. The structure supports sequence adjustment and double-sided design, and the morphology regulation and control capability is expanded. The device has the advantages of low-voltage driving, fast response, large deformation and strong programmability, and is suitable for the fields of soft robots, deformable equipment and the like.

Description

Technical Field

[0001] This invention relates to the fields of flexible electronics, smart materials and soft robotics, and more specifically, to a flexible electrothermal actuator with programmable two-dimensional morphology and its fabrication method. Background Technology

[0002] Flexible actuators are key execution components that connect electrical signals with physical deformation, and they hold great promise in fields such as bionic robots, wearable devices, and adaptive optics. Electrothermal actuation mechanisms have attracted considerable attention due to their high driving force and simple control.

[0003] However, existing flexible electrothermal actuators generally suffer from the following technical bottlenecks: 1) High driving voltage (often above 6V), which is not conducive to portable low-power applications and poses safety hazards; 2) Slow thermal response speed, with the overall deformation time often exceeding 40 seconds, making it difficult to meet the requirements for rapid response; 3) Single deformation mode and non-programmable, mostly only able to achieve simple one-dimensional overall bending, which cannot meet the needs for dynamic control of complex and localized morphology, such as bionic grasping, dynamic changes in surface texture, or antenna reflector reconstruction.

[0004] Therefore, developing a flexible electrothermal actuator that combines low driving voltage, fast response, large deformation range, and programmable two-dimensional morphology is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a programmable flexible thermal response driver and its fabrication method, so as to solve the problems of high driving voltage, slow response and non-programmable morphology in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a programmable flexible thermal response driver, comprising stacked components: A flexible substrate having a first coefficient of thermal expansion; A deformation constraint layer having a second thermal expansion coefficient smaller than the first thermal expansion coefficient, and bonded to the flexible substrate; And an electrothermal drive layer, which is combined with the deformation constraint layer and / or the flexible substrate, is capable of generating heat energy through the Joule heating effect.

[0007] Preferably, the electrothermal drive layer includes multiple independent heating units that are insulated from each other, the multiple independent heating units forming an array or a specific pattern, and each independent heating unit having an independent electrode.

[0008] Preferably, the deformation constraint layer is disposed between the flexible substrate and the electrothermal drive layer.

[0009] Preferably, the electrothermal driving layer is disposed between the flexible substrate and the deformation constraint layer.

[0010] Preferably, the flexible substrate has the deformation constraint layer and the electrothermal driving layer on both opposite sides, forming a symmetrical structure.

[0011] Preferably, the flexible substrate is made of polydimethylsiloxane and has a thickness of 0.1 mm to 1 mm.

[0012] Preferably, the deformation constraint layer is made of a polyimide film with a thickness of 25 micrometers to 125 micrometers.

[0013] Preferably, the electrothermal driving layer is a conductive silver paste pattern.

[0014] In a second aspect, the present invention provides a method for fabricating a programmable flexible thermal response actuator as described in any of the preceding claims, comprising the step of fabricating a stacked structure, the stacked structure comprising a flexible substrate, a deformation constraint layer and an electrothermal driving layer; The formation of the stacked structure includes one of the following methods: Method A: First, form the electrothermal driving layer on the flexible substrate, then cover the electrothermal driving layer with the deformation constraint layer; or Method B: First, attach the deformation constraint layer to the flexible substrate, and then form the electrothermal drive layer on the deformation constraint layer.

[0015] In a second aspect, the present invention provides a method for fabricating a programmable flexible thermal response actuator as described above, comprising the following steps: S1: Preparation of flexible substrate: PDMS prepolymer is molded into a film and pre-cured to form a flexible substrate with an adhesive surface; S2: Adhesive Deformation Constraint Layer: A polyimide film is provided as a deformation constraint layer and adhered to the adhesive surface of the flexible substrate; S3: Forming an electrothermal driving layer: A conductive silver paste pattern is printed on the surface of the deformation constraint layer, and then heated and cured to form an electrothermal driving layer containing multiple independent heating units; S4: Lead-out electrodes: Using conductive paste or anisotropic conductive adhesive, connect wires to the electrode pads of each of the individual heating units.

[0016] The beneficial effects of this invention include: Low-voltage drive and fast response: Utilizing a high-resistivity conductive silver paste pattern as the electrothermal drive layer, sufficient heat can be rapidly generated through the Joule heating effect at DC voltages as low as 3-5V. Simultaneously, the three-layer composite structure design achieves an efficient heat conduction path and low heat capacity, significantly shortening the driver's heating and cooling cycle, reducing the overall response time to less than 15 seconds.

[0017] Large deformation angle: By utilizing the huge difference in thermal expansion coefficients between the flexible substrate (high expansion coefficient, such as PDMS) and the deformation constraint layer (low expansion coefficient, such as polyimide), significant internal stress can be generated under a small temperature rise, driving the structure to produce large-angle bending deformation (the bending angle driven on one side can reach more than 180°).

[0018] Core Innovation: Programmable 2D Topography Spatial programmability: By patterning the electrothermal drive layer into an array of multiple independently controllable heating units, the driver surface can be partitioned and selectively heated. By programming and controlling the on / off state, voltage magnitude, or duty cycle of different units, a non-uniform and controllable temperature field can be generated on the driver surface, thereby inducing two-dimensional curved surface morphologies such as local protrusions, depressions, distortions, or complex waveforms.

[0019] Programmable structure: By changing the stacking order of the three-layer structure (such as the driving layer in the middle or the constraint layer in the middle), the heat flow path and thermal stress distribution can be adjusted to obtain different basic deformation modes and sensitivities, providing flexibility for customized design.

[0020] Double-sided programmable: By constructing a symmetrical double-sided driving structure and independently controlling the heating units on both sides, more complex morphological combinations can be achieved, such as alternating double-sided driving to generate fluctuations, and differential double-sided driving to generate saddle-shaped or spherical hyperbolic surfaces, which greatly expands the degree of freedom of morphological control.

[0021] The preparation process is simple and reliable: the preparation method is based on mature flexible electronics manufacturing processes (such as spin coating and screen printing), with low material costs, simple steps, and good compatibility with large-scale production, which is conducive to the practical application and promotion of the product. Attached Figure Description

[0022] Figure 1 This is a cross-sectional structural diagram of the programmable flexible thermal response actuator provided in Embodiment 1 of the present invention (with the deformation constraint layer in the center).

[0023] Figure 2 This is a planar schematic diagram of the electrothermal drive layer in Embodiment 1 of the present invention.

[0024] Figure 3 This is a cross-sectional structural diagram of the programmable flexible thermal response driver provided in Embodiment 2 of the present invention (the electrothermal driving layer is in the center).

[0025] Figure 4 This is a cross-sectional schematic diagram (double-sided symmetrical structure) of the programmable flexible thermal response driver provided in Embodiment 3 of the present invention.

[0026] Figure 5 This is a schematic diagram of the preparation method according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It is to be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0028] Example 1 like Figure 1 and Figure 2 As shown, this embodiment provides a single-sided programmable flexible thermal response actuator. The actuator includes, from bottom to top, a flexible substrate 1, a deformation constraint layer 2, and an electrothermal driving layer 3.

[0029] The flexible substrate 1 is made of polydimethylsiloxane (PDMS) with a thickness of approximately 0.5 mm. It has a high coefficient of thermal expansion (approximately 310 µm / m·°C) and serves as the main body for active deformation.

[0030] The deformation constraint layer 2 is made of polyimide film (Kapton) with a thickness of approximately 50 micrometers. Its coefficient of thermal expansion is extremely low (approximately 20 µm / m·°C), much lower than that of PDMS. It is firmly bonded to the flexible PDMS substrate 1 to restrict the in-plane (XY direction) thermal expansion of the PDMS, forcing its heat to be primarily converted into out-of-plane (Z direction) bending deformation, while also serving as the supporting substrate for the electrothermal drive layer 3.

[0031] The electrothermal driving layer 3 is formed by printing a conductive silver paste pattern on the surface of a polyimide film using screen printing technology and then curing it. This pattern is designed as at least one heating unit. Figure 2 As shown, the pattern is designed as an array of 4×4 mutually insulated square independent heating units 301. Each heating unit 301 has an independent electrode pad 302, which can be independently voltageed (e.g., 0-5V DC) by an external circuit.

[0032] Working principle: When one or more specific heating units 301 are energized, Joule heating is generated and rapidly conducted to the PDMS flexible substrate 1 through the Kapton deformation constraint layer 2. The PDMS in the heated area attempts to expand, but is constrained by the rigid deformation constraint layer 2 above, resulting in a downward bending moment and forming a local depression. By programming and controlling the activation state of heating units at different locations, the corresponding temperature and morphology fields can be "drawn" on the actuator surface. For example, activating four units in a row sequentially can generate a traveling wave; activating the four central units simultaneously can generate a local bulge. After power is turned off, the structure cools and shrinks, returning to its initial flat state.

[0033] Example 2 like Figure 3 As shown, this embodiment provides an actuator with another stacking order. From bottom to top, it includes: a flexible substrate 1, an electrothermal driving layer 3, and a deformation constraint layer 2.

[0034] The materials and thicknesses of the flexible substrate 1 (PDMS) and the deformation constraint layer 2 (polyimide) are the same as in Example 1. The electrothermal driving layer 3 (conductive silver paste array) is first printed on the surface of the flexible substrate 1 (PDMS) and cured, and then the deformation constraint layer 2 (polyimide) is covered and adhered to it.

[0035] Difference in performance: In this structure, the heat generated by the electrothermal drive layer 3 is directly conducted to the flexible substrate 1 and the deformation constraint layer 2, resulting in a change in the heat transfer path. This may lead to differences in the response speed and deformation radius of the actuator compared to Embodiment 1, providing another optimization option for specific application scenarios.

[0036] Example 3 like Figure 4 As shown, this embodiment provides a double-sided programmable driver. It has identical structures symmetrically arranged on the upper and lower surfaces of a flexible substrate 1: each surface includes a deformation constraint layer 2 and an electrothermal driving layer 3 (patterned array). The heating units on the upper and lower surfaces can be controlled completely independently.

[0037] Working principle and advantages: By independently programming and controlling the heating arrays on the front and back sides, extremely rich morphologies can be achieved. For example, heating only a certain area on the front side produces a forward bend, while heating only the corresponding area on the back side produces a reverse bend. Applying different powers to the heating units in the same area on both sides can generate gradient thermal stress, inducing complex hypercurvature surfaces, such as saddle shapes or near-spherical shapes. By alternately and periodically driving the units on both sides, a wave-like propulsive motion similar to the tail-wagging of a fish can be achieved.

[0038] Experiments show that the driver of this invention can achieve a large-angle bend of over 203° in a short time of about 12 seconds with a low DC voltage of only 2.0V, demonstrating excellent low power consumption and fast response characteristics. More importantly, through the above-mentioned topography programming method, a variety of controllable deformation modes were successfully demonstrated, including but not limited to local bending, symmetrical bending, sinusoidal waveform deformation, local bulging, and simple twisting, fully verifying its powerful topography programmability.

[0039] Example 4: Preparation method Combination Figure 5 This embodiment details the preparation method of the driver as described in Embodiment 1: Step S1: Preparation of the flexible substrate. The PDMS prepolymer and curing agent are thoroughly mixed at a weight ratio of 10:1. After stirring until homogeneous, the mixture is placed in a vacuum drying oven for degassing to remove air bubbles introduced during mixing. Subsequently, using flexible electronic film-forming equipment such as slot coater, spin coater, or doctor blade coater, the degassed PDMS mixture is uniformly coated onto a temporary or permanent substrate (such as a PET film). The coated film is then placed in a forced-air drying oven and cured at 90 degrees Celsius for 20 minutes to form a flexible substrate layer with uniform thickness (e.g., 0.2 mm) and good elasticity and thermal expansion properties.

[0040] Step S2: Applying the Deformation Constraint Layer. Precisely attach the pre-cut polyimide film (Kapton) to the surface of the cured but still slightly tacky PDMS flexible substrate. Apply appropriate pressure to ensure a tight bond between the two layers, with no air bubbles remaining, forming a strong interfacial bond. This intermediate layer will play a crucial role in constraint and thermal conductivity.

[0041] Step S3: Forming the electrothermal driving layer. Using flexible electronic patterning processes such as screen printing, inkjet printing, or photolithography, a pre-designed conductive silver paste pattern is printed on the surface of the deformable constraint layer attached in step S2. This pattern constitutes the electrothermal driving layer, which is divided into multiple independent heating units. After printing, the sample is again placed in an environment of 90 degrees Celsius for 30 minutes to allow the solvent in the conductive silver paste to fully evaporate and the resin to completely cross-link, forming a stable and highly conductive heating electrode layer.

[0042] Step S4: Electrode Outlining and Encapsulation: Using conductive silver paste or anisotropic conductive adhesive, connect thin copper wires or flexible printed circuits (FPCs) to the electrode pad areas of each individual heating unit. This creates an independent external electrical interface for each unit. Finally, depending on environmental stability requirements, a thin layer of PDMS can be selectively coated onto the surface of the structure as a protective layer to complete the fabrication of the entire actuator. For double-sided actuators, steps S2 to S4 need to be repeated on the back side of the flexible substrate.

[0043] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. The scope of protection of the present invention should be determined by the claims.

Claims

1. A programmable flexible thermal response actuator, characterized in that, Including cascading settings: A flexible substrate having a first coefficient of thermal expansion; A deformation constraint layer having a second thermal expansion coefficient smaller than the first thermal expansion coefficient, and bonded to the flexible substrate; And an electrothermal drive layer, which is combined with the deformation constraint layer and / or the flexible substrate, is capable of generating heat energy through the Joule heating effect.

2. The programmable flexible thermal response actuator as described in claim 1, characterized in that, The electrothermal drive layer includes multiple independent heating units that are insulated from each other. The multiple independent heating units form an array or a specific pattern, and each independent heating unit is provided with an independent electrode.

3. The programmable flexible thermal response actuator as described in claim 1 or 2, characterized in that, The deformation constraint layer is disposed between the flexible substrate and the electrothermal drive layer.

4. The programmable flexible thermal response actuator as described in claim 1 or 2, characterized in that, The electrothermal driving layer is disposed between the flexible substrate and the deformation constraint layer.

5. The programmable flexible thermal response actuator as described in claim 1 or 2, characterized in that, The flexible substrate has a deformation constraint layer and an electrothermal driving layer on both opposite sides, forming a symmetrical structure.

6. The programmable flexible thermal response actuator as described in claim 1, characterized in that, The flexible substrate is made of polydimethylsiloxane and has a thickness of 0.1 mm to 1 mm.

7. The programmable flexible thermal response actuator as described in claim 1, characterized in that, The deformation constraint layer is made of a polyimide film with a thickness of 25 micrometers to 125 micrometers.

8. The programmable flexible thermal response actuator as described in claim 1, characterized in that, The electrothermal driving layer has a conductive silver paste pattern.

9. A method for fabricating a programmable flexible thermal response actuator as described in any one of claims 1-8, characterized in that, The process includes the step of preparing a stacked structure, wherein the stacked structure comprises a flexible substrate, a deformation constraint layer, and an electrothermal driving layer; The formation of the stacked structure includes one of the following methods: Method A: First, form the electrothermal driving layer on the flexible substrate, then cover the electrothermal driving layer with the deformation constraint layer; or Method B: First, attach the deformation constraint layer to the flexible substrate, and then form the electrothermal drive layer on the deformation constraint layer.

10. A method for preparing a programmable flexible thermally responsive actuator as described in any one of claims 1-3 and 5-8, characterized in that, Includes the following steps: S1: Preparation of flexible substrate: PDMS prepolymer is molded into a film and pre-cured to form a flexible substrate with an adhesive surface; S2: Adhesive Deformation Constraint Layer: A polyimide film is provided as a deformation constraint layer and adhered to the adhesive surface of the flexible substrate; S3: Forming an electrothermal driving layer: A conductive silver paste pattern is printed on the surface of the deformation constraint layer, and then heated and cured to form an electrothermal driving layer containing multiple independent heating units; S4: Lead-out electrodes: Using conductive paste or anisotropic conductive adhesive, connect wires to the electrode pads of each of the individual heating units.

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