Liquid crystal nanocapsules and capsule solutions, optical films, optical devices, transmittance variable devices using the same

Abstract

This invention relates to liquid crystal nanocapsules and capsule solutions, optical films, optical devices, and transmissivity devices using the same, wherein the liquid crystal nanocapsules comprise: a core containing liquid crystal; and a polymer shell formed on the surface of the core; wherein the sum of the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 is 37.5°C or less.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0133749, filed with the Korean Intellectual Property Office on October 2, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0003] This invention relates to liquid crystal nanocapsules and capsule solutions, optical films, optical devices, and transmissivity devices using the same, which can induce high transmissivity variation rates even at lower voltages by reducing the surface interaction energy of the liquid crystal encapsulated inside the capsule. Background Technology

[0004] Polymer-dispersed liquid crystal (PDLC) films are suitable for high-brightness projection displays or high-contrast reflective display devices. They are composite materials in which liquid crystal molecules of several micrometers are dispersed within a polymer layer between conductive films. The driving principle of PDLC is that light incident on the polymer layer containing the dispersed liquid crystals is scattered due to the refractive index difference between the liquid crystals and the polymer, resulting in an opaque state. However, by applying an electric field, the orientation of the liquid crystals is aligned and the refractive index changes, thereby controlling the scattering and transmission of light to achieve a transparent state.

[0005] Therefore, PDLC devices do not require a separate polarizer and thus do not need a polarizing plate in terms of structure, nor do they require an alignment process in terms of manufacturing, making it possible to manufacture PDLC devices using a simple method. Therefore, PDLC devices can be applied to smart glass and smart screens for buildings and automobiles corresponding to switchable windows, and can also be used as black PDLC films for transparent OLEDs. Furthermore, depending on the material used as the substrate, PDLC devices can be manufactured in a flexible form.

[0006] Specifically, liquid crystal-based smart windows refer to active windows that can control transmittance using glass comprising individual liquid crystal layers, and are a technology applicable to mobility and architecture. Conventional polymer-dispersed liquid crystal (PDLC) technology creates liquid crystal domains of several μm in size by mixing monomers capable of photopolymerization or thermal polymerization with liquid crystals and allowing phase separation between the polymer and liquid crystals during polymerization. PDLC films can achieve light-shielding / transmission modes because the liquid crystals within these μm-sized domains have refractive indices that match / mismatch with the polymer matrix, depending on the applied voltage. However, in PDLCs, the scattering of visible light is difficult to overcome because the liquid crystal domains are larger than the visible light wavelength range.

[0007] On the other hand, when the domain size of the liquid crystal is 380 nm or smaller (which is the smallest wavelength of visible light), the scattering problem can be improved, making it possible to manufacture a liquid crystal film with variable transmittance and excellent haze.

[0008] In particular, in the manufacture of color PDLCs containing dyes, there is a problem of non-uniform orientation of anisotropic dyes in the polymer according to an electric field, and especially, the problem of dye contamination of the polymer matrix. Therefore, various studies are being conducted on liquid crystal composites having a capsule structure in which liquid crystals and anisotropic dyes are encapsulated in a polymer shell to achieve excellent mechanical properties and high uniformity, and to prevent dye contamination of the polymer matrix.

[0009] However, since the liquid crystal and anisotropic dye are encapsulated in a polymer shell, the liquid crystal encapsulated in the capsule has the following limitation: due to the high interaction that occurs with the increased contact area with the material contained in the capsule shell, the orientation of the liquid crystal will only change when a higher voltage is applied. Summary of the Invention

[0010] Technical issues

[0011] The present invention aims to provide liquid crystal nanocapsules that can induce a high rate of change of transmittance even at low voltages by reducing the surface interaction energy of the liquid crystal encapsulated inside the capsule.

[0012] Furthermore, the present invention aims to provide capsule solutions, optical films, optical devices, and variable transmittance devices using the liquid crystal nanocapsules.

[0013] Technical solution

[0014] To address the above issues, this specification provides a liquid crystal nanocapsule comprising: a core containing liquid crystal; and a polymer shell formed on the surface of the core; wherein the sum of the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 is 37.5°C or less.

[0015] [Mathematical Expression 1]

[0016] Initial temperature change = (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystal nanocapsules) - (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystals)

[0017] [Mathematical Expression 2]

[0018] Peak temperature change = (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal nanocapsules) - (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal).

[0019] This specification also provides a capsule solution comprising the liquid crystal nanocapsules and a solvent.

[0020] This specification also provides an optical film containing the liquid crystal nanocapsules.

[0021] This specification also provides an optical device, which includes the optical film.

[0022] This specification also provides a variable transmittance device, which includes the optical film.

[0023] The following will describe in detail the liquid crystal nanocapsules according to specific embodiments of the present invention, and the capsule solutions, optical films, optical devices, and variable transmittance devices using the same.

[0024] Unless otherwise expressly stated herein, the technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0025] Unless the context clearly specifies otherwise, the singular form as used herein also includes the plural form.

[0026] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of the said feature, region, integer, step, action, element, and / or component, but do not exclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components, and / or groups.

[0027] Furthermore, terms including ordinal numbers such as "first," "second," etc., are used only for the purpose of distinguishing one component from another and are not limited by ordinal numbers. For example, without departing from the scope of this disclosure, the first component may be referred to as the second component, or similarly, the second component may be referred to as the first component.

[0028] In addition, derivative compounds refer to compounds that are altered within limits (e.g., the introduction of functional groups, oxidation, reduction, and substitution of atoms) when an organic compound is the parent compound, without significantly changing the structure and properties of the parent compound.

[0029] Furthermore, weight-average molecular weight (Mw) refers to the weight-average molecular weight of polystyrene as measured by gel permeation chromatography (GPC). In measuring the weight-average molecular weight of polystyrene as measured by GPC, detectors and analytical columns can be used, such as commonly known analytical devices and differential refractive index detectors, and commonly applied temperature conditions, solvents, and flow rates can be used. A specific example of measurement conditions is as follows: A Waters PL-GPC220 instrument was used, with a Polymer Laboratories PLgel MIX-B 300 mm long column. The evaluation temperature was 160 °C, and 1,2,4-trichlorobenzene was used as the solvent at a flow rate of 1 mL / min. The sample was prepared at a concentration of 10 mg / 10 mL and then supplied in 200 μL increments, and the Mw value could be determined using a calibration curve derived from polystyrene standards. Nine polystyrene standards with molecular weights of 100 / 500 / 1000 / 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 were used.

[0030] The contents of this disclosure will now be described in more detail.

[0031] 1. Liquid crystal nanocapsules

[0032] According to one embodiment of the present invention, a liquid crystal nanocapsule can be provided, the liquid crystal nanocapsule comprising: a core containing liquid crystal; and a polymer shell formed on the surface of the core; wherein the sum of the initial temperature change value according to the following mathematical formula 1 and the peak temperature change value according to the following mathematical formula 2 is 37.5°C or less:

[0033] [Mathematical Expression 1]

[0034] Initial temperature change = (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystal nanocapsules) - (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystals)

[0035] [Mathematical Expression 2]

[0036] Peak temperature change = (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal nanocapsules) - (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal).

[0037] The inventors have experimentally determined that, as in the liquid crystal nanocapsules of the above embodiments, the sum of the initial temperature change value according to mathematical formula 1 and the peak temperature change value according to mathematical formula 2 is 37.5°C or less, and thus the surface interaction energy of the liquid crystal encapsulated inside the capsule can be reduced, thereby causing a high rate of change in transmittance even at lower voltages, and thus the present invention is completed.

[0038] Thermotropic liquid crystals are essentially materials in which a phase transition occurs due to an increase in molecular mobility caused by an increase in temperature. An example of a thermotropic liquid crystal includes a liquid crystal in which a nematic liquid crystal transforms into an isotropic liquid, and the phase transition temperature at this point is called Tni (the temperature at which the phase transitions from the nematic phase to the isotropic phase).

[0039] Nematic liquid crystals exhibit the property of aligning according to the surface to which they are exposed, a phenomenon known as surface anchoring. With greater interaction with the surface material, a higher voltage is required to move the liquid crystal. Liquid crystals encapsulated within a capsule possess increased surface anchoring energy due to the capsule shell, and therefore their orientation can only be changed when a higher voltage is applied. Consequently, a decrease in the surface anchoring energy of the liquid crystal within the capsule can lead to a higher rate of change in transmittance even at lower voltages.

[0040] The initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 are parameters relating to the difference in Tni (the temperature from the nematic phase to the isotropic phase). When the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 become smaller, it means that the surface anchoring energy of the liquid crystal in the capsule is relatively low, and therefore, even at low voltages, the rate of change of transmittance can increase. Specifically, when the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 become smaller, liquid crystal nanocapsules capable of low-voltage driving at lower threshold voltages and possessing high contrast and excellent variable transmittance characteristics are provided.

[0041] Furthermore, as will be described later, the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 are achieved by reducing the surface anchoring energy of the liquid crystal in the capsule through mixing the unique emulsifier of the present invention with the siloxane-based additive.

[0042] Specifically, the liquid crystal nanocapsules of the described embodiments may include a core containing liquid crystal. The structure of the liquid crystal nanocapsules according to the present invention is characterized in that the liquid crystal is contained within and encapsulated in a shell made of polymer. Therefore, the uniformity of the liquid crystal particles can be improved.

[0043] There are no particular limitations on liquid crystals, but examples can include nematic liquid crystals, smectic liquid crystals, cholesteric liquid crystals, chiral nematic liquid crystals, etc. There are no restrictions on the specific type of liquid crystal compound, and various conventionally known liquid crystals can be used without limitation. There are no particular restrictions on the liquid crystal, but specifically, (trans,trans)-4-vinyl-4'-propyl-1,1'-bicyclohexyl, or 1,2,3-trifluoro-5-[(trans,trans)-4'-ethyl[1,1'-bicyclohexyl]-4-yl]benzene, or 1,2,3-trifluoro-5-[(trans,trans)-4'-propyl[1,1'-bicyclohexyl]-4-yl]benzene, or benzene, 1,2,3-trifluoro-5-[(trans,trans)-4-pentyl[1,1'-bicyclohexyl]-4-yl], or trans-1-ethoxy-4-(4-propylcyclohexyl)benzene, or [trans(trans)]-1,2-difluoro-4-(4-propyl-1'-bicyclohexyl]-4-yl)benzene Or benzene, 1,2-difluoro-4-[(trans, trans)-4'-pentyl[1,1'-bicyclohexyl]-4-yl], or 2,3',4'5'-tetrafluoro-4-[(trans, trans)-4'-propyl[bicyclohexyl]-4-yl]-1,1'-biphenyl, or 5-(difluoro[(trans, trans)-4'-propyl[1,1'-bicyclohexyl]-4-yl]methoxy]-1,2,3-trifluorobenzene, or [1,1-bicyclohexyl]-4-carboxylic acid, 4'-propyl-,3,4,5-trifluorophenyl ester,(trans, trans)-, or [1,1'-bicyclohexyl]-4-carboxylic acid, 4'-pentyl-,3,4,5-trifluorophenyl ester,(trans, trans)-, or mixtures thereof.

[0044] More specifically, the liquid crystal can be a fluorine-based liquid crystal. Fluorine-based liquid crystals are liquid crystal materials with fluorine atoms in their molecular structure, and they possess low viscosity and low relative permittivity, resulting in low introduction of ionic impurities. When fluorine-based liquid crystals are used as liquid crystal materials, the refractive index anisotropy is relatively low, which may therefore lead to low haze. This reduces performance degradation, such as a decrease in voltage retention due to impurities, and can reduce surface anchoring energy when in contact with the capsule shell surface during encapsulation.

[0045] There is no significant limitation on the percentage of liquid crystal contained in the liquid crystal nanocapsules of the described embodiment; however, for example, the liquid crystal can be included in the range of 10% to 20% by mass. Within this range, sufficient liquid crystal performance can be obtained, and at the same time, the thickness of the polymer shell becomes sufficient to improve the durability of the liquid crystal nanocapsules.

[0046] There are no limitations on the method for measuring the ratio of liquid crystal contained in liquid crystal nanocapsules, and various conventionally known methods can be applied without restriction. However, as an example, after freeze-drying 5 mL of the capsule solution, the mass is measured to calculate the solid content per unit volume. Then, 1 mg of the freeze-dried capsule solution is placed in a TGA2 device of METTLER TOLEDO, and the temperature is increased from 50°C to 700°C at a heating rate of 10°C / min. The liquid crystal ratio (mass %) can be obtained by determining the mass reduction according to temperature, as the mass decreases within the range of 200°C to 300°C.

[0047] Additionally, the core may contain emulsifiers and siloxane-based additives. The emulsifier is a surfactant used to form liquid crystal droplets, and when used together with siloxane-based additives, the interfacial tension of the liquid crystal in the capsule is reduced, thereby significantly reducing the surface anchoring energy of the liquid crystal.

[0048] Specifically, the content of the siloxane-based additive based on 100 parts by weight of emulsifier can range from 5 parts by weight to 50 parts by weight, or from 5 parts by weight to 20 parts by weight, or from 9 parts by weight to 19 parts by weight, or from 9.2 parts by weight to 18.4 parts by weight. When the content of the siloxane-based additive based on 100 parts by weight of emulsifier is excessively reduced, the effect of reducing the surface tension of the liquid crystal by the siloxane-based additive may not be sufficiently achieved, thus limiting the ability to sufficiently reduce the surface anchoring energy of the liquid crystal in the capsule. Furthermore, when the content of the siloxane-based additive based on 100 parts by weight of emulsifier is excessively increased, the state of the liquid crystal (intermediate phase) may become an isotropic liquid phase.

[0049] The emulsifier is a nonionic surfactant used to form liquid crystal droplets, and any surfactant that does not ionize in aqueous solution can be used without limitation. Types of nonionic surfactants are well known in the art, and known nonionic surfactants can be used without limitation. In one embodiment, the nonionic surfactant can be, but is not limited to, amphiphilic block copolymers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, sorbitol fatty acid esters, or glycerol fatty acid esters. For example, nonionic surfactants include: polycetol 1000, cetearyl alcohol, cetyl alcohol, cocamide diethanolamine (cocamide DEA), cocamide monoethanolamine (cocamide MEA), decyl glucoside, Igepal CA-630, isocetyl alcohol polyether-20, lauryl glucoside, glyceryl monolaurate, octylphenoxy polyethoxyethanol, nonylphenyl alcohol ether-9, NP-40, octyl glycol monododecyl ether, N-octyl β-D-thiopyranoside, octyl glucoside, oleyl alcohol, pentaethylene glycol monododecyl ether, poloxamer, polyglycerol polyricinoleate, polysorbate, sorbitol monostearate, sorbitol tristearate, stearyl alcohol, Triton X-100, Tween 80, poly(ethylene oxide-b-propylene oxide), polyoxyethylene-b-polydimethylsiloxane, etc.

[0050] However, based on 100 mol% emulsifier, the ethylene oxide repeating unit content of the emulsifier can be less than 0.001 mol%. That is, the emulsifier may not contain ethylene oxide repeating units, or may contain ethylene oxide repeating units in very small amounts. Based on 100 mol% emulsifier, when the ethylene oxide repeating unit content in the emulsifier increases to 0.001 mol% or more, due to the increased van der Waals interaction between the electrophilic fluorine element in the fluorine-based liquid crystal and the ethylene oxide repeating units, the change in onset temperature according to Equation 1 and the change in peak temperature according to Equation 2 increase, making it difficult to sufficiently reduce the surface anchoring energy of the liquid crystal in the capsule.

[0051] More specifically, emulsifiers may include alkynyldiol-based compounds. Alkynyldiol-based compounds may include alkynyldiol compounds or derivatives thereof.

[0052] The HLB (Hydrophile Lipophile Balance) value of compounds based on alkynyldiols can range from 2 to 4, or from 2 to 3. Typically, in order to produce stable oil-in-water emulsions using conventional emulsifiers, the emulsifier must be adsorbed at the aqueous / oil phase interface to form a liquid crystal, and for this purpose, the HLB value of the emulsifier to be used should be finely adjusted according to the polarity of the oil phase.

[0053] Specifically, HLB can be calculated using the following mathematical formula 3.

[0054] [Mathematical Expression 3]

[0055]

[0056] In mathematical formula 3, M H M is the molecular weight (or molar mass) of the hydrophilic group, and M is the molecular weight (or molar mass) of the emulsifier.

[0057] As a more specific example, the acetylenic diol-based compound can be 2,4,7,9-tetramethyl-5-decyn-4,7-diol. Since the acetylenic diol-based compound does not possess an ethylene oxide repeating unit in the emulsifier's structure, the van der Waals interaction with the fluorinated liquid crystal can be relatively reduced compared to emulsifiers containing ethylene oxide repeating units. For this reason, the surface anchoring energy of the liquid crystal in the capsule can be sufficiently reduced when the onset temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 are reduced.

[0058] In addition, the emulsifier may include a siloxane polyether copolymer containing propylene oxide. The weight-average molecular weight of the siloxane polyether copolymer containing propylene oxide may be 1000 g / mol or greater, or in the range of 1000 g / mol to 50000 g / mol, or in the range of 1000 g / mol to 10000 g / mol, or in the range of 1000 g / mol to 5000 g / mol, or in the range of 2000 g / mol to 3000 g / mol, or in the range of 2800 g / mol to 3000 g / mol.

[0059] The HLB (hydrophilic-lipophilic balance) value of propylene oxide-containing siloxane polyether copolymers can range from 0 to 1. Typically, in order to produce stable oil-in-water emulsions using conventional emulsifiers, the emulsifier must be adsorbed at the aqueous / oil phase interface to form a liquid crystal, and for this purpose, the HLB value of the emulsifier to be used should be finely adjusted according to the polarity of the oil phase.

[0060] Specifically, HLB can be calculated using the following mathematical formula 3.

[0061] [Mathematical Expression 3]

[0062]

[0063] In mathematical formula 3, M H M is the molecular weight (or molar mass) of the hydrophilic group, and M is the molecular weight (or molar mass) of the emulsifier.

[0064] As a more specific example, a propylene oxide-containing siloxane polyether copolymer can be a dimethyl polysiloxane graft copolymer of the following chemical formula a (weight average molecular weight 3,000; HLB: 0; CAS No. 68550-66-4) or a dimethyl polysiloxane linear copolymer of the following chemical formula b (weight average molecular weight 2,800; HLB: 0; CAS No.: 161755-53-9).

[0065] [Chemical formula a]

[0066]

[0067] In chemical formula a, x is an integer in the range of 1 to 100, y is an integer in the range of 1 to 100, and n is an integer in the range of 0 to 20.

[0068] [Chemical formula b]

[0069]

[0070] In chemical formula b, p is an integer in the range of 0 to 20, q is an integer in the range of 1 to 100, and r is an integer in the range of 0 to 20.

[0071] The siloxane polyether copolymer containing propylene oxide increases the surface energy of the surface in contact with the liquid crystal to induce the vertical orientation of the liquid crystal. For this reason, the surface anchoring energy of the liquid crystal in the capsule can be sufficiently reduced when the initial temperature change value according to mathematical formula 1 and the peak temperature change value according to mathematical formula 2 are reduced.

[0072] Siloxane-based additives are capable of reducing the interfacial tension of liquid crystals. Therefore, when siloxane-based additives are contained together with liquid crystals in liquid crystal nanocapsules within a core, the surface anchoring energy of the liquid crystals within the capsules can be significantly reduced.

[0073] The molar mass of siloxane-based additives can be 500 g / mol or less, or in the range of 100 g / mol to 500 g / mol. Siloxane-based additives may include trisiloxane-based compounds. Trisiloxane-based compounds may include trisiloxane compounds or their derivatives. As specific examples, siloxane-based additives may be octamethyltrisiloxane or hexamethylcyclotrisiloxane.

[0074] In addition, the core may contain anisotropic dyes. There are no particular restrictions on the anisotropic dyes, as long as they are dopable anisotropic dyes, and specifically, S-428, M-483, M412 (Mitsui Fine Chemical), etc. are provided.

[0075] Furthermore, the liquid crystal nanocapsules of the aforementioned embodiment may include a polymer shell formed on the surface of the core. The shell may be a single-layer shell made of a homopolymer material, or a double-layer shell or multiple shells made of different polymer materials for improved mechanical properties and particle uniformity. Therefore, the uniformity of the liquid crystal particles can be improved, and simultaneously, the contamination problem caused by dyes can be mitigated.

[0076] The material forming the shell has the same refractive index as the matrix polymer in which the liquid crystal composite is dispersed, and there are no particular limitations on specific examples, but it may be selected, for example, from polyvinyl alcohol, polyurea, polyurethane, polyamide (including nylon), polyacetal and polyester.

[0077] However, as a specific example, the polymer shell formed on the surface of the core can be made of polyvinyl alcohol (PVA) resin crosslinked with glyoxal. There are no particular restrictions on the type of PVA, and various PVAs with different molecular weights or degrees of saponification can be appropriately selected depending on the purpose. Glyoxal is used as the crosslinking agent for crosslinking the PVA.

[0078] Meanwhile, in the liquid crystal nanocapsule of the embodiment, the sum of the initial temperature change value according to the following mathematical formula 1 and the peak temperature change value according to the following mathematical formula 2 can be 37.5°C or less, or 37°C or less, or 36°C or less, or 35°C or less, or 1°C or more, or in the range of 1°C to 37.5°C, or in the range of 1°C to 37°C, or in the range of 1°C to 36°C, or in the range of 1°C to 35°C.

[0079] [Mathematical Expression 1]

[0080] Initial temperature change = (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystal nanocapsules) - (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystals)

[0081] [Mathematical Expression 2]

[0082] Peak temperature change = (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal nanocapsules) - (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal).

[0083] In the liquid crystal nanocapsule of the embodiment, when the initial temperature change value according to mathematical formula 1 and the peak temperature change value according to mathematical formula 2 decrease simultaneously, the sum of the initial temperature change value according to mathematical formula 1 and the peak temperature change value according to mathematical formula 2 also tends to decrease.

[0084] Specifically, when the sum of the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 becomes small, it means that the surface anchoring energy of the liquid crystal in the capsule is relatively low, and therefore, the rate of change of transmittance can increase even at low voltages. Specifically, when the sum of the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 becomes small, liquid crystal nanocapsules capable of low-voltage driving at lower threshold voltages and possessing high contrast and excellent transmittance variable characteristics are provided.

[0085] On the other hand, when the sum of the initial temperature change value according to Formula 1 and the peak temperature change value according to Formula 2 increases excessively to more than 37.5°C, the surface anchoring energy of the liquid crystal in the capsule increases, causing the orientation of the liquid crystal to change only when a higher voltage is applied, and thus requiring a greater voltage to move the liquid crystal.

[0086] There are no significant limitations on the examples of DSC measurement methods in Formulas 1 and 2, and conventionally known DSC measurement equipment, conditions, and methods can be applied without restriction. However, as an example, by using the METTLER TOLEDO DSC3 device, the lowest temperature at which endothermic and exothermic processes occur can be measured while the temperature is increased from 25°C to 200°C at a heating rate of 5°C / min.

[0087] More specifically, the initial temperature variation value of the liquid crystal nanocapsule according to Formula 1 in the embodiment can be 18.5°C or less, or 18°C ​​or less, or 17°C or less, or 16°C or less, or 15°C or less, or 14°C or less, or 1°C or more, or in the range of 1°C to 18.5°C, or in the range of 1°C to 18°C, or in the range of 1°C to 17°C, or in the range of 1°C to 16°C, or in the range of 1°C to 15°C, or in the range of 1°C to 14°C.

[0088] Furthermore, the peak temperature variation value of the liquid crystal nanocapsule according to the following mathematical formula 2 in the embodiment can be 21.5°C or less, or 21°C or less, or 20°C or less, or 19°C or less, or 1°C or more, or in the range of 1°C to 21.5°C, or in the range of 1°C to 21°C, or in the range of 1°C to 20°C, or in the range of 1°C to 19°C.

[0089] The average diameter of liquid crystal nanocapsules can range from 200 nm to 300 nm. When the average diameter of the liquid crystal nanocapsules decreases excessively, problems arise due to increased driving voltage and power consumption. Furthermore, when the average diameter of the liquid crystal nanocapsules increases excessively, problems arise due to visible light scattering and increased haze.

[0090] Liquid crystal nanocapsules can be groups of individual particles with an average diameter in the range of 200 nm to 300 nm, and the average diameter of the individual fine particles contained in such a group can be in the range of 200 nm to 300 nm. More specifically, 95% or 99% of the individual fine particles contained in the group have a diameter in the range of 200 nm to 300 nm.

[0091] This application also provides uses for the liquid crystal capsule. The liquid crystal capsule of this application can be used in various light modulation devices suitable for liquid crystals. Therefore, a light modulation device is provided, comprising: a substrate; and a liquid crystal layer formed on a surface of the substrate and including the liquid crystal capsule. Methods and types of manufacturing light modulation devices are well known in the art, and they can be manufactured without limitation using known manufacturing methods. Light modulation devices include, but are not limited to, smart windows, isotropic films, polarization control films, or flexible LCDs.

[0092] There are no significant limitations on the manufacturing methods of liquid crystal nanocapsules, and various conventionally known methods for manufacturing liquid crystal nanocapsules can be applied without limitation. However, as an example, a method comprising: (1) preparing a mixed solution by mixing a mixture of liquid crystal, emulsifier, siloxane-based additive and polyvinyl alcohol (PVA) in a solvent; (2) forming droplets from the mixed solution; (3) arranging polyvinyl alcohol (PVA) around the droplets; and (4) crosslinking polyvinyl alcohol (PVA) using a crosslinking agent to form a polymer shell surrounding the liquid crystal, thereby manufacturing liquid crystal nanocapsules in which the liquid crystal is encapsulated in the polymer shell.

[0093] In (1) the process of preparing a mixed solution by mixing a mixture of liquid crystal, emulsifier, siloxane-based additive and polyvinyl alcohol (PVA) in a solvent, there are no particular limitations on the solvent, and it can be appropriately selected according to the purpose. For example, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water and distilled water, or water such as ultrapure water can be used.

[0094] In (2) the process of forming droplets from the mixed solution, the droplets are dispersed in the dispersion medium, and more specifically, the droplets are dispersed in the dispersion medium in such a state that the emulsifier covers the periphery of the liquid crystal.

[0095] As a method for preparing droplets, a method using a dispersive emulsification device to produce droplets can be used.

[0096] There are no particular limitations on the type of dispersive emulsification device, as long as droplets of the desired particle diameter are obtained, and it can be appropriately selected according to the purpose. For example, a homogenizer can be used as a device for mixing liquids, or a homogenizer as a device for refining and homogenizing particles. Furthermore, there are no particular limitations on the dispersion method, and any dispersion method such as stirring, ultrasonication, or high pressure can be used, for example.

[0097] In this invention, various dispersion-type emulsification devices can be used as dispersion-type emulsification devices, such as high-speed homogenizers, ultrasonic homogenizers, high-pressure homogenizers, and homogenizing mixers.

[0098] Furthermore, as a more preferred embodiment of the method for preparing droplets, a method for preparing droplets is provided, which includes a first preparation process for preparing droplets using a first dispersion emulsification device and a second preparation process for preparing droplets with a particle diameter smaller than that obtained in the first preparation process using a second dispersion emulsification device.

[0099] There are no particular limitations on the first and second dispersion emulsification devices, as long as droplets with the desired particle diameter are obtained, and for example, the various dispersion emulsification devices described above can be used in appropriate combinations.

[0100] In (3) the process of arranging polyvinyl alcohol (PVA) around the droplets, the aggregation of PVA around the liquid crystal composition can take place in the droplet dispersion at a predetermined temperature. As an example, it is preferable to set the solution temperature of the droplet dispersion at 40°C or higher during the aggregation process.

[0101] In (4) the process of crosslinking polyvinyl alcohol (PVA) with a crosslinking agent to form a polymer shell surrounding the liquid crystal, thereby manufacturing liquid crystal nanocapsules, the crosslinking reaction is preferably carried out under acidic conditions. As acidic conditions, the pH is preferably in the range of 1 to 5, and more preferably about 3.

[0102] 2. Capsule solution

[0103] According to another embodiment of the present invention, a capsule solution comprising the liquid crystal nanocapsules of the above embodiments and a solvent can be provided. All details of the liquid crystal nanocapsules of the above embodiments are included in the details described above in the embodiments.

[0104] There are no particular restrictions on the solvent, and it can be appropriately selected according to the purpose. For example, water such as pure water, ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, or ultrapure water are provided.

[0105] In the capsule solution, liquid crystal nanocapsules are dispersed in a solvent. That is, the capsule solution can be a dispersion of liquid crystal nanocapsules. The capsule solution is used as a coating liquid for forming a liquid crystal layer. For example, a liquid crystal layer is formed by coating the capsule solution onto a supporting substrate to form a film.

[0106] 3. Optical film

[0107] According to another embodiment of the present invention, an optical film comprising the liquid crystal nanocapsules of the above embodiments can be provided. All details of the liquid crystal nanocapsules of the above embodiments include the details described above in the embodiments.

[0108] The optical film may include a substrate and liquid crystal capsules of the embodiments described herein dispersed within the substrate. There are no particular limitations on the substrate, but for example, a transparent material may be used. Specific examples of the substrate are not particularly limited, but for example, materials selected from polyvinyl alcohol, polyurea, polyurethane, polyamide (including nylon), polyacetal, and polyester may be used.

[0109] As a more specific example, an optical film can be formed by coating a capsule solution of another embodiment onto a support substrate to form a film.

[0110] Specific information about optical films can be applied, not limited to information about various conventionally known optical films. For example, information about the structure, composition, manufacturing methods, physical properties, and applications of optical films can be applied without restriction, covering a wide range of information widely known in the field of conventional films.

[0111] However, as an example, optical films can be used for films with variable transmittance.

[0112] 4. Optical devices

[0113] According to another embodiment of the present invention, an optical device comprising the optical film of the above embodiments can be provided. All details of the optical film of the above embodiments include the details described above in the embodiments.

[0114] The information regarding optical devices can be applied without limitation to various conventionally known optical devices. For example, the specific structure, dimensions, manufacturing methods, physical properties, and applications of optical devices can be applied without limitation to a wide range of information widely known in the conventional display field.

[0115] However, as an example, the optical device can be a light modulation device that includes an optical film comprising another embodiment. Specific examples of light modulation devices are not particularly limited, but may include, for example, smart windows, isotropic films, polarization control films, liquid crystal displays, organic light-emitting displays, etc.

[0116] More specifically, as an example of an optical device, a liquid crystal display element is provided, the liquid crystal display element having: a set of substrates arranged facing each other, electrodes formed on one or both sides of the facing surface of each of the set of substrates, a liquid crystal layer disposed between the substrates and formed by coating a liquid crystal nanocapsule solution of the present invention, and an electric field applying device for applying an electric field to the liquid crystal nanocapsules of the present invention in the liquid crystal layer through the electrodes.

[0117] The threshold voltage of an optical device can be 64 V or less, or 63 V or less, or 61 V or less, or 1 V or more, or within the range of 1 V to 64 V, or within the range of 1 V to 63 V, or within the range of 1 V to 61 V, or within the range of 60 V to 63 V, or within the range of 60 V to 61 V. The threshold voltage refers to the voltage at 10% of the maximum transmittance, and because the optical device has a threshold voltage within the aforementioned range, it can be driven even at lower voltages. There are no limitations on the method for measuring the threshold voltage, and various methods widely known in the field of optical devices containing liquid crystals can be applied without limitation. However, as an example, it can be measured using a haze meter (NDH7000, Nippon Denshoku) while a voltage is applied via a function generator.

[0118] Furthermore, the contrast ratio of the optical device can be 10 or greater, or 11 or greater, or 20 or less, or in the range of 10 to 20, or in the range of 11 to 20, or in the range of 11.1 to 16.5. Contrast ratio refers to the ratio between the transmittance at 100V and the transmittance at 0V, and because the optical device has a contrast ratio within the aforementioned range, it can achieve excellent transmittance variation even at lower voltages. There are no limitations on the method for measuring contrast ratio, and various methods widely known in the field of optical devices incorporating liquid crystals can be applied without limitation. However, as an example, it can be measured using a haze meter (NDH7000, Nippon Denshoku) while a voltage is applied via a function generator.

[0119] 5. Variable transmittance device

[0120] According to another embodiment of the present invention, a variable transmittance device comprising the optical film of the above embodiments can be provided. All details of the optical film of the above embodiments include those described above in the embodiments.

[0121] The content regarding variable transmittance devices can be applied without limitation to various conventionally known variable transmittance devices. For example, the specific structure, dimensions, manufacturing methods, physical properties, and applications of variable transmittance devices can be applied without limitation to various contents widely known in the conventional liquid crystal capsule field. However, as an example, a variable transmittance device may include a polarizing layer and a variable transmittance layer, and the dichroic dye of the embodiment may be included in the polarizing layer or the variable transmittance layer as a light modulation material.

[0122] The variable transmittance device of this application can be applied to all devices where variability in transmittance can be applied. For example, the variable transmittance device of this application can be applied to sunroofs, vehicle windows, goggles, sunglasses, helmets, etc., to provide a variable transmittance device. As long as the variable transmittance device includes the variable transmittance device of this application, there are no particular limitations on other components or structures, and all content known in the art can be appropriately applied. A variable transmittance device is provided, wherein the variable transmittance device is applied to a sunroof, vehicle window, goggles, sunglasses, or helmet.

[0123] Beneficial effects

[0124] According to the present invention, liquid crystal nanocapsules and capsule solutions, optical films, optical devices, and transmissivity variable devices using the same can be provided, which can induce a high rate of change of transmissivity even at low voltages by reducing the surface interaction energy of the liquid crystal encapsulated inside the capsule. Detailed Implementation

[0125] The present disclosure will be described in detail below with reference to the following embodiments. However, these embodiments are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0126] <Example: Manufacturing of liquid crystal nanocapsules and capsule solutions>

[0127] Example 1

[0128] 0.125 g (0.25 wt% based on the total weight of the aqueous solution) of emulsifier (2,4,7,9-tetramethyl-5-decyn-4,7-diol, HLB:3) was added to an aqueous solution containing 0.7 g of polyvinyl alcohol (PVA) and 49.3 g of water, and the mixture was stirred to dissolve it. Subsequently, 2.2 g of liquid crystal (1,2,3-trifluoro-5-[(trans,trans)-4'-ethyl[1,1'-dicyclohexyl]-4-yl]benzene; manufactured by TCI), 0.11 g of anisotropic dye (Sudan Black B), and 0.023 g of octamethyltrisiloxane (1 wt% based on the total weight of the mixture of liquid crystal and anisotropic dye) were added, and a first emulsification was performed for 1 hour at 18,000 rpm using an IKA homogenizer T25. A second emulsification was then performed 5 times using a microfluidizer at 10,000 psi to form droplets.

[0129] Subsequently, the temperature of the solution was raised to 40°C with stirring, and PVA was adsorbed onto the surface of the droplets for 18 hours.

[0130] Subsequently, 0.8 g of 40% glyoxal aqueous solution was introduced as a crosslinking agent, and the pH of the solution was adjusted to 3 so that the adsorbed PVA could be crosslinked at 40°C for 18 hours.

[0131] After concentrating the solution for 1 hour using a rotary evaporator, the supernatant was recovered by centrifugation at 5,000 rpm for 30 minutes to remove unencapsulated liquid crystals, thereby obtaining a capsule solution containing liquid crystal nanocapsules.

[0132] Example 2

[0133] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 1, except that 0.25 g (0.5 wt% based on the total weight of the aqueous solution) of dimethylpolysiloxane graft copolymer of formula a (weight average molecular weight: 3,000; HLB: 0; CAS No. 68550-66-4) was introduced instead of 0.125 g (0.25 wt% based on the total weight of the aqueous solution) of 2,4,7,9-tetramethyl-5-decyn-4,7-diol as an emulsifier.

[0134] [Chemical formula a]

[0135]

[0136] In chemical formula a, x is an integer in the range of 1 to 100, y is an integer in the range of 1 to 100, and n is an integer in the range of 0 to 20.

[0137] Example 3

[0138] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 1, except that 0.25 g (0.5 wt% based on the total weight of the aqueous solution) of dimethylpolysiloxane linear copolymer of formula b (weight average molecular weight: 2,800; HLB: 0; CAS No. 161755-53-9) was introduced instead of 0.125 g (0.25 wt% based on the total weight of the aqueous solution) of 2,4,7,9-tetramethyl-5-decyn-4,7-diol as an emulsifier.

[0139] [Chemical formula b]

[0140]

[0141] In chemical formula b, p is an integer in the range of 0 to 20, q is an integer in the range of 1 to 100, and r is an integer in the range of 0 to 20.

[0142] <Comparative Example: Manufacturing of Liquid Crystal Nanocapsules and Capsule Solutions>

[0143] Comparative Example 1

[0144] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 1, except that octamethyltrisiloxane was not used.

[0145] Comparative Example 2

[0146] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 2, except that octamethyltrisiloxane was not used.

[0147] Comparative Example 3

[0148] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 3, except that octamethyltrisiloxane was not used.

[0149] Comparative Example 4

[0150] Liquid crystal nanocapsules and capsule solutions were prepared in the same manner as in Example 1, except that 0.25 g (0.50 wt% based on the total weight of the aqueous solution) of ethoxylated tetramethyldecynediol (EO 1.3 mol; CAS No.: 9014-85-1) was used instead of 0.125 g (0.25 wt% based on the total weight of the aqueous solution) of 2,4,7,9-tetramethyl-5-decynedi-4,7-diol as an emulsifier.

[0151] <Experimental Example>

[0152] The physical properties of the liquid crystal nanocapsules or capsule solutions obtained in the above embodiments and comparative examples were measured by the following methods, and the results are shown in Table 1.

[0153] 1. Physical properties of liquid crystal nanocapsules

[0154] (1) Average diameter of capsules in capsule solution (nm)

[0155] The average diameter (nm) of the capsules was measured using a Malvern Zetasizer zs with 4 mL of diluted capsule solution (in which water and capsule solution were mixed at a weight ratio of 4:1) at RI: 1.5 and 25°C.

[0156] (2) The ratio of liquid crystals in the capsule solution (mass%)

[0157] After lyophilizing 5 mL of capsule solution, the mass was measured to calculate the solids content per unit volume. 1 mg of the lyophilized capsule solution was introduced into a METTLER TOLEDO TGA2 device, and the temperature was increased from 50°C to 700°C at a heating rate of 10°C / min. The mass reduction according to the temperature was then measured. The percentage of liquid crystals (mass%) in the capsule solution was obtained by measuring the mass ratio decreasing over a range of 200°C to 300°C.

[0158] 2. Physical properties of liquid crystal nanocapsule membranes

[0159] (1) Thickness (µm)

[0160] 1 mL of the capsule solution was coated onto the ITO layer of a PET-ITO membrane using a 200 μm membrane applicator, and then dried at 70 °C for 2 hours to prepare a liquid crystal nanocapsule membrane. The thickness of the liquid crystal nanocapsule membrane was measured using an alpha step (KLA TENCOR).

[0161] (2) T 关 (%), Haze 关 (%), threshold voltage (V), CR

[0162] After laminating the ITO surface of the PET-ITO film (GMP EXCELAM-SMART 655) onto the top of the liquid crystal nanocapsule film, the electrode strips are attached to the ITO surface.

[0163] T was measured using a haze meter (Nippon Denshoku, NDH7000). 关 (It is the transmittance of the liquid crystal nanocapsule film without applied voltage (transmittance at an applied voltage of 0 V)) and haze. 关(It is the haze of the liquid crystal nanocapsule film on which no voltage is applied (haze at an applied voltage of 0 V)).

[0164] In addition, when a voltage is applied through the function generator, the threshold voltage (which is the voltage at 10% of the maximum transmittance) and contrast ratio (CR) (which is the ratio between the transmittance at 100 V and the transmittance at 0 V) ​​are measured by a haze meter (Nippon Denshoku, NDH7000).

[0165] 3. Tni Analysis of Liquid Crystals

[0166] The disk was placed in the METTLER TOLEDO DSC3 device, and 0.5 mL of capsule solution was introduced. The temperature was increased from 25°C to 200°C at a heating rate of 5°C / min to measure the onset temperature (the lowest temperature at which endothermic and exothermic reactions are first observed) and the peak temperature (the temperature at which endothermic and exothermic reactions occur most actively).

[0167] In addition, the initial temperature of the free liquid crystal not encapsulated in the capsule was measured (121°C), and the change in initial temperature was calculated using the following mathematical formula 1 ( ).

[0168] [Mathematical Expression 1]

[0169] Initial temperature change = (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystal nanocapsules) - (lowest temperature at which heat absorption or release occurs during DSC measurement of liquid crystals)

[0170] In addition, the peak temperature (125°C) of the free liquid crystal not encapsulated in the capsule was measured, and the change in peak temperature was calculated using the following mathematical formula 2. ).

[0171] [Mathematical Expression 2]

[0172] Peak temperature change = (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal nanocapsules) - (Temperature at the peak where heat absorption or release is at its maximum during DSC measurement of liquid crystal).

[0173] [Table 1]

[0174] Experimental measurement results

[0175]

[0176] As shown in Table 1, the liquid crystal nanocapsules of the embodiments were measured to have a temperature range of 35°C to 37°C. The value of the [value] is lower than that of the comparative examples. Therefore, the liquid crystal nanocapsule film of the embodiment was measured to have a threshold voltage in the range of 60 V to 63 V, which is lower than that of the comparative examples, and it was determined that driving is possible even at lower voltages. Furthermore, the liquid crystal nanocapsule film of the embodiment was measured to have a contrast ratio in the range of 11.1 to 16.5, which is equal to or higher than that of the comparative examples, and it was determined that excellent transmittance variation can be achieved even at lower voltages.

Claims

1. A liquid crystal nanocapsule, comprising: The core comprises liquid crystal; and A polymer shell is formed on the surface of the core; The sum of the initial temperature change value according to the following mathematical formula 1 and the peak temperature change value according to the following mathematical formula 2 is 37.5℃ or less: [Mathematical Expression 1] Initial temperature change = (lowest temperature at which heat absorption or release occurs during the DSC measurement of the liquid crystal nanocapsule) - (lowest temperature at which heat absorption or release occurs during the DSC measurement of the liquid crystal) [Mathematical Expression 2] Peak temperature change = (temperature at the peak where heat absorption or release is at its maximum during the DSC measurement of the liquid crystal nanocapsule) - (temperature at the peak where heat absorption or release is at its maximum during the DSC measurement of the liquid crystal).

2. The liquid crystal nanocapsule according to claim 1, The initial temperature change value according to the mathematical formula 1 is 18.5°C or less.

3. The liquid crystal nanocapsule according to claim 1, The peak temperature variation value according to the mathematical formula 2 is 21.5℃ or less.

4. The liquid crystal nanocapsule according to claim 1, The core also contains emulsifiers and siloxane-based additives.

5. The liquid crystal nanocapsule according to claim 4, The emulsifier is based on 100 mol% of the emulsifier, and the content of the ethylene oxide repeating unit of the emulsifier is less than 0.001 mol.

6. The liquid crystal nanocapsule according to claim 4, The emulsifiers mentioned above include alkynyl diol-based compounds or siloxane polyether copolymers containing propylene oxide.

7. The liquid crystal nanocapsule according to claim 4, The molar mass of the siloxane-based additive is 500 g / mol or less.

8. The liquid crystal nanocapsule according to claim 4, The siloxane-based additives mentioned above include trisiloxane-based compounds.

9. The liquid crystal nanocapsule according to claim 4, The siloxane-based additives mentioned above are octamethyltrisiloxane or hexamethylcyclotrisiloxane.

10. The liquid crystal nanocapsule according to claim 4, The content of the siloxane-based additive is in the range of 5 to 50 parts by weight, based on 100 parts by weight of the emulsifier.

11. The liquid crystal nanocapsule according to claim 1, The liquid crystal mentioned therein is a fluorine-based liquid crystal.

12. The liquid crystal nanocapsule according to claim 1, The average diameter of the liquid crystal nanocapsules is in the range of 200 nm to 300 nm.

13. A capsule solution comprising the liquid crystal nanocapsules according to claim 1 and a solvent.

14. An optical film comprising the liquid crystal nanocapsules according to claim 1.

15. An optical device comprising the optical film according to claim 14.

16. A variable transmittance device comprising the optical film according to claim 14.

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