A low poisson's ratio self-regulating intelligent window composite material film and a preparation method thereof

Abstract

The application discloses a low-Poisson-ratio self-regulation and control intelligent window composite film, which comprises a flexible base body, transparent degree regulation particles and a plurality of strip-shaped shape memory polymers distributed in the base body; the shape memory polymers are long and in a bending structure. The composite film has high tensile properties, can effectively reduce the shrinkage perpendicular to the load action direction caused by the Poisson effect, and effectively improves the use effect of the mechanical intelligent window, and meanwhile, the excellent light-induced self-regulation and control effect is considered; and the preparation method is simple and convenient to operate, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of smart window technology, specifically relating to a self-regulating smart window composite film with a low Poisson's ratio and its preparation method. Background Technology

[0002] Smart windows can adjust their light transmittance and regulate the amount of solar radiation entering a building based on external stimuli (light, electricity, force, etc.), thereby regulating room temperature. Mechanosensitive smart windows are typically made of mechanically responsive materials and are a new type of smart window that adjusts various properties through simple mechanical strain. They have advantages such as simple structure, low cost, and fast response time. Patent CN111522151A discloses a highly sensitive mechanically controlled smart window film. This high-sensitivity controlled smart window film, employing a double-layer composite structure, can achieve a 50% transparency change at a strain of 40%. Patent CN110646870A discloses a light transmittance-adjustable film. This film is prepared by repeatedly pre-stretching and treating its surface, resulting in a smart window film that exhibits multiple light transmittance changes after stretching. The literature "Mechanosensitive Color-Changing Control and Anti-counterfeiting Application of Transparent Photonic Crystal Films" utilizes SiO2 colloidal particles to construct a three-dimensional opal photonic crystal array and embeds it within a polydimethylsiloxane (PDMS) elastomer. This elastic film can change color after being subjected to force.

[0003] However, existing mechanical smart windows typically suffer from the following problems: Force-driven smart windows primarily rely on changes in the internal structure or other factors of the window film under stress to alter the window's transparency. However, the window film undergoes unexpected deformations under stress; for example, during longitudinal stretching, the film contracts laterally, causing the film's sides to detach from the window's edge, resulting in localized gaps and affecting the window's usability. The main reason for these problems lies in the Poisson's ratio effect (where a material undergoes elongation (or shortening) deformation along the load direction while simultaneously experiencing shortening (or elongation) deformation perpendicular to the load direction). Therefore, there is an urgent need to further develop composite material films with high elasticity and low Poisson's ratio.

[0004] Currently, methods for reducing Poisson's ratio typically involve incorporating three-dimensional origami structures (such as honeycomb or foam structures) within the material. For example, the paper "Mechanical Design and Analysis of a Negative Poisson's Ratio Intelligent Flexible Metastructure" develops a flexible soft material based on an origami honeycomb structure, which exhibits a negative Poisson's ratio effect during stretching. The paper "Mechanical Metamaterials Foams with Tunable Negative Poisson's Ratio for Enhanced Energy Absorption and Damage Resistance" achieves a negative Poisson's ratio through the use of a three-dimensional mesh structure. Patent CN216715096A discloses a three-node tensile-expanded perforated structure with a negative Poisson's ratio, achieving this effect by adding triangular perforations to the film. However, existing methods for improving low Poisson's ratio all require openings or incorporating large-area three-dimensional structures. For intelligent window films, high light transmittance is required, and perforations and other structures can affect film transparency and the overall performance of the composite film. Incorporating large-area, complex three-dimensional structures essentially reduces the overall Poisson's ratio through the three-dimensional characteristics of the structure, typically involving complex internal operations and leading to a decrease in the overall transparency of the material. In addition, smart windows made in this way still need to rely on other detection methods to adjust the transparency of the smart window manually or through other electronic control methods. They cannot automatically adjust themselves according to changes in light. Summary of the Invention

[0005] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a force-controlled smart window film with a low Poisson's ratio. This film can maintain high tensile properties during stretching while reducing shrinkage perpendicular to the load direction caused by the Poisson effect, thereby effectively improving the performance of mechanical smart windows. It also achieves excellent photo-controlled autonomous regulation. Furthermore, the preparation method involved is relatively simple and easy to operate, making it suitable for widespread application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low Poisson's ratio self-regulating smart window composite film includes a flexible matrix, transparency-regulating particles distributed therein, and several shape memory polymers; the shape memory polymers are long (along the length direction of the composite film) and have a curved strip structure.

[0008] In the above scheme, the shape of the curved strip structure is S-shaped or arc-shaped, etc.

[0009] Furthermore, the shape memory polymer is spaced within the film.

[0010] Furthermore, the transparency-regulating particles are distributed on the surface layer of the flexible substrate.

[0011] In the above scheme, the flexible substrate can be polydimethylsiloxane or silicone, etc., with a transparency of 99.9% or higher; among which, the tear strength of silicone is 10kN / m or higher; both can maintain high transparency while having good tensile properties.

[0012] In the above scheme, the transparency-regulating particles can be selected from silica nanoparticles, polystyrene nanoparticles, silica-encapsulated iron oxide nanospheres, or ferric oxide nanoparticles, etc.; their particle size is 200-300 nm. The selection of particles must first ensure that their addition will not significantly affect the transparency of the smart window film, and secondly, the particles must have suitable bonding force with the substrate material, so that they can separate from the substrate material during stretching to form cavities, thereby changing the film transparency.

[0013] In the above scheme, the thickness of the low Poisson's ratio controlled smart window film is 0.5-1mm.

[0014] In the above scheme, the shape memory polymer is a photoresponsive shape memory polymer material, which is composed of ethylene-vinyl acetate copolymer and silver nanowires as the main raw materials (AgNWs / EVA). This shape memory polymer can change shape under the regulation of light and temperature control.

[0015] In the above scheme, the mass ratio of the ethylene-vinyl acetate copolymer to the silver nanowires is 100:(0.4~0.8).

[0016] In the above scheme, the molecular weight of the ethylene-vinyl acetate copolymer is 1800-2200, and the vinyl acetate content is 15-20%; the diameter of the silver nanowires is 40-60 nm, and the length is 10-15 μm.

[0017] In the above scheme, the total length of the shape memory polymer is the length corresponding to the composite film when the tensile deformation reaches 25-35%, ensuring the reduction effect of Poisson's ratio during stretching.

[0018] In the above scheme, the cross-section of the strip structure can be rectangular, arc-shaped, triangular, or circular, etc.

[0019] In the above scheme, the preparation steps of the shape memory polymer strip structure include: dissolving ethylene-vinyl acetate copolymer and silver nanowires in an organic solvent, heating and stirring, naturally forming a film, and drying; then hot pressing to obtain a curved strip structure, cooling; and then ultraviolet crosslinking to obtain a curved strip shape memory polymer.

[0020] In the above scheme, the organic solvent can be toluene or acetone, etc.

[0021] The above-mentioned method for preparing a force-controlled smart window film with a low Poisson's ratio includes the following steps:

[0022] 1) Preparation of shape memory polymers;

[0023] Ethylene-vinyl acetate copolymer (EVA), initiator, crosslinking agent, and silver nanowires (AgNWs) ethanol dispersion were dispersed in organic solvent I in a certain proportion and stirred under oil bath conditions; the resulting homogeneous solution was allowed to stand overnight to form a film naturally and then dried.

[0024] The mold coated with a release agent is heated, the dried product is placed in the mold, hot-pressed, and cooled to obtain a curved strip structure.

[0025] The obtained strip structure was placed on a hot stage for ultraviolet cross-linking to obtain a shape memory polymer with a curved strip structure;

[0026] 2) Surface treatment of shape memory polymers;

[0027] The obtained shape memory polymer was added to an organosilane coupling agent solution for impregnation and then dried.

[0028] 3) Preparation of composite films;

[0029] The transparency-regulating particles were dispersed in organic solvent II and ultrasonically stirred to obtain a uniformly dispersed transparency-regulating particle dispersion; then it was sprayed onto a substrate.

[0030] A liquid flexible substrate is prepared, and then a step-by-step casting process is adopted: First, a casting is performed on the substrate with sprayed transparency-regulating particles, and the casting amount is 40-60% of the total amount of liquid flexible substrate. Vacuum degassing is performed, and it is left to stand at room temperature for 2-4 hours (the shape is fixed but not completely cured and still has a certain degree of stickiness). Then, several shape memory polymer strip structures from step 2) are placed at intervals on the surface, and a second casting is performed using the remaining liquid flexible substrate. Vacuum degassing is performed, and the substrate is cured. Finally, the substrate is peeled off to obtain the low Poisson's ratio controlled smart window film material.

[0031] In the above scheme, the initiator can be benzoyl peroxide, benzophenone, or thiocarbamate, etc.; the crosslinking agent can be trimethylolpropane triacrylate, triallyl isocyanurate, or dicumyl peroxide, etc.

[0032] In the above scheme, the amount of initiator is 2 to 8% of the mass of the ethylene-vinyl acetate copolymer; the amount of crosslinking agent is 1 to 8% of the mass of the ethylene-vinyl acetate copolymer.

[0033] In the above scheme, the organic solvent I can be one or more of aromatic solvents or chlorinated hydrocarbon solvents such as toluene, acetone, tetrahydrofuran, dichloroethane, and chloroform.

[0034] In the above scheme, the mass ratio of the ethylene-vinyl acetate copolymer, initiator, crosslinking agent, silver nanowire ethanol dispersion, and organic solvent is 1:(0.02~0.03):(0.04~0.06):(0.04~0.08):(0.8~1).

[0035] In the above scheme, the stirring treatment temperature in step 1) is 80-100℃ and the time is 40-50 min; the drying temperature is 60-70℃ and the time is 20-24 h.

[0036] In the above scheme, the mold heating temperature in step 1) is 90-110℃; the hot pressing temperature is 90-100℃, and the pressure is 4-6 kg / cm². 3 The time is 25 to 30 minutes.

[0037] In the above scheme, the ultraviolet light intensity used in the ultraviolet crosslinking step is 1800–2000 mw / cm². 2 The illumination time is 30–60 seconds; the film is 10–18 cm away from the light source.

[0038] In the above scheme, the mass concentration of the organosilane coupling agent in the solution is 5-10%; the solvent used is isopropanol, ethanol, toluene, or xylene, etc.

[0039] In the above scheme, the organosilane coupling agent may be one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane.

[0040] In the above scheme, the immersion treatment temperature is 75-85℃ and the time is 1.5-2.5h.

[0041] In the above scheme, the concentration of the transparency-regulating particles in the organic solvent is 8–12 mg / mL.

[0042] In the above scheme, the organic solvent II can be isopropanol or acetone, etc.

[0043] In the above scheme, the ultrasonic stirring time is 2 to 2.5 hours.

[0044] In the above scheme, the substrate can be made of polymethyl methacrylate or polystyrene.

[0045] In the above scheme, the spraying pressure is 45-50 kPa, the spraying distance is 4-6 cm, the nozzle moving speed is 4-6 cm / s, and the number of sprays is 18-25.

[0046] In the above scheme, the liquid flexible substrate is polydimethylsiloxane or highly transparent silicone.

[0047] Furthermore, the high-transparency silicone comprises silicone and silicone oil, wherein the amount of silicone oil used is 5-10% of the mass of the silicone.

[0048] In the above scheme, the curing temperature is 70-100℃ and the time is 1-2h.

[0049] The low Poisson's ratio smart window film prepared according to the above scheme will experience contraction in the direction perpendicular to the load due to the Poisson's ratio when the film is stretched. Then, the internally curved reinforcing material will gradually straighten and tighten, acting in the opposite direction to the film, causing the film to expand. This results in a reduction in the Poisson's ratio compared to the original ordinary film after stretching (when the deformation is 30%, the contraction in the direction perpendicular to the load is reduced by more than 35%).

[0050] The principle of this invention is as follows:

[0051] This invention employs a simplified three-dimensional origami structure to reduce Poisson's ratio. The shape memory polymer strip structure counteracts the opposing effects of the film during stretching. During stretching, the composite film shrinks perpendicular to the load direction due to the Poisson effect, while the pre-bent strip structure of the shape memory reinforcement tends to straighten during stretching, generating an opposing force, effectively providing the film with a boundary constraint. Furthermore, the formulation, shape, and specifications of the bending structure are optimized to enhance its shrinkage reduction effect. The shape memory polymer AgNWs / EVA composite material converts light energy (preferably under infrared conditions for rapid response) into heat energy through internal AgNWs light-absorbing particles, causing cross-linking and de-cross-linking of the EVA polymer upon temperature changes, thus altering its shape. Additionally, surface treatment of the shape memory polymer with an organosilane coupling agent effectively increases the bonding force between the shape memory polymer as a reinforcing material and the soft matrix material, improving issues such as separation and cracking of the shape memory polymer from the matrix material during stretching.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] 1) This invention is the first to propose applying a boundary constraint effect to the edge of the composite film material by the composition and structure of the material itself to reinforce the material, thereby adding a boundary constraint force to the composite material and providing a new approach for low Poisson's ratio technology;

[0054] 2) The use of light-responsive shape memory polymers can enable force-controlled smart windows to break free from dependence on external forces and achieve a functional transformation of autonomous control; enabling smart windows to automatically adjust their transparency according to changes in light throughout the day;

[0055] 3) By optimizing the formulation, structure, and specifications of shape memory polymers, and further modifying their surface with organosilane coupling agents, shape memory polymers can be efficiently applied in flexible matrix systems, effectively increasing the tensile properties of composite materials. Shape memory polymers undergo shape changes, causing overall stretching and thus changes in transparency. At the same time, the shape returns to a straight state, which can effectively improve the shrinkage problem perpendicular to the load direction, ensuring a low Poisson's ratio and excellent photo-induced autonomous control effect. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of the intelligent window composite material film described in Example 1;

[0057] Figure 2 This is a schematic diagram of the structure of the intelligent window composite material film described in Example 3. Detailed Implementation

[0058] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0059] In the following examples, the concentration of AgNWs in the AgNWs ethanol dispersion was 10 wt%.

[0060] The ethylene-vinyl acetate copolymer used has a molecular weight of approximately 2000 and is P101483 provided by Shanghai Aladdin Biotechnology Co., Ltd., in which the vinyl acetate content is 18 mol%. The silver nanowires have a diameter of 54.2 ± 6 nm and a length of 12.8 ± 2 μm.

[0061] Example 1

[0062] A low Poisson's ratio autonomous force-controlled smart window composite film, the structural schematic diagram of which is shown below. Figure 1 The specific preparation method includes the following steps:

[0063] 1) Preparation of shape memory polymers

[0064] (1) Add EVA (ethylene-vinyl acetate copolymer), BP (initiator), TMPTA (crosslinking agent), AgNWs ethanol dispersion and toluene to a flask at a mass ratio of 1:0.02:0.05:0.005:0.9, heat to 90°C in an oil bath, and stir for 45 min.

[0065] (2) Pour the obtained homogeneous solution into a glass petri dish, let it stand overnight in a fume hood to form a film naturally, and then place the film in a vacuum oven and dry it at 60°C for 24 hours.

[0066] (3) Heat the mold coated with silicone dry film release agent to 100°C, place the dried product in the mold, the mold shape is an S-shaped curved structure with an arc of 30°, and heat it in a hot press at 100°C with a pressure of 5 kg / cm². 3 It is pressed and formed under pressure, and the hot pressing time is 30 minutes;

[0067] (4) After cooling the mold to room temperature, remove the strip structure; wherein, the total length of the obtained strip shape memory polymer is the length corresponding to the silicone rubber film when the tensile deformation reaches 30%;

[0068] (5) The EVA strip structure was placed on a hot stage for ultraviolet cross-linking, wherein the ultraviolet light intensity used was 1800 mw / cm². 2 The film was placed 15cm away from the light source and irradiated with ultraviolet light for 40 seconds before being removed.

[0069] 2) Shape memory polymer surface treatment

[0070] A 5wt% mixed solution was prepared by dispersing γ-aminopropyltriethoxysilane with ethanol. The prepared shape memory polymer was then immersed in the mixed solution and heated to 80°C for 2 hours before being removed and dried.

[0071] 3) Preparation of composite films;

[0072] SiO2 with an average particle size of 300 nm was dispersed in isopropanol at a concentration of 10 mg / mL and stirred with strong ultrasonication for 2 h to prepare a uniformly dispersed SiO2 dispersion. The obtained SiO2 dispersion was then loaded into a Master spray gun (spray gun model G44) and sprayed 20 times on a PMMA substrate at a spraying pressure of 50 kPa, a spraying distance of 5 cm and a moving speed of 5 cm / s. The spraying thickness was about 600-900 nm.

[0073] The elastic polymer was prepared using Dow Corning SYLGARD-184 (Dow Corning 184 for short) silicone rubber. Dow Corning 184 is a two-component kit product consisting of a liquid component, including a basic component silicone rubber precursor A and a curing agent B. The curing agent and the precursor were mixed and stirred at a mass ratio of 1:10, and then degassed for 2 hours. Half of the degassed solution was poured into the film and cured at room temperature on a water platform for 3 hours. The shape memory polymer was then placed on the film surface at intervals. The remaining solution was used for a second pour. The film was then placed in a vacuum oven to degas until it was flat and free of bubbles. Finally, it was cured at 75°C for 2 hours to obtain the cured polydimethylsiloxane (PDMS). Finally, the substrate was mechanically peeled off to obtain the low Poisson's ratio smart window film material.

[0074] The dimensions of the smart window film material obtained in this embodiment are 60cm×30cm×1mm; when the tensile deformation is 30%, the shrinkage perpendicular to the load direction is reduced by 40%; during this process, the shrinkage curve shows a trend of first increasing and then decreasing. This is because the structure that is bent in the early stage will shrink inward along with the smart window film, and then as the stretching increases, the shape memory polymer structure gradually straightens and acts on the film to expand outward.

[0075] In the near-infrared 808nm 2.0W / cm 2 Under infrared light irradiation, the response time of the composite film obtained in this embodiment from its initial state to its final stretched state is 34 seconds. The transmittance of the composite film in its initial state is 99%, and the transparency changes when deformation occurs: the transparency change reaches its maximum value when stretched to 25-35% of its original length, decreasing by 80% relative to the initial state, and the transparency change is not obvious with further stretching.

[0076] The tensile strength of the composite film obtained in this embodiment was tested to be 13 MPa.

[0077] Example 2

[0078] A low Poisson's ratio self-regulating smart window composite film is prepared in a manner similar to that of Example 1, except that the material used in the casting and curing process is replaced with silicone KE-1606. KE-1606 is also a two-component film and is further compounded with silicone oil. The silicone rubber precursor A in KE-1606 is mixed with curing agent B and silicone oil in a mass ratio of 10:1:0.5.

[0079] Testing showed that the composite film obtained in this example exhibited a 35% reduction in shrinkage perpendicular to the load direction when stretched by 30%. Due to the higher modulus of KE-1606, the tensile deformation under illumination only reached 70% of that in Example 1, with a response time of 40 seconds. The composite film had a light transmittance of 99% in its initial state, which decreased by 50% compared to the initial state after 30% tensile deformation.

[0080] The tensile strength of the composite film obtained in this embodiment was tested to be 17 MPa.

[0081] Example 3

[0082] A low Poisson's ratio self-regulating intelligent window composite film is prepared using a method largely the same as in Example 1, except that the pre-bending shape of the shape memory polymer is changed from an S-shape to an arc shape; its structural schematic diagram is shown below. Figure 2 .

[0083] Tests showed that the obtained composite film exhibited a 31% reduction in shrinkage perpendicular to the deformation direction when stretched by 30%. Due to its simple structure, its deformation response time under illumination was 30 seconds. The composite film had a transmittance of 99% in its initial state, but its transparency decreased by 80% compared to the initial state when stretched or irradiated to 30% of its original value.

[0084] The tensile strength of the composite film obtained in this embodiment was tested to be 13 MPa.

[0085] Comparative Example 1

[0086] A low Poisson's ratio self-regulating intelligent window composite film is prepared in a manner similar to that of Example 1, except that the mass ratio of EVA (ethylene-vinyl acetate copolymer), BP (initiator), TMPTA (crosslinking agent), AgNWs ethanol dispersion and toluene in step 1) is 1:0.04:0.05:0.005:0.9.

[0087] Testing revealed that the obtained smart window film exhibited a 25% reduction in shrinkage perpendicular to the deformation direction when deformed by 30%, a decrease in the strength of the shape memory polymer, a reduction in the deformation response speed under illumination to 60 seconds, and a 20% reduction in elongation at the final state compared to Example 1. The obtained composite film had a light transmittance of 99% in its initial state, but its transparency decreased by 40% compared to the initial state when stretched or deformed to the final state under light. The tensile strength of the composite film was 10 MPa.

[0088] Comparative Example 2

[0089] A low Poisson's ratio self-regulating intelligent window composite film is prepared in a manner similar to that of Example 1, except that the total length of the shape memory polymer is increased to the length corresponding to the stretching deformation of the silicone rubber film reaching 40%.

[0090] Tests showed that the deformation of the composite film obtained under the same lighting conditions could only reach 34% of the original length; and when the tensile deformation was 30%, the shrinkage perpendicular to the load direction did not decrease significantly, but only by 10%.

[0091] Comparative Example 3

[0092] A composite film is prepared in a manner similar to that of Example 1, except that the surface treatment described in step 2) is not performed on the shape memory polymer.

[0093] Compared to Example 1, the overall strength of the untreated composite material is reduced. When stretched to only 20% of its original length, the shape memory polymer and the matrix PDMS material crack and separate. When stretched to 30%, the two materials are almost completely separated. At the same time, the tensile strength of the resulting composite film drops sharply, reaching only 4 MPa.

[0094] When the film obtained by this invention is stretched, it first contracts due to Poisson's ratio in the direction of the vertical load. Then, due to the gradual straightening and tightening of the internally bent metal wires, the film expands in the opposite direction, thereby achieving a reduction in Poisson's ratio compared to the original film without wires after stretching.

[0095] Obviously, the above preferred embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low Poisson's ratio self-regulating intelligent window composite material film, characterized in that, It includes a flexible matrix and transparency-regulating particles distributed therein, and several shape memory polymers; the shape memory polymers are arranged along the length of the composite film and have a curved strip structure; The transparency-regulating particles are silica nanoparticles, polystyrene nanoparticles, silica-encapsulated iron oxide nanospheres, or ferric oxide nanoparticles. The shape memory polymer is a photoresponsive shape memory polymer material, which is composed of ethylene-vinyl acetate copolymer and silver nanowires as the main raw materials. The specific preparation steps are as follows: Ethylene-vinyl acetate copolymer, initiator, crosslinking agent, and silver nanowire ethanol dispersion were dispersed in organic solvent I in a certain proportion and stirred under oil bath conditions; the resulting homogeneous solution was allowed to stand overnight to form a film naturally and then dried. The mold coated with a release agent is heated, the dried product is placed in the mold, hot-pressed, and cooled to obtain a curved strip structure. The obtained curved strip structure was placed on a hot stage for ultraviolet cross-linking to obtain a shape memory polymer with a curved strip structure; The shape memory polymer undergoes surface treatment, specifically including: adding the obtained shape memory polymer to an organosilane coupling agent solution for impregnation and drying; The mass ratio of the ethylene-vinyl acetate copolymer, initiator, crosslinking agent, silver nanowire ethanol dispersion, and organic solvent is 1:(0.02~0.03):(0.04~0.06):(0.04~0.08):(0.8~1); The total length of the shape memory polymer is the length of the composite film when the tensile deformation reaches 25-35%.

2. The low Poisson's ratio self-regulating intelligent window composite material film according to claim 1, characterized in that, The mass ratio of the ethylene-vinyl acetate copolymer to the silver nanowires is 100:(0.4~0.8).

3. The low Poisson's ratio self-regulating intelligent window composite material film according to claim 2, characterized in that, The molecular weight of the ethylene-vinyl acetate copolymer is 1800~2200; the diameter of the silver nanowires is 40~60nm and the length is 10~15μm.

4. The low Poisson's ratio self-regulating intelligent window composite material film according to claim 1, characterized in that, The transparency-regulating particles are distributed on the surface layer of the flexible substrate.

5. The low Poisson's ratio self-regulating intelligent window composite material film according to claim 1, characterized in that, The flexible substrate is polydimethylsiloxane or silicone.

6. The low Poisson's ratio self-regulating intelligent window composite material film according to claim 1, characterized in that, The particle size of the transparency-regulating particles is 200~300nm.

7. The method for preparing the low Poisson's ratio autonomously adjustable smart window composite film according to any one of claims 1 to 6, characterized in that, Includes the following steps: 1) Preparation of shape memory polymers; Ethylene-vinyl acetate copolymer, initiator, crosslinking agent, and silver nanowire ethanol dispersion were dispersed in organic solvent I in a certain proportion and stirred under oil bath conditions; the resulting homogeneous solution was allowed to stand overnight to form a film naturally and then dried. The mold coated with a release agent is heated, the dried product is placed in the mold, hot-pressed, and cooled to obtain a curved strip structure. The obtained strip structure was placed on a hot stage for ultraviolet cross-linking to obtain a shape memory polymer with a curved strip structure; 2) Surface treatment of shape memory polymers; The obtained shape memory polymer was added to an organosilane coupling agent solution for impregnation and then dried. 3) Preparation of composite films; The transparency-regulating particles were dispersed in organic solvent II and ultrasonically stirred to obtain a uniformly dispersed transparency-regulating particle dispersion; then it was sprayed onto a substrate. A liquid flexible matrix is ​​prepared, and then a step-by-step casting process is adopted: First, a casting is performed on the substrate with sprayed transparency-regulating particles, and the casting amount is 40-60% of the total amount of liquid flexible matrix. Vacuum degassing is performed, and the substrate is left to stand at room temperature. Then, several shape memory polymer strip structures from step 2) are placed at intervals on the surface. A second casting is performed using the remaining liquid flexible matrix, followed by vacuum degassing and curing. Finally, the substrate is peeled off to obtain the low Poisson's ratio self-regulating smart window composite material film.

8. The preparation method according to claim 7, characterized in that, The ultraviolet crosslinking step uses ultraviolet light intensity of 1800~2000 mw / cm². 2 The illumination time is 30~60s; the film is 10~18 cm away from the light source.

Images