An ito-free pedot-based polymer dispersed liquid crystal dimming film and a preparation method thereof

Abstract

The application discloses an ITO-free PEDOT-based polymer dispersed liquid crystal dimming film and a preparation method thereof, and belongs to the technical field of dimming films.The dimming film comprises a first transparent substrate, a first composite transparent conductive layer, a polymer dispersed liquid crystal layer, a second composite transparent conductive layer and a second transparent substrate, and is a five-layer symmetrical stacking structure.The application uses a covalent bond / coordination bond / chain entanglement multi-level interface combination to greatly improve the peeling strength; through the cooperation of a molecular brush elastic buffer layer and a conductive polymer coating layer, stress is uniformly dissipated, and the dimming film is endowed with excellent bending resistance; by using a sulfonate group to secondarily dope PEDOT, point contact between AgNW and the conductive layer is converted into surface contact, node resistance is reduced, silver corrosion is delayed, low sheet resistance and high stability are realized; by means of uniform wetting of a high hydrophilic molecular brush interface and a limited phase separation effect, the size and distribution of liquid crystal droplets are optimized, the driving voltage is reduced, and the open-state light transmittance and contrast are improved.

Description

Technical Field

[0001] This invention relates to the field of dimming film technology, and in particular to an ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film and its preparation method. Background Technology

[0002] Polymer-dispersed liquid crystal (PDLC) dimming films are optoelectronic thin films that achieve switching between transparent and hazy states by controlling the orientation of liquid crystal microdroplets through an electric field. They are currently widely used in various applications such as architectural dimming, privacy protection, and automotive displays.

[0003] Currently, commercially available PDLC dimming films generally use indium tin oxide (ITO) as a transparent conductive electrode, but ITO electrodes have three inherent drawbacks: Indium resources are scarce, and its preparation relies on vacuum sputtering technology, resulting in high production costs. ITO is a brittle inorganic film that is prone to cracking and failure after bending, making it unsuitable for the current demand for flexible, foldable, and dimming technology. ITO has poor compatibility with organic substrates and liquid crystal layers, and is prone to interlayer delamination during long-term use.

[0004] To replace ITO electrodes and address the problems of existing technologies, silver nanowire (AgNW) / PEDOT:PSS composite conductive systems have become a mainstream research direction. This system combines high conductivity, high light transmittance, and the advantages of solution processing, but significant interfacial bottlenecks still exist. Firstly, the PET substrate has a strong inert surface and weak adhesion to AgNW and PEDOT:PSS, making it easy to fall off after bending or peeling off the tape. Secondly, the AgNW and PEDOT:PSS interface has high contact resistance, and the strong acidity of PEDOT:PSS will slowly corrode the silver nanowires, causing silver ion migration and shortening the device life. Third, the uniformity of coating of water-based PEDOT and AgNW dispersions on low surface energy PET surfaces is poor, and pinholes and color differences are prone to occur, affecting the yield of large-area dimming films.

[0005] Existing technologies mostly modify the PET surface through plasma treatment and coating with easy-to-apply layers. However, these are all physical modifications or weak hydrogen bonding, which are prone to failure under long-term humid and hot environments. Some studies have also improved adhesion by blending PEDOT:PSS, but this cannot simultaneously solve the problems of silver corrosion and contact resistance. Therefore, developing an ITO-free PDLC dimming film with stable interface, excellent performance, and mass production capability is an urgent need in the industry. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing an ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes an ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film, which has a five-layer symmetrical stacked structure, consisting of a first transparent substrate, a first composite transparent conductive layer, a polymer-dispersed liquid crystal layer, a second composite transparent conductive layer, and a second transparent substrate from bottom to top. The transparent substrate is a PET-co-SO3Na copolyester film, and an SH-PSS molecular brush is covalently grafted onto the side of the film facing the conductive layer. The composite transparent conductive layer is an ITO-free structure, composed of a silver nanowire network anchored to the surface of a molecular brush and a PEDOT:PSS conductive layer filling and covering the surface of the silver nanowires.

[0008] Preferably, the PET-co-SO3Na copolyester is prepared by using terephthalic acid, ethylene glycol, and sodium dimethyl isophthalate-5-sulfonate in a molar ratio of 100:100-105:1-3. Among them, terephthalic acid and ethylene glycol are the main monomers, and sodium dimethyl isophthalate-5-sulfonate (SIPM) is the third comonomer; The intrinsic viscosity of the PET-co-SO3Na copolyester is 0.70-0.80 dL / g, the thickness is 50-200 μm, the haze in the visible light band is <0.8%, and the bidirectional heat shrinkage rate at 150℃ for 30 min is <1.5%.

[0009] Preferably, the SH-PSS molecular brush is prepared by RAFT controlled polymerization: Using sodium p-styrenesulfonate as the polymerization monomer, 4-cyano-4-(thiobenzoyl)valerate (CTA) as the RAFT chain transfer agent, and azobisisobutyronitrile (AIBN) as the initiator, a molecular brush with a single-thiol end group was obtained by dissociating the RAFT end group with n-hexylamine amino groups. AIBN decomposes upon heating to generate isobutyronitrile radicals, which initiate the polymerization of sodium p-styrenesulfonate to form chain radicals Pn•. Pn• attacks the thiocarbonyl carbon (C=S) of CTA to form a radical intermediate. The intermediate rapidly undergoes β-cleavage, breaking the SR bond and releasing the •C(CH3)(CN)CH2CH2COOH radical, while simultaneously generating Pn-SC(=S)-Ph (dormant species). Hexylamine reacts with the thiocarbonyl carbon (C=S) in the dormant species to form a tetrahedral intermediate. Subsequently, a proton transfer occurs, generating a more stable intermediate state. After electron rearrangement, the SC (thiocarbonyl) bond at the polymer end breaks, releasing a polymer thiol anion. At the same time, a small thioamide molecule, N-hexylthiobenzamide, is generated. The thiol anion obtains a proton from the environment and transforms into a thiol group. The number-average molecular weight of the SH-PSS is 3000–10000 Da.

[0010] Preferably, the average grafting thickness of the SH-PSS molecular brush is 2-5 nm.

[0011] This invention also proposes a method for preparing the aforementioned ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film, comprising the following steps: S1, Preparation of PET-co-SO3Na copolyester film: A copolyester containing sulfonate is synthesized by direct esterification-polycondensation process, and optical grade PET-co-SO3Na film is obtained by hot pressing or biaxial stretching. Sulfonic acid groups are highly polar groups and will spontaneously migrate and accumulate to the surface of the film during the film formation process. S2. Covalent grafting of SH-PSS molecular brushes onto copolyester surface: First, the sulfonic acid groups on the surface of the PET-co-SO3Na film are activated to introduce allyl double bond functional groups. Then, through the mercapto-olefin UV click chemical reaction, SH-PSS is covalently grafted onto the substrate surface to obtain a transparent substrate. Preparation of S3, AgNW / PEDOT:PSS composite conductive layer: Silver nanowire dispersion and doped and modified PEDOT:PSS dispersion were sequentially coated on the surface of a transparent substrate, and then annealed to form a composite transparent electrode; S4, PDLC dimming film encapsulation: A polymer-dispersed liquid crystal mixture is sandwiched between two transparent substrates with transparent electrodes, and then subjected to ultraviolet light-induced phase separation and curing to obtain a five-layer PEDOT-based polymer-dispersed liquid crystal dimming film.

[0012] Preferably, step S2 specifically includes: S2.1 Protonation and Acyl Chlorination: The PET-co-SO3Na film is immersed in 0.5-2 mol / L dilute sulfuric acid and treated at room temperature for 1-4 h to convert the surface sodium sulfonate into sulfonic acid groups; after cleaning and drying, it is immersed in anhydrous dichloromethane solution containing 3-8 wt% thionyl chloride and catalyzed at 30-50 °C for 2-6 h to convert the sulfonic acid groups into sulfonyl chloride active groups; S2.2 Alkenylation modification: The acyl-chlorinated PET-co-SO3Na film is immersed in an anhydrous tetrahydrofuran solution containing 0.1-0.5 mol / L allylamine and 0.1-0.5 mol / L triethylamine, and reacted at -5-5℃ for 1-3 h or at room temperature for 8-16 h to introduce allyl double bonds through sulfonamide bonds; S2.3, Thiol-Alkyl Click Grafting: The alkenylated film is immersed in an aqueous solution containing 1–10 mg / mL SH-PSS and 0.1–1 mg / mL water-soluble photoinitiator, and grafted under nitrogen protection with 365 nm ultraviolet light and 10–20 mW / cm² light. 2 Irradiate for 5–20 minutes to complete covalent grafting; First, carbon-carbon double bonds are introduced into the substrate surface through the sulfonamide reaction of sulfonyl chloride-allylamine; then, SH-PSS with single-terminal thiol groups is covalently grafted onto the substrate surface through a UV-triggered thiol-alkene radical addition reaction.

[0013] At room temperature, the SH bond energy of a thiol group is about 370 kJ / mol, and the π bond of a common carbon-carbon double bond is also relatively stable. Neither of them can break the activation energy barrier of the reaction by molecular thermal motion alone, and cannot spontaneously break the SH bond to generate active sulfur free radicals. Introducing a water-soluble photoinitiator is a necessary design to ensure grafting efficiency.

[0014] The water-soluble photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone or lithium phenyl-2,4,6-trimethylbenzoylphosphonate (LAP).

[0015] Preferably, step S3 specifically includes: S3.1, AgNW network anchoring: 0.1-1 mg / mL silver nanowire isopropanol dispersion is coated onto the surface of a transparent substrate by spin coating or rod coating, and allowed to stand at room temperature for 0.5-2 h to complete coordination anchoring; the surface PVP coating layer is removed by methanol immersion for 20-60 s to optimize the node contact resistance and form an AgNW network. In the traditional AgNW / PEDOT system, the local concentration of free PSS sulfonic acid groups is high and they easily absorb water to form an acidic microenvironment, which slowly corrodes AgNW and subsequently triggers silver ion migration.

[0016] In this invention, the grafted PSS molecular brush is in a covalently anchored state, without local enrichment of free sulfonic acid groups; at the same time, the dense PEDOT coating layer and the molecular brush barrier work together to isolate water vapor and oxygen from entering the interface, which can significantly delay silver oxidation and ion migration, and greatly improve the resistance to damp heat aging.

[0017] S3.2 PEDOT:PSS Coating and Modification: Add 3-8 vol% dimethyl sulfoxide and 1-2 wt% p-toluenesulfonic acid (PTSA) to the PEDOT:PSS aqueous dispersion, stir evenly, coat it on the surface of AgNW network, and anneal at 120-140℃ for 10-15 min to form a dense composite conductive layer. The composite conductive layer has a sheet resistance of 30–80 Ω / □ and a transmittance of ≥87% at a wavelength of 550 nm.

[0018] PTSA doping and DMSO post-treatment can induce the PEDOT chain to change from the coiled benzene conformation to the extended quinone conformation, promote the phase separation of PEDOT and PSS, significantly improve carrier mobility and concentration, and thus improve bulk conductivity. Meanwhile, PEDOT fully fills the gaps in the AgNW network, forming a continuous three-dimensional conductive path of silver nanowire framework / PEDOT filling, effectively reducing the contact resistance of AgNW nodes and achieving a balance between low sheet resistance and high transmittance.

[0019] Preferably, in step S4, the polymer-dispersed liquid crystal mixture is a mixture of a photocurable prepolymer system and a nematic liquid crystal at a mass ratio of 35:65 to 45:55, with the addition of a benzophenone-based photoinitiator; spherical spacers with a diameter of 15 to 30 μm are used to control the thickness of the liquid crystal layer, and 365 nm ultraviolet light and 1 to 3 mW / cm² are used. 2 Phase separation and curing are completed by irradiation for 1–5 min; the resulting dimming film has a driving voltage of 12–18 VAC, an on-state transmittance of ≥60%, and a contrast ratio of ≥60:1. Preferably, the photocurable prepolymer system contains at least one polythiol compound and at least one acrylate oligomer; the polythiol compound is pentaerythritol tetra(3-mercaptopropionate) or trimethylolpropane tri(3-mercaptopropionate); the acrylate oligomer is polyurethane acrylate or epoxy acrylate.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. In the existing technology, AgNW networks mostly rely on van der Waals forces or weak hydrogen bonds to adhere to the PET substrate surface, which makes them very easy to fall off completely when repeatedly bent.

[0021] This invention first introduces allyl double bonds by reacting sulfonyl chloride with allylamine on the surface of a PET-co-SO3Na film to generate strong sulfonamide bonds. Then, by reacting mercapto groups with alkenes, SH-PSS molecular brushes are covalently grafted onto the substrate via carbon-sulfur bonds, forming an irreversible primary interface. Subsequently, through multi-point coordination of sulfonate groups with AgNW and interpenetrating entanglement of PSS chains with PEDOT:PSS molecular chains, a multi-level bonding system of covalent bonds / coordination bonds / chain entanglement is constructed. This increases the peel strength between the functional conductive layer and the substrate to several times that of existing physical coatings, solving the core engineering problem of conductive layer desorption failure in flexible devices under mechanical deformation.

[0022] 2. Due to the inherent properties of ceramics, traditional ITO electrodes can develop through-cracks and cause circuit breaks even at extremely small bending radii. Although conventional AgNW coatings have a certain degree of flexibility, repeated bending can cause the point contacts between nanowires and the weak bonding between nanowires and the substrate to slip and break due to stress concentration, resulting in a sharp increase in sheet resistance.

[0023] This invention constructs a unique composite system of a molecular brush elastic buffer layer and a conductive polymer flexible coating layer. The covalently grafted SH-PSS molecular brush can extend or compress with substrate deformation, absorbing and dispersing the stress transmitted to the AgNW network and preventing stress concentration. Simultaneously, the PEDOT:PSS layer filling and covering the AgNW network not only repairs the contact gaps between AgNW nodes but also encapsulates the AgNW within an integrated conductive polymer film, making the entire composite conductive layer seamless. During bending, stress is uniformly dissipated by the PEDOT:PSS continuous phase and the underlying molecular brush, preventing the silver nanowires from slipping or breaking. This achieves a dynamically bendable flexible transparent electrode with minimal sheet resistance change even after tens of thousands of bending cycles.

[0024] 3. In the preparation of ITO-free composite transparent conductive layers, AgNW serves as a long-range conductive framework. However, due to the presence of the insulating PVP coating layer and poor physical overlap, the contact resistance of its network nodes is often very high. Furthermore, exposed AgNW is easily oxidized by the environment during subsequent use.

[0025] This invention, after removing PVP through methanol impregnation, utilizes the thiol groups at the ends of molecular brushes to selectively coordinate and anchor the clean silver surface, anchoring the AgNW network to the substrate surface. This prevents AgNW re-slippage, aggregation, or scouring and desorption that may occur during subsequent coating of PEDOT:PSS aqueous dispersion. Furthermore, the abundant sulfonate groups on the molecular brush framework serve as secondary dopants and anchoring sites for PEDOT, inducing preferential enrichment of PEDOT:PSS around the AgNW network and the formation of a dense coating. This not only fills the contact gaps between AgNW nodes, transforming point contacts into surface contacts and significantly reducing node resistance, but also seals the silver nanowires, greatly delaying the electrochemical oxidation and sulfur chemical corrosion of silver. This results in a significant reduction in the sheet resistance of the composite conductive layer and extremely high spatiotemporal stability.

[0026] 4. In the UV curing and encapsulation stage of PDLC dimming film, the initial spreading state and phase separation kinetics of the prepolymer / liquid crystal mixture on the electrode substrate directly determine the size and distribution of liquid crystal droplets, thus affecting electro-optical performance. Conventional PET or substrates that have only undergone corona treatment have low and uneven surface energy, which easily leads to poor wetting of the mixture, resulting in macroscopic thickness unevenness and microscopic structural defects. After curing, the liquid crystal domain size is dispersed, resulting in high driving voltage of the dimming film and severe light leakage in the off-state.

[0027] In this invention, the substrate surface after covalently grafting SH-PSS molecular brushes exhibits high hydrophilicity, enabling the high-viscosity UV-curable prepolymer / liquid crystal mixture to spread uniformly. This ensures that the liquid crystal layer thickness is controlled by spherical spacers, achieving macroscopic uniformity. During UV irradiation phase separation, the interface of this hydrophilic molecular brush exhibits thermodynamic compatibility with the polymer matrix in phase separation, tending to accumulate on the polymer wall, forming an interface confinement effect. This promotes the miniaturization and monodispersity of liquid crystal microdroplets and enhances anchoring strength, thereby resulting in more uniform liquid crystal domain sizes, reduced driving voltage, and decreased open-state transmittance.

[0028] In summary, this invention significantly improves peel strength through multi-level interfacial bonding of covalent bonds, coordination bonds, and chain entanglements; the synergistic effect of the elastic buffer layer formed by the molecular brush and the coating layer formed by the conductive polymer uniformly dissipates stress, giving the dimming film excellent bending resistance; by utilizing the secondary doping of PEDOT with sulfonate groups, the point contact between AgNW and the conductive layer is transformed into a surface contact, reducing node resistance, delaying the silver corrosion process, and achieving low sheet resistance and high stability; and by leveraging the uniform wetting and confined phase separation effect of the highly hydrophilic molecular brush interface, the size and distribution of liquid crystal microdroplets are optimized, reducing the driving voltage and improving the open-state transmittance and contrast. Attached Figure Description

[0029] Figure 1 This is a partial structural schematic diagram of the dimming film of the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example 1: A PET-co-SO3Na copolyester modified with 2 mol% SIPM was used as the substrate. Terephthalic acid and ethylene glycol were the main monomers, with sodium dimethyl isophthalate-5-sulfonate (2% of the molar amount of terephthalic acid) added as the third monomer. The copolyester with an intrinsic viscosity of 0.75 dL / g was synthesized via direct esterification-polymerization and hot-pressed into a 125 μm thick optical-grade film. Subsequently, the film underwent surface sulfonyl chloride treatment and allylamine grafting to introduce double bonds. Then, SH-PSS molecular brushes with a number-average molecular weight of 5 kDa were grafted using a mercapto-olefin UV-Vis click chemistry, achieving a mercapto end-group functionalization rate of 88%. A silver nanowire isopropanol dispersion and a PEDOT:PSS dispersion doped with 5 vol% DMSO and 1.25 wt% p-toluenesulfonic acid were sequentially spin-coated onto the modified substrate surface, followed by annealing at 130 °C to form a composite conductive layer. Finally, a mixture of NOA65 UV-curable prepolymer and E7 nematic liquid crystal at a mass ratio of 4:6 was prepared, and the layer thickness was controlled by 20μm spherical spacers. The mixture was then cured by 365nm UV-induced phase separation and encapsulated into a complete PDLC dimming film.

[0032] Example 2: The overall preparation process is completely consistent with that of Example 1, except that the amount of the third monomer SIPM added is adjusted to 1% of the molar amount of terephthalic acid, and the target number-average molecular weight of SH-PSS is adjusted to 3kDa.

[0033] Example 3: The overall preparation process is completely consistent with that of Example 1, except that the amount of the third monomer SIPM added is adjusted to 3% of the molar amount of terephthalic acid, and the target number-average molecular weight of SH-PSS is adjusted to 10 kDa.

[0034] The following comparison model was also set: Comparative Example 1 (Commercial ITO-PET Benchmark Group): A commercially available 125μm thick conventional ITO-coated PET film was used as the conductive substrate, with an initial sheet resistance of 15Ω / □. The dimming film was prepared directly using the same PDLC formulation and encapsulation process as in Example 1.

[0035] Comparative Example 2 (Pure PEDOT without ITO base group): Using an unmodified ordinary 125μm optical grade PET film as the substrate, after only 30s of oxygen plasma surface treatment to improve wettability, a PEDOT:PSS conductive layer with the same formulation as in the example was directly spin-coated, without silver nanowire network, and the rest of the encapsulation process was the same as in Example 1.

[0036] Comparative Example 3 (Existing mainstream non-ITO benchmark group): Using an unmodified ordinary 125μm optical grade PET film as the substrate, after oxygen plasma surface treatment for 30s, silver nanowire dispersion and PEDOT:PSS conductive layer of the same batch as in Example 1 were sequentially spin-coated. The remaining encapsulation process was the same as in Example 1.

[0037] Comparative Example 4 (Physically Coated PSS Modified Group): Using an unmodified ordinary 125μm optical grade PET film as a substrate, a 1mg / mL sodium polystyrene sulfonate aqueous solution was first spin-coated and dried at 100℃ to form a physically adsorbed PSS coating. Then, silver nanowires and a PEDOT:PSS conductive layer were sequentially coated. The remaining encapsulation process was the same as in Example 1.

[0038] Performance testing: Table 1. Summary of data detection for each experimental group Data Analysis: By comparing Example 1 and Comparative Example 1, it can be seen that the initial driving voltages of the two are 16VAC and 15VAC, respectively, and the initial contrast ratios are 61:1 and 92:1, respectively. Their electro-optical performance is at the same level as that of commercial applications. Although the ITO electrode has a lower initial sheet resistance (15Ω / □) and better damp heat stability, its ceramic nature results in extremely poor bending resistance: after 1000 bends, the sheet resistance change rate of the ITO electrode is as high as 46.2%, and the contrast ratio retention rate of the PDLC is only 51.3%, which basically results in the loss of usability. In contrast, the sheet resistance change rate of the dimming film of the present invention is only 12.3%, and the contrast ratio retention rate reaches 86.2%, which can be adapted to scenarios that ITO cannot cover, such as flexible and foldable, curved dimming.

[0039] A comparison between Example 1 and Comparative Example 2 reveals that the introduction of the AgNW conductive framework significantly improves electrode conductivity and device driving performance. The initial sheet resistance of the pure PEDOT electrode is as high as 218 Ω / □, corresponding to a PDLC driving voltage of 24 VAC. After introducing AgNW to form a composite electrode, the initial sheet resistance can be reduced to 42 Ω / □, and the driving voltage can be reduced to 16 VAC, meeting the requirements for large-scale commercial applications. Simultaneously, the silver nanowire framework / PEDOT-filled structure significantly improves bending stability. After 1000 bends, the dimming film obtained in Comparative Example 4 shows an electrode sheet resistance change rate of only 27.5% and a contrast retention rate of only 64.7%.

[0040] A comparison between Example 1 and Comparative Example 3 reveals that their initial sheet resistance (42Ω / □ vs 48Ω / □) and initial contrast ratio (61:1 vs 62:1) are similar, indicating comparable initial conductivity and optical performance. However, after 1000 bends, Comparative Example 3, activated solely by plasma, exhibits a sheet resistance change rate of 19.8% and a contrast ratio retention rate of only 71.5%. In contrast, this invention, through multi-level interface bonding using molecular brushes, reduces the sheet resistance change rate to 12.3% and increases the contrast ratio retention rate to 86.2%. Furthermore, the on-state reflectance of the film layer in this invention is only 13.3%, significantly lower than the 21.7% of Comparative Example 3. This indicates that the electrode coating is more uniform after molecular brush modification, significantly reducing interface scattering defects and preventing issues such as color difference and localized light leakage in the dimming film.

[0041] A comparison of Example 1 and Comparative Example 4 revealed that their initial performance was similar, and physically coated PSS could temporarily improve electrode wettability and initial adhesion. However, after 1000 bends, the sheet resistance change rate of the physically coated system reached 17.2%, and the contrast retention rate was only 75.8%, both weaker than the covalently grafted system. Physically adsorbed PSS adheres solely through van der Waals forces, making it prone to interlayer slippage and desorption during bending, leading to AgNW network displacement and breakage. In contrast, the covalently grafted molecular brush is anchored to the substrate via CS bonds, achieving long-term stable anchoring of the conductive layer. Under 100h damp heat testing, the sheet resistance increase rates of both systems were on the same order of magnitude, but the covalently grafted system did not have the long-term swelling and detachment failure risk of the physically coated system, making it more suitable for the application requirements of long-life dimming films.

[0042] In summary, this invention significantly improves flexible bending stability and interface reliability while maintaining photoelectric performance levels, and can basically replace ITO electrodes.

[0043] 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. A PEDOT-based polymer-dispersed liquid crystal dimming film without ITO, characterized in that, It has a five-layer symmetrical stacked structure, which, from bottom to top, consists of a first transparent substrate, a first composite transparent conductive layer, a polymer-dispersed liquid crystal layer, a second composite transparent conductive layer, and a second transparent substrate; The transparent substrate is a PET-co-SO3Na copolyester film, and an SH-PSS molecular brush is covalently grafted onto the side of the film facing the conductive layer. The composite transparent conductive layer is an ITO-free structure, composed of a silver nanowire network anchored to the surface of a molecular brush and a PEDOT:PSS conductive layer filling and covering the surface of the silver nanowires.

2. The ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film according to claim 1, characterized in that, The PET-co-SO3Na copolyester was prepared by using terephthalic acid, ethylene glycol, and sodium dimethyl isophthalate-5-sulfonate in a molar ratio of 100:100-105:1-3. The intrinsic viscosity of the PET-co-SO3Na copolyester is 0.70-0.80 dL / g, the thickness is 50-200 μm, the haze in the visible light band is <0.8%, and the bidirectional heat shrinkage rate at 150℃ for 30 min is <1.5%.

3. The ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film according to claim 1, characterized in that, The SH-PSS molecular brush was prepared by RAFT controlled polymerization. Using sodium p-styrenesulfonate as the polymerization monomer, 4-cyano-4-(thiobenzoyl)valerate as the RAFT chain transfer agent, and azobisisobutyronitrile as the initiator, SH-PSS molecular brushes with single-thiol end groups were obtained by dissociating the RAFT end groups of hexylamine amino groups. The number-average molecular weight of the SH-PSS is 3000–10000 Da.

4. The ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film according to claim 1, characterized in that, The average grafting thickness of the SH-PSS molecular brush is 2–5 nm.

5. A method for preparing an ITO-free PEDOT-based polymer-dispersed liquid crystal dimming film as described in any one of claims 1-4, characterized in that, Includes the following steps: S1, Preparation of PET-co-SO3Na copolyester film: A copolyester containing sulfonate is synthesized by direct esterification-polycondensation process, and optical grade PET-co-SO3Na film is obtained by hot pressing or biaxial stretching. S2. Covalent grafting of SH-PSS molecular brushes onto copolyester surface: First, the sulfonic acid groups on the surface of the PET-co-SO3Na film are activated to introduce allyl double bond functional groups. Then, through the mercapto-olefin UV click chemical reaction, SH-PSS is covalently grafted onto the substrate surface to obtain a transparent substrate. Preparation of S3, AgNW / PEDOT:PSS composite conductive layer: Silver nanowire dispersion and doped and modified PEDOT:PSS dispersion were sequentially coated on the surface of a transparent substrate, and then annealed to form a composite transparent electrode; S4, PDLC dimming film encapsulation: A polymer-dispersed liquid crystal mixture is sandwiched between two transparent substrates with transparent electrodes, and then subjected to ultraviolet light-induced phase separation and curing to obtain a five-layer PEDOT-based polymer-dispersed liquid crystal dimming film.

6. The preparation method according to claim 5, characterized in that, Step S2 specifically includes: S2.1 Protonation and Acyl Chlorination: The PET-co-SO3Na film is immersed in 0.5-2 mol / L dilute sulfuric acid and treated at room temperature for 1-4 h to convert the surface sodium sulfonate into sulfonic acid groups; after cleaning and drying, it is immersed in anhydrous dichloromethane solution containing 3-8 wt% thionyl chloride and catalyzed at 30-50 °C for 2-6 h to convert the sulfonic acid groups into sulfonyl chloride active groups; S2.2 Alkenylation modification: The acyl-chlorinated PET-co-SO3Na film is immersed in an anhydrous tetrahydrofuran solution containing 0.1-0.5 mol / L allylamine and 0.1-0.5 mol / L triethylamine, and reacted at -5-5℃ for 1-3 h or at room temperature for 8-16 h to introduce allyl double bonds through sulfonamide bonds; S2.3, Thiol-Alkyl Click Grafting: The alkenylated film is immersed in an aqueous solution containing 1–10 mg / mL SH-PSS and 0.1–1 mg / mL water-soluble photoinitiator, and grafted under nitrogen protection with 365 nm ultraviolet light and 10–20 mW / cm² light. 2 Irradiate for 5–20 minutes to complete covalent grafting; The water-soluble photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone or lithium phenyl-2,4,6-trimethylbenzoylphosphonate.

7. The preparation method according to claim 5, characterized in that, Step S3 specifically includes: S3.1, AgNW network anchoring: A 0.1-1 mg / mL silver nanowire isopropanol dispersion was coated onto a transparent substrate by spin coating or rod coating and allowed to stand at room temperature for 0.5-2 h to complete the coordination and anchoring of the silver nanowires; then, the substrate was immersed in methanol for 20-60 s to remove the PVP coating layer on the surface of the silver nanowires, forming an AgNW network; S3.2 PEDOT:PSS Coating and Modification: Add 3-8 vol% dimethyl sulfoxide and 1-2 wt% p-toluenesulfonic acid to the PEDOT:PSS aqueous dispersion, stir evenly, and then coat it onto the surface of the AgNW network. Anneal at 120-140℃ for 10-15 min to form a dense composite conductive layer. The composite conductive layer has a sheet resistance of 30–80 Ω / □ and a transmittance of ≥87% at a wavelength of 550 nm.

8. The preparation method according to claim 5, characterized in that, In step S4, the polymer-dispersed liquid crystal mixture is made by mixing a photocurable prepolymer system with a nematic liquid crystal at a mass ratio of 35:65 to 45:55, and adding a benzophenone-based photoinitiator; the thickness of the liquid crystal layer is controlled by using spherical spacers with a diameter of 15 to 30 μm, and the liquid crystal layer is exposed to 365 nm ultraviolet light at 1 to 3 mW / cm². 2 Phase separation and curing are completed by irradiation for 1 to 5 minutes; the resulting dimming film has a driving voltage of 12 to 18 VAC, an on-state transmittance of ≥60%, and a contrast ratio of ≥60:

1.

9. The preparation method according to claim 8, characterized in that, The photocurable prepolymer system contains at least one polythiol compound and at least one acrylate oligomer; the polythiol compound is pentaerythritol tetra(3-mercaptopropionate) or trimethylolpropane tri(3-mercaptopropionate); the acrylate oligomer is polyurethane acrylate or epoxy acrylate.

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