Liquid crystal / polymer composite, method for preparing the same, light control film comprising the same, and use thereof

Abstract

The application relates to the technical field of functional liquid crystal materials, and discloses a liquid crystal / polymer composite material, a preparation method thereof, a light-adjusting film and application. The composite material comprises a polymer network skeleton and liquid crystal molecules dispersed in the polymer network skeleton; wherein the liquid crystal molecules have the structure shown in formula I. Liquid crystal molecules, polymerizable monomers, an initiator and spacer particles are mixed to obtain a prepolymer; the obtained prepolymer is solidified through heating or light irradiation to obtain the liquid crystal / polymer composite material. The application also provides a light-adjusting film containing the composite material and application in energy saving of automobiles and buildings. Compared with the prior art, the liquid crystal / polymer composite material provided by the application has greater refrigeration power at the same temperature, has greater potential in energy saving and temperature control, has good mechanical strength, has the ability of large-scale manufacturing, and can be used for manufacturing large-area flexible films.

Description

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202410471763.8, filed on April 19, 2024, entitled "Liquid Crystal / Polymer Composite Material and Preparation Method Thereof, Dimming Film Including the Same and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of functional liquid crystal materials technology, specifically to a liquid crystal / polymer composite material and its preparation method, a dimming film containing the same, and its applications. Background Technology

[0004] With the overuse of fossil fuels, humanity faces a severe energy shortage and the crisis of global warming, threatening the sustainable development of human society. Globally, buildings consume 40% of the world's energy, and windows are among the least energy-efficient components, accounting for approximately 60% of a building's energy consumption and loss.

[0005] Thermal radiation fundamentally arises from random energy level transitions in matter, indicating that objects at any finite temperature can intrinsically emit heat. The universe has temperatures close to absolute zero, and objects on Earth can dissipate heat into outer space via electromagnetic waves, achieving radiative cooling. Radiative cooling achieves cooling without any additional energy input. The atmosphere, existing between the Earth's surface and space, is a complex mixture of various gases. The atmosphere's low transmittance weakens the effect of cosmic thermal radiation on the Earth's surface across most wavelengths. Only within the atmospheric window of 8-13 μm is the atmosphere highly transparent to thermal radiation. This atmospheric window coincides with the peak wavelength of thermal radiation from Earth's objects at typical ambient temperatures (around 25°C). Therefore, any ground object with high emissivity within this atmospheric window can lower its temperature by radiating heat into outer space.

[0006] Liquid crystal / polymer composites are among the most promising building energy-saving materials. By endowing these composites with radiative cooling capabilities, their energy-saving effects can be further enhanced, which is of significant practical importance for achieving efficient energy conservation in automobiles and buildings. However, existing liquid crystal / polymer composites are not well-suited for radiative cooling.

[0007] Therefore, there is an urgent need to develop a liquid crystal / polymer composite material with radiation cooling function. Summary of the Invention

[0008] The present application aims to overcome the problems existing in the prior art, and provides a liquid crystal / polymer composite material with stable radiation refrigeration function, a light control film containing the same, and a preparation method and application thereof.

[0009] The liquid crystal / polymer composite material provided by the present application has a total infrared emissivity of not less than 90% at an ambient temperature of 20-70℃ in an atmospheric window, and thus has a radiation refrigeration effect.

[0010] To achieve the above-mentioned purpose, the present application provides a liquid crystal / polymer composite material in a first aspect, wherein the composite material comprises a polymer network skeleton and liquid crystal molecules dispersed in the interior of the polymer network skeleton.

[0011] The liquid crystal molecules have a structure as shown in Formula I:

[0012]

[0013] R1 is selected from C1-C 16 alkyl, C1-C 16 alkoxy or C1-C 16 siloxane group;

[0014] Y and Z are each independently selected from an ester bond, C1-C4 alkylene, an ether bond or a single bond;

[0015] The ring X is independently selected from the following structures:

[0016]

[0017] When the number of rings X in Formula I is two or more, the rings of each structure are connected through C1-C4 alkylene, an ether bond, an ester bond or a single bond;

[0018] R2 is selected from one of the following structures:

[0019]

[0020] m is a positive integer of 1-8; and n is a positive integer of 0-16.

[0021] The present application provides a preparation method of the composite material according to the first aspect in a second aspect, wherein the method comprises the following steps:

[0022] (1) mixing liquid crystal molecules, polymerizable monomers, initiators and spacer particles to obtain a prepolymer;

[0023] (2) curing the prepolymer obtained in step (1) by heating or light irradiation to obtain a liquid crystal / polymer composite material.

[0024] The third aspect of the present application provides a light-adjusting film comprising the composite material of the first aspect or the composite material obtained by the preparation method of the second aspect. The liquid crystal / polymer composite material provided by the present application can realize reversible switching between light scattering state and transparent state under the control of electric field or temperature, and can be used as a light-adjusting film, and has a radiation refrigeration effect.

[0025] The fourth aspect of the present application provides application of the liquid crystal / polymer composite material of the first aspect or the light-adjusting film of the third aspect in energy saving of automobiles and buildings.

[0026] Through the above technical solution, the present application has the following beneficial technical effects:

[0027] (1) The liquid crystal / polymer composite material provided by the present application has an infrared emissivity of more than 90% for an 8-13 μm atmospheric window in a temperature range of 20-70℃, and has stable radiation refrigeration capacity;

[0028] (2) Compared with the prior art, the liquid crystal / polymer composite material provided by the present application has greater refrigeration power at the same temperature, has greater potential in energy saving and temperature control, has good mechanical strength, and has the ability of large-scale manufacturing, and can manufacture large-area flexible films. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a morphology diagram of the polymer network skeleton in the light-adjusting film prepared in Example 1 of the present application;

[0030] Figure 2 is a morphology diagram of the polymer network skeleton in the light-adjusting film prepared in Example 2 of the present application;

[0031] Figure 3 is a near-infrared absorption spectrum of the liquid crystal molecule used in Example 1 of the present application;

[0032] Figure 4 is a near-infrared absorption spectrum of the liquid crystal molecule used in Comparative Example 1 of the present application;

[0033] Figure 5 is the ultraviolet-visible-near-infrared light transmittance of the light-adjusting film prepared in Example 1 of the present application;

[0034] Figure 6 is the infrared light emissivity curve of 8-13 μm of the light-adjusting film prepared in Example 1 of the present application;

[0035] Figure 7 is the infrared light emissivity curve of 8-13 μm of the light-adjusting film prepared in Example 2 of the present application;

[0036] Figure 8This is the infrared emissivity curve of the dimming film prepared in Example 3 of the present invention at 8-13 μm.

[0037] Figure 9 This is the infrared emissivity curve of the dimming film prepared in Example 4 of this invention at 8-13 μm.

[0038] Figure 10 This is the infrared emissivity curve of the dimming film at 8-13 μm prepared in Comparative Example 1 of this invention;

[0039] Figure 11 This is the infrared emissivity curve of the dimming film at 8-13 μm prepared in Comparative Example 2 of this invention;

[0040] Figure 12 This refers to the light transmittance of the dimming film prepared in Example 2 of the present invention when an electric field is applied and when no electric field is applied;

[0041] Figure 13 The light transmittance of the dimming film prepared in Example 3 of the present invention is the light transmittance when no electric field is applied and when a 100V 50Hz AC electric field is applied.

[0042] Figure 14 This refers to Embodiment 1 of the present invention and the PET film at 800W / m 2 Comparison curves of temperature changes under simulated sunlight conditions. Detailed Implementation

[0043] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0044] The first aspect of the present invention provides a liquid crystal / polymer composite material, wherein the composite material comprises a polymer network framework and liquid crystal molecules dispersed within the polymer network framework;

[0045] The liquid crystal molecules have the structure described in Formula I:

[0046]

[0047] Among them, R1 is selected from C1-C 16 Alkyl, C1-C 16 Alkoxy or C1-C 16 Siloxane;

[0048] Y and Z are each independently selected from ester bonds, C1-C4 alkylene bonds, ether bonds, or single bonds;

[0049] Ring X is independently selected from the following structures:

[0050]

[0051] When the number of ring X in formula I is more than two, the rings of each structure are connected with each other by C1-C4 alkylene, ether bond, ester bond or single bond;

[0052] R2 is selected from one of the following structures:

[0053]

[0054] m is a positive integer from 1 to 8; n is a positive integer from 0 to 16.

[0055] wherein, C1-C 16 Alkyl refers to an alkyl group containing 1-16 carbon atoms, and the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16.

[0056] C1-C 16 Alkoxy refers to an alkoxy group containing 1-16 carbon atoms, and the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16.

[0057] C1-C 16 Siloxane group refers to a siloxane group containing 1-16 carbon atoms, and the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16.

[0058] The value of m can be 1, 2, 3, 4, 5, 6, 7, 8; the value of n can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, preferably m is a positive integer from 2 to 8.

[0059] In formula I, ring X is a ring structure, such as a six-membered ring, a condensed ring, etc. m refers to the total number of X (liquid crystal rigid structure). Please note that the structure shown in formula I is a liquid crystal molecule, which is not a high molecular compound (the relative molecular mass can reach 10 4 -10 7 ), m is not the degree of polymerization (the number of repeating structural units).

[0060] For example, when m is 2, there are two rings; the two groups represented by the two rings can be the same or different. When the two rings are the same group or different groups, they can be connected by C1-C4 alkylene, ether bond, ester bond or single bond. The group refers to the various cyclic structures listed above (the type of ring X).

[0061] The present application improves the radiation cooling properties of liquid crystal / polymer composite materials containing liquid crystal molecules by creatively designing the structure of the liquid crystal molecules, and the infrared emissivity in the atmospheric window (8-13 μm) is greater than 90% at 20-70°C. The liquid crystal molecules are rod-like thermotropic liquid crystals with a liquid crystal phase temperature range covering room temperature. In practical applications, a plurality of liquid crystal molecules falling into formula I are usually selected and mixed as raw materials for preparing liquid crystal / polymer composite materials.

[0062] In some embodiments of the present application, the liquid crystal molecules are selected from at least one of a first component, a second component and a third component;

[0063] wherein the first component is selected from at least one of a compound of formula (1-a) and a compound of formula (1-b):

[0064]

[0065] wherein Ra is C3-C7 alkyl; Rb is C2-C6 alkyl;

[0066] R is selected from one of the following structures:

[0067]

[0068] The second component is selected from at least one of a compound of formula (2-c):

[0069]

[0070] wherein Rc is C2-C4 alkyl; Rd is C3-C5 alkyl;

[0071] The third component is selected from at least one of a compound of formula (3-d):

[0072]

[0073] wherein Re is a group represented by R1-Y; Rf is a group represented by R2-Z.

[0074] wherein C3-C7 alkyl refers to an alkyl group containing 3-7 carbon atoms, and the number of carbon atoms can be 3, 4, 5, 6, 7; C2-C6 alkyl refers to an alkyl group containing 2-6 carbon atoms, and the number of carbon atoms can be 2, 3, 4, 5, 6;

[0075] C2-C4alkyl means an alkyl group containing 2 to 4 carbon atoms, the number of carbon atoms can be 2, 3, 4;

[0076] C3-C5alkyl means an alkyl group containing 3 to 5 carbon atoms, the number of carbon atoms can be 3, 4, 5.

[0077] Each of the compounds of the first component, the second component and the third component falls within the scope of Formula I. For example, when phenylene and cyclohexylene (connected by a single bond) are selected, m is 2, and Formula (1-b) is obtained.

[0078] In some embodiments of the present application, the liquid crystal molecules comprise, by weight percentage, 25-60% of the first component, 5-30% of the second component and 20-45% of the third component. In the present application, the above-mentioned liquid crystal molecules are stable and do not produce adverse results of phase separation caused by long-term storage, and in addition, the birefringence is greater, and the contrast of the corresponding temperature control, electric control composite is higher.

[0079] In some embodiments of the present application, the liquid crystal molecules are selected from at least one of the following structures:

[0080]

[0081] In some embodiments of the present application, the liquid crystal molecules comprise the above six components, and the weight percentages are 26%, 13%, 12%, 6%, 40%, and 3%, respectively. In some embodiments of the present application, the liquid crystal molecules are selected from at least one of the following: trans, trans-4'-propyl-4-(3,4,5-trifluorophenyl) bicyclohexane, 5-4-(3,4-difluorophenyl)-4'-propyl-1,1'-bis(cyclohexane), (trans, trans)-4-ethyl-4'-propyl bicyclohexyl alkane and (trans, trans)-4-propyl-4'-butyl-1,1'-bicyclohexane.

[0082] In some embodiments of the present application, the liquid crystal molecules comprise, by weight percentage, 18.75% of (trans, trans)-4-ethyl-4'-propyl bicyclohexyl alkane, 50% of 5-4-(3,4-difluorophenyl)-4'-propyl-1,1'-bis(cyclohexane), 25% of trans, trans-4'-propyl-4-(3,4,5-trifluorophenyl) bicyclohexane and 6.25% of (trans, trans)-4-propyl-4'-butyl-1,1'-bicyclohexane.

[0083] The structural formula of trans, trans-4'-propyl-4-(3,4,5-trifluorophenyl) bicyclohexane is:

[0084]

[0085] 5-4-(3,4-difluorophenyl)-4'-propyl-1,1'-bicyclohexyl has the following structural formula:

[0086]

[0087] (R,R)-4-ethyl-4'-propylbicyclohexyl has the following structural formula:

[0088]

[0089] (R,R)-4-propyl-4'-butyl-1,1'-bicyclohexyl has the following structural formula:

[0090]

[0091] In some embodiments of the present application, the liquid crystal molecules are selected from at least one of ethylcyclohexylphenyl-2,3-difluorophenyl ether, ethylcyclohexyl-2,3-difluorophenyl ether, propylbicyclohexyl-2,3-difluoromethylbenzene, propylcyclohexyl-2,3-difluorophenyl butyl ether, and propylcyclohexyl-2,3-difluorophenyl ether.

[0092] In some embodiments of the present application, the liquid crystal molecules include the above five components, and the weight percentages of the five components are 53.8%, 23.1%, 8.5%, 7.7%, and 6.9%, respectively.

[0093] In some embodiments of the present application, the polymer network skeleton is selected from at least one of a polymer dispersed liquid crystal (PDLC) structure, a polymer stabilized liquid crystal (PSLC) structure, and a composite structure (PD&SLC) composed of both.

[0094] In some embodiments of the present application, the polymer network skeleton is formed by polymerization of a polymerizable monomer having a mid-infrared emission function under heating or light. The polymerizable monomer contains halogen, saturated aliphatic hydrocarbon, ether bond, silicon-oxygen bond, etc.

[0095] In some embodiments of the present application, the polymerizable monomer includes a polymerizable monomer mainly composed of a flexible alkyl chain (generally non-liquid crystal) and a rigid polymerizable monomer with shape anisotropy (generally liquid crystal, but not absolute).

[0096] The second aspect of the present application provides a preparation method of the composite material according to the first aspect, wherein the method comprises the following steps:

[0097] (1) mixing liquid crystal molecules, polymerizable monomers, initiators, and spacer particles to obtain a prepolymer;

[0098] (2) curing the prepolymer obtained in step (1) by heating or light to obtain a liquid crystal / polymer composite material.

[0099] In step (2), the prepolymer can be sandwiched between two layers of transparent conductive glass or conductive ITO film, with the thickness of the prepolymer being controlled to be 5-50 μm, and then the prepolymer is cured by heating (thermal polymerization of monomers) or light irradiation (free radical or cationic photopolymerization of monomers) to obtain a liquid crystal / polymer composite material with a PDLC structure.

[0100] In some embodiments of the present application, the liquid crystal molecules in step (1) comprise a chiral compound; and step (2) further comprises: vertically aligning the liquid crystal molecules by using a vertical aligning agent or applying a low-frequency alternating electric field, and then curing the prepolymer by heating (thermal polymerization of monomers) or light irradiation (free radical or cationic photopolymerization of monomers) to obtain a liquid crystal / polymer composite material with a PSLC structure; or,

[0101] After the prepolymer is cured to obtain a PDLC structure, the liquid crystal molecules are vertically aligned by applying an electric field, and then a second heating or light irradiation is performed to induce polymerization of the free radical or cationic polymerization monomers, thereby obtaining a liquid crystal / polymer composite material with a PD&SLC structure.

[0102] In step (1), the proportions of the raw materials can be as follows: liquid crystal molecules: 10-80 parts by weight; polymerizable monomers: 10-80 parts by weight; initiator: 0.1-5 parts by weight; and spacer particles: 0.1-2 parts by weight. The spacer particles can be silica.

[0103] The liquid crystal / polymer composite material prepared in the present application has an emissivity of greater than 90% at a window of atmosphere at 20-70°C, and has stable radiation refrigeration function.

[0104] The third aspect of the present application provides a light-adjustable film comprising the composite material of the first aspect or obtained by the preparation method of the second aspect. For example, the light-adjustable film comprises two layers of transparent conductive glass or conductive ITO film and the liquid crystal / polymer composite material provided by the present application sandwiched therebetween.

[0105] The fourth aspect of the present application provides the use of the liquid crystal / polymer composite material of the first aspect or the light-adjustable film of the third aspect in energy saving of automobiles and buildings.

[0106] The present application will be described in detail below through examples.

[0107] In the following examples and comparative examples, the specific conditions not specified are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if not specified by the manufacturer, are conventional products that can be obtained by market purchase.

[0108] In the following examples and comparative examples, the polymerizable monomer in Examples 1-2 and Comparative Example 1 is: 58.2 wt% of isobornyl acrylate IBOA 18.2 wt% of 1,4-butanediol diacrylate BDDA 14.5 wt% of 3-(trimethoxysilyl)methyl propyl methacrylate TMSPMA and 9.1 wt% of C6M

[0109]

[0110] The initiator is a photoinitiator Irg651 (2,2-dimethoxy-1,2-diphenylethan-1-one,

[0111] Spacer particles: purchased from Kishimoto Chemical Industry Co., Ltd.

[0112] Example 1

[0113] This example is used to illustrate the preparation of a light control film comprising a liquid crystal / polymer composite material with a radiative cooling function.

[0114] In this example, the liquid crystal molecules include the components in Table 1 (purchased from Yantai Xianhua Science and Technology Group Co., Ltd.):

[0115] Table 1

[0116]

[0117]

[0118]

[0119] Wherein, Reference can be made to the literature: Abhilash T K, Varghese H, Czerwiński M, et al. Probing the effect of chiral dopant fluorination on dielectric and electro-optical properties of the ferroelectric liquid crystalline mixture [J]. Journal of Molecular Liquids, 2021, 341: 117392.

[0120] (1) 77% liquid crystal molecules, 22% polymerizable monomers, 0.5% initiator and 0.5% spacer particles (average particle size 20 μm) were mixed and stirred at room temperature to form an isotropic mixture; then the mixture was ultrasonically treated for 15 min; the total mass of the mixture was 20 g;

[0121] (2) The obtained mixture was coated between two plastic films coated with indium tin oxide (ITO) transparent conductive film, and the film was formed by rolling; the film was irradiated by 365 nm ultraviolet light at room temperature, the intensity was 1 mw / cm 2 , the light exposure time was 60 s; then the film was made into an upper electrode, a square wave alternating current of 10 Hz and 100 V was applied, and the film was irradiated by 365 nm ultraviolet light for 10 min to form a PD&SLC structure temperature control dimming film.

[0122] Example 2

[0123] This example is used to illustrate the preparation of a dimming film containing a liquid crystal / polymer composite with a radiation cooling function.

[0124] In this example, the liquid crystal molecules include 18.75% (anti, anti)-4-ethyl-4'-propyl bicyclohexyl alkane, 50% 5-4-(3,4-difluorophenyl)-4'-propyl-1,1'-bicyclohexane, 25% anti, anti-4'-propyl-4-(3,4,5-trifluorophenyl) bicyclohexane and 6.25% (anti, anti)-4-propyl-4'-butyl-1,1'-bicyclohexane, all purchased from Yantai Xianhua Science and Technology Group Co., Ltd.

[0125] (1) 77% liquid crystal molecules, 22% polymerizable monomers, 0.5% initiator and 0.5% spacer particles (average particle size 50 μm) were mixed and stirred at room temperature to form an isotropic mixture; then the mixture was ultrasonically treated for 15 min; the total mass of the mixture was 20 g;

[0126] (2) The obtained mixture was coated between two plastic films coated with indium tin oxide (ITO) transparent conductive film, and the film was formed by rolling; the film was irradiated by 365 nm ultraviolet light at room temperature, the intensity was 5 mw / cm 2 , the light exposure time was 600 s, to form an electric field responsive dimming film with a PDLC structure.

[0127] Because the PDLC structure does not need to be polymerized by electricity during polymerization, the thickness can be larger than that of the liquid crystal / polymer composite coexisting system of temperature control PDLC and PSLC structure. Thickness and temperature will affect the transmittance and emissivity in the off state.

[0128] Example 3

[0129] This example is used to illustrate the preparation of a light control film containing a liquid crystal / polymer composite with a radiative cooling function.

[0130] In this example, the negative liquid crystal monomers are purchased from Beijing Eight Billion Time and Space Liquid Crystal Technology Co., Ltd.: 323178-01-4, ethylcyclohexylphenyl-2,3-difluorophenyl ether; 415915-41-2, ethylcyclohexyl-2,3-difluorophenyl ether; 174350-06-2, propylbicyclohexyl-2,3-difluoromethylbenzene; 208709-55-1, propylcyclohexyl-2,3-difluorophenyl butyl ether; 174350-05-1, propylcyclohexyl-2,3-difluorophenyl ether; weight ratio of 53.8%, 23.1%, 8.5%, 7.7%, 6.9%. The liquid crystal mixture composed of the above liquid crystal monomers is used as the liquid crystal molecules of this example.

[0131] Table 2

[0132]

[0133]

[0134] (1) Mix 94% of the liquid crystal molecules, 5% of the polymerizable monomer (C6M), 0.5% of the initiator, and 0.5% of the spacer particles (average particle size of 20 μm), and stir at room temperature to form an isotropic mixture; then, ultrasonically treat the mixture for 15 min; the total mass of the mixture is 20 g;

[0135] (2) Using the capillary principle, the obtained mixture is filled into a 20 μm 4 cm x 5 cm commercial vertical alignment liquid crystal empty box (commercial liquid crystal box, composed of two layers of ITO-coated SiO2 glass, with glass beads in the middle to control the thickness) using a capillary; the filled liquid crystal box is placed on a microscope hot stage set to 50°C, and irradiated with 365 nm ultraviolet light at an intensity of 10 mw / cm 2 , and the light exposure time is 300 s, to prepare an electric field responsive light control film with a PSLC structure.

[0136] Example 4

[0137] This example is used to illustrate the preparation of a light control film containing a liquid crystal / polymer composite with a radiative cooling function.

[0138] In this example, the liquid crystal molecules are the same as in Example 1.

[0139] (1) 94% of liquid crystal molecules, 5% of polymerizable monomers (C6M), 0.5% of initiators and 0.5% of spacer particles (average particle size of 20 μm) were mixed and stirred at room temperature to form an isotropic mixture; then the mixture was ultrasonically treated for 15 min; the total mass of the mixture was 20 g;

[0140] (2) The obtained mixture was filled into a commercial vertical alignment liquid crystal empty box of 20 μm of 4 cm x 5 cm by capillary principle; under the condition of room temperature, irradiation was carried out by 365 nm ultraviolet light with an intensity of 10 mW / cm 2 , and the light irradiation time was 300 s, to prepare a temperature-responsive light-adjustable film with PSLC structure.

[0141] Comparative Example 1

[0142] The light-adjustable film was prepared according to the method of Example 1, except that the liquid crystal molecules were 30 wt% of nematic liquid crystal E8 and 70 wt% of smectic liquid crystal 8CB (4'-octyl-4-biphenyl cyanide), both purchased from Yantai Xianhua Science and Technology Group Co., Ltd.

[0143] Comparative Example 2

[0144] The light-adjustable film was prepared according to the method of Example 2, except that the liquid crystal molecules were all nematic liquid crystal E8, purchased from Yantai Xianhua Science and Technology Group Co., Ltd.

[0145] Test Example 1

[0146] The morphology of the polymer network in the light-adjustable films prepared in Example 1 and Example 2 was studied by scanning electron microscopy (SEM, JSM-6700F). In order to examine the polymer network, the film was first immersed in cyclohexane at room temperature for one week to remove the liquid crystal molecules, and a gold coating was sprayed on the film to remove any charges. The polymer network structure of the liquid crystal / polymer composite material is shown in Figure 1 、 Figure 2 .

[0147] Figure 1 The PD&SLC vertical cross-section porous structure has orientation in the vertical direction, which makes the liquid crystal rod-shaped molecules in the network tend to arrange vertically. When the liquid crystal molecules are in the smectic phase state, the molecules arrange vertically and transmit sunlight. When the liquid crystal is in the cholesteric phase, it tends to arrange in a spiral, which interacts with the vertical polymer network to form a focal conic arrangement of conformation, scattering sunlight.

[0148] Figure 2The PDLC standard porous structure has a pore size of about 10 μm. The polymer monomers are induced to cross-link by means of ultraviolet irradiation or heating, etc. As the polymer monomer molecular chain continuously grows, the solubility of the small molecule liquid crystal material in the polymer continuously decreases, so that the liquid crystal microdroplets are separated, combined and grown in the form of liquid crystal microdroplets. When the polymerization is complete, the liquid crystal microdroplets are uniformly dispersed in the continuous phase of the polymer matrix in the form of a discontinuous phase, and a PDLC film porous structure is obtained.

[0149] Test Example 2

[0150] The near-infrared absorption spectrum of the liquid crystal molecule used in Example 1 and Comparative Example 1 is shown in Figure 3 and Figure 4 .

[0151] E8 in Comparative Example 1 is a liquid crystal molecule containing a cyano group. In Figure 4 , a strong absorption peak of the cyano group can be seen at 2220-2230 cm -1 . The absorption peak of the cyano group is not in the infrared fingerprint region (1500-600 cm -1 ), resulting in its absorption of excess infrared light, a decrease in selective emission in the atmospheric window (8-13 μm), and ultimately a decrease in the radiation cooling efficiency of the composite material.

[0152] While Figure 3 does not have a cyano group peak, it is a fluorine-containing liquid crystal, and the infrared absorption peak is at 1500-600 cm -1 .

[0153] Test Example 3

[0154] The ultraviolet-visible-near-infrared light transmittance of the dimming film prepared in Example 1 was tested at room temperature (25°C) and 45°C, respectively, using a variable temperature ultraviolet-visible-near-infrared spectrophotometer, as shown in Figure 5 , the test wavelength being 300-2500 nm. It was proved that the liquid crystal / polymer composite of Example 1 can achieve a change in the transmittance of the solar wave band.

[0155] Test Example 4

[0156] The 8-14 μm infrared emissivity curve of the dimming film prepared in Examples 1-4 and Comparative Examples 1 and 2 was measured using a Fourier transform infrared spectrometer equipped with a gold integrating sphere (ISR-603), as shown in Figures 6-11 .

[0157] As can be seen from Figure 10 , the emissivity of the dimming film prepared in Comparative Example 1 is about 90%, while the emissivity of the dimming film prepared in Example 1 is about 95% (as shown in Figure 6 ).

[0158] from Figure 11 It can be seen that the emissivity of the dimming film prepared in Comparative Example 2 is below 85%, while the emissivity of the dimming film prepared in Example 2 is above 90%.

[0159] Test Example 5

[0160] The light transmittance of the dimming film prepared in Example 2 was measured using a transformer and a UV-Vis-NIR spectrophotometer, respectively, with and without an applied electric field. Figure 12 As shown, the test wavelength is 500-2500nm.

[0161] The light transmittance of the dimming film prepared in Example 3 was measured using a variable-temperature UV-Vis-NIR spectrophotometer under both no electric field and 100V 50Hz AC electric field conditions. Figure 13 As shown, the test wavelength is 300-2500nm.

[0162] Figure 12 and 13 This invention demonstrates that the dimming film prepared by the present invention can achieve precise temperature control. Given that the material itself has high emissivity, resulting in high radiative cooling power, the input power of sunlight can be affected by controlling the transmittance, thereby affecting the final total cooling power.

[0163] Test Example 6

[0164] In a laboratory with a constant temperature of 25°C, PET films with the same initial temperature and the dimming film of Example 1 were subjected to 800W / m 2 Under the illumination of a simulated sunlight lamp, the materials were continuously exposed for three minutes until their temperatures stabilized. Figure 14 As shown, when the temperatures of the two materials are stable, the difference in stable temperatures is about 13.5°C, indicating that Example 1 achieves a higher total radiative cooling effect compared to the PET film.

[0165] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A liquid crystal / polymer composite material, characterized in that, The composite material includes a polymer network framework and liquid crystal molecules dispersed within the polymer network framework. The liquid crystal molecules comprise six components with the following structure: 、 、 、 、 、 ； The weight percentages of the above six components are 26%, 13%, 12%, 6%, 40%, and 3%, respectively.

2. A liquid crystal / polymer composite material, characterized in that, The composite material includes a polymer network framework and liquid crystal molecules dispersed within the polymer network framework. The liquid crystal molecules, by weight percentage, comprise: 18.75% (trans,trans)-4-ethyl-4'-propylbicyclohexylane, 50% 5-4-(3,4-difluorophenyl)-4'-propyl-1,1'-bis(cyclohexane), 25% trans,trans-4'-propyl-4-(3,4,5-trifluorophenyl)bicyclohexane, and 6.25% (trans,trans)-4-propyl-4'-butyl-1,1'-bicyclohexane.

3. A liquid crystal / polymer composite material, characterized in that, The composite material comprises a polymer network framework and liquid crystal molecules dispersed within the polymer network framework; wherein the liquid crystal molecules include ethylcyclohexylphenyl-2,3-difluorophenylethyl ether, ethylcyclohexyl-2,3-difluorophenylethyl ether, propyl dicyclohexyl-2,3-difluoromethylbenzene, propylcyclohexyl-2,3-difluorophenylbutyl ether, and propylcyclohexyl-2,3-difluorophenylethyl ether; The weight percentages of the five components are 53.8%, 23.1%, 8.5%, 7.7%, and 6.9%, respectively.

4. The composite material according to any one of claims 1-3, wherein, The polymer network framework is selected from at least one of polymeric dispersed liquid crystal structure, polymeric stable liquid crystal structure, and composite structure composed of both.

5. The composite material according to any one of claims 1-3, wherein, The polymer network framework is formed by polymerizing polymerizable monomers with mid-infrared emission function under heating or light irradiation.

6. The composite material according to claim 5, wherein, The polymerizable monomers include polymerizable monomers with flexible alkyl chains as the main component and rigid polymerizable monomers with anisotropic shapes.

7. A method for preparing a composite material according to any one of claims 1-3, characterized in that, The method includes the following steps: (1) A prepolymer is obtained by mixing liquid crystal molecules, polymerizable monomers, initiators and spacer particles; (2) The prepolymer obtained in step (1) is cured by heating or light to obtain a liquid crystal / polymer composite material.

8. The preparation method according to claim 7, wherein, The liquid crystal molecules in step (1) include chiral compounds; step (2) further includes: aligning the liquid crystal molecules vertically before heating or irradiation, or aligning the liquid crystal molecules vertically after curing the prepolymer and then subjecting them to a second heating or irradiation.

9. A dimming film comprising the composite material of any one of claims 1-3 or the composite material obtained by the preparation method according to claim 7.

10. The application of the liquid crystal / polymer composite material according to any one of claims 1-3 or the dimming film according to claim 9 in automotive and building energy conservation.

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