KR20070107439A - Liquid crystal material, preparation method thereof and liquid crystal device using the same - Google Patents

Abstract

A liquid crystal material is provided to produce a liquid crystal display device having excellent heat resistance and showing rapid switching property in a simple and cost-efficient manner. A liquid crystal material comprises a dispersion containing a fragment of a porous template having a nanostructure formed in a nanochannel, or a nanostructure obtained by removing the template from the fragment dispersed therein. The nanostructure is a nanowire, nanorod or nanodisk. The porous template is formed of a material selected from the group consisting of glass, silica and metal oxides including TiO2, ZnO, SnO2 and WO3.

Description

Liquid crystal material, a manufacturing method thereof and a liquid crystal device using the same {LIQUID CRYSTAL MATERIAL, PREPARATION METHOD THEREOF AND LIQUID CRYSTAL DEVICE USING THE SAME}

1A-1B are schematic perspective views of a liquid crystal device using a template in which nanostructures are formed.

2A-2B are schematic perspective views of a liquid crystal device using a nanostructure from which a template is removed.

3 is a cross-sectional schematic diagram showing an example of a liquid crystal element using the liquid crystal material of the present invention.

4 is a process schematic diagram illustrating a method of manufacturing a liquid crystal material according to an embodiment of the present invention.

5 is a schematic diagram illustrating a nanostructure formation process by a solid-liquid-solid (SLS) method.

6 is a schematic diagram illustrating a process for forming a nanostructure by a vapor-liquid-solid (VLS) method.

* Description of the symbols for the main parts of the drawings *

10,10 ': substrate 20: liquid crystal layer

The present invention relates to a liquid crystal material, a method for manufacturing the same, and a liquid crystal device using the same. More particularly, a nanostructure is manufactured by using a porous template, and then cut and cut into a dispersion medium with or without a template. A liquid crystal material, a manufacturing method thereof, and a liquid crystal element using the same.

Recently, researches for realizing large size, light weight, high resolution, thin film, and the like of display devices have been concentrated. Among the various display devices, the liquid crystal display device has the advantages of thin film, light weight, low voltage driving, low power consumption, etc., and therefore has been in the spotlight as the most commercial display device. TN, STN, and TFT type liquid crystal display devices are being produced. . Due to these advantages, the liquid crystal display is widely used as a display device of various portable information devices such as mobile phones and personal portable terminals as well as display devices such as computer monitors and liquid crystal televisions.

Liquid crystal is a material state that combines the liquidity of liquid and the optical properties of a solid (crystal). A liquid crystal is enclosed between two glass plates and a voltage is applied to change the direction of liquid crystal molecules to increase or decrease light transmittance. To display an image.

As the use of liquid crystals expands, the characteristics required for liquid crystal materials also become more diverse. For example, a wide range of operating temperatures, high speed response, low voltage drive, high voltage retention, reduction in reaction time, wide viewing angle characteristics, and reliability are required for liquid crystal materials.

Conventional low molecular weight liquid crystals or polymer liquid crystals have different properties depending on the type, position, etc. of functional groups in the molecule, and liquid crystal materials satisfying all of the above characteristics have not been developed yet.

The present invention is to overcome the problems of the prior art described above, one object of the present invention is to provide a novel liquid crystal material which is excellent in heat resistance, simple in structure and manufacturing process, fast switching and switchable by various methods. To provide.

It is another object of the present invention to provide a novel method for producing a liquid crystal material which can reduce the manufacturing cost since the manufacturing process is simple.

Another object of the present invention is to provide a liquid crystal device or an electro-optical device comprising the novel liquid crystal material of the present invention.

One aspect of the present invention for achieving the above object relates to a liquid crystal material comprising a cut piece of a porous template in which nanostructures are formed in a nanochannel or a dispersion in which a nanostructure from which a template is removed from these cut pieces is dispersed.

The porous template is formed of a material selected from the group consisting of glass, silica and metal oxides such as TiO ₂ , ZnO, SnO ₂ , and WO ₃ , the nanostructures being metal oxides, metal nitrides, semiconductors, metals, polymers, and It may be formed of a material selected from the group consisting of carbon nanotubes.

Another aspect of the present invention for achieving the above object is

 (a) preparing a nanostructure using a porous template comprising a plurality of nanochannels;

(b) cutting the porous template in which the nanostructure is formed in the nanochannel to obtain cut pieces;

and (c) dispersing the cut pieces obtained in the previous step in a dispersion medium.

In the present invention, the template may be removed before dispersing the cut pieces, and only the nanostructures may be separated and dispersed in a dispersion solvent to be used as a liquid crystal material.

In the present invention, the manufacturing step of the nanostructure is prepared by injecting the nanoparticles into the nanochannel and then annealed to prepare the nanostructure, or from the precursor by a solid-liquid-solid (SLS) method or vapor-liquid-solid (VLS) method The structure can be grown.

Another aspect of the present invention for achieving the above object relates to a liquid crystal element and an electro-optical element comprising the novel liquid crystal material of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The liquid crystal material of the present invention includes a cut piece in which nanostructures are formed in each channel of the porous template including a plurality of nanochannels, or a dispersion liquid in which a nanostructure in which a template is removed from these cut pieces is dispersed in a dispersion medium. It features. In the present invention, the nanostructure is meant to include both nanowires, nanorods, or nanodisks. The geometric shape of the liquid crystal material of the present invention is an elongated rod or flat board.

In the present invention, the template includes a plurality of nanochannels, the diameter of the porous template is in the range of 1nm ~ 1mm, the height is in the range of 100nm ~ 1mm. The diameter of the nanochannels of the porous template is preferably in the range of 1 to 100 nm, and the spacing between the nanochannels is preferably in the range of 2 nm to 1 μm. The liquid crystal material of the present invention cuts such a template into an appropriate length, and the length of the cut pieces is preferably 10 nm to 100 mm.

In the present invention, the porous template may be formed of a material selected from the group consisting of glass, silica and metal oxides such as TiO ₂ , ZnO, SnO ₂ , and WO ₃ . The nanostructure may be composed of a material selected from the group consisting of metal oxides, metal nitrides, semiconductors, metals, magnetic materials (dielectrics), polymers, and carbon nanotubes.

Examples of the semiconductor material include, but are not limited to, group II-VI, III-V, IV-VI, or IV compound semiconductors.

In another aspect, the present invention relates to a liquid crystal element or various electro-optical elements comprising the liquid crystal material of the present invention. In the present invention, the electro-optical device includes an electronic paper, an optical switch, a photoelectric conversion device, and the like, but is not necessarily limited thereto.

For example, in the structure of a TFT LCD including the liquid crystal material of the present invention, the liquid crystal panel is filled with the liquid crystal of the present invention between two substrates, and a TFT pixel and a liquid crystal alignment layer are formed on the glass plate on which light is incident. On the other glass plate, a color filter and a liquid crystal alignment layer are coated. Outside the two glass plates, a polarizer is attached. A color image is obtained by combining three types of color filters of R (Red), G (Green), and B (Blue).

1A-1B are schematic perspective views of a liquid crystal device using the liquid crystal material of the present invention using the cut template as it is, and FIGS. 2A-2B are schematic perspective views of a liquid crystal device using a nanostructure from which the template has been removed.

As shown in Figs. 1A and 1B, the liquid crystal material of the present invention can be injected into a liquid crystal cell such as a liquid crystal element to form a liquid crystal layer. The liquid crystal material of the present invention may be controlled to maintain a vertical alignment state as shown in FIG. 1A, or to maintain a horizontal alignment state as shown in FIG. 1B, and to have an inclined alignment in some cases. At this time, switching can be performed using an electrical, magnetic, or optical method. For example, in the case of electrically switching, the liquid crystal materials are aligned in the horizontal direction as shown in FIG. 1B when no voltage is applied, and when the voltage is applied, the liquid crystal materials are displayed in an electric field as shown in FIG. 1A. Can be aligned vertically).

On the other hand, when the template is dispersed in a removed state can be configured as shown in Figures 2a and 2b. The nanostructures separated from the template may be controlled to maintain a vertical alignment state as shown in FIG. 2A, or to maintain a horizontal alignment state as shown in FIG. 2B, and to have an oblique alignment in some cases.

The liquid crystal material of the present invention can be used for the production of various electro-optical elements such as electronic paper photoelectric conversion elements, optical switches, as well as liquid crystal display devices.

3 is a cross-sectional schematic diagram showing an example of a liquid crystal element using the liquid crystal material of the present invention. As shown in FIG. 3, in the structure of the liquid crystal cell, a liquid crystal layer 20 is formed between two sealed substrates 10 and 10 ', and an electrode for displaying an image to be displayed on the inner surface of the substrate, respectively. Are formed, and these electrodes are electrically connected to external terminals.

The manufacturing method of such a liquid crystal element is not specifically limited, It can manufacture by arbitrary methods well known in the technical field to which this invention belongs. For example, a sealing agent is printed on the glass substrates 10 and 10 'on which the ITO electrode is formed on the inner side, an alignment film is applied, and a liquid crystal material is injected into the liquid crystal through the injection hole while maintaining a constant gap. After encapsulation can be prepared. A general method of manufacturing a liquid crystal display is described in detail in a related article (E. Kaneko, Liquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displays, KTK Scientific Publishers, 1987, pp 12-30 & 163-172).

The liquid crystal element including the liquid crystal material of the present invention can be switched by various methods such as electrical, magnetic, and optical methods. For example, the liquid crystal element of the present invention is interposed between two polarizing plates to apply an external voltage to the liquid crystal element and change the alignment vector of the liquid crystal material to switch using the birefringence of the two polarizing plates and the liquid crystal material. have. On the other hand, if the nanostructure formed in the nano-channel of the porous template in the present invention has a magnetic susceptibility anisotropy, it can be switched by an optical method because it reacts anisotropically by light such as polarized UV.

In the liquid crystal element of the present invention, switching operation is possible and low voltage driving is possible only by changing the alignment direction of the liquid crystal material. In addition, since high-speed response can be realized by using the liquid crystal element of the present invention, a large area display (liquid crystal display device) can be easily manufactured by using the liquid crystal element of the present invention.

In another aspect, the present invention relates to a method for producing a liquid crystal material of the present invention. Method for producing a liquid crystal material of the present invention is characterized in that after fabricating the nanostructures using a porous template, it is cut and dispersed in the dispersion medium as the template itself or the template is removed.

4 is a flowchart illustrating a method of manufacturing a liquid crystal material according to the present invention. Referring to FIG. 4, first, a nanostructure is prepared using a porous template including a plurality of nanochannels (steps a to c), and the cut pieces are obtained by cutting the porous template in which the nanostructures are formed in the nanochannels. (Step d). Subsequently, the cut pieces obtained in the previous step are dispersed in a dispersion medium and used as a liquid crystal material. At this time, if necessary, as shown in step e in FIG. 1, the template may be removed and only the nanostructures may be dispersed and used in the dispersion medium. The step of removing the template may be performed by any method such as chemical etching, wet etching or pyrolysis.

The manufacturing step of the nanostructure is prepared by a porous template (step a) and placed on a metal catalyst-coated substrate (step b), a solid-liquid-solid (SLS) method or a vapor-liquid-solid (VLS) method By the process of growing into a nanostructure (step c). Alternatively, nanostructures may be prepared by implanting nanoparticles into the nanochannels of the porous template and then annealing them.

Hereinafter, each step of the present invention will be described in more detail.

Nanostructure manufacturing step

In the case of manufacturing a nanostructure using a porous template, as shown in FIG. 4, first, a porous template including a plurality of long nanochannels in the form of a channel is prepared, and using this template, solid-liquid- Nanostructures are formed by solid or vapor-liquid-solid (VLS) methods. In this case, the nanostructure may be manufactured in the form of nanowires, nanorods, or nanodisks.

Alternatively, the method for preparing the nanostructure using the porous template is not particularly limited, and various methods may be used. For example, the nanostructure may be prepared by injecting and then annealing the nanoparticles into the nanochannel of the porous template. Specifically, when nanoparticles or nanoparticle precursors are injected into the nanochannels of the porous template, the nanostructures are formed by heat treatment, electrical resistance heating, or mechanical pressure. Injected nanoparticles are heated above the melting point through this method to be connected to each other to form a nanostructure structure. In this case, the heat treatment may be performed at 100 ° C. or more for 1 minute or more.

In the present invention, it is possible to easily control the size, shape, and regularity of the nano-channel by making the size, length and spacing between the nano-channels of the porous template to the required specifications. In the present invention, the template may be formed of a material selected from the group consisting of glass, silica and metal oxides such as TiO ₂ , ZnO, SnO ₂ , and WO ₃ .

The production of a template is basically divided into a process of making a template base material and a process of extracting a template form from the base material. The formation of nanochannels is determined by the extraction speed and cooling conditions of the extraction process, and in particular, by pre-processing the desired shape of the nanochannels in the base material, it is possible to obtain a structure in which the original shape is reduced to nano size through the extraction process. Do.

Since the diameter or height of the porous template is high, it can be selected according to the size of the substrate on which the nanostructure is grown, but the diameter is preferably 1 nm to 1 mm and the height is 100 nm to 1 mm. Several templates may be used depending on the size of the substrate. In addition, the nanochannels in the porous template is dependent on the specifications of the nanostructures to be prepared, the diameter is 1 ~ 100nm, and the nanochannel spacing is preferably 2nm ~ 1㎛.

In the present invention, the nanostructure may be composed of a metal oxide, a metal nitride, a semiconductor, a metal, a polymer, or a carbon nanotube, and the semiconductor may be a group II-VI, III-V, IV-VI or IV compound semiconductor. Can be used. Preferred examples thereof include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InP, InAs, InSb, SiC, Fe, Pt, Ni, Co, Al , Ag, Au, Cu, FePt, Fe ₂ O ₃ , Fe ₃ O ₄ , Si, Ge, but are not necessarily limited to these. In the present invention, nanoparticles of a core-shell alloy structure may also be used.

If a porous template is provided, it is placed on the substrate on which the metal catalyst layer is formed. In the present invention, the metal catalyst layer is formed by coating a metal catalyst, for example, an Au metal catalyst, on a substrate. At this time, the substrate may be washed in advance according to a conventional method to remove impurities.

Examples of the substrate that can be used in the present invention include a silicon substrate or a substrate coated with silicon on glass.

In addition, nanoparticle precursors may be formed into nanoparticles by injecting the nanoparticle precursors into appropriate pores instead of nanoparticles. Specifically, the nanoparticle precursor is reacted by separately adding a metal precursor and a chalcogenide precursor, or using a single precursor. Examples of the solvent for dissolving the nanoparticle precursors include alkyl phosphines having 6 to 22 carbon atoms, alkyl phosphine oxides having 6 to 22 carbon atoms, alkyl amines having 6 to 22 carbon atoms, or mixtures thereof.

On the other hand, in the case of forming the nanostructure by the SMS or VLS method, a metal catalyst is coated on the substrate. In this case, the metal catalyst to be coated may be used as long as it is a metal catalyst capable of growing a nanostructure. Specifically, Au, Ni, Fe, Ag, Pd, Pd / Ni may be exemplified, but is not limited thereto. In this case, the metal catalyst may be coated on the substrate in the form of nanoparticles, or a thin film, the thickness of the metal catalyst coating layer coated on the substrate is preferably 50nm or less.

The metal catalyst is deposited on a substrate by conventional methods such as chemical vapor deposition (CVD), sputtering, e-beam evaporation, vacuum deposition, spin coating, dipping, and the like. Can be deposited.

After coating the catalyst layer on the substrate, the nanostructure is grown by a solid-liquid-solid (SLS) process or a vapor-liquid-solid (VLS) process.

The solid-liquid-solid (SLS) process condenses silicon diffused from a solid substrate (e.g., a silicon substrate) onto the surface of the molten catalyst without supplying additional vapor phase silicon, as shown in FIG. It is a method of growing into a nanostructure by crystallization.

In contrast, a vapor-liquid-solid (VLS) process, as shown in FIG. 6, is carried out on the surface of a molten catalyst such as gold, cobalt, nickel, or the like, containing vapor phase silicon-containing paper transported inside a high temperature furnace. It is a method of growing silicon nanostructures by condensing and crystallizing silicon.

Specifically, the solid-liquid-solid (SLS) process of the present invention can be carried out by placing the substrate on which the template is placed into a reactor and heating it while injecting gas to form nanostructures with nanostructured sources diffused from the substrate. have. In this case, a force may be applied so that the metal on the substrate may be included in the growth of the nanostructure.

In addition, the vapor-liquid-solid (VLS) process may be performed by placing a substrate on which a template is placed in a reactor and heating it while injecting a gas and a nanostructure source to form a nanostructure.

Specifically, the gas used in the solid-liquid-solid (SLS) and vapor-liquid-solid (VLS) processes may be selected from the group consisting of Ar, N ₂ , He, and H ₂ , but is not limited thereto. It doesn't happen.

In the solid-liquid-solid (SLS) and vapor-liquid-solid (VLS) processes, the pressure may be performed at 760 torr or less, and the temperature may be performed at 800 to 1200 ° C for SLS and 370 to 600 ° C for VLS. Can be. Meanwhile, in the case of a vapor-liquid-solid (VLS) process, silicon nanowires may be SiH ₄ , SiCl ₄ , SiH ₂ Cl _2, or the like.

Cutting steps of the template

Once the nanorods are formed in the nanochannels of the porous template they are cut to the appropriate length. In this case, the template may be cut in a template or nanostructure having a length of mm or less by using a focused ion beam in addition to a method of cutting a glass. At this time, the size of the cut pieces is preferably in the range of 10 nm to 100 mm in length.

In the present invention, the step of removing the template may optionally be further processed before dispersing the cut pieces. Once the nanorods are formed in the nanochannels of the porous template, pure nanostructures are obtained by removing the template using an etchant, such as hydrofluoric acid, as shown in FIG. Specifically, the etching may be performed using a solvent having selectivity with respect to the template and the screw structure.

Cutting  Dispersion stage

The cut pieces may be used by dissolving them in a dispersion solvent such as an arbitrary organic solvent or an aqueous solution and, if necessary, mixing a dispersant or the like so that the nanostructures are well dispersed in the precursor solution.

The dispersant that can be used is composed of a head including a polar group that can adsorb to the surface of the cut piece and a non-polar tail that can adsorb to the solvent. Such dispersant is not particularly limited, but preferably includes a polar group such as an amine group or a salt thereof, a carboxyl group or a salt thereof, a phosphoric acid group or a salt thereof, a sulfonic acid group or a salt thereof, or a hydroxy group as a head part, and polyethylene glycol, poly Propylene glycol, an alkyl group having 5 to 30 carbon atoms, and the like may be included as a tail portion.

At this time, the dispersion medium usable may include aromatic hydrocarbon compounds such as toluene and xylene, ether compounds such as tetrahydrofuran and 1,2-butoxyethane, ketone compounds such as acetone and methyl ethyl ketone, ethyl acetate, butyl acetate and butylcar Ester compounds such as bitol acetate (BCA; butyl carbitol acetate), alcohol compounds such as isopropyl alcohol, diethylene glycol monobutyl ether, terpineol, 2-phenoxyethanol, and mixed solvents thereof.

Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiments, and it will be apparent to those skilled in the art that many modifications are possible within the scope of the technical idea of the present invention.

The liquid crystal material of the present invention has the advantages of being heat resistant, simple in structure and manufacturing process, inexpensive, low power consumption, high response and switching in various ways. Therefore, the liquid crystal material of the present invention can be utilized as a high functional material in a wide range of fields such as an optical filter, a liquid crystal alignment film, a large area display, a projection display, an electronic and electrical functional material, and a liquid crystal elastomer.

Claims (24)

A liquid crystal material comprising a cut piece of a porous template in which nanostructures are formed in a nanochannel or a dispersion in which a nanostructure from which a template is removed is dispersed from these cut pieces. The liquid crystal material of claim 1, wherein the nanostructures are nanowires, nanorods, or nanodisks. The liquid crystal material according to claim 1, wherein the porous template is formed of a material selected from the group consisting of glass, silica and metal oxides such as TiO ₂ , ZnO, SnO ₂ , and WO ₃ . The liquid crystal material of claim 1, wherein the nanostructure is formed of a material selected from the group consisting of metal oxides, metal nitrides, semiconductors, metals, polymers, and carbon nanotubes. The liquid crystal material according to claim 4, wherein the semiconductor is a Group II-VI, III-V, IV-VI or Group IV compound semiconductor. The liquid crystal material according to claim 1, wherein the porous template has a diameter of 1 nm to 1 mm and a height of 100 nm to 1 mm. The liquid crystal material according to claim 1, wherein the nanochannel of the porous template has a diameter of 1 to 100 nm, a gap between the nanochannels of 2 nm to 1 m, and a length of the cut piece of 10 nm to 100 mm. A liquid crystal element comprising the liquid crystal material of claim 1 between two substrates having a transparent electrode layer. An electro-optical device comprising the liquid crystal material of claim 1. 10. A device according to claim 9, wherein the device is an electron-paper, an optical switch, or a photoelectric conversion device. (a) preparing a nanostructure using a porous template comprising a plurality of nanochannels; (b) cutting the porous template in which the nanostructure is formed in the nanochannel to obtain cut pieces; (c) Dispersing the cut pieces obtained in the previous step in a dispersion medium. The method of claim 11, wherein the manufacturing of the nanostructures comprises injecting the nanoparticles into the nanochannels and then annealing to prepare the nanostructures. The method of claim 11, wherein the manufacturing of the nanostructures comprises growing the nanostructures in the nanochannels by a solid-liquid-solid (SLS) method or a vapor-liquid-solid (VLS) method. The method of claim 13, wherein the solid-liquid-solid (SLS) process is to insert the substrate on which the template is placed in the reactor to heat the gas injection to form a nanostructure from the nanostructure source diffused from the substrate Way. The method of claim 13, wherein the vapor-liquid-solid (VLS) process involves placing the substrate on which the template is placed in a reactor and heating it while injecting gas and nanostructure sources to form nanostructures. 12. The method of claim 11, wherein the porous template is formed of glass, silica and a material selected from the group consisting of metal oxides such as TiO ₂ , ZnO, SnO ₂ , and WO ₃ . The method of claim 11, wherein the nanostructure is formed of a material selected from the group consisting of metal oxides, metal nitrides, semiconductors, metals, polymers, and carbon nanotubes. 18. The method of claim 17, wherein the semiconductor is a Group II-VI, III-V, IV-VI or Group IV compound semiconductor. The method of claim 11, wherein the porous template has a diameter of 1 nm to 1 mm and a height of 100 nm to 1 mm. 20. The method of claim 19, wherein the nanochannel of the porous template has a diameter of 1-100 nm, a gap between nanochannels of 2 nm-1 μm, and a nanostructure having a length of 10 nm-100 mm. 12. The method of claim 11, wherein said cutting of said template is cutting by aiming ion beams. 12. The method of claim 11, wherein the method further comprises removing a template before dispersing the cut piece. 23. The method of claim 22, wherein removing the template is removing the template by chemical etching, wet etching, or pyrolysis. The method according to claim 11, wherein the dispersion medium is selected from the group consisting of aromatic hydrocarbon compounds, ether compounds, ketone compounds, ethyl acetate, ester compounds, alcohol compounds and mixed solvents thereof.

Images