A flexible bistable light-driven composite beam device and a preparation method thereof

Abstract

The application discloses a flexible bistable light-driven composite beam device and a preparation method thereof, and belongs to the technical field of flexible electronic devices. The composite beam device comprises, from top to bottom, an upper film layer coated with a photo-thermal conversion agent on the upper surface, a heat preservation interlayer, a lower film layer coated with a photo-thermal conversion agent on the lower surface and support frames on both sides. The upper and lower film layers are formed of liquid crystal elastomers, and the surfaces of the upper and lower film layers are coated with photo-thermal conversion agents, so that photo-thermal contraction strain can be generated in response to an external light source (808 nm laser). The heat preservation interlayer is formed of silica aerogel and is located between the two film layers, has excellent heat insulation, is suitable for the contraction movement of the film layers and simultaneously enhances the flexibility and rigidity of the structure. The device has two stable states of upturning and downturn, can realize the switching of the stable states through the stimulation of an 808 nm light source, has a lower switching threshold, higher response efficiency and better stability.

Description

Technical Field

[0001] This invention belongs to the field of flexible electronic device technology, and relates to a flexible bistable light-driven composite beam device and its preparation method; specifically, it relates to a bistable device based on a liquid crystal elastomer (LCE) and a silica insulation cotton interlayer and its preparation method. Background Technology

[0002] With the rapid development of smart materials and flexible electronics, bistable structures have been widely used in many fields (such as self-locking structures and micromechanical drives). A bistable structure has two stable states and can maintain these states without requiring continuous external energy input. Energy input is only needed during the switching process to achieve steady-state transition, thus enabling low-energy operation in the system. The existence of bistable structures significantly improves system energy efficiency and stability.

[0003] Most current bistable devices rely on mechanical strain or external excitation forces for state switching. In traditional bistable beam structures, when a vertical displacement load is applied to the center of the upper surface, the curved beam will buckle and become unstable, and the structure will transition from energy absorption to energy release. However, existing technologies often suffer from problems such as reliance on external loads, insufficient shape diversity of rigid materials, high steady-state switching thresholds, and short device lifetimes. Especially in the field of flexible devices, designing a bistable structure that possesses both good flexibility and low-energy triggering remains a technical challenge. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a novel flexible bistable optical-driven composite beam device and its fabrication method, which has a lower switching threshold, higher response efficiency, and better stability, and can maintain bistable state under different temperature and environmental conditions.

[0005] Another objective of this invention is to provide a method for fabricating a flexible bistable optically driven composite beam device.

[0006] The technical solution of the present invention is as follows: The flexible bistable light-driven composite beam device of the present invention comprises, from top to bottom, an upper thin film layer coated with a photothermal conversion agent on its upper surface, a thermal insulation cotton interlayer, a lower thin film layer coated with a photothermal conversion agent on its lower surface, and a support frame installed on both sides of the upper thin film layer, the thermal insulation cotton interlayer, and the lower thin film layer.

[0007] Furthermore, this flexible bistable optically driven composite beam device has two stable states: an upward flip and a downward flip.

[0008] Furthermore, this flexible bistable light-driven composite beam device has three different structures, with the three material layers having driving, heat insulation, and driving functions from top to bottom.

[0009] Furthermore, both the upper and lower thin film layers are made of liquid crystal elastomer, with a thickness of 25~40μm, and have thermal shrinkage properties.

[0010] Furthermore, the photothermal conversion agent coated on the upper surface of the upper film layer and the lower surface of the lower film layer is graphite, which has photothermal shrinkage properties.

[0011] Furthermore, the insulation cotton interlayer is made of silica aerogel insulation cotton with a thickness of 1~2mm.

[0012] Furthermore, the inner width of the support frame is 2.8~5.5cm.

[0013] Furthermore, the beam structure formed by the upper film layer, the insulation cotton interlayer, and the lower film layer has a flat dimension length, width, and thickness ratio of 30:3:1.

[0014] Furthermore, a method for fabricating a flexible bistable optically driven composite beam device includes the following steps: Step (1) Prepare a liquid crystal elastomer film in a polytetrafluoroethylene bath; The specific process is as follows: 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) was dissolved in toluene sample vials at temperatures above room temperature (50~75℃); Then, at room temperature (25~26℃), pentaerythritol tetra-3-mercaptopropionate (PETMP), 3,6-dioxa-1,8-octanedithiol (DODT), 2,2-dimethoxy-2-phenylacetophenone (photoinitiator I-651) and di-n-propylamine (DPA) were dissolved in another toluene sample vial. After cooling to room temperature, the two solutions are mixed and poured into a polytetrafluoroethylene (PTFE) tank. The PTFE tank is then placed in a vacuum drying oven to remove air bubbles, and the solution is cured overnight at 50°C to form a slightly cross-linked multi-domain LCE film. After uniaxial pre-stretching, the film is exposed to ultraviolet (UV) light for two-stage polymerization. The polymerized liquid crystal elastomer film is then cut into strips. This composite beam device exhibits bistable characteristics, meaning that under external light (808nm laser) excitation, it can switch between two stable states, including an upward-flipped state and a downward-flipped state. When the device is in the upward-flipped state, the surface of the upper thin film layer coated with the photothermal conversion agent graphite is irradiated by an 808nm laser source. Under the stimulation of the 808nm laser, the photothermal conversion agent absorbs light energy and converts it into heat energy, causing the temperature of the liquid crystal elastomer film to rise. This causes the liquid crystal units to change from ordered to disordered, and the upper thin film layer of the liquid crystal elastomer undergoes contraction deformation, which drives the entire beam structure to generate a vertically downward load. Under the action of the silica aerogel insulation layer, the thermal influence on the lower thin film layer is greatly reduced, and no contraction deformation occurs. Under the above-mentioned vertically downward load and horizontal expansion restraint, the curved beam quickly springs to the downward-flipped state. When the device is in the flip-down state, the surface of the lower thin film layer coated with photothermal conversion agent graphite is irradiated with an 808nm laser light source. Under the stimulation of the 808nm laser, the photothermal conversion agent absorbs light energy and converts it into heat energy, which raises the temperature of the liquid crystal elastomer film. This causes the liquid crystal units to change from ordered to disordered, and the lower thin film layer of the liquid crystal elastomer undergoes contraction deformation, which drives the entire beam structure to generate a vertically upward load. Under the action of the silica aerogel insulation layer, the thermal influence on the upper thin film layer is greatly reduced, and no contraction deformation occurs. Under the above vertically upward load and horizontal expansion restraint, the curved beam quickly springs back to the flip-up state. Step (2) Coat the surface of the prepared liquid crystal elastomer film with a photothermal conversion agent to obtain a crossbeam without curvature, which is formed by bonding the upper film layer and the lower film layer with the thermal insulation interlayer. Step (3) Fix the two sides of the beam structure to the support frame with adhesive to form a curved beam with natural curvature, the curvature of which is a composite cosine curve; that is, a bistable light-driven flexible composite beam device.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the structure is driven by the photothermal effect, which can realize the bistable switching of the beam under low light intensity, and by optimizing the design of materials and structure, the stability and lifespan of the device can be guaranteed in multiple applications. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the highest steady-state switching temperature of the bistable light-driven flexible composite beam device in Embodiment 1 of the present invention; Figure 3 This is a force-displacement curve of the bistable light-driven flexible composite beam device in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the highest steady-state switching temperature of the bistable light-driven flexible composite beam device in Embodiment 2 of the present invention; Figure 5 This is a temperature curve of the steady-state switching process of the bistable light-driven flexible composite beam device in Embodiment 2 of the present invention; Figure 6 This is a diagram illustrating the steady-state switching process of the bistable light-driven flexible composite beam device in Embodiment 3 of the present invention. Figure 7 This is a schematic diagram of the highest steady-state switching temperature of the bistable light-driven flexible composite beam device in Embodiment 4 of the present invention; Figure 8 This is a schematic diagram of the highest steady-state switching temperature of the bistable light-driven flexible composite beam device in Embodiment 5 of the present invention; In the diagram, 1 is the upper film layer, 2 is the insulation cotton interlayer, 3 is the lower film layer, and 4 is the support frame. Detailed Implementation

[0017] The specific technical solution of the present invention will be further described in detail below with reference to specific examples.

[0018] As shown in the figure, the flexible bistable light-driven composite beam device of the present invention includes, from top to bottom, an upper thin film layer 1 with a photothermal conversion agent coated on its upper surface, a thermal insulation cotton interlayer 2, a lower thin film layer 3 with a photothermal conversion agent coated on its lower surface, and a support frame 4 on both sides.

[0019] Combination Figure 1 The bistable light-driven flexible composite beam device is described.

[0020] In this invention, the upper thin film layer 1 is formed of a liquid crystal elastomer, which is a liquid crystal elastomer film with a crosslinking agent to chain extender ratio of 6:1. It is cut into strips with a length of 6cm and a width of 6mm and is located on the upper surface of the composite beam. The upper surface of the strip is coated with a photothermal conversion agent (graphite). The thickness of the upper thin film layer 1 is in the range of 25~40μm.

[0021] In this invention, the photothermal conversion agent is preferably graphite. Graphite is easy to adhere to and is a mature electrodeless photothermal conversion agent. Under 808nm laser stimulation, the photothermal conversion agent absorbs light energy and converts it into heat energy, causing the temperature of the liquid crystal elastomer film to rise. This causes the liquid crystal units to change from ordered to disordered, and the liquid crystal elastomer generates contraction strain, thereby realizing the steady-state switching function of the bistable light-driven flexible composite beam device; that is, it can respond to external light source (808 nm laser) to generate photothermal contraction strain.

[0022] In this invention, the thermal insulation cotton interlayer 2 is a silica aerogel with a thickness of 1-2 mm, specifically 1, 1.2, 1.4, 1.6, 1.8 or 2 mm; preferably, the thickness is 1 mm, cut into strips 6 cm long and 6 mm wide, located between the two LCE film layers, which has excellent thermal insulation properties, adapts to the shrinkage movement of the film layers, and enhances the flexibility and rigidity of the structure.

[0023] The lower thin film layer 3 is formed of liquid crystal elastomer, with a crosslinking agent to chain extender ratio of 6:1 and a thickness in the range of 25~40μm. It is cut into strips with a length of 6cm and a width of 6mm and is located on the lower surface of the composite beam. The lower surface of the lower thin film 3 is coated with a photothermal conversion agent (graphite), which can generate photothermal contraction strain in response to an external light source (808nm laser).

[0024] The support frame 4 is located on both sides of the beam, is formed using plastic material, has stable support performance, supports the stability of the beam and restrains the beam's expansion displacement in the horizontal direction.

[0025] The lower surface of the upper film layer 1 and the upper surface of the thermal insulation cotton interlayer 2, and the lower surface of the thermal insulation cotton interlayer 2 and the upper surface of the lower film layer 3 are fixed together by adhesive to form a non-curved beam.

[0026] The two sides of the crossbeam structure are fixed to the support frame 4 with adhesive. Due to the horizontal constraint, a curved beam with a natural curvature is formed, and the curvature of the curved beam is a composite cosine function curve.

[0027] This invention also provides a method for fabricating the bistable optically driven flexible composite beam device described above, comprising the following steps: Step (1): Prepare a liquid crystal elastomer film with a crosslinking agent to chain extender ratio of 6:1 in a polytetrafluoroethylene tank: Dissolve 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) in a toluene sample vial at a temperature above room temperature, and then add pentaerythritol tetra-3-mercaptopropionate (PETMP), 3,6-dioxa-1,8-octanedithiol (DODT), and 2,2-dimethoxy-2-phenylphenylacetoether at room temperature. Ketone (photoinitiator I-651) and di-n-propylamine (DPA) were dissolved in another toluene sample vial; after cooling to room temperature, the two solutions were mixed and poured into a polytetrafluoroethylene (PTFE) bath. The PTFE bath was then placed in a vacuum drying oven to remove air bubbles, and the solution was cured overnight at 50°C to form a slightly cross-linked multi-domain LCE film. After uniaxial pre-stretching, the film was exposed to ultraviolet (UV) light for two-stage polymerization. The polymerized liquid crystal elastomer film was cut into strips 6 cm long and 6 mm wide. Step (2): Coat the surface of the liquid crystal elastomer film with a photothermal conversion agent to obtain the upper film layer 1 and the lower film layer 3, which are then bonded to the insulation cotton interlayer 2 to obtain a crossbeam without curvature. Step (3): Fix the two sides of the beam structure to the support frame 4 with adhesive. Due to the horizontal constraint, a curved beam with natural curvature is formed, resulting in a bistable light-driven flexible composite beam device.

[0028] The support structure described in this invention is manufactured by 3D printing, and its inner width and length are preferably 2.8~5.5cm.

[0029] In this invention, the liquid crystal monomer is preferably RM257, the solvent is preferably toluene, and the ratio of liquid crystal monomer to solvent is preferably 1080mg:4ml.

[0030] In this invention, the catalyst is preferably DPA, the photoinitiator is preferably I-651, and the ratio of the liquid crystal monomer to the catalyst and photoinitiator is preferably 1080mg:50μL:30mg.

[0031] In this invention, the preferred dissolution temperature of the liquid crystal monomer in toluene is 50~80℃, and the dissolution time is not particularly limited, as long as the liquid crystal monomer is just completely dissolved without self-crosslinking.

[0032] In this invention, there is no special limitation on the cooling time of the toluene solution of the liquid crystal monomer to room temperature, as long as it can be cooled to room temperature.

[0033] In this invention, the preferred method for removing bubbles is ultrasonic or vacuum removal. This invention does not have any particular limitations on the ultrasonic time, the time for placing the solution in a vacuum drying oven to remove bubbles, or the degree of vacuum. Any method known to those skilled in the art can be used to remove small bubbles from the solution.

[0034] In this invention, the overnight curing time of the solution is preferably 18 to 24 hours, specifically 18, 19, 20, 21, 22, 23, or 24 hours.

[0035] In this invention, the ratio of uniaxial pre-stretching to the length before two-stage polymerization is 2:1. There are no special limitations on the uniaxial pre-stretching method; any method known to those skilled in the art can be used.

[0036] The adhesive used in this invention is preferably silicone adhesive. There are no special limitations on the amount of adhesive used or the specific bonding method. Any method known to those skilled in the art can be used.

[0037] Example 1: The specific steps for fabricating a bistable composite beam with an inner width of 5.5cm are as follows: 1. Preparation of photothermal responsive liquid crystal elastomer film: A liquid crystal elastomer film with a crosslinking agent to chain extender ratio of 6:1 was prepared in a polytetrafluoroethylene tank. 1080 mg of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) was weighed and dissolved in a toluene sample vial at a temperature above room temperature. Then, pentaerythritol tetra-3-mercaptopropionate (PETMP), 3,6-dioxa-1,8-octanedithiol (DODT), and photoinitiator 2,2-dimethoxy-2-phenylacetophenone (I) were added at room temperature. -651) and di-n-propylamine (DPA) were dissolved in another toluene sample vial; after cooling to room temperature, the two solutions were mixed and poured into a polytetrafluoroethylene (PTFE) tank, and then the PTFE tank was placed in a vacuum drying oven to remove air bubbles, and the solution was cured overnight at 50°C to form a slightly cross-linked multi-domain LCE film. After uniaxial pre-stretching, it was exposed to ultraviolet light (UV) for two-stage polymerization. The polymerized liquid crystal elastomer film was cut into strips 6 cm long and 6 mm wide, and coated with photothermal conversion agent graphite powder to obtain upper and lower liquid crystal elastomer film layers with photothermal effect. 2. Fabrication of a bistable light-driven flexible composite beam device: The upper and lower thin film layers are bonded to the insulation cotton interlayer 2 to obtain a crossbeam without curvature; a support frame with an inner width of 5.5cm is fabricated using 3D printing, and the two sides of the crossbeam structure are fixed to the support frame 4 with adhesive. Due to the horizontal constraint, a curved beam with natural curvature is formed, which has two stable states: upturn and downturn, to obtain a bistable light-driven flexible composite beam device with an arch height of 1.1cm. Figure 2 This is a graph showing the highest temperature during the steady-state switching process of the infrared thermal imager measuring device in Example 1. The highest temperature is 73.5℃. Figure 3 The force-displacement curve of the transition from the upward to the downward state was measured by a universal tensile testing machine. The maximum force was 0.1N. It can be seen that under 808 laser irradiation, the bistable light-driven flexible composite beam device can achieve a steady-state transition at 73.5℃.

[0038] Example 2 is similar to Example 1, except that the inner width of the support frame 4 is 5.0cm, and the arch height of the bistable flexible composite beam device is 1.5cm. Figure 4 The highest temperature during the steady-state switching process of the infrared thermal imager measuring device in Example 2 is 95.3℃. It can be seen that under 808 laser irradiation, the bistable light-driven flexible composite beam device can achieve steady-state transition at 95.3℃. Figure 5 The temperature curve is shown for the steady-state transition process in Example 2.

[0039] Example 3 is similar to Example 1, except that the inner width of the support frame 4 is 4.5cm, and the arch height of the bistable flexible composite beam device is 1.7cm. Figure 6The figure shows the highest temperature during the steady-state switching process of the infrared thermal imager measuring device in Example 3. The highest temperature is 110.0℃. It can be seen that under 808 laser irradiation, the bistable light-driven flexible composite beam device can achieve steady-state transition at 110.0℃.

[0040] Example 4 is similar to Example 1, except that the inner width of the support frame 4 is 4.0cm, and the arch height of the bistable flexible composite beam device is 1.9cm. Figure 7 The figure shows the highest temperature during the steady-state switching process of the infrared thermal imager measuring device in Example 4. The highest temperature is 126.5℃. It can be seen that under 808 laser irradiation, the bistable light-driven flexible composite beam device can achieve steady-state transition at 126.5℃.

[0041] Example 5 is similar to Example 1, except that the inner width of the support frame 4 is 3.0cm, and the arch height of the bistable flexible composite beam device is 2.2cm. Figure 8 The figure shows the highest temperature during the steady-state switching process of the infrared thermal imager measuring device in Example 5. The highest temperature is 129.8℃. It can be seen that the bistable light-driven flexible composite beam device can achieve steady state at 129.8℃ under 808 laser irradiation.

Claims

1. A flexible bistable optically driven composite beam device, characterized in that, From top to bottom, it includes an upper film layer, an insulation cotton interlayer, a lower film layer, and a support frame installed on both sides.

2. The flexible bistable optically driven composite beam device according to claim 1, characterized in that, Both the upper and lower thin film layers are made of liquid crystal elastomer, and their thickness is 25~40μm.

3. The flexible bistable optically driven composite beam device according to claim 1, characterized in that, A photothermal conversion agent is coated on the upper surface of the upper film layer and the lower surface of the lower film layer.

4. The flexible bistable optically driven composite beam device according to claim 3, characterized in that, The photothermal conversion agent applied is graphite.

5. The flexible bistable optically driven composite beam device according to claim 1, characterized in that, The insulation cotton interlayer is made of silica aerogel insulation cotton with a thickness of 1~2mm.

6. The flexible bistable optically driven composite beam device according to claim 1, characterized in that, The beam structure, consisting of the upper film layer, the insulation cotton interlayer, and the lower film layer, has a length, width, and thickness ratio of 30:3:

1.

7. The flexible bistable optically driven composite beam device according to claim 1, characterized in that, The inner width of the support frame is 2.8~5.5cm.

8. The method for fabricating a flexible bistable optically driven composite beam device as described in any one of claims 1-7, characterized in that, Includes the following steps: Step (1) Prepare a liquid crystal elastomer film in a polytetrafluoroethylene bath; Step (2) Coat the surface of the prepared liquid crystal elastomer film with a photothermal conversion agent to obtain a beam structure without curvature, which is formed by bonding the upper film layer and the lower film layer together with the thermal insulation interlayer. Step (3) Fix the two sides of the beam structure to the support frame with adhesive to finally obtain a flexible bistable light-driven composite beam device.

9. The method for fabricating the flexible bistable optically driven composite beam device according to claim 8, characterized in that, The specific process for preparing the liquid crystal elastomer film in step (1) is as follows: 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene was dissolved in a toluene sample vial at a temperature above room temperature; Then, at room temperature, pentaerythritol tetra-3-mercaptopropionate, 3,6-dioxa-1,8-octanedithiol, 2,2-dimethoxy-2-phenylacetophenone and di-n-propylamine were dissolved in another toluene sample vial. After cooling to room temperature, the two solutions are mixed and poured into a polytetrafluoroethylene (PTFE) bath. The PTFE bath is then placed in a vacuum drying oven to remove air bubbles, and the solution is cured overnight at 50°C to form a slightly cross-linked multi-domain LCE film. After uniaxial pre-stretching, the film is exposed to ultraviolet light for two-stage polymerization. The polymerized liquid crystal elastomer film is then cut into strips.

10. The method for fabricating the flexible bistable optically driven composite beam device according to claim 9, characterized in that, The room temperature is 25~26℃; The temperature above room temperature is 50~75℃.

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