Liquid crystal, liquid crystal lens and preparation method thereof based on cellulose derivatives

Abstract

The present invention provides a liquid crystal based on a cellulose derivative, a liquid crystal lens and a preparation method thereof, wherein the liquid crystal of the cellulose derivative is composed of a solute and a solvent, wherein the solute is ethyl cellulose, and the solvent and the solute are in a three-dimensional Hansen space, wherein the center of the Hansen space is determined by three coordinates called Hansen solubility parameters, D=20.1, P=6.9, H=5.9, and the Hansen space is a space sphere with a radius of 9.9 units around the center. The liquid crystal has the characteristics of a lyotropic cholesteric phase liquid crystal, and has good dielectric anisotropy, light transmittance, etc., and is suitable for use in the manufacture of optoelectronic devices, such as the manufacture of liquid crystal lenses, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of nanomaterials, and in particular relates to a liquid crystal based on cellulose derivatives, a liquid crystal lens and a preparation method thereof. Background Art

[0002] In recent years, cellulose materials have attracted widespread attention due to their unique properties. Cellulose nanocrystals (CNCs) are renewable polymers with high structural regularity, generally derived from plants, marine algae and bacteria. Cellulose polymers can be produced through a variety of methods, such as defibrillation, enzymatic hydrolysis, 2,2,6,6-tetramethylpiperidine-1-oxyl (2,2,6,6-Tetramethylpiperidine-1-Oxyl, TEMPO) oxidation, and dicarboxylic acid hydrolysis to produce a large series of different cellulose derivatives, such as carboxymethyl cellulose (CMC), ethyl cellulose (EC) and cyanoethyl cellulose (CEC), among which EC and CEC are both white powders, insoluble in aqueous solution, but soluble in some organic solvents. Ethyl cellulose, with the molecular formula (C 12 H 22 O 5 )n, is a long-chain polymer with β-anhydroglucose as the unit, connected by acetal, and is one of the most widely used cellulose derivatives. Cyanoethyl cellulose is a soluble organic cellulose ether with a molecular formula of C 36 H 46 N 8 O 11 The properties of cyanoethyl cellulose are related to its degree of substitution. Partially cyanoethylated cellulose has good heat resistance, mechanical properties, antibacterial properties and high water recovery rate. After treatment, it is expected to be used as an antibacterial material, adsorbent material, reducing agent and stabilizer, and can also be used to prepare porous materials.

[0003] Cellulose and its derivatives such as ethyl cellulose (EC) belong to a class of liquid crystal polymer materials, which are generally soluble in organic and inorganic solvents, such as amine oxide, LiOH / dimethylacetamide, ionic liquids, NaOH / urea, etc. Cellulose and its derivatives form cholesteric lyotropic liquid crystals in most cases due to their strong intermolecular and intramolecular hydrogen bonds, and only a few easily fusible cellulose derivatives can form thermotropic liquid crystals. For lyotropic liquid crystals, when the polymer exceeds a certain concentration, the solution will form a liquid crystal phase, and the concentration at this time is the critical concentration C1. After continuing to increase the concentration of the solution, there will be no liquid crystal when the solution exceeds a concentration, and the concentration at this time is the critical concentration C2. With the change of concentration, the structure of the solution changes from a completely disordered structure to a structure in which the molecules are ordered to a certain extent, so the refractive index of the solution will also change, and the refractive index of the solution is related to the concentration and temperature. For example, the refractive index of the EC / acetic acid system increases linearly with the increase of concentration, and birefringence occurs in 47.2wt% and 35.0wt% acetic acid and m-cresol.

[0004] Solutions of cellulose and its derivatives flow like viscous liquids but can display physical properties such as crystalline anisotropy, which can be used for new applications in nanophotonics and optics.

[0005] Ethyl cellulose has excellent light and heat stability, and its chemical stability is also excellent among cellulose derivatives. Studies have shown that ethyl cellulose can be dissolved in some organic substances to form lyotropic cholesteric liquid crystals. Due to the presence of its semi-rigid molecular chains, it can form a highly ordered liquid crystal phase, which is used in liquid crystal displays, optical devices and other fields.

[0006] In summary, the liquid crystal properties of cellulose and its derivatives have been widely studied and applied in solid films, etc., but their application in liquid state is still relatively small. Especially in the field of new 3D display, the materials of the current zoom liquid crystal lens are mostly nematic liquid crystal, and circular hole electrodes and Fresnel ring electrodes are used. The principle is to adjust its focal length through the electric field to achieve the effect of zoom. Cholesteric liquid crystal can be used in VR (Virtual Reality Display, VR) and AR (Augmented Reality Display, AR) devices due to the optical properties caused by its helical structure - selective reflection, circular dichroism and optical rotation. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a liquid crystal based on a cellulose derivative, which can be used in the display field in a liquid state and applied to optoelectronic devices such as liquid crystal lenses.

[0008] In one aspect of the present invention, a liquid crystal based on a cellulose derivative is provided, wherein the liquid crystal is composed of a solute and a solvent, wherein the solute is ethyl cellulose, and the solvent and the solute are in a three-dimensional Hansen space, wherein the center of the Hansen space is determined by three coordinates called Hansen solubility parameters, D=20.1, P=6.9, H=5.9; the Hansen space is a spatial sphere with a radius of 9.9 units around the center.

[0009] In some embodiments of the present invention, the solvent is a DCA solution, or an ionic liquid [BMIM]CL / DCA composite solution.

[0010] In some embodiments of the present invention, in the composite solution, the mass ratio of [BMIM]CL to the composite solution is 0.1-0.3, and the solubility performance is better.

[0011] In some embodiments of the present invention, in the liquid crystal, the mass ratio of ethyl cellulose to solvent is 0.4-0.6.

[0012] In some embodiments of the present invention, the solvent is DCA, and the mass ratio of the ethyl fiber to the DCA is 0.4, 0.45, 0.5 or 0.6.

[0013] In some embodiments of the present invention, when the thickness is 40 μm, the light transmittance of the liquid crystal is ≥ 80%, which is more suitable for application in the field of optoelectronic display.

[0014] In some embodiments of the present invention, when the thickness is 40 μm, the refractive index of the liquid crystal is 1.45-1.52, and the extinction coefficient is 0.03-0.08.

[0015] In some embodiments of the present invention, when the thickness is 40 μm, the difference Δε of the dielectric anisotropy of the liquid crystal is ≥3. The difference Δε of the dielectric anisotropy dominates the movement of the liquid crystal molecules in the electric field. The larger Δε is, the lower the threshold voltage of the liquid crystal device is, and it is more suitable for application in the manufacture of optoelectronic devices.

[0016] Another aspect of the present invention provides a method for preparing the above-mentioned cellulose derivative-based liquid crystal, wherein the solute and the solvent are heated and stirred at 50° C. for 4 hours, and then left at room temperature for 7 days after stirring.

[0017] Another aspect of the present invention further provides a liquid crystal lens, wherein the lens is filled with the cellulose derivative-based liquid crystal according to an embodiment of the present invention.

[0018] The present invention defines solutes and solvents through Hansen solubility parameters, and establishes a liquid crystal system based on cellulose derivatives in a liquid state. The liquid crystal has good dielectric anisotropy, light transmittance, etc., and is suitable for use in the manufacture of optoelectronic devices, such as liquid crystal lens manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a 3D diagram of the dissolution of ethyl cellulose in several solvents in Table 3.

[0020] Figure 2 This is a 3D diagram of the dissolution of ethyl cellulose in several solvents in Table 4.

[0021] Figure 3 This is a 3D diagram of the dissolution of ethyl cellulose in several solvents in Table 5.

[0022] Figure 4 For the liquid crystal cell (parallel orientation) production process,

[0023] Figure 5 This is the structure diagram of the cholesteric liquid crystal cell (vertical orientation).

[0024] Figure 6 This is the POM diagram of the vertically oriented liquid crystal cell.

[0025] Figure 7 This is the POM diagram of the parallel-oriented liquid crystal cell.

[0026] Figure 8 The POM diagram of ethyl fiber / dichloroacetic acid liquid crystal cell with a mass ratio of 0.6 under different light incident modes.

[0027] Fig. 9 The liquid crystal cell (parallel orientation) made of EC / DCA solution with a mass ratio of 0.45 was observed under different conditions.

[0028] Fig.10 The refractive index and extinction coefficient test results of the EC / DCA liquid crystal box with a mass ratio of 0.4 are shown in Figure 2.

[0029] Fig.11 The capacitance and voltage test results of the parallel-oriented EC / DCA liquid crystal cell are shown in the figure.

[0030] Fig.12 The relationship curves between voltage and capacitance of parallel-aligned liquid crystal cells with different mass ratios EC / DCA are shown in Figure 2.

[0031] Fig.13 This is a schematic diagram of the VR optical system principle and the optical path diagram of the amplification principle.

[0032] Fig.14 This is the effect of the cholesteric liquid crystal lens on the optical path after power is applied.

[0033] Fig.15 To optimize the optical path diagram of the liquid crystal lens before and after,

[0034] Fig.16 The light path diagram of the diffuse spot produced by the lens and the point diagram of the lens with and without the liquid crystal cell simulated by Zemax,

[0035] Fig.17 This is the MTF diagram of the front and rear lenses after adding the liquid crystal cell. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments and drawings, but they do not constitute a limitation on the protection scope of the present invention.

[0037] In the description of the present invention, unless otherwise clearly defined, terms such as heating, cleaning, and weighing should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0038] In the description of the present invention, the description with reference to the terms "some embodiments", "examples", etc. means that the specific methods and materials described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific methods and materials described can be combined in any one or more embodiments or examples in a suitable manner.

[0039] In one aspect of the present invention, a liquid crystal based on a cellulose derivative is provided, wherein the liquid crystal is composed of a solute and a solvent, wherein the solute is ethyl cellulose, and the solvent and the solute are in a three-dimensional Hansen space, wherein the center of the Hansen space is determined by three coordinates called Hansen solubility parameters, D=20.1, P=6.9, H=5.9, and the Hansen space is a spatial sphere with a radius of 9.9 units around the center.

[0040] Here, the Hansen solubility parameter (hereinafter also referred to as "HSP") is a value for predicting the solubility of a substance published by Charles M. Hansen in 1967, and is a parameter based on the idea that "two substances with similar intermolecular interactions tend to dissolve each other".

[0041] Hansen solubility parameters include the following parameters: dispersion force also known as van der Waals force δD, polar force δP, hydrogen bond adhesion δH and Hillbrad total parameter δT. This simulation calculates the solubility by calculating the values ​​of the above parameters, and the formula is:

[0042] δT 2 =δ D 2 +δ P 2 +δ H 2

[0043] Because like dissolves like, the closer the HSP (δT) values ​​are, the greater the compatibility is. However, we cannot only consider δ r In addition to the similarity of the values ​​of D (δD), P (δP) and H (δH), the similarity of the three values ​​of solvent (δD), P (δP) and H (δH) must also be considered, because not only the intermolecular forces of the solvent and solute need to be similar, but their composition must also be similar in order for them to dissolve.

[0044] Calculate the distance Ra between parameters:

[0045] R a 2 =4(δ D1 -δ D2 ) 2 +(δ P1 -δ P2 ) 2 +(δ H1 -δ H2 ) 2

[0046] Knowing the interaction radius R0, the relative energy difference RED is obtained as follows:

[0047] RED=R a / R 0

[0048] After calculation, when RED=1, it is partially dissolved; when RED>1, it is immiscible; when RED<1, the molecules are similar and will dissolve. It is represented by 3D space, that is, three-dimensional Hansen space, with the coordinate system of D, P and H values. In the coordinate system, a circle is drawn with the solute as the center and R0 as the radius. The position of each solvent is marked in the coordinate system. When the point is in the ball, it means that it will dissolve. The closer to the center of the circle, the better the solubility. The R0 of ethyl cellulose is 9.9, D=20.1, P=6.9, H=5.9. Therefore, in principle, any solvent in a space ball with D=20.1, P=6.9, H=5.9 as the center and a radius of 9.9 units around the center can dissolve ethyl cellulose.

[0049] Specifically, the software HSPIP (Hansen Solubility Parameters In Practice, HSPIP) can be used for calculation. In some embodiments of the present invention, the solvent is a DCA solution, or an ionic liquid [BMIM]CL / DCA composite solution. Since the dichloroacetic acid (DCA) solution is similar to ethyl cellulose HSP. Ionic liquid is a green and non-toxic solvent with the characteristics of high polarity, stable properties, flame retardancy, high ionic conductivity, etc., but the solubility of (1-butyl-3-methylimidazole chloride) [BMIM]CL and ethyl cellulose is not good, so a composite solvent system introducing ionic liquids is selected. The composite solution can select a suitable [BMIM]CL mass ratio by calculating the Hansen solubility parameters of different ratios. Preferably, in the composite solution, the mass ratio of [BMIM]CL to the composite solution is 0.1-0.3, and the solubility performance is better.

[0050] In the specific implementation, the dissolution of ethyl cellulose in various solvents can be simulated and calculated by using the software HSPIP (Hansen Solubility Parameters In Practice, HSPIP), and the simulation results can be verified and screened to obtain the best one through experiments. The following will be further described in conjunction with specific embodiments. The list of materials and reagents used in the embodiments is shown in Table 1, and Table 2 is a list of test equipment used.

[0051] Table 1

[0052]

[0053]

[0054] a: The diameter of the polystyrene culture dish is 3.5 cm.

[0055] Table 2

[0056]

[0057] Example 1 Simulation and calculation of HSP value

[0058] The software HSPIP was used to simulate ethyl cellulose in several common single solvents, including pure water (Water), N, N-dimethylformamide (DMF), methanol (Methanol), dimethyl sulfoxide (DMSO), dichloroacetic acid (DCA), etc. The HSP values ​​were derived from the software, and the HSP value of ethyl cellulose was derived from the literature. The calculation results are shown in Table 3.

[0059] Table 3

[0060]

[0061]

[0062] Figure 1 The 3D graph of ethyl cellulose dissolving in several solvents in Table 3, the X-axis is δD parameter, the Y-axis is δP parameter, and the Z-axis is δH parameter. The blue dots represent the solvents DMF and DCA respectively. The red dots in the red box are the positions when water is used as the solvent. At this time, the RED value of ethyl cellulose in water is 3.9, indicating that it is difficult to dissolve, which is also consistent with the characteristic that ethyl cellulose is insoluble in water. Figure 1 The data of the blue part clearly show that among the six solvents, the best solubility is in DCA and DMF, with RED of 0.75 and 1.03 respectively.

[0063] Calculation of HSP value of composite solution

[0064] [BMIM]CL was mixed with dichloroacetic acid DCA and N,N-dimethylformamide DMF in different proportions, and the results of Hansen solubility parameter calculation are shown in Table 4. Figure 2 This is a 3D graph of the dissolution of ethyl cellulose in the ionic liquid composite solvents in Table 4. The red dots are pure [BMIM]CL, and the remaining blue dots are [BMIM]CL / DCA mixed solvents with different mass ratios. The results show that the composite solvent [BMIM]CL / DCA can better dissolve ethyl cellulose.

[0065] Table 4

[0066]

[0067]

[0068] Table 5 summarizes the simulation results of the solubility parameters of ethyl cellulose in different solvents. The dissolution of ethyl cellulose in the above solvents is simulated and presented in the form of a 3D graph. Figure 3. The green sphere in the figure is the range where the RED of ethyl cellulose is less than 1, the central yellow dot is ethyl cellulose, and the blue and red dots represent different solvents. Blue represents several solvents with better solubility, namely DCA (RED is 0.75) and [BMIM]CL / DCA with mass ratios of 0.1, 0.2, and 0.3 (RED are 0.82, 0.92, and 0.97, respectively). In order to increase the mass ratio of the ionic liquid as much as possible, a solution with the smallest RED value is selected as the solvent. Preferably, [BMIM]CL / DCA with a RED value of 0.97 and a mass ratio of 0.3 is used as the ionic liquid composite solvent.

[0069] Table 5

[0070]

[0071]

[0072] Example 2 Preparation of Liquid Crystal Solution

[0073] At room temperature, ethyl cellulose was mixed with DCA and [BMIM]CL / DCA ionic liquid composite solution with a mass ratio (ionic liquid [BMIM]CL / composite solution [BMIM]CL / DCA) of 0.1, 0.2, and 0.3, respectively, and the mass ratio (solute / solvent) was 0.4, 0.45, 0.5, and 0.6, respectively. The mixed sample was sealed in a test tube, a stirring magnet was placed, and heated and stirred at 50°C for 4 hours using a magnetic heating mantle. After stirring, it was placed at room temperature for 7 days to obtain a balanced and uniform solution.

[0074] Example 3 Optical Properties Characterization

[0075] Liquid crystal cell preparation

[0076] Some of the liquid crystal solution samples prepared above were used to fill and prepare a liquid crystal box with a liquid crystal layer thickness of 40 μm for performance characterization. The detailed steps of liquid crystal box preparation are shown in Figure 4 .

[0077] Parallel alignment liquid crystal cell production:

[0078] First, use ultrasound and cleaning agent (organic solvent) to clean the glass substrate, then spin-coat a polyimide (PI) solution on the front side containing the ITO electrode, fix the conductive side facing up, drop a few drops of PI solution on the surface, spin-coat at 2000rpm for 20s, form a uniform PI film on the surface of the substrate, and place the substrate with PI spin-coated on a 90℃ hot stage for curing for 40 minutes, and orient it parallel on a black flannel. Place a piece of oriented ITO glass facing up, and apply a mixture of UV glue and spacers on the four corners to ensure the thickness of the box. Use another piece of ITO glass facing down and gently press the two glass substrates to stick them together. Use ultraviolet light to cure the newly glued liquid crystal box, and take it out after 60s. Pour the liquid crystal into the liquid crystal box from one side on a 60℃ hot stage until the liquid crystal box is filled with liquid crystal material. Continue to heat the liquid crystal box on the hot stage for 5 minutes to make the liquid crystal molecules in it fully move and complete the production of the liquid crystal box. For specific processes, please refer to Figure 4 .

[0079] Vertically aligned liquid crystal cell production:

[0080] like Figure 5 The steps for making a vertically oriented liquid crystal box are similar to the above steps. The difference is that in the second step, the orientation layer is spin-coated on the ITO glass with polyvinyl alcohol (PVA), and no friction orientation is required, only high-temperature curing is required.

[0081] Liquid crystal texture and light transmittance of liquid crystal cell

[0082] Figure 6 The POM diagram of a vertically oriented liquid crystal box, where the solution in the liquid crystal box: (a, c) mass ratio is 0.4EC / (0.3[BMIM]CL / DCA); (b, d) mass ratio is 0.4EC / DCA; (e) transmission spectrum diagram. Under the same mass ratio, the composite solution liquid crystal is more aggregated in the liquid crystal box, with a more obvious and clear focal conic texture, so EC / DCA is better as a liquid crystal material in terms of the presence of liquid crystal phase and high light transmittance.

[0083] Figure 7 The POM diagram of the parallel-oriented liquid crystal cell, where (ac) are the liquid crystal textures of EC / DCA with mass ratios of 0.4, 0.45, and 0.5 respectively; (d) light transmission spectrum. The internal textures of the liquid crystal cell formed by EC / DCA solutions with different mass ratios are different. When the mass ratio is slightly lower, the anisotropic area in the liquid crystal cell is relatively small, as shown in Fig. Figure 6 (a), the relative light transmittance is also high. And compared with the EC / DCA liquid crystal cell with a mass ratio of 0.4, Figure 6(b) and Figure 7 (b) It can be found that the textures in the two orientation liquid crystal cells are different. The 0.4 mass ratio of ethyl cellulose / dichloroacetic acid solution has a clear disc texture in the parallel orientation liquid crystal cell and a large distribution of anisotropic regions. The light transmittance is also above 80%, which is more suitable for use as a display device.

[0084] Combination Figure 6 and Figure 7 It can be seen that the light transmittance of the two types of liquid crystal cells is basically above 80%, which is suitable for use as display devices.

[0085] Selective reflection properties of liquid crystal cells

[0086] Figure 8 POM images of ethyl fiber / dichloroacetic acid liquid crystal cell with a mass ratio of 0.6 under different light incident modes, (a) 5 times, in transmission mode; (b) 20 times, in transmission mode; (c) 5 times, in reflection mode; (d) 20 times, in reflection mode. Figure 8 It can be seen that the solution will have a colorful fingerprint texture, proving that the texture in the solution is the fingerprint texture of cholesteric liquid crystal. The liquid crystal is poured into a parallel oriented liquid crystal cell, and the internal texture is as follows Figure 8 (a) and (b). Adjust the light incident mode of the polarizing microscope to the reflection mode, and you can see that the colored part appears in the picture. Figure 8 In (c) and (d), blue and green areas can be seen. This is due to the Bragg reflection characteristics unique to cholesteric liquid crystals, which will reflect a certain monochromatic light according to its pitch and refractive index.

[0087] Fig. 9 Liquid crystal box made of EC / DCA solution with a mass ratio of 0.45 (parallel orientation): (a) observed with the naked eye and (b) observed under polarization; (cd) the sample is placed between the polarizer and the screen, and the human eye observes the pictures at different angles. The sample is an EC / DCA liquid film with a mass ratio of 0.6. It can be seen that when the sample is placed directly on the black platform and observed with the naked eye, clear colors can be found. Fig. 9 (a), add a polarizer in front of the light source and the sample. Due to its liquid crystal properties, light can pass through the sample and the polarizer. Fig. 9 (cd), increase the mass ratio of the sample EC / DCA solution, place the sample between the light-emitting screen and the polarizer, and rotate the sample angle, the picture on the screen can be clearly seen. This shows that the liquid crystal solution of the present invention has the characteristics of cholesteric liquid crystal and has good light transmittance.

[0088] Refractive index characteristics of liquid crystal cells

[0089] The refractive index and extinction coefficient of the blue and green reflection points on the liquid crystal box were tested using an ellipsometer. The test results are as follows: Fig.10 As shown in the figure, (a) the relationship between the refractive index n, extinction coefficient K and wavelength at different points on the EC / DCA liquid crystal box with a mass ratio of 0.4; (b) the relationship between the refractive index and wavelength at the same point under different voltages. The higher the refractive index n of the sample, the stronger the ability of incident light to refract. The extinction coefficient K describes the light absorption characteristics of the sample. The larger the extinction coefficient, the greater the absorption of light and the darker the color of the solution. Fig.10 It can be seen that in the visible light range, the refractive index of the sample ranges from 1.46 to 1.51, and the extinction coefficient is between 0.04 and 0.075.

[0090] Calculation of dielectric constant of liquid crystal materials

[0091] Calculation principle of dielectric constant of liquid crystal materials

[0092] The dielectric constant is measured with a capacitance tester. According to the definition of the dielectric constant, as long as the capacitance value before and after the dielectric is added is measured, the dielectric constant of the dielectric can be obtained. The specific steps are as follows:

[0093] Empty LCD box test

[0094] ε 0 =C 1 ×S / d (4-2)

[0095] After filling the LCD

[0096] ε=C 2 ×S / d (4-3)

[0097] so

[0098] ε / ε 0 =C 2 / C 1 =ε r (4-4)

[0099] where ε 0 : Dielectric constant, C 1 : Capacitance of the empty liquid crystal cell, C 2 : Capacitance after filling with liquid crystal, S: The area of ​​the upper and lower overlapping parts of the liquid crystal box, d: The thickness of the liquid crystal box, ε r : Relative dielectric constant of liquid crystal.

[0100] That is, the relative dielectric constant of the liquid crystal material is determined by calculating the ratio of the capacitance value after filling the liquid crystal to that of the empty box. Because liquid crystals are divided into positive liquid crystals and negative liquid crystals, the dielectric constant components in the parallel and vertical directions can be calculated based on the data before and after the threshold voltage. However, since the liquid crystal molecules will adhere to the surface of the substrate, there will be a certain error.

[0101] The measured data are processed and the relative dielectric constant values ​​of the vertical components are calculated respectively:

[0102] ε ⊥ / ε 0 =C ⊥ / C 1 (4-5)

[0103] The relative permittivity value of the parallel component is:

[0104] ε || / ε 0 =C || / C 1 (4-6)

[0105] Thus, the anisotropic liquid crystal is induced to move along the director Through the interaction between polarities, dielectric anisotropy is exhibited. Parallel to the electric field ( When the dielectric constant is small and does not interfere with alignment, the dielectric constant is ε / / ,when Perpendicular to the electric field, the dielectric constant is ε ⊥ , and ε / / -ε ⊥ ≠0, the dielectric anisotropy difference is:

[0106] Δε=ε / / -ε ⊥ (4-7)

[0107] From this formula we can calculate the dielectric anisotropy difference Δε of the liquid crystal material.

[0108] In addition to the error caused by the adhesion of the liquid crystal molecules themselves, other errors must also be considered. This error is due to the presence of the static capacitance of the orientation layer and the electrode resistance, so we need to calculate and use a suitable electric field frequency to avoid the influence of this error. Finally, 1kHz was chosen as the electric field frequency.

[0109] The dielectric constant of the liquid crystal in the embodiment of the present invention is calculated by taking a parallel-aligned liquid crystal cell as an example.

[0110] Dielectric constant of parallel-aligned liquid crystal cell

[0111] First, test the capacitance of the empty box, and measure it multiple times in the empty box state to get the average value. For the parallel-oriented liquid crystal box of EC / DCA solution with a mass ratio of 0.4, apply a voltage of 0-30V to the liquid crystal box, and measure the capacitance value every 0.5V. The arrangement of molecules in the parallel-oriented liquid crystal box is perpendicular to the direction of the electric field. For positive liquid crystals such as cellulose derivatives, after the electric field is applied, the molecules will slowly turn parallel to the direction of the electric field. Therefore, if the voltage applied during the test is less than the threshold voltage, the test data value is C ⊥ Otherwise, the measured value is approximately (taking into account the error caused by the adhesion of the liquid crystal molecules) C || .

[0112] The relative dielectric constant of the liquid crystal material is calculated by testing the capacitance, such as Fig.11 After the data is processed, Fig.11 (a) The capacitance of the empty liquid crystal cell is approximately C 1 is 220pF. The relationship between the capacitance and voltage of the liquid crystal cell after filling with solution is shown in Fig.11 (b) It can be found that the data is divided into three parts in the voltage range of 0-30V. According to the dielectric properties of liquid crystal, the inflection point A is the threshold voltage, and after point C, it can be seen that the capacitance value has an erroneous value, which means that the liquid crystal box may be broken down. Fig.11 In part (c), before point A, the liquid crystal molecules are arranged perpendicular to the electric field. After fitting the data, the vertical coordinate value 1736pF on the Y axis is taken as the vertical capacitance value, and the vertical dielectric constant component ε can be calculated. ⊥ is 8.0.

[0113] Zoom in on the data before and after point B, see Fig.11 In (d), it can be found that the capacitance value first increases and then gradually stabilizes, and the fitting line is approximately a straight line. According to the principle, after the electric field is applied, the liquid crystal box will slowly rotate and finally be parallel to the electric field distribution, so we take the average value of 2575pF as the capacitance value in the parallel direction, and calculate the dielectric constant component ε in the vertical direction || is 11.7. Finally, the calculated difference in dielectric anisotropy Δε is 3.7.

[0114] The relationship between voltage and capacitance of EC / DCA liquid crystal cells with different mass ratios (parallel orientation, ITO glass size 2×2cm) was tested. The results are as follows: Fig.12 As shown, (a) 0.45 (b) 0.5. The calculation is also carried out according to the above steps, where the empty cell capacitance is about 1.5 pF, and the parallel-oriented ethyl cellulose dichloroacetic acid liquid crystal cell Δε of 0.45 mass ratio is 3.16, and the parallel-oriented ethyl cellulose dichloroacetic acid liquid crystal cell Δε of 0.5 mass ratio is 3.45. The results show that the ethyl cellulose dichloroacetic acid liquid crystal cell with a relatively stable liquid crystal phase has a Δε>3.

[0115] The difference in dielectric anisotropy of cellulose is generally between 0.1 and 0.3, while the difference in dielectric anisotropy of EC / DCA in the embodiment of the present invention is greater than 3, which is significantly increased and is more suitable for use in the manufacture of optoelectronic devices.

[0116] Example 4 Application in Liquid Crystal Lens

[0117] Liquid crystal lens is a device that changes the focal position of liquid crystal lens by applying external voltage. It has a wide range of application prospects, such as three-dimensional displays, imaging systems, microscopes, zoom systems, etc. Cholesteric liquid crystal lens mainly has the following directions. One is zoom lens. Since the light transmittance and reflectivity of cholesteric liquid crystal are mainly determined by the pitch, and the pitch changes with the changes of the external environment, the focal length of the liquid crystal lens can be adjusted by changing the external environment. The optical system composed of cholesteric liquid crystal lens meets the requirements of high transmittance in the visible light range, fast response speed, low driving voltage, and appropriate focusing range.

[0118] For example, liquid crystal lenses are used in virtual reality technology (VR). Fig.13 When different voltages are applied to the driving electrodes, the electric field strength in different areas changes differently, causing the liquid crystal molecules to be distributed in a gradual manner, and the refractive index and phase also form a lens-like distribution, thereby achieving the focusing function. That is, by applying voltage to the lens to change the focal length of the liquid crystal lens, the image projected by the micro display screen is displayed at different depths, thereby achieving a zoom effect. Zooming allows the human eye to see a 3D effect, which is also applicable to augmented reality technology (AR).

[0119] When the pitch of cholesteric liquid crystal is below the critical electric field, the pitch will increase with the increase of voltage, and because of its special spiral structure, it will selectively reflect and transmit left-rotated circularly polarized light (LCP) or right-rotated circularly polarized light (RCP). Fig.14 The blue line in the middle is the optical path diagram of the lens group in static state, and the green line is the optical path diagram of the lens group after applying an electric field. After applying voltage, the increase in pitch leads to an increase in refractive index and a decrease in focal length. The orange line represents the optical path of the lens selective circularly polarized light. The left-handed chiral cholesteric liquid crystal will transmit right-handed circularly polarized light and scatter left-handed circularly polarized light.

[0120] Optical system simulation with Zemax

[0121] according to Fig.13 As can be seen from the optical path diagram in (b), the lens group in the VR system can be simply regarded as a group of magnification systems, that is, the image on the micro display is magnified and enters the human eye as parallel light, and then an enlarged virtual image is formed in front through the adjustment of the human eye. In order to verify whether the above-mentioned liquid crystal lens can be applied to the VR optical system, this embodiment chooses to simulate the magnification lens part in the VR system. Since the optical path is reversible, the object plane in the design is actually the image plane accepted by the human eye, and the image plane is the micro display screen (image plane) in the actual system.

[0122] For VR optical systems, the larger the field of view, the stronger the sense of immersion. That is, the display screen should be on the focal plane of the equivalent eyepiece or within one focal length, so the distance between the human eye and the lens group in the VR optical system should be 15-20mm. We choose to use the K9 lens and the above-mentioned liquid crystal box to form a lens group. First, simulate the single K9 lens in Zemax. Set the full field of view angle to 90°, the entrance pupil diameter to 6mm, the entrance pupil distance to 15mm, and the effective focal length of the K9 lens to 8mm. For other data, see Fig.15 (a), after simulation, the total axial length of the system is 23.74mm. We add the liquid crystal box to the optical system, and add the liquid crystal box close to the back of the K9 lens. The thickness of the I T0 glass is 1.1mm, the refractive index n is 1.57, and the thickness of the liquid crystal layer is 0.04mm. According to the data in 4.3.3, the refractive index is 1.47, see Fig.15 (c), we can see that the focal position of the system has changed. By optimizing the optical system, we get Fig.15 (d), at this time the total axial length of the optical system is 24.56 mm.

[0123] Evaluation system

[0124] When an optical system images monochromatic light, it produces five kinds of monochromatic aberrations: astigmatism, field curvature, spherical aberration, coma and distortion. When imaging white light, in addition to monochromatic aberrations, axial chromatic aberration and vertical chromatic aberration may also occur.

[0125] There is a big difference between the actual optical system and the ideal optical system. When an object point emits light in the object space, after passing through the actual optical system, the light will no longer focus on a point in the image space, but will form a diffuse spot. The size of the diffuse spot is related to the aberration of the system. The Zemax point diagram describes that after the light source passes through the optical system, due to the existence of aberration, the light forms a diffuse pattern on the image plane, also called a diffuse spot, such as Fig.16 (a), where L' represents the image distance of the intersection point of the high-light rays of a certain aperture, l' is the image distance of the paraxial image point, and the spherical aberration of the optical system is:

[0126] δL′=L′-l′ (4-7)

[0127] The radius of the diffuse spot δT′ is:

[0128] δT′=δL′tan U (4-8)

[0129] From the formula, we can see that the larger the spherical aberration, the larger the image square aperture angle, and the larger the diffuse spot on the Gaussian image plane, which will make the image of the light passing through the lens blurred. Zemax's point diagram can be used to evaluate the size of the aberration, that is, to quantitatively determine the size of the actual spot of the optical system through the root mean square radius (RMS radius).

[0130] Fig.16 (a) The light path diagram of the diffuse spot produced by the lens; Zemax simulated lens point array diagram (b) K9 lens and (c) lens group containing liquid crystal cell, where the blue, green and red points correspond to wavelengths of 486nm, 587nm and 656nm respectively

[0131] By observing the RMS radius of the two optical systems on the image plane, it can be found that the lens group optical system with the addition of the liquid crystal cell has a smaller RMS radius, see Fig.16 In the middle red data, the diffuse spot size of the optical system did not increase after adding the liquid crystal lens, but decreased from 6.120 when there was only a K9 lens to 5.932, which means that the addition of the liquid crystal box reduced the size of the diffuse spot on the image plane.

[0132] The optical modulation transfer function MTF (Modulation Transfer Function) is used to evaluate the imaging quality of the lens, including judging the resolution and sharpness of the lens group. The closer the MTF value is to 1, the higher the imaging quality of the optical system. The spatial frequency represents the density of the sinusoidal grating, that is, the resolution, and the unit is lp / mm. Generally speaking, the MTF value at the cutoff frequency of the optical system is required to be greater than 0.2, such as Fig.17 As shown in the figure, before and after adding the liquid crystal box, the spatial frequencies corresponding to the MTF values ​​of the two optical systems being greater than 0.2 are 66lp / mm and 70lp / mm respectively, and the MTF curve of the lens group with the liquid crystal box added is relatively smooth, indicating that the resolution of the lens group with the liquid crystal box added is improved.

[0133] The experiment of Example 4 shows that the addition of the liquid crystal cell reduces the size of the diffuse light spot on the image plane, improves the imaging quality of the lens, and enhances the imaging resolution, which indicates that the liquid crystal of the embodiment of the present invention can be used in a liquid crystal lens device.

[0134] The above embodiment prepared the liquid crystal solution of the present invention, and then made parallel-oriented and vertical-oriented liquid crystal boxes, and respectively filled with liquid crystal solutions of different proportions. The light transmittance of the liquid crystal box was tested, and the transmittance was >80%, and it was found that the liquid crystal box containing ionic liquid solvent at the same mass ratio (0.4) had better light transmittance, but through polarizing microscope observation, it can be found that the liquid crystal box without ionic liquid has a more obvious and clear focal cone texture, and has the characteristics of lyotropic cholesteric phase; and the difference in dielectric anisotropy Δε>3 of the liquid crystal material of the present invention was calculated, among which Δε=3.7 of the ethyl cellulose / dichloroacetic acid liquid crystal material, which is significantly higher than Δε (0.13) of cellulose, is more suitable as a photoelectric material. Finally, the Zemax software was used to simulate the optical system of the magnified part in the VR display, and it was found that after adding the liquid crystal box, the RMS radius was reduced, the resolution was improved, and the lens group system had better imaging quality. It shows that the liquid crystal of the present invention can be used for liquid crystal lenses, etc.

Claims

1. A liquid crystal based on a cellulose derivative, characterized in that The liquid crystal is composed of a solute and a solvent, the solute is ethyl cellulose, and the solvent and the solute are in a three-dimensional Hansen space, wherein the center of the Hansen space is determined by three coordinates called Hansen solubility parameters, D=20.1, P=6.9, H=5.9; the Hansen space is a space sphere with a radius of 9.9 units around the center, and the solvent is an ionic liquid [BMIM]CL / DCA composite solution, in which the mass ratio of [BMIM]CL to the entire composite solution is 0.1-0.

3.

2. The liquid crystal based on cellulose derivatives according to claim 1, characterized in that In the liquid crystal, the mass ratio of ethyl cellulose to solvent is 0.4-0.

6.

3. The liquid crystal based on cellulose derivatives according to any one of claims 1 to 2, characterized in that: When the thickness is 40 μm, the light transmittance of the liquid crystal is ≥80%.

4. The liquid crystal based on cellulose derivatives according to claim 3, characterized in that When the thickness is 40 μm, the refractive index of the liquid crystal is 1.45-1.52, and the extinction coefficient is 0.03-0.

08.

5. The liquid crystal based on cellulose derivatives according to claim 4, characterized in that When the thickness is 40 μm, the difference in dielectric anisotropy of the liquid crystal Δ ε is ≥3.

6. The method for preparing a liquid crystal based on a cellulose derivative according to any one of claims 1 to 5, characterized in that: The solute and the solvent were heated and stirred at 50° C. for 4 hours and then left at room temperature for 7 days.

7. A liquid crystal lens, characterized in that: The lens is filled with a liquid crystal based on a cellulose derivative as claimed in any one of claims 1-5.

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