Quantum dot / graphene / NiO doped polymer bistable liquid crystal material and preparation method thereof

Abstract

The invention discloses a quantum dot / graphene / NiO doped polymer bistable liquid crystal material and a preparation method thereof. The preparation method comprises the following steps: preparing an InP / ZnSeS / ZnS quantum dot solution; preparing graphene powder; preparing the NiO nano particles; and synthesizing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material. The quantum dot / graphene / NiO doped polymer bistable liquid crystal material provided by the invention has good light transmittance in a projection state and a scattering state, and shows obvious bistable performance. When the polymer bistable liquid crystal material and a PET thin film with an ITO layer are used as a substrate for preparing a sample, the optical performance and the bistable structure of the thin film are not obviously changed after the polymer bistable liquid crystal material is greatly bent, and the polymer bistable liquid crystal material has good film-forming property and flexibility in a bending state.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal materials, and particularly relates to a quantum dot / graphene / NiO-doped polymer bistable liquid crystal material and a preparation method thereof. Background Art

[0002] Liquid crystals have excellent optoelectronic properties and are one of the widely used optical device materials at present. Since liquid crystal materials are between liquids and crystals, having both the fluidity of liquids and the optical anisotropy of crystals and other characteristics, this enables liquid crystals to occupy an important position in the fields of display technology, optical devices, sensors, etc. However, some problems have also emerged during use. The modification of liquid crystals has become a current hotspot. Common modification methods include polymer composite modification, doping with nanoparticles, etc. The main purpose of these modification methods is to enhance the optoelectronic properties of liquid crystal materials and improve the stability during use.

[0003] Quantum dots are a type of zero-dimensional material with a diameter generally less than 10 nm. Due to the reduction in their size and the control of their shape and structure, they have unique optical and electrical properties and are widely used in electronic device materials. NiO nanoparticles have specific electrical properties, such as semiconductor properties, etc. It can play a role in regulating the local electric field in the liquid crystal system, enabling liquid crystal molecules to be more likely to change their orientation when subjected to an external driving electric field, thereby reducing the external driving voltage required to achieve state switching. Graphene has good mechanical properties, which can improve the mechanical properties of materials and at the same time enhance the electrical properties and thermal stability of liquid crystals. Based on this, the present application intends to dope the above-mentioned quantum dot materials, NiO nanoparticles, and graphene into bistable liquid crystal materials to obtain a new polymer bistable liquid crystal material. Summary of the Invention

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: a preparation method of a quantum dot / graphene / NiO-doped polymer bistable liquid crystal material, including the following steps:

[0005] Step 1: Preparation of InP / ZnSeS / ZnS quantum dot solution:

[0006] 1) Preparation of zinc precursor solution: Weigh a certain amount of zinc stearate and dissolve it in a certain amount of 1-octadecene to obtain a zinc precursor solution;

[0007] 2) Preparation of Se / S-TOP precursor solution: Dissolve a certain amount of selenium powder and sulfur powder in a certain amount of trioctylphosphine to obtain a Se / S-TOP precursor solution;

[0008] 3) Preparation of phosphorus precursor solution: Dissolve a certain amount of tripyrrolidino phosphine oxide in a certain amount of oleylamine to obtain a phosphorus precursor solution;

[0009] 4) Synthesis of InP / ZnSeS / ZnS quantum dots: Dissolve a certain amount of InI3 and ZnBr2 in a certain amount of oleylamine, heat up to remove water and oxygen by degassing; at a certain temperature, successively add a certain amount of phosphorus precursor solution, a certain amount of zinc precursor solution, a certain amount of Se / S-TOP precursor solution, a certain amount of zinc precursor solution, and introduce a certain amount of dodecanethiol solution; after the reaction is completed, cool the solution to room temperature; add a certain amount of n-hexane for dissolution, and centrifuge to obtain the supernatant; add an equal volume of ethanol to the supernatant for precipitation, centrifuge multiple times to obtain the quantum dots; disperse the quantum dots in n-hexane to obtain the InP / ZnSeS / ZnS quantum dot solution;

[0010] Step 2: Prepare graphene powder;

[0011] Step 3: Preparation of NiO nanoparticles: Dissolve a certain amount of nickel nitrate hexahydrate in deionized water to obtain a nickel nitrate hexahydrate solution; add a certain amount of sodium hydroxide to deionized water to obtain a sodium hydroxide solution; drop the sodium hydroxide solution into the nickel nitrate hexahydrate solution on a magnetic stirrer, stir to form a uniform green solution; let it stand, filter to obtain a green precursor precipitate, dry the prepared precursor precipitate, then heat it in a muffle furnace, and cool it to room temperature to obtain NiO nanoparticles;

[0012] Step 4: Synthesis of quantum dot / graphene / NiO-doped polymer bistable liquid crystal material: Mix nematic liquid crystal, chiral dopant, polymerizable monomer, photoinitiator and the above-prepared InP / ZnSeS / ZnS quantum dot solution, graphene powder and NiO nanoparticles in a certain proportion, then heat and stir in a dark room with a magnetic stirrer until it is in a uniform state, then perform ultrasonic treatment, and let it stand at room temperature for a period of time to obtain the quantum dot / graphene / NiO-doped polymer bistable liquid crystal material.

[0013] Preferably, in the preparation process of the zinc precursor solution: weigh 5 g of zinc stearate, and under a nitrogen atmosphere, stir well and heat to 150 °C to dissolve it in 20 ml of 1-octadecene to obtain the zinc precursor solution; in the preparation process of the Se / S-TOP precursor solution: weigh 3 mmol of selenium powder and 3 mmol of sulfur powder into a sample bottle, add 3 ml of trioctylphosphine to dissolve, and heat and stir at 75 °C for 30 minutes to prepare the Se / S-TOP precursor solution; in the preparation process of the phosphorus precursor solution: dissolve 3.8 mmol of tripyrrolidino phosphine oxide in 2 ml of oleylamine and stir at 50 °C for 10 min to obtain the phosphorus precursor solution; in the synthesis process of the InP / ZnSeS / ZnS quantum dots: weigh 0.45 mmol of InI3 and 2.2 mmol of ZnBr2 and dissolve them in 5 ml of oleylamine; under a nitrogen atmosphere, gradually heat up to 130 °C and degas for 1 h to remove water and oxygen; re-introduce nitrogen and further heat up to 200 °C, then quickly inject 1.45 ml of the phosphorus precursor solution, and react for 20 min; add 12 ml of the zinc precursor solution, heat up to 230 °C and keep warm; dropwise add 1.5 ml of the Se / S-TOP precursor solution at a rate of 0.1 ml / min; heat up to 280 °C and keep for 120 min; heat up to 290 °C, add 6 ml of the zinc precursor solution, and introduce 1.5 ml of dodecane thiol solution at a rate of 0.15 ml / min, and keep warm for 60 min; after the reaction is completed, cool the solution to room temperature; add 12 ml of n-hexane for dissolution, centrifuge at 10000 r / min for 3 min and then separate to obtain the supernatant; add an equal volume of ethanol to the supernatant for precipitation, and then centrifuge multiple times with the same parameters to obtain the quantum dots; disperse the quantum dots in n-hexane to obtain an InP / ZnSeS / ZnS quantum dot solution with a concentration of 5 mg / mL.

[0014] Preferably, in the preparation process of the graphene powder: select a copper foil as the substrate, place the copper foil in a quartz tube furnace, evacuate to make the pressure in the furnace reach 10-3 Torr, and then introduce argon and hydrogen; increase the furnace temperature to 970 °C at a heating rate of 27 °C / min, and then slowly increase the temperature to 1060 °C at a heating rate of 6 °C / min; keep the temperature at 1060 °C for 30 min; use methane as the carbon source at 1 sccm, and at the same time use argon at 500 sccm and hydrogen at 60 sccm as the carrier gas to grow for 20 min. After the growth is completed, cool the system to room temperature at a cooling rate of about 50 °C / min to obtain graphene on the copper foil; etch the copper substrate with a copper etchant, wash with deionized water and dry to obtain the graphene with the substrate peeled off; put the dried graphene flakes into a mortar and make them into powder by mechanical grinding to obtain the graphene powder.

[0015] Preferably, in the preparation process of the NiO nanoparticles: 0.03 mol of nickel nitrate hexahydrate is dissolved in 60 ml of deionized water to obtain a nickel nitrate hexahydrate solution; 0.02 mol of sodium hydroxide is added to 150 mL of deionized water to obtain a sodium hydroxide solution; the sodium hydroxide solution is added dropwise to the nickel nitrate hexahydrate solution at 75 °C and 300 rpm on a magnetic stirrer, and stirring is continued for 1 h to form a uniform green solution; it is left standing at room temperature for 1 h, and then filtered to obtain a green precursor precipitate, and the prepared precursor precipitate is dried in an oven at 110 °C for 24 h; it is heated in a muffle furnace at a heating rate of 3.3 °C / min at 400 °C for 4 h, and then left standing at room temperature for 24 h, and the obtained black particulate matter is the NiO nanoparticles.

[0016] Preferably, in the synthesis process of the quantum dot / graphene / NiO-doped polymer bistable liquid crystal material: a nematic liquid crystal, a chiral dopant, a polymerizable monomer, a photoinitiator, and the prepared InP / ZnSeS / ZnS quantum dot solution, graphene powder, and NiO nanoparticles are mixed in a certain proportion to obtain a mixed solution; the mixed solution is heated and stirred to a uniform state with a magnetic stirrer in a dark room, then ultrasonically treated for 1 h, and then the n-hexane solvent introduced by the InP / ZnSeS / ZnS quantum dot solution is volatilized at room temperature to obtain the quantum dot / graphene / NiO-doped polymer bistable liquid crystal material.

[0017] Preferably, the nematic liquid crystal is composed of a mixture of 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanotriphenyl, and the ratio of 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanotriphenyl is 46:30:18:7; the chiral dopant is 4-(4-hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester; the polymerizable monomer is one or more of 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene and 1,6-hexanediol diacrylate; the photoinitiator is benzoin diethyl ether.

[0018] Preferably, in the mixed liquid, the weight ratio of the nematic liquid crystal is 70-85wt%, the chiral dopant accounts for 1-5wt%, the polymerizable monomer accounts for 10-20wt%, the photoinitiator accounts for 0.5-2wt%, the InP / ZnSeS / ZnS quantum dot solution accounts for 0.1-1wt%, the graphene powder accounts for 0.05-0.5wt%, and the NiO nanoparticles account for 0.05-0.5wt%.

[0019] The quantum dot / graphene / NiO-doped polymer bistable liquid crystal material is prepared by the above preparation method.

[0020] 1. InP quantum dots, as optical modifiers, regulate the light absorption and emission characteristics through the quantum confinement effect. Its size-dependent energy band structure can precisely match the transmission wavelength range of the liquid crystal system, reduce light scattering, and improve the light transmittance in the transmission state.

[0021] Its working principle and effects include:

[0022] Light absorption regulation: The bandgap of InP quantum dots can be adjusted by size (such as the core-shell structure InP / ZnSeS / ZnS) to absorb stray light of specific wavelengths and reduce light loss.

[0023] Light emission enhancement: The fluorescence characteristics of quantum dots can partially compensate for the light loss in the scattering state of the liquid crystal and improve the overall optical efficiency.

[0024] Interface effect: There is a van der Waals force between the surface ligands of quantum dots (such as oleylamine, n-dodecanethiol) and liquid crystal molecules, which improves the dispersibility and avoids phase separation.

[0025] 2. Graphene, as a conductive enhancer and mechanical stabilizer, improves the electrical response speed and flexibility of the composite material.

[0026] Its working principle and effects include:

[0027] Electric field homogenization: The high conductivity of graphene promotes the uniform distribution of the external electric field and reduces the threshold voltage for the orientation switching of liquid crystal molecules.

[0028] Enhanced thermal stability: The high thermal conductivity of graphene accelerates heat diffusion and prevents the liquid crystal phase transition from becoming unstable due to local overheating.

[0029] Mechanical support: The two-dimensional network structure of graphene is embedded in the polymer to inhibit the structural damage of the liquid crystal cell caused by bending or vibration.

[0030] 3. NiO nanoparticles, as electric field regulators and bistability promoters, reduce the driving voltage and accelerate the state switching.

[0031] Its working principle and effects include:

[0032] Local electric field enhancement: The semiconductor properties of NiO (such as p-type semiconductor) form a microelectric field around liquid crystal molecules, amplifying the external field effect and reducing the driving voltage.

[0033] Interface anchoring effect: The hydroxyl groups or defect sites on the surface of NiO generate dipole-dipole interactions with liquid crystal molecules, inducing the ordered arrangement of liquid crystal molecules and shortening the response time.

[0034] Bistable stability: Nanoparticles hinder the spontaneous relaxation of liquid crystal molecules and extend the bistable maintenance time.

[0035] 4. Polymerizable monomers form a crosslinked network to stabilize the helical structure of cholesteric liquid crystals.

[0036] Its working principle and effects include:

[0037] Bistable locking: The network formed by photopolymerization fixes the helical axis direction of cholesteric liquid crystals through physical crosslinking, achieving bistable maintenance without an external field.

[0038] Mechanical strengthening: The polymer network improves the shear resistance of the composite material and prevents the disorder of liquid crystal molecules due to external force disturbance.

[0039] Interface compatibility: The long alkyl chains of monomers are similar in structure to liquid crystal molecules, reducing phase separation and enhancing uniformity.

[0040] The beneficial effects of the present invention are:

[0041] The quantum dot / graphene / NiO-doped polymer bistable liquid crystal material of the present invention has good light transmittance in both the projection state and the scattering state, showing obvious bistable performance. Using it and a PET film with an ITO layer as the substrate to prepare a sample, after being bent significantly, there are no significant changes in the optical properties and bistable structure of the film, and the polymer bistable liquid crystal material has good film-forming property and flexibility in the bent state. Description of the Drawings

[0042] Figure 1 It is the SEM image of the polymer bistable liquid crystal material in Example 1;

[0043] Figure 2 It is the XRD image of the polymer bistable liquid crystal material in Example 1;

[0044] Figure 3 It is the observation image of the liquid crystal cell prepared from the polymer bistable liquid crystal material in Example 1 under an orthogonal polarized light microscope. Detailed Implementation Modes

[0045] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0046] Example 1

[0047] Weigh 5 g of zinc stearate, and under a nitrogen atmosphere, stir it well and heat it to 150 °C to dissolve it in 20 ml of 1-octadecene to obtain a zinc precursor solution; in the preparation process of the Se / S-TOP precursor solution: weigh 3 mmol of selenium powder and 3 mmol of sulfur powder into a sample bottle, add 3 ml of trioctylphosphine to dissolve, and heat and stir at a temperature of 75 °C for 30 minutes to prepare the Se / S-TOP precursor solution; in the preparation process of the phosphorus precursor solution: dissolve 3.8 mmol of tripyrrolidino phosphine oxide in 2 ml of oleylamine and stir at 50 °C for 10 min to obtain the phosphorus precursor solution; in the synthesis process of InP / ZnSeS / ZnS quantum dots: weigh 0.45 mmol of InI3 and 2.2 mmol of ZnBr2 and dissolve them in 5 ml of oleylamine; under a nitrogen atmosphere (in a three-necked flask), gradually heat up to 130 °C and degas for 1 h to remove water and oxygen; re-introduce nitrogen and further heat up to 200 °C, then quickly inject 1.45 ml of the phosphorus precursor solution and react for 20 min; add 12 ml of the zinc precursor solution, heat up to 230 °C and keep warm; dropwise add 1.5 ml of the Se / S-TOP precursor solution at a rate of 0.1 ml / min; heat up to 280 °C and keep for 120 min; heat up to 290 °C, add 6 ml of the zinc precursor solution, and introduce 1.5 ml of n-dodecanethiol solution at a rate of 0.15 ml / min and keep warm for 60 min; after the reaction is completed, cool the solution to room temperature; add 12 ml of n-hexane for dissolution, centrifuge at a speed of 10000 r / min for 3 min and then separate to obtain the supernatant; add an equal volume of ethanol to the supernatant for precipitation, and then centrifuge multiple times with the same parameters to obtain the quantum dots; disperse the quantum dots in n-hexane to obtain an InP / ZnSeS / ZnS quantum dot solution with a concentration of 5 mg / mL.

[0048] Select copper foil as the substrate, place the copper foil in a quartz tube furnace, evacuate to make the pressure in the furnace reach 10-3 Torr, and then introduce argon and hydrogen. Raise the temperature in the furnace to 970 °C at a heating rate of 27 °C / min, and then slowly increase the temperature to 1060 °C at a heating rate of 6 °C / min; maintain the temperature at 1060 °C for 30 min; use methane at 1 sccm as the carbon source, and at the same time use argon at 500 sccm and hydrogen at 60 sccm as the carrier gas to grow for 20 min. After growth, cool the system to room temperature at a cooling rate of about 50 °C / min to obtain graphene on the copper foil; etch the copper substrate with a copper etchant, wash with deionized water and dry to obtain graphene with the substrate peeled off; put the dried graphene flakes into a mortar and grind them into powder by mechanical grinding to obtain graphene powder.

[0049] Dissolve 0.03 mol of nickel nitrate hexahydrate in 60 ml of deionized water to obtain a nickel nitrate hexahydrate solution; add 0.02 mol of sodium hydroxide to 150 mL of deionized water to obtain a sodium hydroxide solution; add the sodium hydroxide solution dropwise to the nickel nitrate hexahydrate solution on a magnetic stirrer at 75 °C and 300 rpm, and continue stirring for 1 h to form a uniform green solution; let it stand at room temperature for 1 h, then filter to obtain a green precursor precipitate, and dry the prepared precursor precipitate in an oven at 110 °C for 24 h; heat in a muffle furnace at a heating rate of 3.3 °C / min at 400 °C for 4 h, and then let it stand at room temperature for 24 h. The obtained black particles are NiO nanoparticles.

[0050] Mix 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanotriphenyl in a ratio of 46:30:18:7 to obtain a nematic liquid crystal. Select 4-(4-hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester as the chiral dopant, select 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene or 1,6-hexanediol diacrylate as the polymerizable monomer, and select benzoin diethyl ether as the photoinitiator. Mix the nematic liquid crystal (85 wt%), chiral dopant (4.3 wt%), polymerizable monomer (10 wt%), photoinitiator (0.5 wt%), and the above-prepared InP / ZnSeS / ZnS quantum dot solution (0.1 wt%), graphene powder (0.05 wt%), and NiO nanoparticles (0.05 wt%) to obtain a mixture; heat and stir the mixture with a magnetic stirrer in a dark room until it is in a uniform state, then ultrasonically treat it for 1 h, and then volatilize the n-hexane solvent introduced by the InP / ZnSeS / ZnS quantum dot solution at room temperature to obtain a quantum dot / graphene / NiO-doped polymer bistable liquid crystal material.

[0051] Example 2

[0052] The preparation processes of the InP / ZnSeS / ZnS quantum dot solution, the graphene powder, and the NiO nanoparticles are the same as those in Example 1. 4-Cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanoterphenyl are mixed in a ratio of 46:30:18:7 to obtain a nematic liquid crystal. 4-(4-Hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester is selected as the chiral dopant, 1,6-hexanediol diacrylate is selected as the polymerizable monomer, and benzoin diethyl ether is selected as the photoinitiator. The nematic liquid crystal (71 wt%), the chiral dopant (5 wt%), the polymerizable monomer (20 wt%), the photoinitiator (2 wt%), and the above-prepared InP / ZnSeS / ZnS quantum dot solution (1 wt%), graphene powder (0.5 wt%), and NiO nanoparticles (0.5 wt%) are mixed to obtain a mixed solution; the mixed solution is heated and stirred with a magnetic stirrer in a dark room until it is in a uniform state, then ultrasonically treated for 1 h, and then the n-hexane solvent introduced by the InP / ZnSeS / ZnS quantum dot solution is volatilized at room temperature to obtain a quantum dot / graphene / NiO-doped polymer bistable liquid crystal material.

[0053] Example 3

[0054] The preparation processes of the InP / ZnSeS / ZnS quantum dot solution, the graphene powder, and the NiO nanoparticles are the same as those in Example 1. 4-Cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanoterphenyl are mixed in a ratio of 46:30:18:7 to obtain a nematic liquid crystal. 4-(4-Hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester is selected as the chiral dopant, 1,6-hexanediol diacrylate is selected as the polymerizable monomer, and benzoin diethyl ether is selected as the photoinitiator. The nematic liquid crystal (79.8 wt%), the chiral dopant (3 wt%), the polymerizable monomer (15 wt%), the photoinitiator (1 wt%), and the above-prepared InP / ZnSeS / ZnS quantum dot solution (0.5 wt%), graphene powder (0.4 wt%), and NiO nanoparticles (0.3 wt%) are mixed to obtain a mixed solution; the mixed solution is heated and stirred with a magnetic stirrer in a dark room until it is in a uniform state, then ultrasonically treated for 1 h, and then the n-hexane solvent introduced by the InP / ZnSeS / ZnS quantum dot solution is volatilized at room temperature to obtain a quantum dot / graphene / NiO-doped polymer bistable liquid crystal material.

[0055] Comparative Example 1

[0056] Mix 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile, and 4''-n-pentyl-4-cyanoterphenyl in a ratio of 46:30:18:7 to obtain a nematic liquid crystal. Select 4-(4-hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester as the chiral dopant, select 1,6-hexanediol diacrylate as the polymerizable monomer, and select benzoin diethyl ether as the photoinitiator. Mix the nematic liquid crystal (70 wt%), chiral dopant (5 wt%), polymerizable monomer (20 wt%), and photoinitiator (5 wt%) to obtain a mixed solution; heat and stir the mixed solution with a magnetic stirrer in a dark room until it is in a homogeneous state, then perform ultrasonic treatment for 1 h, and then volatilize the n-hexane solvent introduced by the InP / ZnSeS / ZnS quantum dot solution at room temperature to obtain the liquid crystal material.

[0057] Preparation of liquid crystal cell: Inject the materials prepared in the above examples and comparative examples into a liquid crystal cell with an ITO coating (glass substrate or PET substrate) by capillary action, use a 20-μm spacer to space, control the temperature (20 °C) during the injection process, and then irradiate under an ultraviolet lamp (365 nm, 5.6 mW / cm 2 ) for 10 min to obtain liquid crystal cells respectively.

[0058] Electro-optical performance test

[0059] (1) Use a UV-Vis-NIR spectrophotometer to measure the light transmittance of the sample at a wavelength of 632 nm, with an empty liquid crystal cell as the reference.

[0060] The method for measuring the transmittance in the transparent state is to gradually apply a voltage of 20 V to 160 V at a frequency of 5 kHz (step size: 20 V) and measure the light transmittance; after each test, apply a voltage of 160 V at a frequency of 0.01 Hz to restore the sample to the scattered state.

[0061] The method for measuring the transmittance in the scattered state is to gradually apply a voltage of 20 V to 160 V at a frequency of 0.01 Hz (step size: 20 V) and measure the light transmittance; after each test, apply a voltage of 160 V at a frequency of 5 kHz to restore the sample to the transparent state.

[0062] The test results are shown in the following table:

[0063] Voltage (V) Example 1 Example 2 Example 3 Comparative Example 1 Empty liquid crystal cell 20 48.2 45.7 50.1 25.3 90.0 40 68.5 65.2 70.3 38.6 90.0 60 82.1 78.9 84.7 51.2 90.0 80 88.6 85.4 89.2 63.8 90.0 100 89.5 87.1 89.8 72.4 90.0 120 89.7 88.3 89.9 78.9 90.0 140 89.8 88.5 90.0 83.2 90.0 160 89.9 88.6 90.0 85.7 90.0

[0064] Table 1: Light transmittance (%) in the transmission state (applying a 5 kHz high-frequency electric field)

[0065] Voltage (V) Example 1 Example 2 Example 3 Comparative Example 1 Empty liquid crystal cell 20 12.5 14.8 10.2 35.6 90.0 40 8.3 10.1 6.7 28.4 90.0 60 5.1 7.5 4.2 21.3 90.0 80 3.8 5.9 2.9 15.7 90.0 100 2.5 4.3 1.8 10.4 90.0 120 1.9 3.1 1.2 7.6 90.0 140 1.3 2.4 0.9 5.2 90.0 160 0.8 1.7 0.5 3.1 90.0

[0066] Table 2: Light transmittance (%) in the scattered state (applying a 0.01 Hz low-frequency electric field)

[0067] As can be seen from the above table, the light transmittance of the sample can be reversibly converted between the transparent state and the scattering state as the voltage changes, showing obvious bistable performance.

[0068] (2) Polarizing microscope test

[0069] The texture change and stability of the liquid crystal cell under different voltages were observed using an orthogonal polarizing microscope. The test results are as follows: Figure 1 As shown. Figure 1 It can be seen that when a high-frequency electric field of 100V and 5kHz is applied, a planar texture is observed, and the sample is in a transparent state with high transmittance; after the electric field is removed, it is observed that the sample maintains the stability of the transparent state structure. When a low-frequency electric field of 100V and 50Hz is applied, a focal conic texture is observed, and the sample presents a scattering state of light scattering; after the electric field is removed, the scattering state remains stable.

[0070] (3)Flexibility test

[0071] The sample was prepared using a PET film with an ITO layer as a substrate. The test data is shown in the table below.

[0072] Test parameters Example 1 Example 2 Example 3 Comparative Example 1 Initial haze (%) 89 91 90 88 Haze after 20 bends 87 89 88 74 Resistance change rate (%) 2.1 3.5 2.8 18.7 Elongation at break (%) 23 19 21 8

[0073] Table 3: Flexibility test data

[0074] From the above test results, it can be seen that by bending the sample significantly (radius of curvature is 3 cm, repeated 20 times), it was found that the optical properties and bistable structure of the film did not change significantly, indicating that the prepared bistable cholesterol liquid crystal film has good film-forming properties and flexibility in the bent state.

[0075] It is worth mentioning that the technical features such as the orthogonal polarizing microscope involved in the patent application of this invention should be regarded as the prior art. The specific structure, working principle and possible control method and spatial arrangement method of these technical features can be selected by conventional methods in the field, and should not be regarded as the inventive point of this patent. This patent will not be further elaborated.

[0076] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in this field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in this technical field through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the existing technology should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a quantum dot / graphene / NiO doped polymer bistable liquid crystal material, characterized in that: The following steps are included: Step 1: Preparation of InP / ZnSeS / ZnS quantum dot solution: 1) Preparation of zinc precursor solution: Weigh a certain amount of zinc stearate and dissolve it in a certain amount of 1-octadecene to obtain a zinc precursor solution; 2) Preparation of Se / S-TOP precursor solution: dissolving a certain amount of selenium powder and sulfur powder in a certain amount of trioctylphosphine to obtain a Se / S-TOP precursor solution; 3) Preparation of phosphorus precursor solution: dissolving a certain amount of tripyrrolidine phosphine oxide in a certain amount of oleylamine to obtain a phosphorus precursor solution; 4) Synthesis of InP / ZnSeS / ZnS quantum dots: a certain amount of InI3 and ZnBr2 are dissolved in a certain amount of oleylamine, and the temperature is raised to degas to remove water and oxygen; a certain amount of phosphorus precursor solution, a certain amount of zinc precursor solution, a certain amount of Se / S-TOP precursor solution, a certain amount of zinc precursor solution are successively added at a certain temperature, and a certain amount of n-dodecanethiol solution is introduced; After the reaction is completed, the solution is cooled to room temperature; a certain amount of n-hexane is added to dissolve, and the supernatant is obtained by centrifugation; an equal volume of ethanol is added to the supernatant to precipitate, and the supernatant is centrifuged several times to obtain quantum dots; the quantum dots are dispersed in n-hexane to obtain an InP / ZnSeS / ZnS quantum dot solution; Step 2: preparing graphene powder; Step 3, preparation of NiO nanoparticles: dissolving a certain amount of nickel nitrate hexahydrate in deionized water to obtain a nickel nitrate hexahydrate solution; adding a certain amount of sodium hydroxide to the deionized water to obtain a sodium hydroxide solution; adding the sodium hydroxide solution dropwise to the nickel nitrate hexahydrate solution on a magnetic stirrer, and stirring to generate a uniform green solution; The product was allowed to stand and filtered to obtain a green precursor precipitate, the prepared precursor precipitate was dried, and then heated in a muffle furnace and cooled to room temperature to obtain NiO nanoparticles; Step 4. Synthesis of quantum dot / graphene / NiO doped polymer bistable liquid crystal material: Mix the nematic liquid crystal, chiral dopant, polymerizable monomer, photoinitiator and the InP / ZnSeS / ZnS quantum dot solution, graphene powder and NiO nanoparticles prepared above in a certain proportion, then heat and stir with a magnetic stirrer in a dark room until a uniform state, followed by ultrasonic treatment and standing at room temperature for a period of time to obtain a quantum dot / graphene / NiO doped polymer bistable liquid crystal material.

2. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 1, characterized in that: In the preparation process of the zinc precursor solution, 5 g of zinc stearate was weighed, fully stirred and heated to 150° C. under a nitrogen atmosphere, and dissolved in 20 ml of 1-octadecene to obtain a zinc precursor solution; in the preparation process of the Se / S-TOP precursor solution, 3 mmol of selenium powder and 3 mmol of sulfur powder were weighed into a sample bottle, 3 ml of trioctylphosphine was added to dissolve, and heated and stirred at 75° C. for 30 minutes to prepare a Se / S-TOP precursor solution; in the preparation process of the phosphorus precursor solution, 3.8 mmol of tripyrrolidine phosphine oxide was dissolved in The solution was dissolved in 2 ml of oleylamine and stirred at 50°C for 10 min to obtain a phosphorus precursor solution; in the synthesis process of the InP / ZnSeS / ZnS quantum dots: 0.45 mmol of InI3 and 2.2 mmol of ZnBr2 were weighed and dissolved in 5 ml of oleylamine; under a nitrogen atmosphere, the temperature was gradually raised to 130°C and degassed for 1 hour to remove water and oxygen; nitrogen was re-introduced and the temperature was further raised to 200°C, and then 1.45 ml of the phosphorus precursor solution was quickly injected and the reaction was carried out for 20 min; 12 ml of the zinc precursor solution was added, the temperature was raised to 230°C and kept warm; 1.5 ml of Se / S-TOP precursor solution was added dropwise at a rate of 0.1 ml / min; The temperature was raised to 280°C and maintained for 120 min; the temperature was raised to 290°C, 6 ml of zinc precursor solution was added, and 1.5 ml of n-dodecyl mercaptan solution was introduced at a rate of 0.15 ml / min, and the temperature was maintained for 60 min; after the reaction was completed, the solution was cooled to room temperature; 12 ml of n-hexane was added for dissolution, and the supernatant was obtained after centrifugation at a speed of 10000 r / min for 3 min; an equal volume of ethanol was added to the supernatant for precipitation, and then the supernatant was centrifuged for multiple times with the same parameters to obtain quantum dots; the quantum dots were dispersed in n-hexane to obtain an InP / ZnSeS / ZnS quantum dot solution with a concentration of 5 mg / mL.

3. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 1, characterized in that: In the preparation process of the graphene powder, copper foil is selected as the substrate, the copper foil is placed in a quartz tube furnace, and the pressure in the furnace is evacuated to 10 -3 Torr, followed by argon and hydrogen; the temperature in the furnace is increased to 970°C at a heating rate of 27°C / min, and then slowly increased to 1060°C at a heating rate of 6°C / min; the temperature is maintained at 1060°C for 30 minutes; 1sccm of methane is used as a carbon source, and 500sccm of argon and 60sccm of hydrogen are used as carrier gases for 20 minutes of growth. After the growth is completed, the system is cooled to room temperature at a cooling rate of 50°C / min to obtain graphene on copper foil; the copper substrate is etched with a copper etchant, washed with deionized water and then dried to obtain graphene peeled from the substrate; the dried graphene flakes are placed in a mortar and made into powder by mechanical grinding to obtain graphene powder.

4. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 1, characterized in that: In the preparation process of the NiO nanoparticles, 0.03 mol of nickel nitrate hexahydrate is dissolved in 60 ml of deionized water to obtain a nickel nitrate hexahydrate solution; 0.02 mol of sodium hydroxide is added to 150 mL of deionized water to obtain a sodium hydroxide solution; the sodium hydroxide solution is added dropwise to the nickel nitrate hexahydrate solution at 75° C. and 300 rpm on a magnetic stirrer, and stirring is continued for 1 hour to generate a uniform green solution; the solution is allowed to stand at room temperature for 1 hour, and then filtered to obtain a green precursor precipitate, and the prepared precursor precipitate is dried in a 110° C. oven for 24 hours; the solution is heated at 400° C. for 4 hours at a heating rate of 3.3° C. / min in a muffle furnace, and then allowed to stand at room temperature for 24 hours, and the obtained black particles are NiO nanoparticles.

5. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 1, characterized in that: In the synthesis process of the quantum dot / graphene / NiO doped polymer bistable liquid crystal material: a nematic liquid crystal, a chiral dopant, a polymerizable monomer, a photoinitiator and the prepared InP / ZnSeS / ZnS quantum dot solution, graphene powder and NiO nanoparticles are mixed in a certain proportion to obtain a mixed solution; the mixed solution is heated and stirred in a dark room with a magnetic stirrer to a uniform state, then ultrasonically treated for 1 hour, and then the n-hexane solvent introduced into the InP / ZnSeS / ZnS quantum dot solution is volatilized at room temperature to obtain a quantum dot / graphene / NiO doped polymer bistable liquid crystal material.

6. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 5, characterized in that: The nematic liquid crystal is composed of a mixture of 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile and 4"-n-pentyl-4-cyanoterphenyl, wherein the ratio of 4-cyano-4'-pentylbiphenyl, 4-heptyl-4'-cyanobiphenyl, 4'-octyl-4-biphenylcarbonitrile and 4"-n-pentyl-4-cyanoterphenyl is 46:30:18:7; the chiral dopant is 4-(4-hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester; the polymerizable monomer is one or more of 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene and 1,6-hexanediol diacrylate; and the photoinitiator is benzoin diethyl ether.

7. The method for preparing the quantum dot / graphene / NiO doped polymer bistable liquid crystal material according to claim 6, characterized in that: The weight proportion of nematic liquid crystal in the mixed solution is 70-85wt%, the proportion of chiral dopant is 1-5wt%, the proportion of polymerizable monomer is 10-20wt%, the proportion of photoinitiator is 0.5-2wt%, the proportion of InP / ZnSeS / ZnS quantum dot solution is 0.1-1wt%, the proportion of graphene powder is 0.05-0.5wt%, and the proportion of NiO nanoparticles is 0.05-0.5wt%.

8. Quantum dot / graphene / NiO doped polymer bistable liquid crystal material, characterized in that: Prepared by the preparation method described in any one of claims 1 to 7.

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