Low irradiation light-heat soft driver and preparation method and application thereof

Abstract

The application discloses a low-irradiation photothermal soft driver and a preparation method and application thereof. The soft driver comprises a heat preservation layer film, a photothermal conversion layer film and a thermal response driving layer film arranged in a top-down stacking mode. The photothermal conversion layer film can absorb solar energy and convert the solar energy into heat energy through a photothermal effect. The heat preservation layer film and the thermal response driving layer film are deformed to different degrees under the action of heat, so that the low-irradiation photothermal soft driver is bent and deformed. The structure can realize good heat management of the photothermal soft driver. Even under low irradiation, the heat transfer mode of the management system can realize rapid heating and effective driving under a low-irradiation environment, and the application has a wide application in the field of photothermal soft robots.

Description

Technical Field

[0001] This invention relates to the field of software actuator technology, specifically to a low-irradiation photothermal software actuator, its preparation method, and its application. Background Technology

[0002] Soft actuators, with their superior mechanical compliance, environmental adaptability, interactive safety, biomimetic motion capabilities, and diverse combinations of soft materials, possess advantages unmatched by traditional rigid actuators, and are continuously revolutionizing the concept and application of traditional actuators. The introduction of stimulus-responsive polymers and other active materials will provide an opportunity for soft actuators to achieve autonomous motion and even true intelligence.

[0003] Cableless actuation methods such as light, electricity, and magnetism represent a trend in the development of soft actuators. However, both electric and magnetic field actuation often require additional power supply equipment, increasing system complexity and necessitating constant adjustments to stimulate the actuator. Light stimulation is considered one of the most convenient and promising actuation methods. Currently, regarding the design and fabrication of photothermal soft actuators based on photothermal materials, He Ximin et al. from UCLA introduced candle ash into a liquid crystal elastomer through blending, preparing a photothermal soft actuator with a liquid crystal elastomer-polydimethylsiloxane bilayer structure. This actuator exhibited controllable near-infrared response deformation, but the required light intensity exceeded that of a sun (100 mW / cm²). 2 () Science Robotics , 2023, 8(77): eadf4753.), making it difficult to achieve motion under low light intensity such as natural light. Zhang Li et al. of the Chinese University of Hong Kong introduced graphene into hydrogels through blending to prepare hydrogel-based photothermal actuators, which can deform and generate bouncing motion under near-infrared light induction. However, the driving light intensity of this hydrogel photothermal soft actuator is about 20 solar masses (2000 mW / cm). 2 The required light intensity far exceeds the light intensity obtainable in the natural environment, limiting its further application in low-radiation light stimulation environments such as natural environments. Nature Materials , 2024, 23(10):1428-1435.); Chinese patent CN116289170B discloses a liquid crystal elastomer / MXene composite fiber soft actuator with multiple stimulus responses, its preparation method and application; Chinese patent CN108484951B discloses a photothermal responsive material and its method and application for preparing a photothermal driven robot; Chinese patent CN119461339A discloses a carbon nanosheet-based photothermal responsive thin film actuator, its preparation method and application; however, these photothermal soft actuators share a common drawback: the driving light sources used are all high-power lamps or laser light sources, which cannot achieve rapid driving and rapid recovery in low-irradiance environments. In summary, the ambient solar irradiance is generally low (<100 mW / cm).2 Furthermore, most of the energy is lost through heat conduction, heat convection, and heat radiation. This means that traditional photothermal soft actuators generally rely on high-energy lasers and cannot meet the driving requirements in low-irradiation environments, which severely restricts the practical application of photothermal soft actuators. Summary of the Invention

[0004] To address the problems existing in the background art, the purpose of this invention is to provide a low-irradiation photothermal soft actuator, which addresses the issues of most photothermal soft actuators relying on high-energy lasers and having poor mechanical properties. This invention employs a thermal management strategy to efficiently utilize limited light energy for driving the photothermal soft actuator. It uses a laminated design composed of two materials with different deformation behaviors combined with a photothermal material. This design provides high strain mismatch, resulting in higher bending moments and greater material and structural customizability. Simultaneously, it effectively manages the heat energy converted by the photothermal conversion layer, significantly reducing the heat energy lost by the soft actuator to the environment.

[0005] The technical solution adopted in this invention is as follows:

[0006] 1. A low-irradiation photothermal soft actuator

[0007] The low-irradiance photothermal soft actuator comprises a thermal insulation layer film, a photothermal conversion layer film, and a thermal response driving layer film stacked from top to bottom. The low-irradiance photothermal soft actuator is used to bend and deform after absorbing solar energy. The photothermal conversion layer film can absorb solar energy and convert it into heat energy through the photothermal effect. The thermal insulation layer film and the thermal response driving layer film deform to different degrees under the action of heat, causing the low-irradiance photothermal soft actuator to bend and deform. The actuator can operate at 100 mW / cm². 2 Achieving effective bending drive under low irradiance conditions.

[0008] The thermal insulation layer film is a porous broadband transparent polymer film, which is a combination of one or more of the following materials that have undergone porous treatment: polyethylene (PE), styrene-ethylene-butene-styrene block copolymer (SEBS), polypropylene (PP), and polymethyl methacrylate (PMMA). The thermal insulation layer material is preferably styrene-ethylene / butene-styrene block copolymer (SEBS). The porous broadband transparent polymer film has a porous structure to reduce thermal conductivity. The porous broadband transparent polymer film has high transmittance in both the solar irradiation band (0.3-2.5 μm) and the mid-infrared band (0.3-20 μm), while also exhibiting low thermal conductivity due to its porous structure.

[0009] The porous processing method specifically includes one or more of the following processes: wet spinning, freeze drying, sacrificial template, sol-gel, and introducing hollow microspheres to construct a multi-pore structure, in order to obtain a porous, broadband transparent polymer film.

[0010] The photothermal conversion layer film is a selective solar energy absorption composite material film. The selective solar energy absorption composite material film is mainly composed of a selective solar energy absorption film and a performance modulation material. The selective solar energy absorption structure is an intrinsic solar energy absorption material. The selective solar energy absorption film is one or more of two-dimensional transition metal carbides (MXenes), transition metal nitrides, and transition metal borides. The performance modulation material is one or more of nanocellulose (CNF), aluminum hydroxide gel, and nanoalumina. The performance modulation material is preferably nanocellulose (CNF).

[0011] The mass ratio of the selective solar energy absorption film to the performance modulation material is 9:1 to 5:5.

[0012] The photothermal conversion layer film exhibits high absorption in the solar irradiation band (0.3-2.5 μm) and low emission characteristics in the mid-infrared band (2.5-20 μm).

[0013] The MXenes material includes Ti3C2T x Nb2CT x Ti3CT x and V2C2T x etc., of which T x The terminal group is selected from one or more of -OH, -F, and -O, and the value of x ranges from 0 to 2. The transition metal nitride is one or more of ZrN and TiN; the transition metal boride is one or more of TiB2 and ZrB2.

[0014] The thermally responsive driving layer film is a thermally responsive smart material, which is one or more of liquid crystal elastomer (LCE), shape memory polymer (SMP), shape memory alloy, shape memory ceramic and hydrogel. The thermally responsive driving layer film has temperature / thermal stimulation response characteristics. The phase state of the thermally responsive driving layer film will exhibit order-disorder transition characteristics under thermal stimulation, thereby causing it to macroscopically produce reversible shape changes.

[0015] II. A method for preparing a low-irradiation photothermal soft actuator, the method comprising the following steps:

[0016] S1. Prepare porous broadband transparent polymer films and treat them with oxygen plasma;

[0017] S2. Prepare a thermally responsive driving layer thin film and perform oxygen plasma treatment;

[0018] S3. Selective solar energy absorption composite film is prepared on the surface of thermally responsive driving layer film through one or two-step process;

[0019] S4. A porous, broadband transparent polymer film is naturally attached to a selective solar energy absorption composite film to obtain a low-irradiance photothermal soft actuator.

[0020] Step S1 specifically involves the following: the porous broadband transparent polymer film is prepared by one or more of the following methods in combination: spin coating, blade coating, spray coating, physical vapor deposition, and chemical vapor deposition; the porous structure on the porous broadband transparent polymer film is prepared by one or more of the following methods in combination: wet spinning, freeze drying, sacrificial template, sol-gel, and introducing hollow microspheres to construct a multi-pore structure; after obtaining the porous broadband transparent polymer film, it is treated with oxygen plasma in a vacuum environment. Specifically, the thickness of the insulation layer ranges from 30 to 100 μm.

[0021] Step S2 specifically involves preparing the thermally responsive driving layer film using one or more of the following methods: molding, spin coating, spraying, 3D printing, and direct ink writing. After obtaining the thermally responsive driving layer film, it is treated with oxygen plasma in a vacuum environment. Specifically, the thickness of the thermally responsive driving layer is 50-1000 μm; the thickness ratio of the insulation layer to the thermally responsive driving layer is 1:4.5-5.5.

[0022] In step S3, a performance modulation material is doped into the selective solar energy absorption film to obtain a selective solar energy absorption composite film. This selective solar energy absorption composite film is then fabricated on the surface of the thermally responsive driving layer film using a one-step or two-step process. Specifically, the thickness of the photothermal conversion layer is between 100 nm and 20 μm.

[0023] In step S3, the one-step process is to directly prepare a selective solar energy absorption composite film on the surface of the thermal response driving layer film. The one-step process is one or a combination of spin coating, spray coating, brush coating, physical vapor deposition, and chemical vapor deposition methods.

[0024] The two-step process involves first preparing the selective solar energy absorption composite material onto the target substrate using a solution deposition process such as vacuum-assisted filtration, and then transferring the selective solar energy absorption composite material film onto the surface of the thermal response driving layer film by utilizing the difference in adhesion between the composite material and the target substrate and the thermal response driving layer film through an external force-assisted method.

[0025] The target substrate is one or more of the following filter membranes: porous cellulose membrane, porous nylon membrane, porous polyvinylidene fluoride membrane, etc.

[0026] III. Applications of Low-Irradiation Photothermal Software Drivers

[0027] Applications in soft crawling robots, rolling robots, flexible sensing, and artificial muscles.

[0028] IV. Driving Method of Low-Irradiation Photothermal Software Driver

[0029] The low-irradiance photothermal soft actuator achieves photothermal actuation through thermal management. When sunlight shines on the low-irradiance photothermal soft actuator, the insulating film allows most of the sunlight to pass through, enabling the sunlight to reach the photothermal conversion layer film. When the photothermal conversion layer film is exposed to light, it converts light energy into heat energy, which serves as the energy source for the actuator. The insulating film prevents the heat energy converted by the photothermal conversion layer film from being transferred upwards. At the same time, the low emissivity of the photothermal conversion layer film itself significantly reduces the heat radiation from the low-irradiance photothermal soft actuator to the external environment, allowing most of the heat energy to be transferred to the lower thermal response driving layer film. After receiving thermal energy stimulation, the thermal response driving layer film undergoes macroscopic deformation caused by phase transitions, converting the heat energy into the mechanical energy required for actuation, thus causing the low-irradiance photothermal soft actuator to deform as a whole.

[0030] Specifically, this invention provides a thermal management structure for a low-irradiance photothermal soft actuator as described above, utilizing a thermal management strategy to achieve photothermal actuation in low-irradiance environments. The thermal management strategy for the low-irradiance photothermal soft actuator specifically includes:

[0031] The aforementioned photothermal conversion layer film exhibits high absorptivity in the solar radiation band and low emissivity in the mid-to-far-infrared band of thermal radiation, thus possessing photothermal conversion efficiency superior to conventional blackbody materials. The upper insulation layer film has a porous structure, low scattering characteristics in the solar radiation band, and high transmittance characteristics in the mid-to-far-infrared band. Its porous structure endows it with ultra-low thermal conductivity; simultaneously, its low scattering characteristics in the solar radiation band ensure high transmittance of solar radiation, allowing most solar radiation to effectively act on the photothermal conversion layer film beneath the insulation layer film. The low thermal conductivity of the insulation layer film significantly hinders heat conduction from the photothermal conversion layer film to the upper layer (insulation layer film), causing heat to be mainly transferred to the lower layer (thermal response driving layer film). Furthermore, thanks to the low emissivity characteristics of the photothermal conversion layer film in the mid-to-far-infrared band, and the high transmittance and low emissivity characteristics of the insulation layer film in the mid-to-far-infrared band, the overall external thermal radiation loss of the actuator is significantly suppressed. The above thermal management strategies significantly improve the conversion efficiency of light energy to heat energy to mechanical energy, which is beneficial for the effective operation of photothermal soft actuators in low-irradiation environments.

[0032] The proposed low-irradiance photothermal soft actuator structure achieves photothermal actuation in low-irradiance environments through a thermal management strategy. The insulating film possesses low thermal conductivity and high transmittance across a wide wavelength range. The photothermal conversion layer exhibits selective absorption characteristics, displaying high absorption in the solar spectrum and low emission in the mid-to-far-infrared band. The thermally responsive actuation layer can generate significant actuation strain in response to temperature / heat. The three-layer film stack design deforms to varying degrees under photothermal influence, causing the composite film to bend and deform. The structure proposed in this invention achieves excellent thermal management for the photothermal soft actuator. Even under low irradiance, by managing the heat transfer mechanism of the system, it can achieve rapid heating and effective actuation in low-irradiance environments, making it widely applicable in the field of photothermal soft robotics.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) This invention employs a structural design of a thermal insulation layer, a photothermal conversion layer, and a thermal response driving layer to fabricate a low-irradiation photothermal soft actuator. Under external light stimulation, the MXene-CNF composite film can convert absorbed light energy into heat energy and transfer it to the LCE surface. Due to the ultra-low thermal conductivity of the thermal insulation layer and its high transmittance and low emissivity in the infrared, the heat loss through heat transfer is significantly reduced, overcoming the problem of traditional photothermal soft actuators being difficult to drive under low light intensity due to low energy utilization. This makes the actuator more suitable for applications in low-irradiation environments, providing a possibility for the research of photothermal soft actuators in the fields of energy harvesting and intelligent response to move from theory to practical production applications.

[0035] (2) The SEBS film prepared by this invention has high broad-spectral transmittance (average transmittance >92% for 0.3-2.5 μm, average transmittance >75% for 2.5-17 μm) and ultra-low storage modulus (~1 MPa) and low thermal conductivity (<0.12 W / mK). Compared with conventional LCE, the LCE prepared by this invention has a lower Young's modulus (~7 MPa). Compared with MXene nanosheet stacked films prepared by other methods, the MXene-CNF composite film prepared by the solution deposition method (vacuum-assisted filtration method) of this invention has an absorptivity of over 80% in the solar band and an emissivity of less than 25% in the mid- and far-infrared band. This material system helps the actuator achieve rapid and uniform deformation when absorbing light energy and converts light energy into mechanical energy more efficiently.

[0036] (3) Compared with the previously reported multilayer photothermal soft actuator, the process of using external force-assisted transfer and oxygen plasma treatment produces a low-irradiation photothermal soft actuator with strong bonding force between layers (about 120 Nm). The preparation process is simple and low-cost. The soft actuator obtained also has a large bending range, fast response and excellent mechanical properties.

[0037] (4) The low-irradiation photothermal soft actuator has good programmability and long-term light-driven characteristics. The thermal management structure design provided by this invention can also be applied to soft actuators that use heat as a stimulus source, such as electrothermal and magnetothermal actuators. The photothermal soft actuator prepared by this invention integrates sensing, driving and built-in feedback loops, and can design and manufacture a variety of photothermal devices with excellent remote and precise control performance. The designed natural light-driven bionic soft robot can crawl stably at a speed of 0.1 mm / s. It is small in size and light in weight and can adapt to a variety of environments, effectively realizing functions such as environmental exploration. Attached Figure Description

[0038] Figure 1 This is a schematic diagram illustrating the thermal management principle of a low-irradiance photothermal soft actuator according to the present invention.

[0039] Figure 2 This is a schematic diagram of the operation of a low-irradiation photothermal soft driver according to the present invention;

[0040] Figure 3 The image shows a cross-sectional SEM image and physical image of a low-irradiation photothermal soft actuator prepared according to the present invention, wherein (a) represents a physical image of the photothermal soft actuator prepared in Example 1, and (b) represents a cross-sectional scanning electron microscope image of the photothermal soft actuator prepared in Example 1.

[0041] The image shown is a physical diagram of the photothermal soft actuator prepared in Example 1. Figure 3(b) shows a cross-sectional scanning electron microscope image of the photothermal soft actuator prepared in Example 1;

[0042] Figure 4 The images show the results of the porous SEBS film prepared in Example 1 of this invention and the PDMS results in Comparative Examples 1-3.

[0043] Figure 5 The transmittance spectrum of the SEBS film prepared in Example 1 of this invention is a wide-band (0.3-17 μm) spectrum.

[0044] Figure 6 The tensile stress-strain curve of the SEBS thin film material prepared in Example 1 of this invention is shown.

[0045] Figure 7 Absorption / emissivity spectra of the soft actuators prepared in Example 1 and Comparative Examples 1-4 of this invention in a wide wavelength range (0.3-17 μm);

[0046] Figure 8 Comparison of photothermal conversion efficiency of the soft actuator films prepared in Example 1 and Comparative Examples 1-4 of this invention in the solar band (0.3-2.5 μm) and infrared band (2.5-17 μm);

[0047] Figure 9 For Example 1 and Comparative Examples 1-3 of the present invention, at 100mW / cm 2 Below is a comparison chart of temperature rise and fall within the same time period;

[0048] Figure 10 For Example 1 and Comparative Example 1 of the present invention, at 100 mW / cm 2 Curve showing the relationship between bending curvature and response time under light intensity;

[0049] Figure 11 This is a schematic diagram of the crawling of the biomimetic soft crawling robot prepared in Embodiment 2 of the present invention;

[0050] Figure 12 This is a schematic diagram of the rolling motion of the annular rolling driver prepared in Embodiment 3 of the present invention;

[0051] Figure 13 This is a key meteorological information data chart from an outdoor experiment in Embodiment 4 of the present invention;

[0052] Figure 14 This is a schematic diagram of the outdoor crawling of the biomimetic soft crawling robot prepared in Embodiment 4 of the present invention;

[0053] Figure 15 This is an outdoor crawling displacement-time diagram of the biomimetic soft crawling robot prepared in Example 4 of the present invention.

[0054] In the figure: 10, low-irradiation photothermal soft actuator; 11, thermal insulation film; 12, photothermal conversion layer film; 13, thermal response driving layer film. Detailed Implementation

[0055] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] In order to make the technical solution of the present invention clearer during the specific implementation process, the present invention will be clearly and completely described below with reference to specific examples. The described examples are only a part of the examples of the present invention, and cannot represent all examples.

[0057] Unless otherwise specified, all materials and reagents used in the examples are commercially available or can be obtained by those skilled in the art using well-known methods. Specific experimental methods and operating conditions are generally performed according to standard process conditions, those described in the manual, or those recommended by the manufacturer.

[0058] The low-irradiance photothermal soft actuator 10 includes a heat-insulating layer film 11, a photothermal conversion layer film 12, and a thermally responsive driving layer film 13 stacked from top to bottom. The low-irradiance photothermal soft actuator 10 is used to bend and deform after absorbing solar energy. The photothermal conversion layer film 12 can absorb solar energy and convert it into heat energy through the photothermal effect. The heat-insulating layer film 11 and the thermally responsive driving layer film 13 deform to different degrees under the action of heat, causing the low-irradiance photothermal soft actuator 10 to bend and deform. The actuator can operate at 100mW / cm². 2 Achieving effective bending drive under low irradiance conditions.

[0059] The thermal insulation film 11 is a porous broadband transparent polymer film. This film is made from one or more of the following materials that have undergone porous treatment: polyethylene (PE), styrene-ethylene-butene-styrene block copolymer (SEBS), polypropylene (PP), and polymethyl methacrylate (PMMA). The preferred thermal insulation material is styrene-ethylene / butene-styrene block copolymer (SEBS). The porous broadband transparent polymer film has a porous structure to reduce thermal conductivity. It exhibits high transmittance in both the solar irradiation band (0.3-2.5 μm) and the mid-infrared band (0.3-20 μm), while also possessing low thermal conductivity due to its porous structure.

[0060] The porous processing methods include one or more of the following combinations: wet spinning, freeze drying, sacrificial template, sol-gel, and the introduction of hollow microspheres to construct a multi-pore structure, in order to obtain porous broadband transparent polymer films.

[0061] The photothermal conversion layer film 12 is a selective solar energy absorption composite film. The selective solar energy absorption composite film is mainly composed of a selective solar energy absorption film and a performance modulation material. The selective solar energy absorption structure is an intrinsic solar energy absorption material. The selective solar energy absorption film is one or more of two-dimensional transition metal carbides (MXenes), transition metal nitrides, and transition metal borides. The performance modulation material is one or more of nanocellulose (CNF), aluminum hydroxide gel, and nanoalumina. The preferred performance modulation material is nanocellulose (CNF).

[0062] The mass ratio of selective solar absorption thin film to performance modulation material is 9:1 to 5:5.

[0063] The photothermal conversion layer film 12 exhibits high absorption in the solar irradiation band (0.3-2.5 μm) and low emission in the mid-infrared band (2.5-20 μm).

[0064] MXenes materials include Ti3C2T x Nb2CT x Ti3CT x and V2C2T x etc., of which T x The terminal group is selected from one or more of -OH, -F, and -O, and the value of x ranges from 0 to 2. Transition metal nitrides are combinations of one or more of ZrN and TiN; transition metal borides are combinations of one or more of TiB2 and ZrB2.

[0065] The thermally responsive driving layer film 13 is a thermally responsive smart material. The thermally responsive smart material is one or more of the following: liquid crystal elastomer (LCE), shape memory polymer (SMP), shape memory alloy, shape memory ceramic and hydrogel. The thermally responsive driving layer film 13 has temperature / thermal stimulation response characteristics. The phase state of the thermally responsive driving layer film 13 will exhibit order-disorder transition characteristics under thermal stimulation, thereby causing it to macroscopically produce reversible shape changes. Example 1:

[0066] A method for fabricating a low-irradiation photothermal soft actuator specifically includes the following steps:

[0067] (1) Dissolve 15 g of SEBS solid particles in 25 g of toluene, heat and stir for 120 min at 80℃ and 500 rpm magnetic stirring, mix evenly, place in a vacuum drying oven for vacuum degassing for 5 min, then use an adjustable coating tool to evenly coat the SEBS-toluene mixture onto PET sheet, and then place in a high temperature oven at 80℃ overnight to promote the volatilization of the dispersant and solidify the SEBS film into a porous SEBS film; the thickness of the film is 50 μm.

[0068] (2) 640 μL of MXene aqueous solution with a concentration of 5 mg / ml was diluted to 0.1 mg / ml with deionized water, and then 54.86 mg of CNF with a solid content of 2.5% was added and ultrasonically mixed to form a uniform dispersion. 8 ml of MXene-CNF solution was extracted, and MXene-CNF nanosheets were prepared by vacuum-assisted filtration. Then, the MXene-CNF nanosheets were stacked on a porous cellulose filter membrane.

[0069] (3) LCE samples were synthesized by modifying the previously reported Michael addition reaction method of mercapto-acrylate. The liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM 257) was first fully dissolved in 3g of toluene under magnetic stirring at 85°C in a typical synthesis process, and then cooled to room temperature. Then, 0.315 g of chain extender (2,2'-(ethylenedioxy)diethylthiol), 0.135 g of crosslinking agent (pentaerythritol tetra(3-mercaptopropionate)), and 0.009 g of photoinitiator (2,2-dimethoxy-2-phenylacetophenone) were added to the solution. The mixture was then stirred at 85 °C and 1500 rpm for 8 min under magnetic stirring. After cooling to room temperature, 0.216 g of a catalyst solution, dipropylamine (DPA) solution (2 wt%, in toluene), was added to the solution. After thorough mixing and degassing, the solution was poured into a prepared PTFE mold (10 cm long, 10 cm wide, and 1 cm deep) to obtain the first-step crosslinking system solution, in which the molar ratio of acrylate groups in the liquid crystal monomer to mercapto groups in EDDET and PETMP was 6:1.

[0070] The mold was then placed in a sealed container overnight to allow for complete reaction. After vacuum drying at 80°C for 24 h, a cured LCE sample was obtained. A 1.5 cm × 6 cm sample was cut, and the LCE was uniaxially stretched to twice its initial length by adjusting the displacement of the slide table equipped with a fixture. During the stretching process, the LCE gradually became transparent, and the liquid crystal cells exhibited a high degree of orientation uniformity along the stretching direction. Subsequently, at a strength of 20 mJ / cm², the LCE was further refined. 2By irradiating the LCE with 365 nm ultraviolet light for 10 min to fix the alignment direction of the liquid crystal building blocks and molecular chains, an oriented LCE can be obtained.

[0071] (4) The LCE and SEBS prepared above are subjected to oxygen plasma treatment under vacuum for 60 s; after removal, the MXene-CNF composite film prepared in step (2) is first transferred to the surface of the LCE prepared in step (3) through the difference in bonding force between it and the filter membrane and LCE, and the SEBS film after plasma treatment in step (3) is naturally bonded to the MXene-LCE, thus obtaining a low-irradiation photothermal soft actuator such as Figure 1 As shown, the working principle of the prepared photothermal soft actuator is as follows: Figure 2 As shown.

[0072] Comparative Example 1:

[0073] A method for fabricating a photothermal soft actuator, which has no thermal management strategy, includes the following steps:

[0074] (1) Mix 10 g of polydimethylsiloxane prepolymer with 1 g of crosslinking agent, then add 0.55 g of carbon black, mix for 3 min under a planetary stirrer, degas for 2 min, and apply the mixture onto a PET sheet using an adjustable coating tool. Place the PET sheet in a vacuum drying oven (80℃) and cure for 2 h. The resulting PDMS-CB composite film has a thickness of 50 μm.

[0075] (2) LCE samples were synthesized by modifying the previously reported Michael addition reaction method of mercapto-acrylate. The liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM 257) was first fully dissolved in 3g of toluene under magnetic stirring at 85°C in a typical synthesis process, and then cooled to room temperature. Then, 0.315 g of chain extender (2,2'-(ethylenedioxy)diethylthiol), 0.135 g of crosslinking agent (pentaerythritol tetra(3-mercaptopropionate)), and 0.009 g of photoinitiator (2,2-dimethoxy-2-phenylacetophenone) were added to the solution. The mixture was then stirred at 85 °C and 1500 rpm for 8 min under magnetic stirring. After cooling to room temperature, 0.216 g of a catalyst solution, dipropylamine (DPA) solution (2 wt%, in toluene), was added to the solution. After thorough mixing and degassing, the solution was poured into a prepared PTFE mold (10 cm long, 10 cm wide, and 1 cm deep) to obtain the first-step crosslinking system solution, in which the molar ratio of acrylate groups in the liquid crystal monomer to mercapto groups in EDDET and PETMP was 6:1.

[0076] The mold was then placed in a sealed container overnight to allow for complete reaction. After vacuum drying at 80°C for 24 h, a cured LCE sample was obtained. A 1.5 cm × 6 cm sample was cut, and the LCE was uniaxially stretched to twice its initial length by adjusting the displacement of the slide table equipped with a fixture. During the stretching process, the LCE gradually became transparent, and the liquid crystal cells exhibited a high degree of orientation uniformity along the stretching direction. Subsequently, at a strength of 20 mJ / cm², the LCE was further refined. 2 By irradiating the LCE with 365 nm ultraviolet light for 10 min to fix the alignment direction of the liquid crystal building blocks and molecular chains, an oriented LCE can be obtained.

[0077] (3) The only difference from Example 1 is that the porous SEBS and MXene-CNF composite film is adjusted to a PDMS-CB film naturally bonded to LCE. Thus, a photothermal soft actuator without thermal management strategy is obtained.

[0078] Comparative Example 2:

[0079] A method for fabricating a photothermal soft actuator, which has no thermal management strategy, includes the following steps:

[0080] (1) Mix 10 g of polydimethylsiloxane prepolymer with 1 g of crosslinking agent, then add 0.55 g of graphene, mix for 3 min under a planetary stirrer, degas for 2 min, and apply the mixture onto a PET sheet using an adjustable coating tool. Place the PET sheet in a vacuum drying oven (80℃) and cure for 2 h. The resulting PDMS-GO composite film has a thickness of 50 μm.

[0081] (2) LCE samples were synthesized by modifying the previously reported Michael addition reaction method of mercapto-acrylate. The liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM 257) was first fully dissolved in 3g of toluene under magnetic stirring at 85°C in a typical synthesis process, and then cooled to room temperature. Then, 0.315 g of chain extender (2,2'-(ethylenedioxy)diethylthiol), 0.135 g of crosslinking agent (pentaerythritol tetra(3-mercaptopropionate)), and 0.009 g of photoinitiator (2,2-dimethoxy-2-phenylacetophenone) were added to the solution. The mixture was then stirred at 85 °C and 1500 rpm for 8 min under magnetic stirring. After cooling to room temperature, 0.216 g of a catalyst solution, dipropylamine (DPA) solution (2 wt%, in toluene), was added to the solution. After thorough mixing and degassing, the solution was poured into a prepared PTFE mold (10 cm long, 10 cm wide, and 1 cm deep) to obtain the first-step crosslinking system solution, in which the molar ratio of acrylate groups in the liquid crystal monomer to mercapto groups in EDDET and PETMP was 6:1.

[0082] The mold was then placed in a sealed container overnight to allow for complete reaction. After vacuum drying at 80°C for 24 h, a cured LCE sample was obtained. A 1.5 cm × 6 cm sample was cut, and the LCE was uniaxially stretched to twice its initial length by adjusting the displacement of the slide table equipped with a fixture. During the stretching process, the LCE gradually became transparent, and the liquid crystal cells exhibited a high degree of orientation uniformity along the stretching direction. Subsequently, at a strength of 20 mJ / cm², the LCE was further refined. 2 By irradiating the LCE with 365 nm ultraviolet light for 10 min to fix the alignment direction of the liquid crystal building blocks and molecular chains, an oriented LCE can be obtained.

[0083] (3) The only difference from Example 1 is that the porous SEBS and MXene-CNF composite film is adjusted to a PDMS-Graphene film naturally bonded to LCE. Thus, a photothermal soft actuator without thermal management strategy is obtained.

[0084] Comparative Example 3:

[0085] A method for fabricating a photothermal soft actuator, which has no thermal management strategy, includes the following steps:

[0086] (1) Mix 10 g of polydimethylsiloxane prepolymer with 1 g of crosslinking agent, then add 0.55 g of graphene oxide. Mix for 3 min under a planetary stirrer, degas for 2 min, and apply the mixture onto a PET sheet using an adjustable coating tool. Place the PET sheet in a vacuum drying oven (80℃) and cure for 2 h. The resulting PDMS-GO composite film has a thickness of 50 μm.

[0087] (2) LCE samples were synthesized by modifying the previously reported Michael addition reaction method of mercapto-acrylate. The liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM 257) was first fully dissolved in 3g of toluene under magnetic stirring at 85°C in a typical synthesis process, and then cooled to room temperature. Then, 0.315 g of chain extender (2,2'-(ethylenedioxy)diethylthiol), 0.135 g of crosslinking agent (pentaerythritol tetra(3-mercaptopropionate)), and 0.009 g of photoinitiator (2,2-dimethoxy-2-phenylacetophenone) were added to the solution. The mixture was then stirred at 85 °C and 1500 rpm for 8 min under magnetic stirring. After cooling to room temperature, 0.216 g of a catalyst solution, dipropylamine (DPA) solution (2 wt%, in toluene), was added to the solution. After thorough mixing and degassing, the solution was poured into a prepared PTFE mold (10 cm long, 10 cm wide, and 1 cm deep) to obtain the first-step crosslinking system solution, in which the molar ratio of acrylate groups in the liquid crystal monomer to mercapto groups in EDDET and PETMP was 6:1.

[0088] The mold was then placed in a sealed container overnight to allow for complete reaction. After vacuum drying at 80°C for 24 h, a cured LCE sample was obtained. A 1.5 cm × 6 cm sample was cut, and the LCE was uniaxially stretched to twice its initial length by adjusting the displacement of the slide table equipped with a fixture. During the stretching process, the LCE gradually became transparent, and the liquid crystal cells exhibited a high degree of orientation uniformity along the stretching direction. Subsequently, at a strength of 20 mJ / cm², the LCE was further refined. 2 By irradiating the LCE with 365 nm ultraviolet light for 10 min to fix the alignment direction of the liquid crystal building blocks and molecular chains, an oriented LCE can be obtained.

[0089] (3) The only difference from Example 1 is that the porous SEBS and MXene-CNF composite film is adjusted to a PDMS-GO film naturally bonded to LCE. Thus, a photothermal soft actuator without thermal management strategy is obtained.

[0090] Comparative Example 4:

[0091] A method for fabricating a photothermal soft actuator, which has no thermal management strategy, includes the following steps:

[0092] (1) Mix 10 g of polydimethylsiloxane prepolymer with 1 g of crosslinking agent, then add 0.55 g of carbon nanotubes, mix for 3 min under a planetary stirrer, degas for 2 min, and apply the mixture onto a PET sheet using an adjustable coating tool. Place the PET sheet in a vacuum drying oven (80℃) and cure for 2 h. The resulting PDMS-CB composite film has a thickness of 50 μm.

[0093] (2) LCE samples were synthesized by modifying the previously reported Michael addition reaction method of mercapto-acrylate. The liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM 257) was first fully dissolved in 3g of toluene under magnetic stirring at 85°C in a typical synthesis process, and then cooled to room temperature. Then, 0.315 g of chain extender (2,2'-(ethylenedioxy)diethylthiol), 0.135 g of crosslinking agent (pentaerythritol tetra(3-mercaptopropionate)), and 0.009 g of photoinitiator (2,2-dimethoxy-2-phenylacetophenone) were added to the solution. The mixture was then stirred at 85 °C and 1500 rpm for 8 min under magnetic stirring. After cooling to room temperature, 0.216 g of a catalyst solution, dipropylamine (DPA) solution (2 wt%, in toluene), was added to the solution. After thorough mixing and degassing, the solution was poured into a prepared PTFE mold (10 cm long, 10 cm wide, and 1 cm deep) to obtain the first-step crosslinking system solution, in which the molar ratio of acrylate groups in the liquid crystal monomer to mercapto groups in EDDET and PETMP was 6:1.

[0094] The mold was then placed in a sealed container overnight to allow for complete reaction. After vacuum drying at 80°C for 24 h, a cured LCE sample was obtained. A 1.5 cm × 6 cm sample was cut, and the LCE was uniaxially stretched to twice its initial length by adjusting the displacement of the slide table equipped with a fixture. During the stretching process, the LCE gradually became transparent, and the liquid crystal cells exhibited a high degree of orientation uniformity along the stretching direction. Subsequently, at a strength of 20 mJ / cm², the LCE was further refined. 2 By irradiating the LCE with 365 nm ultraviolet light for 10 min to fix the alignment direction of the liquid crystal building blocks and molecular chains, an oriented LCE can be obtained.

[0095] (3) The only difference from Example 1 is that the porous SEBS and MXene-CNF composite film is adjusted to a PDMS-CNT film naturally bonded to LCE. Thus, a photothermal soft actuator without thermal management strategy is obtained.

[0096] Results analysis:

[0097] (1) Analysis of the thermal conductivity, broadband transmittance and mechanical properties of the soft actuator and porous SEBS film

[0098] Figure 3 Image (a) shows a physical image of the photothermal soft actuator prepared in Example 1. Figure 3 Image (b) shows a cross-sectional scanning electron microscope image of the photothermal soft actuator prepared in Example 1. The results show that the soft actuator preparation method provided by the present invention can prepare a multilayer photothermal soft actuator with good interface connectivity. Figure 4 The results of the thermal conductivity test of PDMS in Example 1 are shown. The results show that the thermal conductivity of the porous SEBS film is more than 45% lower than that of PDMS. Figure 5 The transmittance spectrum of the porous SEBS film in a wide wavelength range (0.3-17 μm) is shown. The results show that the porous SEBS film has an average transmittance of over 92% in the solar wavelength range (0.3-2.5 μm) and an average transmittance of over 85% in the mid- and far-infrared wavelength range. This allows the photothermal conversion layer to absorb sunlight to the maximum extent while suppressing the transfer of heat from the system surface to the outside through radiation to the maximum extent. Figure 6 The stress-strain curve of Example 1 is shown. The results show that the porous SEBS exhibits a fracture strain exceeding 1000% and a low Young's modulus of 1.5 MPa, which meets the mechanical requirements for bending deformation of the photothermal soft robot during actuation. Under illumination, sunlight (0.3-2.5 μm) can efficiently pass through the insulation layer (transmittance > 90%) and be absorbed by the underlying photothermal conversion layer, converting it into heat energy. In this system, heat loss is effectively suppressed: firstly, thanks to the low emissivity (< 0.2) of the photothermal conversion layer and the high transmittance (> 85%) of the insulation layer in the mid-far-infrared band (2.5-17 μm), the system's thermal radiation loss is significantly reduced; secondly, the low thermal conductivity of the insulation layer itself hinders upward heat conduction. Through the above synergistic effect, the heat energy generated by photothermal conversion is concentrated on the deformation of the actuator, thereby achieving efficient actuation under low irradiance. Compared with traditional photothermal soft robots without thermal management, it has a more significant actuation advantage in low-irradiance environments.

[0099] (2) Analysis of the absorptivity / emissivity spectra and photothermal conversion efficiency of the photothermal soft actuator films prepared in Example 1 and Comparative Examples 1-4 in the 0.3-17 μm wavelength range.

[0100] Figure 7The images show the absorptivity and emissivity spectra of the soft actuator film in Example 1 in the solar band (0.3-2.5 μm) and the mid-to-far infrared band (2.5-17 μm). The results show that MXene-CNF exhibits high absorptivity (~88%) in the solar band and low emissivity (~15%) in the infrared band. The absorptivity and emissivity spectra of the photothermal conversion layers in Comparative Examples 1-4 in the solar band (0.3-2.5 μm) and the mid-to-far infrared band (2.5-17 μm) show that they exhibit high absorption (~92%) in the solar band and high emissivity (~95%) in the infrared band. Figure 8 According to the theoretical photothermal conversion efficiency calculation formula, when the operating temperature is 80℃ and the ambient temperature is 20℃, the photothermal conversion efficiency of Example 1 is about 0.8, while the photothermal conversion efficiency of the traditional PDMS-CB film is only about 0.5.

[0101] (3) Thermal insulation performance analysis of Example 1 and Comparative Examples 1-4

[0102] Figure 9 The image shows the photothermal soft actuators prepared in Example 1 and Comparative Examples 1-4 at 100 mW / cm². 2 The light irradiation and cooling performance tests showed that, within the same light irradiation time, Example 1 reached an equilibrium temperature of approximately 85 degrees Celsius through radiation thermal management, while Comparative Examples 1-4, due to continuous outward radiation, only reached an equilibrium temperature of approximately 75 degrees Celsius. The photothermal soft actuator with radiation thermal management significantly reduced heat loss within the same time period, which is more conducive to the effective driving of the photothermal soft robot in low-irradiation environments.

[0103] (4) Motion performance analysis of Example 1 and Comparative Example 1

[0104] Figure 10 The image shows the photothermal soft actuators prepared in Example 1 and Comparative Example 1 at 100 mW / cm². 2 Curves showing the relationship between bending curvature and time under illumination. The results indicate that, under the same irradiance and irradiance time, the low-irradiance photothermal soft actuator based on a thermal management strategy exhibits superior performance under a solar intensity of 100 mW / cm². 2 It exhibits better driving performance than traditional photothermal soft actuators. Example 2:

[0105] The specific fabrication process of a biomimetic soft crawling robot is as follows:

[0106] Specifically, the MXene-CNF composite film prepared in Example 1 was patterned and transferred to the LCE surface prepared in Example 1, wherein the length ratio of MXene-CNF to LCE was 1:2. Then, the SEBS prepared in Example 1 was naturally bonded to the LCE with MXene-CNF transferred in this example; a biomimetic soft crawling robot was designed and manufactured.

[0107] Programmable light stimulation (100 mW / cm) 2 This enables the bending and releasing of the soft crawling robot; the robot's crawling process under low-irradiance light was recorded using an Apple 14 Pro Max phone, and its motion photos are as follows. Figure 11 As shown.

[0108] The results show that a biomimetic soft crawling robot made with a low-irradiation photothermal soft actuator has good motion performance under low-irradiation light, with an average crawling speed of 0.1 mm / s. Example 3:

[0109] A circular rolling actuator, the specific manufacturing process of which is as follows:

[0110] Specifically, the strip-shaped photothermal soft actuators prepared in Example 1 are connected end to end to form a ring, with silicone used for the connection; at 100 mW / cm 2 Under light stimulation, only the illuminated side experiences a change in curvature. This change in curvature causes a shift in the roller's center of mass, resulting in the roller rolling on the plane. (See motion photographs.) Figure 12 As shown.

[0111] The results show that the ring actuator prepared by a low-irradiation photothermal soft actuator has good continuous motion performance under low-irradiation light, and its average rolling speed can reach 0.5 mm / s. Example 4:

[0112] The specific fabrication process of a photothermal soft crawling robot that can be driven under natural light is as follows:

[0113] The preparation process was the same as in Example 2. The bending and releasing movements of the soft robot were achieved by periodically blocking natural light. The robot's crawling process in a winter natural light environment was recorded using an Apple 14 Pro Max phone, and the environmental irradiance and wind speed information are as follows: Figure 13 As shown, its motion photos are as follows Figure 14 As shown.

[0114] The results show that a biomimetic soft crawling robot fabricated with a low-irradiation photothermal soft actuator can crawl rapidly under natural light, with a crawling speed of up to 0.1 mm / s and a displacement time of... Figure 15 As shown.

[0115] The above description is merely a partial example of the present invention. It is intended to provide a better understanding of the method and core ideas of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above examples based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A low-irradiation photothermal soft actuator, characterized in that: The low-irradiance photothermal soft actuator (10) includes a heat-insulating layer film (11), a photothermal conversion layer film (12), and a thermal response driving layer film (13) stacked from top to bottom. The low-irradiance photothermal soft actuator (10) is used to bend and deform after absorbing solar energy. The photothermal conversion layer film (12) can absorb solar energy and convert it into heat energy through the photothermal effect. The heat-insulating layer film (11) and the thermal response driving layer film (13) deform to different degrees under the action of heat, so that the low-irradiance photothermal soft actuator (10) bends and deforms. The heat-insulating layer film (11) is a porous broadband transparent polymer film. The porous broadband transparent polymer film is one or more of polyethylene, styrene-ethylene-butene-styrene block copolymer, polypropylene, and polymethyl methacrylate materials that have undergone porous treatment. The porous broadband transparent polymer film is provided with a porous structure for reducing thermal conductivity.

2. The low-irradiance photothermal soft actuator according to claim 1, characterized in that, The photothermal conversion layer film (12) is a selective solar energy absorption composite film. The selective solar energy absorption composite film is mainly composed of a selective solar energy absorption film and a performance modulation material. The selective solar energy absorption film is one or more of two-dimensional transition metal carbides, transition metal nitrides, and transition metal borides. The performance modulation material is one or more of nanocellulose, aluminum hydroxide gel, and nanoalumina. The mass ratio of the selective solar energy absorption film to the performance modulation material is 9:1 to 5:

5.

3. The low-irradiance photothermal soft actuator according to claim 2, characterized in that, The transition metal nitride is one or a combination of ZrN and TiN; the transition metal boride is one or a combination of TiB2 and ZrB2.

4. The low-irradiance photothermal soft actuator according to claim 1, characterized in that, The thermally responsive driving layer film (13) is a thermally responsive smart material, which is one or more of the following: liquid crystal elastomer, shape memory polymer, shape memory alloy, shape memory ceramic and hydrogel.

5. A method for preparing a low-irradiation photothermal soft actuator according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: S1. Prepare porous broadband transparent polymer films and treat them with oxygen plasma; S2. Prepare a thermally responsive driving layer thin film (13) and perform oxygen plasma treatment; S3, Selective solar energy absorption composite film is prepared on the surface of thermally responsive driving layer film (13) by one or two steps; S4. A porous broadband transparent polymer film is attached to a selective solar energy absorption composite film to obtain a low-irradiation photothermal soft actuator (10).

6. The method for preparing a low-irradiation photothermal soft actuator according to claim 5, characterized in that, Specifically, step S1 involves the following: the porous broadband transparent polymer film is prepared by one or more of the following methods: spin coating, blade coating, spray coating, physical vapor deposition, and chemical vapor deposition; the porous structure on the porous broadband transparent polymer film is prepared by one or more of the following methods: wet spinning, freeze drying, sacrificial template, sol-gel, and introducing hollow microspheres to construct a multi-pore structure. After the porous broadband transparent polymer film was prepared, it was treated with oxygen plasma in a vacuum environment.

7. The method for preparing a low-irradiation photothermal soft actuator according to claim 5, characterized in that, Specifically, step S2 involves preparing the thermally responsive driving layer film (13) by one or more of the following methods: mold making, spin coating, spraying, 3D printing, and direct ink writing. After obtaining the thermally responsive driving layer film (13), oxygen plasma is used to process the thermally responsive driving layer film (13) in a vacuum environment.

8. The method for preparing a low-irradiation photothermal soft actuator according to claim 5, characterized in that, In step S3, a selective solar energy absorption composite material film is obtained by doping a performance modulation material into a selective solar energy absorption film. Then, the selective solar energy absorption composite material film is prepared on the surface of the thermal response driving layer film (13) by a one-step or two-step process. The one-step process is to directly prepare the selective solar energy absorption composite material film on the surface of the thermal response driving layer film (13). The one-step process is one or more of the following methods: spin coating, spray coating, brush coating, physical vapor deposition, and chemical vapor deposition. The two-step process is to first prepare the selective solar energy absorption composite material onto the target substrate by solution deposition, and then transfer the selective solar energy absorption composite material film to the surface of the thermal response driving layer film (13) by utilizing the difference in the bonding force between the composite material and the target substrate and the thermal response driving layer film (13). The target substrate is one or more of the following: porous cellulose membrane, porous nylon membrane, and porous polyvinylidene fluoride membrane.

9. The application of a low-irradiance photothermal soft actuator according to any one of claims 1-4 or a low-irradiance photothermal soft actuator prepared by the preparation method according to any one of claims 5-8, characterized in that, Applications in soft crawling robots, rolling robots, flexible sensing, and artificial muscles.

10. A driving method for a low-irradiation photothermal soft actuator as described in any one of claims 1-4 or a low-irradiation photothermal soft actuator prepared by the preparation method described in any one of claims 5-8, characterized in that, The low-irradiance photothermal soft actuator (10) achieves photothermal drive through thermal management. When sunlight shines on the low-irradiance photothermal soft actuator (10), the heat insulation film (11) is irradiated by sunlight, so that the sunlight irradiates the photothermal conversion layer film (12). When the photothermal conversion layer film (12) is affected by light, it converts light energy into heat energy. The heat insulation film (11) blocks the heat energy converted by the photothermal conversion layer film (12) from being transferred upward. At the same time, the emissivity characteristics of the surface of the photothermal conversion layer film (12) reduce the heat radiation of the low-irradiance photothermal soft actuator (10) to the external environment, so that the heat energy is transferred to the lower thermal response driving layer film (13). After receiving the heat energy stimulus, the thermal response driving layer film (13) produces macroscopic deformation, converting the heat energy into the mechanical energy required for driving, so that the low-irradiance photothermal soft actuator (10) is driven to deform as a whole.

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