JP2012082082A - Liquid crystal dispersion silica nanoparticle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide liquid crystal dispersion silica nanoparticles capable of manufacturing a liquid crystal display element that is bright and high contrast, has a low driving voltage, and shows outstanding display performance.SOLUTION: The silica nanoparticles containing a liquid crystal comprises dispersing a liquid-crystalline material in silica nanoparticles whose average particle size is 400 nm or smaller.

Description

  The present invention relates to a liquid crystal-containing silica nanoparticle and a liquid crystal display device using the same.

  The liquid crystal display device has advantages such as thinness, light weight, low power driving, and low power consumption. The current liquid crystal display device is mainly driven by TFT. The orientation of the liquid crystal is regulated by applying a rubbing treatment after thinly applying polyimide, drying and curing. In order to align the liquid crystal vertically when no voltage is applied, it is usually performed by introducing an alkyl chain standing perpendicular to the coating film made of polyimide.

  In addition, in order to manufacture a liquid crystal panel, it is necessary to inject liquid crystal between two substrates subjected to alignment treatment. There is a problem that the gap is small and injection is difficult. Furthermore, since light switching is performed by using a polarizer, the light use efficiency is low, and particularly in the case of a reflective liquid crystal panel using external light, there is a problem that the reflectance of white is low. .

  The sol-gel method by Stober et al. Is generally used for the preparation of silica nanoparticles. Tetraethyl orthosilicate (TEOS) and concentrated aqueous ammonia are added for polycondensation in a mixed solvent of water and ethanol (4: 1). The method is prepared by stirring at room temperature. At that time, the particle size can be adjusted by the concentration of alcohol, TEOS or ammonia water used and the reaction time. However, this is the first time that the liquid crystal is fixed to nano-sized silica particles using this method.

  In order to solve such a problem, various methods are taken. For example, Patent Documents 1 to 3 disclose liquid crystal display elements using liquid crystal silica nanoparticles. However, these liquid crystal silica nanoparticles have problems in terms of transparency, colorability, contrast and the like.

JP-A-11-142822 Japanese Patent Laid-Open No. 10-081882 JP2002-275471

  An object of the present invention is to provide liquid crystal silica nanoparticles capable of producing a liquid crystal display element having excellent display performance that is bright, has high contrast, and has a low driving voltage.

  Another object of the present invention is to provide liquid crystal silica nanoparticles capable of producing a liquid crystal display element having excellent display performance that is bright, has high contrast, and has a low driving voltage.

  It is another object of the present invention to provide an energy saving alternative member for the current liquid crystal display.

The present inventor has succeeded in producing new functional nanoparticles in which a liquid crystalline substance such as nematic liquid crystal is dispersed in silica nanoparticles. The resulting nanoparticles have optical anisotropy,
The present invention provides the following liquid crystal-containing silica nanoparticles and a liquid crystal display device using the same.
Item 1. Liquid crystal-containing silica nanoparticles obtained by dispersing a liquid crystalline substance in silica nanoparticles having an average particle diameter (major diameter or radius) of 400 nm or less.
Item 2. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, which have optical anisotropy generated by the presence of a liquid crystalline substance in a minute space dispersed in silica.
Item 3. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, wherein the liquid crystal substance contained therein is a liquid crystal having a nematic phase.
Item 4. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, wherein the encapsulated liquid crystalline substance exhibits a reversible phase transition with a crystalline solid or liquid depending on temperature.
Item 5. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, wherein the alignment of the encapsulated liquid crystalline substance can be changed by an electric field applied from the outside.
Item 6. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, wherein the birefringence changes by application of an electric field.
Item 7. Item 2. The liquid crystal-containing silica nanoparticles according to item 1, which are single crystals.
Item 8. Item 8. A liquid crystal display device comprising the liquid crystal-containing silica nanoparticles according to any one of items 1 to 7.

  The liquid crystal-containing silica nanoparticles of the present invention can include a liquid crystal material so as to have the properties, and can provide a bright, high-contrast liquid crystal display device with excellent display quality.

  When the silica nanoparticles of the present invention are applied to a substrate to form a liquid crystal silica nanoparticle film, a liquid crystal display element having good orientation can be obtained.

  The present invention is useful as an energy saving alternative member of the current liquid crystal display.

Silica nanoparticle aqueous dispersion containing ZLI1132. Absorption spectrum of silica nanoparticle aqueous dispersion containing ZLI1132. Polarized light micrograph of a crystal-like solid piece. When viewed under crossed Nicols, it looks like the left picture, but when the sample is rotated 45 °, the quenching occurs uniformly as shown in the right figure.

  Silica nanoparticles containing a liquid crystalline material can be synthesized according to existing methods for synthesizing silica nanoparticles. Specifically, silica nanoparticles are synthesized by dissolving or dispersing a silane alkoxide, which is a raw material of silica nanoparticles, and a liquid crystalline material in a lower alcohol or a mixed solvent of lower alcohol and water, and polymerizing with a basic substance such as concentrated aqueous ammonia. It can be obtained according to conventional methods such as A preferred synthesis method is the Stover method.

  Silica nanoparticles containing a liquid crystalline material include crystals having optical anisotropy. The silica nanoparticles of the present invention may consist only of optically anisotropic crystals, and a mixture of optically anisotropic particles (crystals) and optically isotropic particles (crystals). It may be.

  As the liquid crystal material, any material can be used, and examples thereof include ZLI1132 (Merk, aeutectic mixture of alkylcyclohexylcyanobenzenes and alkylcyclohexylcyclobiphenyls), 5CB (Aldrich, 4'-Pentyl-4-biphenyl-carbonitrile) and the like.

  The silica nanoparticles of the present invention have an average particle size of 400 nm or less, preferably 15 to 400 nm, more preferably 15 to 100 nm. The polydispersity is 1.5 or less, preferably 1.4 or less, more preferably 1.3 or less, further preferably 1.2 or less, particularly preferably 1.1 or less, and particularly 1.05 or less. The silica nanoparticles of the present invention have the same particle size, many particles having a particle size near the average particle size, and low polydispersity. Since the polydispersity is small, there is an advantage that the particle diameter does not vary and the transparency is high.

  The diameter (major axis) of the silica nanoparticles can be measured with an electron microscope, and the arithmetic average of the diameters can be used as the average particle diameter.

  The liquid crystal-containing silica nanoparticles of the present invention are composed of 99.9 Wt% to 99 wt% by weight of silica nanoparticles, preferably 99.9 wt% to 99.2 wt%, more preferably 99.85 wt% to 99.4 wt% and 0.1 wt% of the liquid crystalline material. % To 1 wt% by weight, preferably 0.1 wt% to 0.8 wt% by weight, more preferably 0.15 wt% to 0.6 wt% by weight.

  Although the liquid crystalline material used for the liquid crystal silica nanoparticles is not particularly limited, nematic liquid crystals, smectic liquid crystals, cholesteric liquid crystals, and the like can be used, including single or two or more kinds of liquid crystalline compounds and substances other than liquid crystalline compounds. It may be a mixture.

  By using a GH liquid crystal material in which a dichroic dye is added to the liquid crystal material, a polarizing plate is not necessary, so that good display characteristics can be obtained. The dichroic dye to be used should have as high a dichroic ratio as possible, and preferably has a dichroic ratio of 10 or more.

  The liquid crystal display element of the present invention can perform either monochrome display or color display. In the case of monochrome display, a black dichroic dye is added to the liquid crystal material. In the case of color display, a three-layer GH host type in which three colors of liquid crystal silica nanoparticles are prepared using a color filter or using a liquid crystal to which yellow, cyan, and magenta dichroic dyes are added. This is realized by configuring a liquid crystal display element. In addition, when particles are prepared using liquid crystal materials to which red, blue, and green dichroic dyes are added, these can be printed on the substrate in the same manner as the color filter and displayed by juxtaposed color mixing. is there.

  Hereinafter, the liquid crystal silica nanoparticles and the display device of the present invention will be described in more detail with reference to examples.

Example 1
Silica nanoparticles are prepared by hydrolysis and polycondensation reaction of silane alkoxide using Stober sol-gel method. That is, the volume ratio of ethanol and distilled water was set to 4: 1, and liquid crystal ZLI1132 (Merk, aeutectic mixture of alkylcyclohexylcyanobenzenes and alkylcyclohexylcyanobiphenyls) was added thereto, followed by hydrolysis by adding tetraethylorthosilicate (TEOS). Then, silica nanoparticles containing ZLI1132 were prepared by polycondensation by adding concentrated aqueous ammonia. After the preparation, in order to remove ZLI1132 remaining in the solution, it was washed with ethanol four times by ultrafiltration, and then substituted with distilled water to obtain a silica nanoparticle aqueous dispersion containing ZLI1132.

  Actually, 50 μl of ZLI1132 was added to 4 ml of ethanol in a glass sample bottle on a hot plate at 80-100 ° C. and magnetically stirred. Thereafter, 50 μl of TEOS was added and stirring was continued, and further 1 ml of distilled water and 50 μl of concentrated aqueous ammonia were added and left magnetically stirred for 1 day. Subsequently, ultrafiltration (Amicon, YM-100 membrane filter, using a pore size of about 10 nm) was washed four times with ethanol, and further washed with distilled water to obtain an aqueous silica nanoparticle dispersion containing ZLI1132. (Figure 1). The absorption spectrum is shown in FIG. Then, it dried in the desiccator and obtained white powder about 1.6mg.

Example 2
Silica nanoparticles are prepared by hydrolysis and polycondensation reaction of silane alkoxide using Stober sol-gel method. That is, the volume ratio of ethanol and distilled water was 4: 1, and liquid crystal 5CB (Aldrich, 4'-Pentyl-4-biphenyl-carbonitrile, 98%) was added to this, followed by tetraethylorthosilicate (TEOS). This was hydrolyzed, and concentrated ammonia water was added and polycondensed to prepare silica nanoparticles containing 5CB. After the preparation, in order to remove 5CB remaining in the solution, it was washed with ethanol four times by ultrafiltration, and then centrifuged to obtain a precipitate. The precipitate was dried to obtain white powder of silica nanoparticles containing 5CB.

  Actually, 100 μl of 5CB was added to 20 ml of ethanol in a glass sample bottle at room temperature and magnetically stirred. Thereafter, 250 μl of TEOS was added and stirring was continued. Further, 5 ml of distilled water and 250 μl of concentrated aqueous ammonia were added and left stirring for 1 day. Then, after washing 7 times with ultrafiltration (Amicon, YM-100 membrane filter, using a pore size of about 10 nm) using ethanol, it was dried at room temperature in a desiccator, and about 59.6 silica white particles containing 5CB were obtained. mg was obtained. A crystal-like solid piece was present in the powder solid, and it was confirmed that a single crystal having optical anisotropy as shown in FIG.

  The amount of 5CB dispersed in silica nanoparticles was 0.1-1 wt% by comparing the absorbance of UV-visible absorption spectrum of 5CB solution with the dispersion solution spectrum of prepared liquid crystal dispersed silica nanoparticles.

Claims (8)

Liquid crystal-containing silica nanoparticles obtained by dispersing a liquid crystalline substance in silica nanoparticles having an average particle diameter (major diameter or radius) of 400 nm or less. 2. The liquid crystal-containing silica nanoparticles according to claim 1, wherein the liquid crystal-containing silica nanoparticles have optical anisotropy generated when the liquid crystal substance is present in a minute space dispersed in silica. The liquid crystal-containing silica nanoparticles according to claim 1, wherein the liquid crystal substance contained therein is a liquid crystal having a nematic phase. The liquid crystal-containing silica nanoparticles according to claim 1, wherein the liquid crystal substance contained therein exhibits a reversible phase transition between a crystalline solid and a liquid depending on temperature. The liquid crystal-containing silica nanoparticles according to claim 1, wherein the alignment of the liquid crystal substance contained therein can be changed by an electric field applied from the outside. The liquid crystal-containing silica nanoparticles according to claim 1, wherein birefringence changes by application of an electric field. The liquid crystal-containing silica nanoparticles according to claim 1, which are single crystals. The liquid crystal display element containing the liquid crystal containing silica nanoparticle of any one of Claims 1-7.