阅读说明：本技术 一种纳米氧化锌薄膜扩散法制备宽波反射薄膜材料的方法 (Method for preparing wide wave reflection film material by nano zinc oxide film diffusion method ) 是由 曹晖 甘萍 赵立敏 史玮婷 张学涛 韩锐 杨洲 王冬 何万里 于 2020-11-22 设计创作，主要内容包括：本发明提供了一种纳米氧化锌薄膜扩散法制备宽波反射薄膜材料的方法。将向列相液晶、手性化合物、可聚合单体、光引发剂按照一定的质量比混合均匀,制成特定螺距的胆甾相液晶复合体系。将纳米氧化锌粒子分散液通过匀胶机旋涂在氧化铟锡(ITO)玻璃上,制备含有纳米氧化锌薄膜的玻璃基板,将此基板的纳米氧化锌薄膜内侧与ITO玻璃基板组合成单侧含有纳米氧化锌薄膜的液晶盒。将胆甾相液晶复合体系通过虹吸作用灌入此液晶盒。将液晶盒的薄膜侧朝上放置在热台上,纳米氧化锌粒子会扩散到液晶盒中,利用纳米氧化锌吸收紫外光的特性,通过紫外光的照射,在液晶盒厚方向上会形成紫外光强梯度,造成自由基聚合单体的消耗速率不同,从而在体系中诱导出螺距的梯度分布。(The invention provides a method for preparing a wide wave reflection film material by a nano zinc oxide film diffusion method. Uniformly mixing nematic liquid crystal, chiral compound, polymerizable monomer and photoinitiator according to a certain mass ratio to prepare a cholesteric liquid crystal composite system with a specific pitch. The nano zinc oxide particle dispersion liquid is coated on Indium Tin Oxide (ITO) glass in a spinning way through a spin coater to prepare a glass substrate containing a nano zinc oxide film, and the inner side of the nano zinc oxide film of the substrate and the ITO glass substrate are combined into a liquid crystal box with the nano zinc oxide film on one side. The cholesteric liquid crystal composite system is filled into the liquid crystal box through the siphon action. The film side of the liquid crystal box is placed on a hot table upwards, nano zinc oxide particles can be diffused into the liquid crystal box, and by utilizing the characteristic that the nano zinc oxide absorbs ultraviolet light, an ultraviolet light intensity gradient can be formed in the thickness direction of the liquid crystal box through the irradiation of the ultraviolet light, so that the consumption rates of free radical polymerization monomers are different, and the gradient distribution of the screw pitch is induced in the system.)

1. A method for preparing a wide wave reflection film material by a nano zinc oxide film diffusion method is characterized by comprising the following steps:

step 1: uniformly mixing small molecular nematic liquid crystal, a chiral compound, an ultraviolet free radical polymerizable monomer and a photoinitiator according to a certain weight percentage, wherein the weight percentage of the small molecular nematic liquid crystal is as follows: 73.9-85.9%; the weight percentage of the ultraviolet free radical polymerizable monomer is as follows: 3.8-15.8%; the chiral compound comprises the following components in percentage by weight: 1-20%; the weight percentage of the photoinitiator is as follows: 0.1-3%, oscillating the mixture for multiple times by using an oscillator, ultrasonically processing the mixture for multiple times by using an ultrasonic instrument, and uniformly mixing the mixture to obtain a cholesteric liquid crystal composite system, wherein the cholesteric liquid crystal composite system is protected from light in the operation process;

step 2: dripping the zinc oxide nano particle dispersion liquid on ITO (indium tin oxide) conductive glass, and putting the ITO conductive glass into an oven for drying after the ITO conductive glass is spin-coated by a spin coater, thus preparing the nano zinc oxide film substrate; combining the inner side of the nano zinc oxide film of the substrate with ITO conductive glass to form a liquid crystal box with a nano zinc oxide film on one side, wherein the thickness of the liquid crystal box is 10-80 mu m;

and step 3: pouring the cholesteric liquid crystal composite system mixed in the step 1 into a pretreated liquid crystal box with a nano zinc oxide film on one side, and then performing optimized planar texture treatment on the poured liquid crystal box by using an oven to ensure that the system is in a stable planar texture state, wherein the temperature of the oven is 10 ℃ lower than the clearing point of the system, and the clearing point temperature of the system is measured by DSC;

and 4, step 4: placing the liquid crystal box subjected to the optimized planar texture treatment in the step 3 on a hot stage with one side of the nano zinc oxide film facing upwards, setting the temperature of the hot stage to be 10-70 ℃, and irradiating by using ultraviolet light, wherein the wavelength of the ultraviolet light is 365nm, the irradiation time of the ultraviolet light is 10-200 min, and the illumination intensity of the ultraviolet light is 0.05-5 mW/cm²And polymerizing the polymerizable monomer to form a polymer network anchoring pitch to prepare the liquid crystal film material for realizing wide wave reflection.

2. The method for preparing the wide wave reflection film material by the nano zinc oxide film diffusion method according to claim 1, which is characterized in that: the weight percentage of the zinc oxide nano particle dispersion liquid is 1-40%, the particle size of the dispersoid is 1-100 nm, and the dispersant is one or more of water, absolute ethyl alcohol, isopropanol and 1, 2-propylene glycol monomethyl ether acetate.

3. The method for preparing the wide wave reflection film material by the nano zinc oxide film diffusion method according to claim 1, which is characterized in that: the chiral compound comprises 4- (4 '-hexyloxy) benzoyloxybenzoic acid-R- (-) -2-octyl alcohol ester, 4- (4' -hexyloxy) benzoyloxybenzoic acid-S- (-) -2-octyl alcohol ester, (13BR) -5, 6-dihydro-5- (trans-4-propylcyclohexyl) -4H-dinaphtho [2,1-F:1',2' -H ] [1,5] dioxononatetraene, (13BS) -5, 6-dihydro-5- (trans-4-propylcyclohexyl) -4H-dinaphtho [2,1-F:1',2' -H ] [1,5] dioxononatetraene or a plurality of dioxononatetraenes.

4. The method for preparing the wide wave reflection film material by the nano zinc oxide film diffusion method according to claim 1, which is characterized in that: the polymerizable monomer is one or more of acrylates, methacrylates, styryls and diacetyl, and the number of active functional groups is 1-5.

5. The method for preparing the wide wave reflection film material by the nano zinc oxide film diffusion method according to claim 1, which is characterized in that: the photoinitiator comprises benzil dimethyl ketal or aromatic ketone.

6. The method for preparing the wide wave reflection film material by the nano zinc oxide film diffusion method according to claim 1, which is characterized in that: the inner surface of the liquid crystal box is a single-side nano zinc oxide film, and the film preparation method is a spin-coating method or a dripping coating method.

7. Use of the broad wavelength reflective film obtained by the preparation method according to claims 1 to 6, wherein the film is used for an optical brightness enhancement film for liquid crystal display and an energy-saving and environment-friendly film for architectural glass.

Technical Field

The invention belongs to the field of functional material application, and provides a method for preparing a wide wave reflection film material by using a nano zinc oxide film diffusion method. The material can be widely applied to the fields of optical brightening films, gratings, laser protection, optical devices, sensors and the like.

Background

The liquid crystal is partially ordered anisotropic liquid, is between three-dimensional ordered solid and isotropic liquid, can flow like liquid, and can also have isotropic ordered arrangement like crystals. The liquid crystal is an optically anisotropic substance sensitive to an external field because the centroid of the liquid crystal molecules is disordered (the crystals are ordered) and the director thereof is ordered (the ordinary liquid disorder). Due to this special structure, liquid crystals can modulate light and are widely used in the display field. The cholesteric liquid crystal material with the reflection wave band in the visible light region can be applied to an optical brightness enhancement film of a liquid crystal display, the optical utilization rate and the brightness of the liquid crystal display screen can be remarkably increased by using the optical brightness enhancement film, and the optical brightness enhancement film can be realized by a wide wave reflection thin film material; the cholesteric liquid crystal with the reflection wave band in the visible light region can also be applied to temperature indication, tumor inspection, anti-counterfeiting trademarks, reflection liquid crystal display, color filters, reflection-type circular polarizers and the like; the cholesteric liquid crystal with the reflection wave band in the near infrared light region can be applied to energy-saving and environment-friendly building glass or paint; the cholesteric liquid crystal with the reflection wave band in the mid-infrared light region has potential application prospect in shielding and hiding aspects in military affairs.

Generally, cholesteric liquid crystal (N)^*Phase liquid crystal) is formed by adding a chiral compound to nematic liquid crystal, liquid crystal molecules are arranged into a periodic spiral structure, which can be approximately regarded as layered arrangement, the layers are parallel, the directions of long axes of molecules in the layers are basically consistent, the long axes of liquid crystal molecules between adjacent layers are sequentially and regularly rotated by a certain angle, the liquid crystal molecules are arranged into a spiral structure along the normal direction of the layers, and the long axes of the molecules are recovered after being rotated by 360 degrees. The closest interlayer distance at which the long axes of the two molecules are aligned the same (i.e. rotated 360 °) is called the pitch (P) of the cholesteric liquid crystal. Due to the unique supermolecular helical structure of the cholesteric liquid crystal, the circularly polarized light with the same rotating direction as the cholesteric liquid crystal is reflected, and the circularly polarized light with the opposite rotating direction to the cholesteric liquid crystal is transmitted, which is the selective reflection of the cholesteric liquid crystal. Part of the natural light is completely transmitted beyond the reflection range. The wavelength range of the cholesteric liquid crystal with single pitch selectively reflecting the incident light is between lambda_max＝n_eP and lambda_min＝n_oP between (n)_eAnd n_oExtraordinary and ordinary refractive indices, respectively); reflection bandwidth Δ λ ═ λ_max-λ_min＝(n_e-n_o)P＝ΔnP(Δn＝n_e-n_oIs the birefringence index).

The birefringence of liquid crystals depends on the molecular structure thereof, and generally, Δ n is smaller than 0.3, and the wavelength width Δ λ of selective reflection in the visible light region is limited to about 100 nm. The narrow bandwidth limits the application of cholesteric liquid crystals in the ultraviolet, visible and infrared regions. In general, widening the reflection wave width generally requires changing the pitch of the cholesteric liquid crystal. In recent years, researchers have broadened the application of broad wave reflection by inducing uneven distribution of pitches or gradient distribution of pitches in cholesteric liquid crystals to increase the reflection bandwidth of cholesteric liquid crystals for selectively reflecting incident light.

Disclosure of Invention

The invention aims to provide a simple preparation method of a polymer stabilized cholesteric liquid crystal wide wave reflection film material, which can be spin-coated on one side of a liquid crystal box by utilizing the characteristic that zinc oxide nano particles absorb ultraviolet light, and ultraviolet light intensity gradient is formed in the thickness direction of the liquid crystal box through the irradiation of the ultraviolet light, so that different consumption rates of free radical polymerization monomers are caused, further, relative migration of chiral compounds is caused, the gradient distribution of screw pitches is induced, and the reflection wave width of a sample is widened. The reflection bandwidth of the sample can be regulated and controlled by regulating the ultraviolet irradiation intensity, and the central wavelength of the reflection band of the sample can also be regulated and controlled by regulating the concentration of the chiral compound in the liquid crystal composite system. The invention has the advantages of rich raw material sources, low cost, easy obtainment and simple process, and can be applied in large scale.

A method for preparing a wide wave reflection film material by a nano zinc oxide film diffusion method comprises the following specific preparation processes:

step 1: uniformly mixing small molecular nematic liquid crystal, a chiral compound, an ultraviolet free radical polymerizable monomer and a photoinitiator according to a certain weight percentage, wherein the weight percentage of the small molecular nematic liquid crystal is as follows: 73.9-85.9%; the weight percentage of the ultraviolet free radical polymerizable monomer is as follows: 3.8-15.8%; the chiral compound comprises the following components in percentage by weight: 1-20%; the weight percentage of the photoinitiator is as follows: 0.1-3%, oscillating the mixture for multiple times by using an oscillator, ultrasonically processing the mixture for multiple times by using an ultrasonic instrument, and uniformly mixing the mixture to obtain a cholesteric liquid crystal composite system, wherein the cholesteric liquid crystal composite system is protected from light in the operation process;

step 2: and dripping the zinc oxide nano particle dispersion liquid on ITO (indium tin oxide) conductive glass, and putting the ITO conductive glass into an oven for drying after spin coating by a spin coater to prepare the nano zinc oxide film substrate. Combining the inner side of the nano zinc oxide film of the substrate and an ITO glass substrate into a liquid crystal box with a nano zinc oxide film on one side, wherein the thickness of the liquid crystal box is 10-80 mu m;

and step 3: pouring the cholesteric liquid crystal composite system mixed in the step 1 into a liquid crystal box of a pretreated single-side nano zinc oxide film, and then performing optimized plane texture treatment on the poured liquid crystal box by using an oven to ensure that the system is in a stable plane texture state, wherein the temperature of the oven is about 10 ℃ lower than the clearing point of the system, and the clearing point temperature of the system is measured by DSC;

and 4, step 4: placing the liquid crystal box subjected to the optimized planar texture treatment in the step 3 on a hot stage with one side of the nano zinc oxide film facing upwards, setting the temperature of the hot stage to be 10-70 ℃, and irradiating by using ultraviolet light, wherein the wavelength of the ultraviolet light is 365nm, the irradiation time of the ultraviolet light is 10-200 min, and the illumination intensity of the ultraviolet light is 0.05-5 mW/cm²Polymerizing the polymerizable monomer to form a polymer network anchoring pitch to prepare the liquid crystal film material for realizing wide wave reflection;

further, the weight percentage of the zinc oxide nanoparticle dispersion liquid is 1-40%, the particle size of the dispersoid is 1-100 nm, and the dispersant is one or more of water, absolute ethyl alcohol, isopropanol and 1, 2-propylene glycol monomethyl ether acetate.

Further, the chiral compound includes 4- (4 '-hexyloxy) benzoyloxybenzoic acid-R- (-) -2-octyl alcohol ester, 4- (4' -hexyloxy) benzoyloxybenzoic acid-S- (-) -2-octyl alcohol ester, (13BR) -5, 6-dihydro-5- (trans-4-propylcyclohexyl) -4H-dinaphtho [2,1-F:1',2' -H ] [1,5] dioxononatetraene, (13BS) -5, 6-dihydro-5- (trans-4-propylcyclohexyl) -4H-dinaphtho [2,1-F:1',2' -H ] [1,5] dioxononatetraene or a plurality of dioxonantetraenes.

Further, the polymerizable monomer is one or more of acrylates, methacrylates, styryls and diacetyl, and the number of active functional groups is 1-5.

Further, the photoinitiator comprises benzil dimethyl ketal or aromatic ketone.

Further, the inner surface of the liquid crystal box is a single-side nano zinc oxide film, and the film preparation method is a spin coating method or a dropping coating method.

The principle of broadening the reflection wave width of a sample in the method is explained as follows: the nano zinc oxide particle dispersion liquid is coated on ITO (indium tin oxide) conductive glass by a spin coater to prepare a nano zinc oxide film substrate, and the nano zinc oxide film side of the substrate and the ITO conductive glass substrate are combined into a liquid crystal box. Uniformly mixing nematic liquid crystal, chiral compound, polymerizable monomer and photoinitiator according to a certain weight percentage to prepare a cholesteric liquid crystal composite system with a specific pitch. And (3) pouring the cholesteric liquid crystal composite system into a liquid crystal box with a nano zinc oxide film on one side through a siphoning effect. The film side in the liquid crystal box is upward and placed on a hot table, nano zinc oxide particles are diffused into a liquid crystal composite system, and ultraviolet light intensity gradient is formed in the thickness direction of the liquid crystal box by utilizing the characteristic that the nano zinc oxide absorbs ultraviolet light and irradiating the liquid crystal composite system by the ultraviolet light. Thus, the ultraviolet intensity is large at the low beam side and small at the high beam side, and the consumption rate of the ultraviolet polymerizable monomer is large at a place where the light intensity is large. Due to the difference in the consumption rate, the ultraviolet polymerizable monomer migrates from the high beam side to the low beam side, and, in contrast, the chiral compound diffuses from the low beam side to the high beam side, eventually forming a concentration gradient of the chiral compound. As the pitch in the system is reduced along with the increase of the concentration of the chiral compound, the gradient distribution of the pitch is formed in the thickness direction of the liquid crystal box, and the reflection wave width of the sample is widened. In the method, the reflection wave band of the sample can be adjusted by adjusting the ultraviolet light irradiance according to the requirement; the central wavelength of the reflection band can be adjusted to a required light region by adjusting the concentration of the chiral compound in the liquid crystal composite system.

The invention has the advantages that:

1 the wide wave reflection film material has the advantages of simple raw material system, low material cost, rich sources, simple manufacturing process and easy realization of large-scale production.

2, the method utilizes the characteristic that zinc oxide nano particles absorb ultraviolet light to spin the zinc oxide nano particles on one side of a liquid crystal box, ultraviolet light intensity gradient is formed in the thickness direction of the liquid crystal box through the irradiation of the ultraviolet light, so that polymerizable monomers in a system have different consumption rates, the concentration gradient of a chiral compound is formed, the gradient distribution of screw pitches is formed through induction, and the reflection wave width of a sample is widened.

3 the method can adjust the central wavelength of the reflection band of the sample by adjusting the concentration of the chiral compound in the step 1, and fix the central wavelength in a visible light region or an infrared light region; and (4) adjusting the ultraviolet irradiation intensity in the step (4) to regulate and control the reflection wave band of the sample.

Drawings

FIG. 1 is a diagram showing an ultraviolet absorption spectrum of a nano zinc oxide particle used in the present invention. The experiment shows that the nano zinc oxide particles have strong absorption peaks in an ultraviolet light region, which indicates that the single-side nano zinc oxide film liquid crystal box can form an ultraviolet light intensity gradient through ultraviolet light irradiation.

Fig. 2 is a graph of the transmission spectra of the liquid crystal film materials of the samples of example 1, example 2 and example 3 under different ultraviolet irradiances. The curve is a transmission spectrum plot of sample 1 at 25 ℃ without polymerization prior to polymerization; after the curve sample 1 is polymerized, the ultraviolet irradiance of the sample 1 is 0.2mW/cm²A transmitted light spectrum after polymerization at 40 ℃; after the curve sample 2 is polymerized, the ultraviolet irradiance of the sample 2 is 0.8mW/cm²A transmitted light spectrum after polymerization at 40 ℃; curve sample 3 was polymerized followed by sample 3 at 1.2mW/cm UV light irradiance²A transmitted light spectrum after polymerization at 40 ℃; in the experiment, the reflection wave width of the sample before polymerization can be compared, and the reflection wave width of the sample after polymerization is obviously widened; meanwhile, according to experiments, the ultraviolet light irradiance of the sample 1 is 0.2mW/cm under the condition that other polymerization conditions are not changed²Increasing the irradiance of the ultraviolet light in the sample 2 to 0.8mW/cm²And then the intensity of the ultraviolet light in the sample 3 is increased to 1.2mW/cm²In the process, the reflection wave width of the sample gradually increases. Therefore, the single-side nano zinc oxide film liquid crystal box can generate an ultraviolet light intensity gradient through the irradiation of ultraviolet light, the ultraviolet light intensity in the liquid crystal composite system is increased along with the increase of the irradiation intensity of the ultraviolet light, the speed of the polymerizable monomer is increased, the diffusion speed of the chiral compound is increased correspondingly, the polymerization speed of the polymerizable monomer is balanced with the diffusion speed of the chiral compound, and the pitch gradient distribution is easier to induce. Therefore, the invention provides a wide-wave reflection film material which can be used for preparing different reflection wave bands by adjusting different ultraviolet light irradiance according to the actual living needs.

FIG. 3 is a scanning electron microscope image of a cross-sectional surface of a wide wave reflective film of sample 3 in accordance with the present invention. It can be seen from the electron micrograph that the pitch of the sample shows a gradient distribution.

Detailed Description

The technical solution of the present invention is further described with reference to the following specific embodiments.

Example 1

Manufacturing a liquid crystal box: and (3) placing the cleaned ITO (indium tin oxide) glass in a drying oven at 60 ℃ for 3h for drying. And (2) dripping a nano zinc oxide dispersion (more than or equal to 30 percent and 90nm, wherein the solvent is 1, 2-propylene glycol monomethyl ether acetate) on an ITO glass substrate, coating the ITO glass by using a spin coater at an initial speed of 600r/min for 6s and at a high speed of 2000r/min for 30s, and then carrying out heat treatment on the glass substrate coated with the nano zinc oxide film at the temperature of 60 ℃ for 60min to obtain the nano zinc oxide film glass substrate. The nano zinc oxide film glass substrate is combined with an ITO glass substrate, a PET film with the thickness of 55 mu m is used as a spacer, the two sides are sealed by glue, and an inlet is reserved, so that the liquid crystal box with the nano zinc oxide film on one side is prepared.

Respectively mixing nematic liquid crystal SLC1717, chiral compound R811, polymerizable monomer C6M and photoinitiator Irg651 (benzildimethylketal) according to the mass ratio of 83.9: 9.8: 5.8: 0.5, mixing evenly, and pouring into a liquid crystal box with one side containing the nano zinc oxide film by utilizing the siphon action at room temperature.

R811 chemical structural formula:

C6M chemical structural formula:

photoinitiator Irg651 has the chemical structural formula:

after the system is stabilized, the samples are mixed evenly according to the proportion and then poured into a nano zinc oxide film liquid crystal box, the thickness of the liquid crystal box is 55 mu m, the side of the liquid crystal box with a nano zinc oxide film substrate is upward, and the ultraviolet light irradiance is 0.2mW/cm at 40 DEG C²And (3) irradiating for 60min by using 365nm ultraviolet light to obtain a sample 1, and curing and crosslinking the polymerizable monomer to form a network to obtain the final polymer network cholesteric liquid crystal film. The transmission spectrogram of the sample can be measured at room temperature by using an ultraviolet-visible-near infrared spectrophotometer (Jasco V-570), and the reflection waveband of the film at room temperature is 1272-1618 nm.

The ultraviolet irradiance can be controlled by adjusting the power of the ultraviolet lamp and the distance between the lamp and the sample, and the ultraviolet irradiance is measured by using an ultraviolet radiometer. The clearing point of the mixed system, namely the temperature of the mixed system during anisotropic phase transition can be accurately measured by Differential Scanning Calorimetry (DSC).

Example 2

Respectively mixing nematic liquid crystal SLC1717, chiral compound R811, polymerizable monomer C6M and photoinitiator Irg651 (benzildimethylketal) according to the mass ratio of 79.9: 9.8: 9.8: 0.5, mixing evenly, and pouring into a liquid crystal box with one side containing the nano zinc oxide film by utilizing the siphon action at room temperature.

The sample mixed in the example 2 is poured into a liquid crystal box with a nano zinc oxide film on one side, the thickness of the liquid crystal box is 55 mu m, the side of the liquid crystal box with the nano zinc oxide film substrate is upward, and the ultraviolet irradiation illuminance is 0.8mW/cm at 40 DEG C²And (3) irradiating for 60min by 365nm ultraviolet light to obtain a sample 2, curing and crosslinking the polymerizable monomer to form a network to obtain the final polymer network cholesteric liquid crystal film, wherein the reflection waveband of the film at room temperature is 1174 nm-1738 nm. The transmitted spectrum of the sample prepared by the above method can be measured at room temperature using an ultraviolet-visible-near infrared spectrophotometer (Jasco V-570). The reflection bandwidth of the sample prepared by the method increases with increasing uv irradiance, and the reflection bandwidth of the sample increases compared to the reflection bandwidth range of example 1.

Example 3

Respectively mixing nematic liquid crystal SLC1717, chiral compound R811, polymerizable monomer C6M and photoinitiator Irg651 (benzildimethylketal) according to the mass ratio of 77.9: 9.8: 11.8: 0.5, mixing evenly, and pouring into a liquid crystal box with one side containing the nano zinc oxide film by utilizing the siphon action at room temperature.

The sample mixed in the example 3 is poured into a liquid crystal box with a nano zinc oxide film on one side, the thickness of the liquid crystal box is 55 mu m, the side of the liquid crystal box with the nano zinc oxide film substrate is upward, and the ultraviolet irradiation intensity is 1.2mW/cm at 40 DEG C²And (3) irradiating for 60min by using 365nm ultraviolet light to obtain a sample 3, and curing and crosslinking the polymerizable monomer to form a network to obtain the final polymer network cholesteric liquid crystal film. The transmitted spectrum of the sample can be measured at room temperature by using an ultraviolet-visible-near infrared spectrophotometer (Jasco V-570), and the reflection waveband of the film at room temperature is 1114-1746 nm. The reflection bandwidth of the sample prepared by the method increases with increasing uv irradiance, and the reflection bandwidth of the sample increases compared to the reflection bandwidth range of example 2.