An ultra-flexible stretchable dimming film and a preparation method thereof

Abstract

The application discloses a super-flexible stretchable dimming film and a preparation method thereof, relates to the technical field of dimming films, and comprises an upper transparent electrode layer, a dimming function layer and a lower transparent electrode layer which are sequentially stacked from top to bottom; the preparation method comprises the following steps: 1) preparing a main body matrix material / ultraviolet curing resin mixture; 2) assembling the dimming film; and 3) ultraviolet light curing. The application realizes covalent bond anchoring of cerium oxide nanoparticles on a thermoplastic polyurethane fiber network through surface phosphonic acid functionalization treatment; by constructing a full thermoplastic polyurethane material system, the interface compatibility of the fiber reinforced phase and the polymer matrix is broken through, so that the film has high tensile strain capacity and excellent fatigue resistance under the premise of maintaining high transparency.

Description

Technical Field

[0001] This invention relates to the field of dimming film technology, and in particular to an ultra-flexible stretchable dimming film and its preparation method. Background Technology

[0002] Polymer-dispersed liquid crystal films, as an important electro-modulated dimming material, are widely used in smart windows, displays, and other fields. Their traditional structure involves dispersing liquid crystals in the form of microdroplets within a three-dimensional polymer network, using an electric field to control the orientation of the liquid crystals to achieve switching between transparent and hazy states. However, traditional polymer-dispersed liquid crystal films are typically based on rigid polymers such as epoxy or acrylic resins, resulting in high brittleness and failing to meet the requirements for flexibility and stretchability in emerging fields such as wearable electronics and flexible displays.

[0003] To impart flexibility, researchers have attempted to dope nanoparticles (such as cerium oxide and barium titanate) to improve performance or introduce them into elastic polymer matrices. However, these methods have inherent drawbacks: nanoparticles tend to aggregate in the matrix and easily detach during deformation, leading to performance degradation; furthermore, poor interfacial compatibility and mechanical mismatch between different materials (such as rigid fibers and elastic matrices) can easily result in interfacial delamination under stress. Existing technologies struggle to achieve stable, large-scale stretchable deformation of devices while maintaining excellent electro-optical performance such as high contrast and fast response.

[0004] Therefore, developing a dimming film that can balance high performance and ultra-flexibility has become an urgent technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing an ultra-flexible stretchable dimming film and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention first proposes an ultra-flexible stretchable dimming film, comprising an upper transparent electrode layer, a dimming functional layer, and a lower transparent electrode layer stacked sequentially from top to bottom;

[0008] The dimming functional layer includes a polymer matrix, microdroplets of main matrix material dispersed in the polymer matrix, and a reinforcing fiber web embedded in the polymer matrix;

[0009] The reinforcing fiber web is a thermoplastic polyurethane fiber web, and its surface is covalently anchored with cerium oxide nanoparticles through phosphonic acid groups.

[0010] The polymer matrix is ​​a UV-curable polyurethane acrylate resin;

[0011] Both the upper and lower transparent electrode layers are stretchable transparent electrodes, which are conductive layers with micro-wrinkled structures formed on a pre-stretched thermoplastic polyurethane substrate.

[0012] Preferably, the cerium oxide nanoparticles have a particle size of 40-60 nm;

[0013] The conductive layer is a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate / silver nanowires / waterborne polyurethane composite conductive layer.

[0014] The thickness of the dimming functional layer is 50-100 μm.

[0015] Preferably, the preparation process of the reinforcing fiber web includes the following steps:

[0016] a. Thermoplastic polyurethane particles are dissolved in a mixed solvent of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution, and thermoplastic polyurethane fiber web is obtained by electrospinning.

[0017] Thermoplastic polyurethane particles are dissolved in a mixed solvent of N,N-dimethylformamide (DMF) / tetrahydrofuran (THF). The spinning solution is stretched and the solvent evaporates under a high voltage electric field to form a fiber web with a diameter in the μm range.

[0018] b. The thermoplastic polyurethane fiber web is subjected to oxygen plasma treatment to activate its surface;

[0019] The CH and C bonds on the fiber surface are destroyed by reactive oxygen species (O2) in the plasma. + By breaking down hydroxyl (-OH) groups and introducing polar groups such as hydroxyl (-OH) and carboxyl (-COOH), the surface energy is significantly improved, transforming it from hydrophobic to hydrophilic.

[0020] c. Immerse the activated fiber web in an ethanol / water solution containing (3-triethoxysilylpropyl)phosphonic acid and react at a constant temperature of 50°C for 60 minutes to graft phosphonic acid groups onto its surface;

[0021] (3-Triethoxysilylpropyl)phosphonic acid is hydrolyzed in ethanol / water to generate an active molecule containing silanol groups (-Si-OH) and phosphonic acid groups (-PO(OH)2); the silanol groups undergo a condensation reaction with the -OH groups on the fiber surface (-Si-OC-covalent bond), grafting the phosphonic acid groups onto the fiber surface;

[0022] d. The grafted fiber web was immersed in a 0.6 mg / ml cerium oxide nanoparticle dispersion and shaken at 50°C for 3 hours to anchor the cerium oxide nanoparticles to the fiber surface through phosphonic acid groups. After vacuum drying, the reinforced fiber web was obtained.

[0023]

[0024] The hydroxyl (-OH) group of phosphonic acid reacts with the CeO2 on the surface of cerium oxide (CeO2) nanoparticles. 3+ / Ce 4+ Coordination occurs (forming -OPO-Ce- bonds), achieving covalent anchoring of nanoparticles.

[0025] Using anhydrous tetrahydrofuran (THF) or N,N-dimethylformamide (DMF) as the reaction solvent, 3-chloropropyltriethoxysilane and diethyl phosphite were reacted under nitrogen protection with a catalyst added and stirred at 40-50°C for 8-10 hours to produce diethyl 3-triethoxysilylpropylphosphonate.

[0026] Hydrolysis was then carried out under acidic conditions. 5-8 times the molar amount of 3-chloropropyltriethoxysilane in 6 mol / L concentrated hydrochloric acid was added, and the mixture was refluxed at 70-75℃ for 8-10 h to convert the diethyl phosphonate group into a phosphonic acid group. Excess hydrochloric acid and the generated ethanol were removed by vacuum distillation. After purification, the mixture was concentrated again under vacuum to obtain a white solid product (3-triethoxysilylpropyl)phosphonic acid.

[0027]

[0028] The catalyst is an alkaline initiator selected from potassium tert-butoxide, sodium hydride, lithium bis(trimethylsilyl)amino, sodium tert-butoxide, sodium amino, and sodium ethoxide, and is used in an amount of 0.5-1.5% of the reactant mass; the molar ratio of 3-chloropropyltriethoxysilane to diethyl phosphite is 1:1.2.

[0029] This compound contains two ethoxy groups in different environments, with significantly different hydrolytic activities; the phosphorus-oxygen bond (P-OEt) is more polar (P...). + -O - Furthermore, phosphorus atoms are more electrophilic than silicon atoms, making them more susceptible to hydrolysis by water molecules. Under conditions of 6 mol / L concentrated hydrochloric acid and 70-75℃, the hydrolysis rate of this type of ethoxy group is rapid, completely converting to hydroxyl groups (-PO(OH)2) in 4-7 hours, generating the target phosphonic acid group. The silicon-oxygen bond (Si-OEt) has stronger covalent properties and a higher bond energy (approximately 452 kJ / mol, higher than P-OEt's 350 kJ / mol), resulting in lower hydrolysis reactivity; this process is much slower than the hydrolysis of ethoxy groups on phosphorus.

[0030] The amount of water used during hydrolysis is 5-8 times that of the phosphonate intermediate, which theoretically only meets the hydrolysis requirements of the two ethoxy groups on phosphorus. In reality, a very small portion of the ethoxy groups on silicon are still hydrolyzed. After the reaction is completed, the water is removed by vacuum distillation to prevent further hydrolysis of the ethoxy groups on silicon.

[0031] Preferably, in the preparation process of the reinforcing fiber web, in the mixed solvent of N,N-dimethylformamide and tetrahydrofuran, the volume ratio of N,N-dimethylformamide to tetrahydrofuran is 1:1; in the ethanol / water solution, the volume concentration of (3-triethoxysilylpropyl)phosphonic acid is 2%, and the volume ratio of ethanol to water is 95:5; the diameter of the reinforcing fiber web is controlled between 0.5-1.5 μm.

[0032] Preferably, the fabrication process of the stretchable transparent electrode includes the following steps:

[0033] ① Mix poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide evenly to prepare composite electrode slurry;

[0034] Poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate, silver nanowires, and waterborne polyurethane are dispersed in ethylene glycol (EG) and dimethyl sulfoxide (DMSO) to form a homogeneous colloidal system. DMSO acts as a dopant, inducing the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate molecular chains to change from a coiled state to an extended state, thus improving conductivity. EG acts as a humectant, reducing shrinkage stress during the slurry drying process and minimizing the breakage of silver nanowires. The amino groups of the waterborne polyurethane react with the sulfonic acid groups (-SO3) of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate. - Hydrogen bonds are formed, and silver nanowires are encapsulated to enhance the flexibility of the conductive layer.

[0035] ② The 125μm thick thermoplastic polyurethane film substrate is unidirectionally pre-stretched to a strain of 30%-50% and held.

[0036] ③ The substrate in the pre-stretched state is subjected to oxygen plasma treatment;

[0037] ④ The composite electrode paste is coated onto the treated substrate and dried on a hot table at 70°C for 30 minutes. The pre-stretching force is then released to form a stretchable transparent electrode with a micro-wrinkled structure. The electrode surface then forms a micro-wrinkled structure.

[0038] The thermoplastic polyurethane substrate is unidirectionally pre-stretched to 30%-50% strain. The polymer chains are oriented along the stretching direction, storing elastic potential energy. After drying, the stress is released, and the substrate shrinks, causing the conductive layer to bend, forming periodic micro-folds. The fold structure counteracts the stretching deformation.

[0039] Oxygen plasma treatment increases the surface polarity of the substrate, improves the adhesion between the conductive layer and the substrate, and ensures the stability of the wrinkled structure.

[0040] The corrugated electrode formed by pre-stretching technology achieves its conductivity primarily by adapting to macroscopic strain through the unfolding of the corrugations, rather than relying on the stretching of the conductive material itself. This avoids the brittle conductive layer from breaking under direct tension.

[0041] Thermoplastic polyurethane reinforced fiber mesh serves as an elastic skeleton, with a modulus on the same order of magnitude as the electrode substrate and polymer matrix. Under tension, it deforms synchronously with the surrounding material, uniformly distributing stress throughout the network and preventing localized stress concentration.

[0042] Because the electrode substrate and the reinforcing fiber are chemically homologous, they exhibit strong interfacial bonding. Under strain, stress is effectively transferred between them through this robust interface. The fiber network bears and disperses most of the mechanical stress, thereby protecting the cerium oxide nanoparticles anchored on its surface and the conductive electrode layer in contact with them from excessive direct tensile stress, ensuring the high stability of the electro-optic and conductive functions under dynamic deformation.

[0043] Preferably, in the preparation process of the stretchable transparent electrode, the mass ratio of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide is 100:5-10:10-20:6:6.

[0044] The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion is 1-1.5%.

[0045] This invention also proposes a method for preparing an ultra-flexible stretchable dimming film, comprising the following steps:

[0046] (1) Preparation of the main matrix material / UV curing resin mixture: Mix the main matrix material, UV curing polyurethane acrylate resin, photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and dioctyl phthalate in the dark, and stir on a hot table at 45°C for 3 hours until a uniform and transparent main matrix material / UV curing resin mixture is formed.

[0047] (2) Assemble the dimming film: Take a stretchable transparent electrode with the conductive side facing up, lay the reinforcing fiber mesh in the center of the electrode, use a 60-100μm thick elastic spacer to control the film thickness, inject the main matrix material / UV curing resin mixture between the fiber mesh and the lower electrode, cover it with another stretchable transparent electrode with the conductive side facing down, apply slight pressure to ensure contact, and preliminarily seal the edges with UV curing adhesive to obtain the dimming film rough product;

[0048] The nano-sized CeO2 particles have a diameter of about 50nm, which is much smaller than the wavelength of visible light (400-760nm). According to the Mie scattering theory, when the particle size is much smaller than the wavelength of light, the light scattering effect is extremely weak and will not interfere with the propagation of visible light. Therefore, it will not reduce the transmittance under the power-on state.

[0049] Meanwhile, CeO2's core optical property is its absorption of ultraviolet light, exhibiting extremely low absorption coefficients in the visible light band. When energized, the transmittance of the dimming film depends on visible light propagation, but CeO2 does not absorb or block visible light. It only regulates the polymerization reaction rate and optimizes the polymer network structure by absorbing ultraviolet light, without interfering with the visible light transmission path. The key to the dimming film's transmittance after energization is the transformation of the host matrix material's molecules from disordered to ordered arrangement. Although nanoscale CeO2 affects the anchoring energy of the host matrix material through weak interactions, this influence only optimizes the driving voltage and response time, without hindering the ordered orientation of the host matrix material molecules under the electric field. Therefore, the core mechanism of light transmission remains intact, and the transmittance remains stable.

[0050] (3) UV curing: The assembled dimming film crude product is placed in the UV curing system. Under gentle heating and UV irradiation, the polyurethane acrylate resin undergoes cross-linking polymerization and phase separation from the main matrix material to form a stable composite film structure, namely an ultra-flexible stretchable dimming film.

[0051] Under ultraviolet light irradiation, the photoinitiator (phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide) decomposes to generate free radicals, which initiate the double bond (C=C) polymerization of polyurethane acrylate resin to form a three-dimensional cross-linked network. As the degree of polymerization of the resin increases, the compatibility with the main matrix material decreases, and phase separation occurs: the main matrix material is dispersed in the polymer matrix in the form of microdroplets, and the reinforcing fiber network is embedded in it to form a support structure.

[0052] Preferably, in step (1), the mass ratio of the main matrix material, UV-curable polyurethane acrylate resin, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and dioctyl phthalate is 55-60:30-35:1.5:3.5;

[0053] The main matrix material is a homogeneous mixture of microcrystalline media with more than 10 monomer molecular structures that are compatible at the molecular level.

[0054] Preferably, in step (2), the amount of reinforcing fiber web used is 0.5-2.0 mg / cm². 2 .

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] 1. Traditional methods involve directly physical doping nanoparticles (such as CeO2, BaTiO3, ITO) into polymer / matrix precursor materials. The mechanism relies on the random distribution of particles within the matrix. However, due to the extremely high surface energy of nanoparticles, they are highly prone to aggregation, forming large aggregates. This not only leads to a decrease in scattering efficiency but also creates stress concentration points during matrix deformation, causing particles to easily detach from the flexible polymer matrix, resulting in a sharp decline in performance.

[0057] This invention establishes a robust "Ce-OP" covalent bond interface between fibers and nanoparticles through surface modification with phosphonic acid groups. This achieves precise molecular-level positioning and fixation of nanoparticles on the fiber surface, fundamentally eliminating the possibility of particle migration and aggregation. The anchored CeO2 nanoparticles become permanent, efficient, and uniformly distributed scattering centers, continuously and stably providing extremely strong off-state scattering, ensuring high contrast (>150) without attenuation under repeated deformation. Because the particles are firmly fixed to the fiber skeleton, rather than dispersed in a deformable soft matrix, the nanoparticles will not detach during film bending and stretching, resulting in an order-of-magnitude improvement in the durability of electro-optical properties.

[0058] 2. Existing PDLCs or flexible PDLCs typically use materials of different properties, such as gelatin fibers / acrylic polymers or rigid fibers / elastomers. These materials have poor interfacial compatibility and modulus mismatch. Under mechanical stress, stress cannot be effectively transferred, leading to interfacial delamination between fibers / matrix and electrodes / matrix, thus causing device failure.

[0059] This invention employs a fully thermoplastic polyurethane system, comprising thermoplastic polyurethane fibers, a thermoplastic polyurethane matrix (UV-curable polyurethane acrylate), and a thermoplastic polyurethane electrode substrate. These components are chemically homologous or highly similar, forming a thermodynamically compatible and mechanically matched interface. Stress can be uniformly transferred and dissipated between the interfaces, avoiding stress concentration. Simultaneously, the components can deform synergistically, enabling the film as a whole to withstand tensile strain exceeding 50%, which is impossible to achieve with traditional techniques using rigid fibers or matrices. After repeated bending and stretching, the device exhibits no delamination or cracking, demonstrating an extremely long service life, making it particularly suitable for dynamic applications such as wearable devices.

[0060] 3. Existing technologies often improve one performance aspect by sacrificing another. For example, adding rigid nanoparticles improves contrast but sacrifices flexibility; using elastic substrates to achieve flexibility leads to increased driving voltage and slower response.

[0061] The "fiber-anchored nanoparticle" structure of this invention constitutes a multifunctional synergistic network. The fiber network provides structural strength and elasticity, while also anchoring the microdroplets of the host matrix material. This is optimized due to the flexibility of the thermoplastic polyurethane fiber, significantly shortening the turn-off response time while maintaining a low driving voltage. The nanoparticles provide stable and efficient light scattering, serving as haze enhancement centers. Utilizing the ultraviolet absorption characteristics of CeO2, the polymer network pore size is finely adjusted during curing, which also helps to optimize and moderately reduce the driving voltage. Based on the above, this invention successfully unifies high contrast (>150), fast response (turn-off time <30ms), low driving voltage (<30V), and ultra-flexible stretchability—performances that are difficult to achieve simultaneously in traditional technologies—into a single device, achieving a breakthrough in comprehensive performance.

[0062] This invention achieves covalent anchoring of cerium oxide nanoparticles on a thermoplastic polyurethane fiber network through surface phosphonic acid functionalization treatment; by constructing an all-thermoplastic polyurethane material system, a breakthrough in the interfacial compatibility between the fiber reinforcement phase and the polymer matrix is ​​achieved, enabling the film to maintain high transparency while possessing high tensile strain capacity and excellent fatigue resistance. Attached Figure Description

[0063] Figure 1 The 1H NMR spectrum of (3-triethoxysilylpropyl)phosphonic acid produced by this invention. Detailed Implementation

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and related figures. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0065] Preparation Example 1:

[0066] The preparation process of the reinforced fiber web includes the following steps:

[0067] a. Thermoplastic polyurethane particles are dissolved in a mixed solvent of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution, and thermoplastic polyurethane fiber web is obtained by electrospinning.

[0068] b. The thermoplastic polyurethane fiber web is subjected to oxygen plasma treatment to activate its surface;

[0069] c. Immerse the activated fiber web in an ethanol / water solution containing (3-triethoxysilylpropyl)phosphonic acid and react at a constant temperature of 50°C for 60 minutes to graft phosphonic acid groups onto its surface;

[0070] d. Immerse the grafted fiber web in a 0.6 mg / ml cerium oxide nanoparticle dispersion and shake at 50°C for 3 hours to anchor the cerium oxide nanoparticles to the fiber surface via phosphonic acid groups. After vacuum drying, the reinforced fiber web is obtained.

[0071] In the preparation of the reinforcing fiber web, in the mixed solvent of N,N-dimethylformamide and tetrahydrofuran, the volume ratio of N,N-dimethylformamide to tetrahydrofuran is 1:1; in the ethanol / water solution, the volume concentration of (3-triethoxysilylpropyl)phosphonic acid is 2%, and the volume ratio of ethanol to water is 95:5; the diameter of the reinforcing fiber web is controlled between 0.5-1.5 μm.

[0072] The (3-triethoxysilylpropyl)phosphonic acid is obtained by reacting 3-chloropropyltriethoxysilane with diethyl phosphite under anhydrous conditions with a catalyst to generate diethyl 3-triethoxysilylpropylphosphonic acid, followed by hydrolysis under acidic conditions to convert the diethyl phosphonate group into a phosphonic acid group.

[0073] The catalyst is an alkaline initiator, such as potassium tert-butoxide or sodium hydride, and is used at 1% of the reactant mass; the molar ratio of 3-chloropropyltriethoxysilane to diethyl phosphite is 1:1.2.

[0074] A portion of (3-triethoxysilylpropyl)phosphonic acid ((EtO)3Si-CH2CH2CH2-PO(OH)2) was dissolved in dimethyl sulfoxide and analyzed by 1H NMR spectroscopy. The results are as follows: Figure 1 As shown:

[0075] The target compound is (3-triethoxysilylpropyl)phosphonic acid, which contains three key hydrogen environments: the ethoxy hydrogen of the triethoxysilyl group has a chemical shift in the range of 3.5-4.2 ppm due to the electronegativity of oxygen. This group has three ethoxy groups, resulting in three sets of -CH2-O-, with a hydrogen atom count of 3*2=6. The peak shape is a quartet due to coupling with the adjacent -CH3 group. The methyl group of the ethyl group has a chemical shift in the range of 1.0-1.5 ppm. It has nine methyl hydrogens due to the three ethoxy groups. The peak shape is a triplet due to coupling with -CH2-O-. The methylene hydrogen of the middle carbon chain has different chemical shifts due to the different electronic effects of the carbon chain with electron-withdrawing phosphonic acid group -PO(OH)2 and silicon group (EtO)3Si-: the -CH2- group near the phosphonic acid group has a slightly higher chemical shift (-2.0-2.5 ppm) due to the electron-withdrawing effect of the phosphonic acid group; the -CH2- group in the middle and near the silicon group has a slightly lower chemical shift (-1.5-2.0 ppm). The peaks near 2.0-2.1 ppm in the spectrum correspond to the superimposed signals of these methylene hydrogens. The peak positions, peak shapes, and integrals of this ¹H NMR spectrum correspond one-to-one with the hydrogen atom environments of the target compound, verifying the correctness of the compound structure.

[0076] The fabrication process of the stretchable transparent electrode includes the following steps:

[0077] ① Mix poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide evenly to prepare composite electrode slurry;

[0078] ② The 125μm thick thermoplastic polyurethane film substrate is unidirectionally pre-stretched to a strain of 30%-50% and held.

[0079] ③ The substrate in the pre-stretched state is subjected to oxygen plasma treatment;

[0080] ④ The composite electrode paste is coated onto the treated substrate and dried on a hot table at 70°C for 30 minutes. The pre-stretching force is then released to form a stretchable transparent electrode with a micro-wrinkled structure. The electrode surface then forms a micro-wrinkled structure.

[0081] In the preparation of the stretchable transparent electrode, the mass ratio of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide is 100:10:10:6:6.

[0082] The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion is 1-1.5%.

[0083] Preparation Example 2:

[0084] The preparation method is the same as in Preparation Example 1, but in the preparation process of the stretchable transparent electrode, the mass ratio of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide is 100:8:15:6:6.

[0085] The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion is 1-1.5%.

[0086] Preparation Example 3:

[0087] The preparation method is the same as in Preparation Example 1, but in the preparation process of the stretchable transparent electrode, the mass ratio of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide is 100:5:20:6:6.

[0088] The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion is 1-1.5%.

[0089] Example 1:

[0090] A method for preparing an ultra-flexible stretchable dimming film includes the following steps:

[0091] (1) Preparation of the main matrix material / UV curing resin mixture: Mix the main matrix material, UV curing polyurethane acrylate resin, photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and dioctyl phthalate in the dark, and stir on a hot table at 45°C for 3 hours until a uniform and transparent main matrix material / UV curing resin mixture is formed.

[0092] (2) Assemble the dimming film: Take a stretchable transparent electrode with the conductive side facing up, lay the reinforcing fiber mesh in the center of the electrode, use an 80m thick elastic spacer to control the film thickness, inject the main matrix material / UV curing resin mixture between the fiber mesh and the lower electrode, cover it with another stretchable transparent electrode with the conductive side facing down, apply slight pressure to ensure contact, and preliminarily seal the edges with UV curing adhesive to obtain the dimming film rough product;

[0093] (3) UV curing: The assembled dimming film crude product is placed in the UV curing system. Under gentle heating and UV irradiation, the polyurethane acrylate resin undergoes cross-linking polymerization and phase separation from the main matrix material to form a stable composite film structure, namely an ultra-flexible stretchable dimming film.

[0094] Using the raw materials obtained in Preparation Example 3, in step (1), the mass ratio of the main matrix material, UV-curable polyurethane acrylate resin, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and dioctyl phthalate is 55:35:1.5:3.5.

[0095] The main matrix material is a homogeneous mixture of microcrystalline media with more than 10 monomer molecular structures that are compatible at the molecular level.

[0096] In step (2), the amount of reinforcing fiber web used is 2.0 mg / cm². 2 .

[0097] Example 2:

[0098] The preparation method is the same as in Example 1, but the raw materials obtained in Preparation Example 2 are used. In step (1), the mass ratio of the main matrix material, UV-curable polyurethane acrylate resin, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and dioctyl phthalate is 58:37:1.5:3.5.

[0099] The main matrix material is a homogeneous mixture of microcrystalline media with more than 10 monomer molecular structures that are compatible at the molecular level.

[0100] In step (2), the amount of reinforcing fiber web used is 1.5 mg / cm². 2 .

[0101] Example 3:

[0102] The preparation method is the same as in Example 1, but the raw materials obtained in Preparation Example 1 are used. In step (1), the mass ratio of the main matrix material, UV-curable polyurethane acrylate resin, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and dioctyl phthalate is 60:30:1.5:3.5.

[0103] The main matrix material is a homogeneous mixture of microcrystalline media with more than 10 monomer molecular structures that are compatible at the molecular level.

[0104] In step (2), the amount of reinforcing fiber web used is 0.5 mg / cm². 2 .

[0105] Based on this, the following design was also created:

[0106] Comparative Example 1: The formulation and experimental method were the same as those in Preparation Example 2, but no phosphonic acid groups were grafted onto the surface of the reinforcing fiber web;

[0107] Comparative Example 2: The formulation and experimental method were the same as those in Preparation Example 2, but cerium oxide nanoparticles were not added to the reinforcing fiber web;

[0108] Comparative Example 3: The formulation and experimental method were the same as those in Preparation Example 2, but colorless PI was used as the reinforcing fiber in the reinforcing fiber web;

[0109] Comparative Example 4: The formulation and experimental method were the same as in Example 2, but the amount of reinforcing fiber web used was 5 mg / cm². 2 .

[0110] For each embodiment and comparative example, the following standards were applied: GB / T 35847-2018 Electro-liquid crystal film dimming glass; GB / T 31370.5-2018 Flat panel display (FPD) color filter test method part 5: contrast ratio; GB / T 1040.3-2006 Plastics tensile properties determination part 3: test strips for thin plastics and sheets; ASTM D7791-12 Standard test method for uniaxial fatigue properties of plastics; The driving voltage (threshold voltage Vth, saturation voltage Vsat), contrast ratio (CR), response time (on-ton, off-toff), transmittance (on-state T-on, off-state T-off), maximum tensile strength, breaking strength, tensile cycle stability, etc. of the dimming film were tested. The corresponding results are shown in Table 1.

[0111] Table 1. Performance test data of the dimming film

[0112]

[0113] Data Analysis:

[0114] In the electrode paste, silver nanowires are primarily responsible for constructing a highly conductive percolation network, while waterborne polyurethane acts as an elastic matrix to buffer stress and prevent the silver nanowires from breaking under tension. PEDOT: PSS fills the voids and reduces contact resistance.

[0115] From Example 3 (electrode preparation example 1: 10 parts silver nanowires, 10 parts aqueous polyurethane) to Example 2 (electrode preparation example 2: 8 parts silver nanowires, 15 parts aqueous polyurethane), the rate of change in resistance was optimized from 21.3% to 15.6%. This indicates that appropriately reducing the amount of silver nanowires and significantly increasing the content of aqueous polyurethane greatly enhances the tensile stability and durability of the electrode. This is because a richer elastic matrix can more effectively protect the conductive network, which is entirely consistent with the stress buffering mechanism. The driving voltage and contrast of Example 1 (electrode preparation example 3: 5 parts silver nanowires, 20 parts aqueous polyurethane) decreased slightly, possibly because the silver nanowire content was close to the conductive percolation threshold, and the stability of the conductive network began to be affected.

[0116] The fiber web density directly determines the mechanical reinforcement effect, the total nanoparticle load, and the anchoring strength to the host matrix material. The host matrix material content, in turn, affects the size and density of the host matrix material droplets after phase separation.

[0117] Example 2 (fiber web 1.5 mg / cm) 2 The optimal overall performance was achieved with a matrix material content of 58% (144), the lowest off-state transmittance (2.8%), and excellent stability (contrast retention rate of 94.2%). At this ratio, the fiber network provides ample anchoring points and high scattering centers, while the 58% matrix material content likely forms matrix material droplets with the most ideal size and distribution, achieving an optimal balance between the refractive indices of the polymer and fibers in terms of "off-state scattering / on-state matching".

[0118] Example 3 (fiber web 0.5 mg / cm) 2 (Main matrix material 60%): The fiber network is too sparse, resulting in insufficient total nanoparticle loading and decreased off-state scattering ability (T-off increased to 3.5%), thus resulting in the lowest contrast (126). At the same time, the sparse network weakens the reinforcing effect on the matrix and the anchoring effect on the main matrix material, resulting in the lowest fracture strength (7.8 MPa) and maximum elongation (100%) in the examples.

[0119] Example 1 (fiber web 2.0 mg / cm) 2(Main matrix material 55%): The fiber web is too dense. Although the tensile strength is high, it may excessively block light, resulting in an open-state transmittance (86.3%) that is slightly lower than that of Example 2 (87.5%). Excessive anchoring may also cause a slight increase in the driving voltage.

[0120] The success of Examples 1, 2, and 3 demonstrates the adjustability and reliability of the present invention. The parameter combination for Example 2 (preparation of the electrode from Example 2 + 1.5 mg / cm³) 2 The combination of fiber web and 58% matrix material represents the optimal balance of mechanical, optical, and electrical properties.

[0121] The only difference between Comparative Example 1 and Example 2 is that no phosphonic acid groups are grafted onto the surface of the reinforcing fiber web.

[0122] In this invention (Example 2): Phosphonic acid groups and CeO2 are bonded together by strong Ce-OP covalent bonds, forming a molecular pinning effect.

[0123] Comparative Example 1: Cerium oxide nanoparticles are physically adsorbed onto the fiber surface only through weak van der Waals forces, resulting in extremely weak binding force.

[0124] The contrast ratio (92) of Comparative Example 1 was much lower than that of Example 2 (144), and the off-state transmittance (4.9%) was higher. This is because during the preparation and curing process, the unanchored nanoparticles are prone to agglomeration and detachment, making it impossible to form a uniform and efficient scattering layer on the fiber surface, resulting in a significant decrease in off-state scattering ability.

[0125] Catastrophic decline in stability: After 500 stretching cycles, the contrast retention rate of Comparative Example 1 was only 72.8%, while that of Example 2 was as high as 94.2%. This directly proves that physically adsorbed nanoparticles will detach in large quantities under continuous mechanical stress, thus causing the dimming function to deteriorate rapidly. The rate of change in resistance (32.4%) was also greater than that of Example 2 (15.6%), and the detached agglomerated particles may damage the electrode interface or create short circuits in the conductive path.

[0126] Comparative Example 1 shows that without chemical anchoring, the high performance and high stability of this invention would be impossible.

[0127] The only difference between Comparative Example 2 and Example 2 is that cerium oxide nanoparticles are not added.

[0128] This invention (Example 2): Cerium oxide has the dual functions of high refractive index (strong scattering) and ultraviolet absorption (regulating polymerization).

[0129] Comparative Example 2: Scattering and anchoring relying solely on fiber networks.

[0130] The contrast ratio of Comparative Example 2 (98) was significantly lower than that of Example 2 (144). This demonstrates that although the fiber network itself has a certain scattering ability, the cerium oxide nanoparticles, as high refractive index scattering centers, play an irreplaceable leading role in achieving extremely low off-state transmittance (high haze).

[0131] The driving voltage of Comparative Example 2 (Vth=16.2V, Vsat=48.5V) was higher than that of Example 2 (Vth=11.8V, Vsat=35.7V). This confirms the UV absorption regulation mechanism of cerium oxide. Without the UV shielding effect of cerium oxide, the polymerization reaction is faster and more complete, forming a denser polymer network with stronger anchoring ability for the microdroplets of the host matrix material, thus leading to an increase in driving voltage.

[0132] Comparative Example 2 demonstrates that cerium oxide nanoparticles are not only a haze enhancer but also a polymerization regulator, and the synergy between the two is the key to achieving high contrast and low driving voltage.

[0133] The only difference between Comparative Example 3 and Example 2 is that colorless PI (polyimide) was used as the reinforcing fiber.

[0134] This invention (Example 2): TPU fibers and TPU matrix form a homologous system with excellent interfacial compatibility, modulus matching, and synergistic deformation.

[0135] Comparative Example 3: PI is a rigid material with high modulus and high strength, but it has poor interfacial compatibility with the soft TPU matrix, resulting in a severe modulus mismatch.

[0136] The maximum elongation of Comparative Example 3 (110%) was much lower than that of Example 2 (150%). During stretching, the rigid PI fibers could not deform accordingly, resulting in huge shear stress at the fiber / matrix interface, leading to early interface failure and causing the film to fail as a whole at a lower strain.

[0137] The high driving voltage is likely due to the difference in interfacial energy between the PI fiber and the host matrix material, which affects droplet formation. More importantly, during cyclic stretching, the rigid PI fiber repeatedly punctures the surrounding soft matrix and electrodes, resulting in poor resistance change rate (42.6%) and contrast retention rate (80.1%).

[0138] Comparative Example 3 uses a negative example to demonstrate the irreplaceable nature of the all-TPU homologous system for achieving ultra-high elongation and dynamic stability.

[0139] The only difference between Comparative Example 4 and Example 2 is that the amount of reinforcing fiber web used is as high as 5.0 mg / cm². 2 .

[0140] This invention (Example 2): 1.5 mg / cm 2The areal density provides a moderate enhancement and functionalization.

[0141] Comparative Example 4: Excessive fiber density makes the composite material tend to be "over-reinforced".

[0142] The open-state transmittance of Comparative Example 4 (75.3%) dropped sharply because the overly dense fiber network caused severe light blocking and scattering.

[0143] Although it has the highest tensile strength (9.8 MPa), its maximum elongation (100%) is very low. The overly dense fiber network significantly restricts the deformation capability of the TPU matrix, making the material brittle. At the same time, the rigid fiber network is more likely to transfer stress directly to the electrodes during stretching, resulting in a lower resistivity change rate (29.7%) than in Example 2.

[0144] Comparative Example 4 shows that more fiber network is not necessarily better; there exists an optimal areal density window. Exceeding this window disrupts mechanical balance, sacrificing optical performance and dynamic stability, thus confirming the design principle of moderate reinforcement.

[0145] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An ultra-flexible stretchable dimming film, characterized in that, It includes an upper transparent electrode layer, a dimming function layer, and a lower transparent electrode layer, which are stacked sequentially from top to bottom; The dimming functional layer includes a polymer matrix, microdroplets of main matrix material dispersed in the polymer matrix, and a reinforcing fiber web embedded in the polymer matrix; The reinforcing fiber web is a thermoplastic polyurethane fiber web, and its surface is covalently anchored with cerium oxide nanoparticles through phosphonic acid groups. The polymer matrix is ​​a UV-curable polyurethane acrylate resin; Both the upper and lower transparent electrode layers are stretchable transparent electrodes used as conductive layers. The main matrix material is a homogeneous mixture of microcrystalline media with more than 10 monomer molecular structures that are compatible at the molecular level.

2. The ultra-flexible stretchable dimming film according to claim 1, characterized in that, The cerium oxide nanoparticles have a particle size of 40-60 nm; The conductive layer is a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate / silver nanowires / waterborne polyurethane composite conductive layer. The thickness of the dimming functional layer is 50-100 μm.

3. The ultra-flexible stretchable dimming film according to claim 1, characterized in that, The preparation process of the reinforced fiber web includes the following steps: a. Thermoplastic polyurethane particles are dissolved in a mixed solvent of N,N-dimethylformamide and tetrahydrofuran to prepare a spinning solution, and thermoplastic polyurethane fiber web is obtained by electrospinning. b. The thermoplastic polyurethane fiber web is subjected to oxygen plasma treatment to activate its surface; c. Immerse the activated fiber web in an ethanol / water solution containing (3-triethoxysilylpropyl)phosphonic acid and react at a constant temperature of 50°C for 60 minutes to graft phosphonic acid groups onto its surface; d. The grafted fiber web was immersed in a 0.6 mg / ml cerium oxide nanoparticle dispersion and shaken at 50°C for 3 hours to anchor the cerium oxide nanoparticles to the fiber surface through phosphonic acid groups. After vacuum drying, the reinforced fiber web was obtained. The (3-triethoxysilylpropyl)phosphonic acid is obtained by reacting 3-chloropropyltriethoxysilane with diethyl phosphite under anhydrous conditions with a catalyst to generate diethyl 3-triethoxysilylpropylphosphonic acid, followed by hydrolysis under acidic conditions to convert the diethyl phosphonate group into a phosphonic acid group. The catalyst is an alkaline initiator selected from potassium tert-butoxide, sodium hydride, lithium bis(trimethylsilyl)amino, sodium tert-butoxide, sodium amino, and sodium ethoxide, and is used in an amount of 0.5-1.5% of the reactant mass; the molar ratio of 3-chloropropyltriethoxysilane to diethyl phosphite is 1:1.

2.

4. The ultra-flexible stretchable dimming film according to claim 1, characterized in that, In the preparation of the reinforcing fiber web, in the mixed solvent of N,N-dimethylformamide and tetrahydrofuran, the volume ratio of N,N-dimethylformamide to tetrahydrofuran is 1:1; in the ethanol / water solution, the volume concentration of (3-triethoxysilylpropyl)phosphonic acid is 2%, and the volume ratio of ethanol to water is 95:5; the diameter of the reinforcing fiber web is controlled between 0.5-1.5 μm.

5. The ultra-flexible stretchable dimming film according to claim 1, characterized in that, The fabrication process of the stretchable transparent electrode includes the following steps: ① Mix poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide evenly to prepare composite electrode slurry; ② The 125μm thick thermoplastic polyurethane film substrate is unidirectionally pre-stretched to a strain of 30%-50% and held. ③ The substrate in the pre-stretched state is subjected to oxygen plasma treatment; ④ The composite electrode paste is coated onto the treated substrate and dried on a hot table at 70°C for 30 minutes. The pre-stretching force is then released to form a stretchable transparent electrode with a micro-wrinkled structure. The electrode surface then forms a micro-wrinkled structure.

6. The ultra-flexible stretchable dimming film according to claim 1, characterized in that, In the preparation process of the stretchable transparent electrode, the mass ratio of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion, silver nanowire dispersion, aqueous polyurethane dispersion, ethylene glycol and dimethyl sulfoxide is 100:5-10:10-20:6:

6. The solid content of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate aqueous dispersion is 1-1.5%.

7. A method for preparing an ultra-flexible stretchable dimming film according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of the main matrix material / UV curing resin mixture: Mix the main matrix material, UV curing polyurethane acrylate resin, photoinitiator phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and dioctyl phthalate in the dark, and stir on a hot table at 45°C for 3 hours until a uniform and transparent main matrix material / UV curing resin mixture is formed. (2) Assemble the dimming film: Take a stretchable transparent electrode with the conductive side facing up, lay the reinforcing fiber mesh in the center of the electrode, use a 60-100μm thick elastic spacer to control the film thickness, inject the main matrix material / UV curing resin mixture between the fiber mesh and the lower electrode, cover it with another stretchable transparent electrode with the conductive side facing down, apply slight pressure to ensure contact, and preliminarily seal the edges with UV curing adhesive to obtain the dimming film rough product; (3) UV curing: The assembled dimming film crude product is placed in the UV curing system. Under gentle heating and UV irradiation, the polyurethane acrylate resin undergoes cross-linking polymerization and phase separation from the main matrix material to form a stable composite film structure, namely an ultra-flexible stretchable dimming film.

8. The method for preparing an ultra-flexible stretchable dimming film according to claim 7, characterized in that, In step (1), the mass ratio of the main matrix material, UV-curable polyurethane acrylate resin, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and dioctyl phthalate is 55-60:30-35:1.5:3.

5.

9. The method for preparing an ultra-flexible stretchable dimming film according to claim 7, characterized in that, In step (2), the amount of reinforcing fiber web used is 0.5-2.0 mg / cm². 2 .

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