A polymer dispersed liquid crystal device and a preparation method thereof

Abstract

The present invention relates to a polymer dispersed liquid crystal device and a preparation method thereof, belonging to the technical field of polymer dispersed liquid crystal devices. The device includes a transparent bottom electrode layer, a liquid crystal layer, and a transparent top electrode layer that are sequentially stacked; the liquid crystal layer is prepared from a polymer dispersed liquid crystal hybrid material containing an ionic compound and a polymer dispersed liquid crystal hybrid material without an ionic compound; the polymer dispersed liquid crystal hybrid material containing an ionic compound includes, by mass: 22-25 parts of a liquid crystal material, 12-23 parts of a polyester resin, and 2-10 parts of an ionic compound; the polymer dispersed liquid crystal hybrid material without an ionic compound includes, by mass: 22-25 parts of a liquid crystal material and 12-23 parts of a polyester resin. By adding an ionic compound to the polymer dispersed liquid crystal hybrid material, the device can achieve the combination of the electro-controlled transmittance of the polymer dispersed liquid crystal and the color control of the electrochromic device, and broaden the applications in large-area displays, smart windows, and electro-optical blinds.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer dispersed liquid crystal devices, and particularly relates to a polymer dispersed liquid crystal device and a preparation method thereof. Background Art

[0002] Polymer dispersed liquid crystal (PDLC) is generally prepared by phase separation to uniformly disperse low molecular liquid crystal in a transparent polymer matrix. The liquid crystal molecules exist in the form of micron-sized droplets, and the polymer matrix provides a stable network structure for it.

[0003] Electrochromic (EC) refers to a technology in which a stable and reversible redox reaction occurs under the action of an electric field, and the appearance shows a reversible change in color or light transmittance. Due to its advantages such as low cost, low driving voltage, power saving, simple structure, functional flexibility, and ideal visual friendliness, EC display is widely used.

[0004] Since liquid crystal molecules have dielectric and optical anisotropy, it will affect the rotational orientation behavior of liquid crystal molecules under the action of an external field. Therefore, by applying an external electric field, the orientation of liquid crystal molecules can be changed, and then the refractive index of liquid crystal droplets can be changed to match the refractive index of the polymer matrix, realizing the change from a foggy state to a transparent state in appearance. At present, due to its electro-optical properties, PDLC is widely used in smart glass windows, projection displays, and color-changing camouflage technology. Polymer dispersed liquid crystal has problems such as a large driving voltage and poor contrast, and the adjustment method is single.

[0005] Therefore, developing a device with multi-primary color modulation characteristics and a simple preparation process is an urgent problem to be solved in its application in the field of color display. Summary of the Invention

[0006] For this reason, the technical problem to be solved by the present invention is to overcome the problems in the prior art that the introduction of traditional dye molecules and dichroic dyes in polymer dispersed liquid crystal devices leads to poor polymerization of the polymer network, changes in the absorption of ultraviolet light due to dye contamination, and it is difficult to achieve dynamic color change.

[0007] To solve the above technical problems, the present invention provides a polymer dispersed liquid crystal device and a preparation method thereof.

[0008] The first object of the present invention is to provide a polymer-dispersed liquid crystal device, which includes a transparent bottom electrode layer, a liquid crystal layer, and a transparent top electrode layer that are sequentially stacked; the liquid crystal layer is prepared from a polymer-dispersed liquid crystal hybrid material containing an ionic compound and a polymer-dispersed liquid crystal hybrid material without an ionic compound; the polymer-dispersed liquid crystal hybrid material containing an ionic compound includes, by mass: 22-25 parts of a liquid crystal material, 12-23 parts of a polyester resin, and 2-10 parts of an ionic compound; the polymer-dispersed liquid crystal hybrid material without an ionic compound includes, by mass: 22-25 parts of a liquid crystal material and 12-23 parts of a polyester resin.

[0009] In one embodiment of the present invention, the liquid crystal material is selected from liquid crystals such as biphenyl nitriles, esters, cyclohexyl (bi)phenyls, oxygen-containing heterocyclic benzenes, pyrimidine rings, diphenylacetylenes, ethyl bridge bonds, ene end groups, fluorine-containing benzene ring-containing biphenyls, or alkoxybenzylidene cyanoanilines.

[0010] In one embodiment of the present invention, the polyester resin is selected from amino polyesters, polyurethane-based copolyesters, polymethyl methacrylate, or polyethylene glycol diacrylate.

[0011] In one embodiment of the present invention, the ionic compound is selected from one or more of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium carbonate, ammonium bicarbonate, ammonium fluoride, ammonium iodide, ammonium bromide, tetrabutylammonium tetrafluoroborate, tetrabutylammonium perchlorate, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide, dodecyldimethylbenzylammonium chloride, tetrabutylammonium chloride ester quaternary ammonium salt, alkyltrimethylammonium salt-type cationic surfactants, dialkyldimethylammonium salt-type cationic surfactants, pyridinium salt-type cationic surfactants, and quaternary ammonium salt cationic surfactants.

[0012] In one embodiment of the present invention, the polymer-dispersed liquid crystal hybrid material further includes 8-10 parts of a diluent monomer and / or 2-4 parts of a photoinitiator.

[0013] In one embodiment of the present invention, the diluent monomer is selected from one or more of acrylate monomers, lauryl methacrylate, isophorone diisocyanate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, acryloylmorpholine, trimethylolpropane tris(3-mercaptopropionate), and 4-dimethylaminopyridine. The diluent monomer can dilute the polyester resin and dissolve the photoinitiator, so it plays an important role in the basic properties of the prepared liquid crystal layer. If the dilution ability of the diluent monomer is too strong, the formed liquid crystal layer will be too soft and the bonding performance will not be strong. Although increasing the monomer functionality is beneficial for forming a crosslinked network, increasing the crosslink density, and increasing the strength, it will also increase the anchoring force on the liquid crystal droplets and increase the driving voltage.

[0014] In one embodiment of the present invention, the thickness of the liquid crystal layer is 18 - 22 μm.

[0015] The second object of the present invention is to provide a method for preparing the polymer dispersed liquid crystal device as described above, comprising the following steps: filling a polymer dispersed liquid crystal hybrid material containing an ionic compound and a polymer dispersed liquid crystal hybrid material without an ionic compound between a transparent bottom electrode layer and a transparent top electrode layer to form a liquid crystal layer, thereby obtaining the polymer dispersed liquid crystal device.

[0016] In one embodiment of the present invention, an operation of patterning the liquid crystal layer is further included.

[0017] In one embodiment of the present invention, the patterning method is screen printing or inkjet printing.

[0018] The technical solution of the present invention has the following advantages compared with the prior art:

[0019] (1) By adding an ionic compound to the polymer dispersed liquid crystal hybrid material, the polymer dispersed liquid crystal device of the present invention can combine the electro - controlled transmittance of polymer dispersed liquid crystal with the color control of electrochromic devices, which will broaden potential applications in large - area displays, smart windows, and electro - optical blinds. Because they do not need to use any specific chemicals, such as conductive oligomers, nor do they need to use other electrochromic molecules. The liquid crystal material dispersed in the polymer matrix acts as a chromogenic molecule to play a chromogenic role, improving the process and effectively solving the shortcoming of the single color of traditional electrochromics. From a safety perspective, in the case of the rupture or damage of the electrochromic device, the polymer matrix can prevent the leakage of fluid components in the environment.

[0020] (2) The polymer dispersed liquid crystal device of the present invention utilizes a colored complex formed by the redox reaction between a benzene ring and a cation when powered on to construct an electrochromic polymer dispersed liquid crystal device, achieving dual responses of electro - optics and electrochromics. By changing the type of electrolyte cation, the color intensity and hue of the device can be adjusted; also, the electrochemically induced color can be changed by different types of liquid crystals, that is, the type of end groups forming the components.

[0021] (3) The polymer dispersed liquid crystal device of the present invention can become transparent when an alternating current field is applied and can independently become colored when a direct current field is applied. Through techniques such as screen printing and inkjet printing, multi - primary - color patterned display can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to make the content of the present invention be more clearly understood, the following further describes the present invention in detail according to specific embodiments of the present invention in conjunction with the drawings, wherein:

[0023] Figure 1 Structural diagram of the electrochromic polymer dispersed liquid crystal device of Embodiment 1 of the present invention.

[0024] Figure 2 Polarizing microscope image of Test Example 1 of the present invention.

[0025] Figure 3 Sample images of the present invention under DC and AC voltages in Test Example 2.

[0026] Figure 4 Graph showing the trend of transmittance change with voltage for different ratios of polyester resin and diluent monomer in Test Example 3 of the present invention.

[0027] Figure 5 Physical images of electrochromic polymer dispersed liquid crystal devices at different ionic compound concentrations in Test Example 4 of the present invention.

[0028] Figure 6 Graph showing the change in transmittance of electrochromic polymer dispersed liquid crystal devices at different ionic compound concentrations in Test Example 4 of the present invention.

[0029] Explanation of reference numerals in the drawings: 1 - ITO glass, 2 - indium tin oxide coating, 3 - middle spacer, 4 - polymer dispersed liquid crystal hybrid material, 5 - polymer dispersed liquid crystal hybrid material containing ionic compound, 6 - polymer dispersed liquid crystal hybrid material without ionic compound. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0031] In the present invention, unless otherwise specified, referring to Figure 1 As shown, the indium tin oxide conductive glass is covered with an indium tin oxide coating 2 on the ITO glass 1. The sheet resistance value of the ITO glass is 6 - 8 Ω / sq, the glass thickness is 1.1 mm, and the transmittance is 84% (in the visible light range of 400 - 700).

[0032] In the present invention, unless otherwise specified, the diameter of the polystyrene microspheres is 5 - 20 μm.

[0033] In the present invention, unless otherwise specified, the liquid crystal material E7 is purchased from Yantai Xianhua Technology Group Co., Ltd.

[0034] In the present invention, unless otherwise specified, the ultraviolet curable adhesive NOA61 is purchased from Shenzhen Hongbangtai Technology Co., Ltd.

[0035] In the present invention, unless otherwise specified, the liquid crystal material 5CB is purchased from Yantai Xianhua Technology Group Co., Ltd.

[0036] Example 1

[0037] Reference Figure 1 As shown, a polymer-dispersed liquid crystal device and its preparation method specifically include the following steps: ITO glass 1, indium tin oxide coating 2, intermediate spacer 3, polymer-dispersed liquid crystal hybrid material 4, and the polymer-dispersed liquid crystal hybrid material 4 includes a polymer-dispersed liquid crystal hybrid material 5 containing an ionic compound and a polymer-dispersed liquid crystal hybrid material 6 without an ionic compound.

[0038] (1) Polymer-dispersed liquid crystal hybrid material 4: Take 750 parts by mass of liquid crystal material E7, 24 parts by mass of polyester resin polymethyl methacrylate, 12 parts by mass of diluent monomer acrylate monomer (BA), 4 parts by mass of diluent monomer lauryl methacrylate (LMA), and 4 parts by mass of photoinitiator TPO. Divide them into two parts, and add 6 parts by mass of ionic compound didodecyldimethylammonium bromide to one of them. Stir these evenly in the dark until the materials are completely dissolved to form a colorless and transparent solution. Through polymerization reaction until phase separation occurs, liquid crystal droplets are formed to obtain a polymer-dispersed liquid crystal hybrid material containing an ionic compound and a polymer-dispersed liquid crystal hybrid material without an ionic compound.

[0039] (2) Polymer-dispersed liquid crystal device: Cut a large piece of indium tin oxide conductive glass (ITO) into 2 cm × 1.5 cm, then ultrasonically clean it with a deionized aqueous solution of a mixed detergent to remove oil stains, and then use ethanol for ultrasonic cleaning to remove dust. Take it out after drying in an oven for standby. Use a PDMS mask mesh with a butterfly shape, and evenly print the polymer-dispersed liquid crystal hybrid material 5 containing an ionic compound on the ITO substrate by screen printing method, control the thickness of the liquid crystal layer containing an ionic compound to be 20 μm, and ensure that the surface of the obtained liquid crystal layer containing an ionic compound is smooth and the thickness is uniform to obtain a butterfly-shaped pattern. At the four corners of the ITO substrate of the butterfly-shaped liquid crystal layer, apply a photo-curable glue containing polystyrene spheres as the intermediate spacer 3, cover another piece of ITO glass 1 on top and bottom (staggered), and cure it by ultraviolet light (ultraviolet power is 3 mW / cm 2 , cure for 15 min). Finally, through capillary action, the polymer-dispersed liquid crystal hybrid material 6 without an ionic compound is poured into the liquid crystal cell to form a liquid crystal layer, and an electrochromic polymer-dispersed liquid crystal device is obtained by ultraviolet irradiation.

[0040] Example 2

[0041] A polymer-dispersed liquid crystal device and its preparation method specifically include the following steps:

[0042] (1) Polymer dispersed liquid crystal hybrid material: Take 47.5 parts by mass of liquid crystal material E7, 30.2 parts by mass of polyester resin polyethylene glycol diacrylate (PEGDA575), 0.2 parts by mass of diluent monomer 4-dimethylaminopyridine (DMAP), 2.8 parts by mass of diluent monomer isophorone diisocyanate (IPDI), and 16.8 parts by mass of diluent monomer trimethylolpropane tris(3-mercaptopropionate) (TMPMP). Divide them into two parts, and add 2.5 parts by mass of ionic compound didodecyldimethylammonium bromide to one of them. Magnetically stir the polyester resin, 4-dimethylaminopyridine and isophorone diisocyanate at room temperature until completely dissolved, then add the liquid crystal material and ionic compound (or without ionic compound) and magnetically stir at room temperature for 1 h until it becomes colorless and transparent. Finally, add trimethylolpropane tris(3-mercaptopropionate) and magnetically stir for 2 min to obtain polymer dispersed liquid crystal hybrid materials with and without ionic compounds.

[0043] (2) Polymer dispersed liquid crystal device: Cut large indium tin oxide conductive glass (ITO) into pieces of 2 cm × 1.5 cm, then ultrasonically clean it with deionized aqueous solution of mixed detergent to remove oil stains, and then ultrasonically clean it with ethanol to remove dust. Take it out after drying in an oven for standby. Then, encapsulate two glass slides with parallel orientation up and down, apply and paste the edge area of the two glass slides with ultraviolet curable glue NOA61 mixed with polystyrene microspheres inside, and then irradiate the liquid crystal cell with ultraviolet light to solidify the area where the photocurable glue is applied. Pour the polymer dispersed liquid crystal hybrid material containing ionic compound obtained in step (1) into the liquid crystal cell, and perform ultraviolet curing (ultraviolet power is 3 mW / cm 2 , cure for 15 min). Finally, through capillary action, pour the polymer dispersed liquid crystal hybrid material without ionic compound into the liquid crystal cell to form a liquid crystal layer, and obtain an electrochromic polymer dispersed liquid crystal device through ultraviolet light irradiation.

[0044] Example 3

[0045] A polymer dispersed liquid crystal device and its preparation method specifically include the following steps:

[0046] (1) Polymer dispersed liquid crystal hybrid material: Take 45 parts by mass of liquid crystal material 5CB and 45 parts by mass of polyester resin polymethyl methacrylate. Dissolve the liquid crystal material and polyester resin in tetrahydrofuran, divide them into two parts, and add 10 parts by mass of ionic compound didodecyldimethylammonium bromide to one of them to obtain polymer dispersed liquid crystal hybrid materials with and without ionic compounds.

[0047] (2) Polymer dispersed liquid crystal device: A large piece of indium tin oxide conductive glass (ITO) was cut into pieces of 2 cm × 1.5 cm, and then ultrasonically cleaned with an aqueous solution of deionized water mixed with detergent to remove oil stains, and then ultrasonically cleaned with ethanol to remove dust. After drying in an oven, it was taken out for standby. Then, two glass slides with parallel orientation were encapsulated up and down, and a UV-curable adhesive NOA61 mixed with polystyrene microspheres inside was used to smear and paste the edge regions of the two glass slides, and then the liquid crystal cell was irradiated with ultraviolet light to solidify the smeared area of the photocurable adhesive. The polymer dispersed liquid crystal hybrid material containing ionic compounds obtained in step (1) was poured into the liquid crystal cell, and an XY-type intelligent heating and temperature control platform was used to control the curing temperature of the sample. Finally, through capillary action, the polymer dispersed liquid crystal hybrid material without ionic compounds was poured into the liquid crystal cell to form a liquid crystal layer, and an electrochromic polymer dispersed liquid crystal device was obtained through ultraviolet light irradiation.

[0048] Test Example 1

[0049] Based on Example 1, the liquid crystal layer of the electrochromic polymer dispersed liquid crystal device was photographed by a polarizing microscope (POM), and the results are as Figure 2 shown. From Figure 2 it can be seen that when the mass ratio of polyester resin, liquid crystal material, and photoinitiator is 12:25:2, and the mass ratio of diluent monomer to polyester resin is 2:3, the driving voltage is the lowest, and the size and dimensions of the liquid crystal microdroplets in the prepared liquid crystal layer are very uniform under POM.

[0050] Test Example 2

[0051] A DC and AC electric field were applied to the electrochromic polymer dispersed liquid crystal device prepared in Example 1, and the results are as Figure 3 shown. From Figure 3 it can be seen that when a 14V AC electric field is applied, the electrochromic polymer dispersed liquid crystal device changes from a foggy state to a transparent state; when a DC electric current is applied, it is found that the screen-printed part changes from colorless to colored. After applying a 5V DC electric current, a yellow butterfly pattern can be seen, and the area around the pattern still shows a colorless foggy state. This is because when a DC electric field is applied, cations in the electrolyte migrate to the cathode and react with the liquid crystal at the cathode to form a colored complex, and at the same time, halide molecules are generated at the anode; after removing the DC electric field, the halide molecules diffuse and react with the colored complex to bleach.

[0052] Test Example 3

[0053] The intensity of the incident and transmitted light of the electrochromic polymer dispersed liquid crystal device prepared in Example 1 was compared, and its voltage-transmittance change was measured. The results are as Figure 4 shown. From Figure 4It can be seen that for the liquid crystal layer prepared when the mass ratio of the polyester resin, liquid crystal material, and photoinitiator is 12:25:2 and the mass ratio of the diluting monomer to the polyester resin is 2:3, the haze is the highest at 0V, and the driving voltage and saturation voltage are the lowest, being 3.4V and 14.3V respectively.

[0054] Test Example 4

[0055] Based on the electrochromic polymer-dispersed liquid crystal device prepared in Example 3, the change in the transmittance of the electrochromic polymer-dispersed liquid crystal device under different ionic compound concentrations was explored. A DC electric field of 4.5V was applied, and the results are as Figures 5 - 6 shown. From Figures 5 - 6 it can be seen that when a DC voltage of 4.5V is applied, as the concentration of the ionic compound increases, the absorbance and color of the device also increase. The coloring process was observed along the cross-section of the thick sample under an optical microscope. The colored area on the cathode increases with the DC current time and the concentration of the ionic compound. Therefore, the coloring is due to the increase in the thickness of the colored complex layer on the cathode. When a DC current is applied to the liquid crystal cell, a colored complex is generated on the cathode. The absorbance reaches a plateau value within a few seconds, and the time depends on the ionic compound concentration and the DC current application time. After removing the electric field, the color fades spontaneously within a few seconds. This also depends on the ionic compound concentration. The choice of anion does not affect the color of the cell. Similar colors can be obtained using different ionic compounds. The liquid crystal types used in the formulation have different absorption spectra, so the colors of the devices are also different.

[0056] By combining the electro-optical properties of the polymer-dispersed liquid crystal without ionic compounds and the electrochromic properties of the polymer-dispersed liquid crystal with ionic compounds, this device can change its electro-optical transmittance and color. The application of an alternating current field can weaken the light intensity, while the addition of a direct current field can obtain a better contrast, solving the problem that it is difficult to achieve dynamic color change due to the change in ultraviolet absorption caused by the introduction of traditional dye molecules. Using screen printing and inkjet printing technologies, patterned displays can be achieved, and by changing the type of liquid crystal, the color of the color change can be changed, broadening the application in the anti-counterfeiting field.

[0057] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of this invention.

Claims

1. A polymer-dispersed liquid crystal device, characterized in that, it includes a transparent bottom electrode layer, a liquid crystal layer, and a transparent top electrode layer that are stacked in sequence; the liquid crystal layer is prepared from a polymer-dispersed liquid crystal hybrid material containing an ionic compound and a polymer-dispersed liquid crystal hybrid material without an ionic compound; the polymer-dispersed liquid crystal hybrid material containing an ionic compound includes, by mass: 22-25 parts of a liquid crystal material, 12-23 parts of a polyester resin, and 2-10 parts of an ionic compound; the polymer-dispersed liquid crystal hybrid material without an ionic compound includes, by mass: 22-25 parts of a liquid crystal material and 12-23 parts of a polyester resin; the polymer-dispersed liquid crystal hybrid material further includes 8-10 parts of a diluent monomer and / or 2-4 parts of a photoinitiator; the preparation of the polymer-dispersed liquid crystal device includes the following steps: First, prepare the polymer-dispersed liquid crystal hybrid material containing an ionic compound and the polymer-dispersed liquid crystal hybrid material without an ionic compound according to the above ratios; then fill the polymer-dispersed liquid crystal hybrid material containing an ionic compound between the transparent bottom electrode layer and the transparent top electrode layer, and then pour in the polymer-dispersed liquid crystal hybrid material without an ionic compound through capillary action to form a liquid crystal layer, and obtain the polymer-dispersed liquid crystal device through ultraviolet light irradiation.

2. The polymer-dispersed liquid crystal device according to claim 1, characterized in that, the liquid crystal material is selected from liquid crystals such as cyanobiphenyls, esters, cyclohexyl (bi)phenyls, oxygen-containing heterocyclic benzenes, pyrimidine rings, diphenylacetylenes, ethyl bridge bonds, vinyl end groups, fluorine-containing benzene ring-containing biphenyls, or alkoxybenzylidene cyanoanilines.

3. The polymer-dispersed liquid crystal device according to claim 1, characterized in that, the polyester resin is selected from amino polyesters, polyurethane-type copolyesters, polymethyl methacrylate, or polyethylene glycol diacrylate.

4. The polymer-dispersed liquid crystal device according to claim 1, characterized in that, the ionic compound is selected from one or more of ammonium chloride, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium carbonate, ammonium bicarbonate, ammonium fluoride, ammonium iodide, ammonium bromide, tetrabutylammonium tetrafluoroborate, tetrabutylammonium perchlorate, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide, dodecyldimethylbenzylammonium chloride, tetrabutylammonium chloride ester quaternary ammonium salt, alkyltrimethylammonium salt-type cationic surfactants, dialkyldimethylammonium salt-type cationic surfactants, pyridinium salt-type cationic surfactants, and quaternary ammonium salt cationic surfactants.

5. The polymer-dispersed liquid crystal device according to claim 1, characterized in that, the diluent monomer is selected from one or more of acrylate monomers, lauryl methacrylate, isophorone diisocyanate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, acryloylmorpholine, trimethylolpropane tris(3-mercaptopropionate), and 4-dimethylaminopyridine.

6. The polymer-dispersed liquid crystal device according to claim 1, characterized in that, the thickness of the liquid crystal layer is 18-22 μm.

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