CN115657375A

CN115657375A - Composition of cobalt chloride modified azo dye photoalignment layer and preparation method thereof

Info

Publication number: CN115657375A
Application number: CN202211346612.7A
Authority: CN
Inventors: 刘奡
Original assignee: Jinling Institute of Technology
Current assignee: Jinling Institute of Technology
Priority date: 2022-10-31
Filing date: 2022-10-31
Publication date: 2023-01-31

Abstract

The invention discloses a cobalt chloride modified azo dye photo-alignment layer composition, which comprises a hydrophilic azo dye compound and cobalt chloride, and can keep the excellent alignment quality of a photo-alignment layer in a large humidity range environment.

Description

Composition of cobalt chloride modified azo dye photoalignment layer and preparation method thereof

Technical Field

The invention relates to a composition of a photoalignment layer and a preparation method thereof, in particular to a composition of a cobalt chloride modified azo dye photoalignment layer and a preparation method thereof.

Background

The hydrophilic azo dye compound is an excellent liquid crystal photo-alignment layer material and is used as a cobalt chloride compound for optimally adjusting the humidity problem sensitive in the hydrophilic azo dye photo-alignment process.

The optical alignment method is a non-contact alignment method commonly used in the field of liquid crystal. Among them, azo dye materials such as azobenzene sulfonic acid dye SD1 and Brilliant Yellow (BY) are often used as photosensitive materials in photoalignment because of the possibility of photo-induced molecular rotation. Meanwhile, water-soluble azo dyes such as BY, SD1 and the like are easy to capture moisture in the air due to hydroxyl groups to generate crystals, so that the prepared film is difficult to orient, the order parameter of an oriented molecule is greatly reduced, or a large dose of exposure intensity is required to obtain a considerable orientation level. The environmental humidity has a great influence on the photoalignment quality of the hydrophilic azo dye material, both for the non-composite azo dye layer and the azo dye composite layer. The photo-induced phase retardation, the order parameters of the alignment layers, and the alignment quality of the corresponding liquid crystal are very different at different humidities. For BY, the photo-stability of the alignment layer is also significantly affected BY the Relative Humidity (RH). Rewriting is ensured at a very low RH (< 10%), but gradually disappears with increasing relative humidity, and at 40% relative humidity or higher, the alignment layer becomes resistant to further exposure. The RH range of the BY alignment layer is lower than 50%, especially the relative humidity is lower than 40%, good photo-alignment quality can be ensured, the BY alignment layer is recommended to be used as a working window of BY photo-alignment application, and when the RH is higher than 50%, the photo-alignment quality is poor, and the use is avoided. While the RH working window of the SD1 material is recommended to be 50% -70%. Due to such characteristics of the water-soluble azo dye, in the conventional process for preparing a photoalignment film and the exposure process, a large amount of resources are consumed to ensure the temperature and the relative humidity of the process environment, and part of the process even needs to be completed in a glove box filled with inert gas, which is not favorable for mass production of the photoalignment technology.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a composition of a cobalt chloride modified azo dye photoalignment layer, which can keep the excellent alignment quality of the photoalignment layer in a large humidity range environment; another object of the present invention is to provide a method for preparing the photo-alignment layer composition.

The technical scheme is as follows: the cobalt chloride modified azo dye photoalignment layer composition comprises a hydrophilic azo dye compound and cobalt chloride.

Preferably, the azo dye compound of hydrophilic type is brilliant yellow or tetrasodium 5,5' - ((1e, 1' e) - (2, 2' -disulfonic acid- [1,1' -biphenyl ] -4,4' -diyl) bis (diazene-2, 1-diyl)) bis (2-hydroxybenzoic acid) (SD 1), CD1 or congo red; disazo dyes are generally preferred, which contain azo-containing-N = N-structures in the formula, and are routinely stored in nitrogen gas cabinets or other moisture-protected environments.

Preferably, the molar weight ratio of the cobalt chloride to the azo dye compound is 1.

Preferably, the composition further comprises one or more of a viscosity modifier, an acrylate polymer liquid crystal, an initiator or a photosensitizer.

A method for preparing the cobalt chloride modified azo dye photoalignment layer, which comprises the steps of dissolving the photoalignment material consisting of the composition of any one of claims 1 to 4 in an organic solvent by means of spin coating, slit coating, tape casting, ink-jet printing or printing, coating the solution on a substrate, annealing, heating in a hot stage or an oven at 60 ℃ to 100 ℃ for 5 to 10 minutes to evaporate the residual solvent to form an amorphous photoalignment film, and irradiating the photoalignment layer on the substrate with polarized ultraviolet light or blue light in an orientation perpendicular to the polarization direction of the polarized light to obtain a predetermined photoalignment orientation of azo dye molecules. Azo dye molecules with Co during annealing ²⁺ The metal ions form a metal complex through a complexing reaction, and the formation of the complex further contributes to the long-term property stability of the dye molecule alignment layer.

Preferably, the organic solvent is one or more of DMF, DMSO, absolute ethanol, nitromethane, methanol, ethylene glycol, ethanolamine, aniline, isopropanol, benzyl alcohol, or butyl cellosolve.

Preferably, the organic solvent is a mixed solvent of anhydrous ethanol and DMF in a mass ratio of 5 to 10.

Preferably, the weight ratio of the azo dye compound to the organic solvent is 0.1-5%, more preferably 0.5-1%.

Preferably, the substrate is hard glass, organic glass, an ITO glass substrate, a flexible PET or TAC film.

The composition can be used for preparing a photoalignment layer under the condition that the relative humidity of the environment is 5-70%.

The optimization modification is to uniformly mix anhydrous cobalt chloride in the photoalignment material, wherein the molar ratio of the anhydrous cobalt chloride to the photoalignment material is 1-1.

The invention optimizes the adaptive humidity range for processing the photo-alignment material. In a natural state, the environmental humidity needs to be controlled to satisfy the use condition of the azo dye as the photo-alignment material. For the photo-alignment process, the solid film of the azo dye has the advantages that along with the increase of humidity, the inserted water molecules are increased, the molecules of the azo dye can generate intrinsic crystals or semi-crystals in the film forming process, the water molecules are combined with the hydrophilic function of the azobenzene molecules, the semi-crystal interaction between the molecules becomes stronger, so that the molecules of the azo dye are firmly combined with each other before polarized light exposure, the energy of the polarized light for aligning the molecules of the azo dye is smaller than the interaction between the crystals or the semi-crystals, and therefore, the photo-alignment material film loses the photo-alignment capability. According to the invention, anhydrous cobalt chloride is mixed in the azo dye photoalignment composition according to a certain proportion according to the environmental humidity, the affinity of hydrophilic groups such as sodium sulfonate in the middle of azo dye molecules and hydrogen bonds between terminal hydroxyl groups to water molecules is far less than the capturing force of the anhydrous cobalt chloride to the water molecules in the synthesis of hexahydrate by the hydration of the anhydrous cobalt chloride, and the water molecules combined by the corresponding hydrophilic groups are captured by the anhydrous cobalt chloride, thereby causing a relatively anhydrous microenvironment among the azo dye molecules. In this case, the aggregation of azo dye molecules is hindered by intermolecular repulsive electrostatic force of the hydrophilic group, thereby forming a photoalignable amorphous state thin film without additional resource consumption for controlling the humidity of a large environment.

Furthermore, in the irradiation process of the polarized light to the optical alignment film, the cobalt chloride hexahydrate generated in the hydration process is also irradiated by light to release moisture and reduce the moisture into anhydrous cobalt chloride. The released crystal water can be inserted into the azo dye molecules prearranged by polarized light, and the process can promote the azo dye molecules which are not accurately ordered around the ordered molecules to be further accurately ordered, thereby improving the ordering of the orientation of the film.

The process that the cobalt chloride hexahydrate releases crystal water and increases the orderliness, namely the reference order quantity, of the photoalignment film is as follows: the azo dye film in an amorphous state has one-dimensional column-like sequence by molecular self-assembly under polarized illumination. In the illumination process, cobalt chloride hexahydrate generated as optimized modification releases crystal water, selectively hydrates around hydrophilic functional groups of azo dye molecules, utilizes the easily soluble liquid crystal property of the azo dye to promote molecular reordering, and changes the molecular components originally having one-dimensional nematic order into high-order two-dimensional columnar order with larger structural anisotropy, so that the order parameters of the final photoalignment film are increased rapidly, and the corresponding order quantity can be as high as more than 0.7.

In the process of preparing the film, the cobalt chloride takes moisture in the microenvironment of the azo dye to form cobalt chloride hexahydrate, and the azo dye is difficult to crystallize because of being taken away the moisture, so that an amorphous film required by photo-orientation is formed; then, when the cobalt chloride hexahydrate is exposed to light for orientation, the cobalt chloride hexahydrate releases moisture and is reduced into cobalt chloride. The released water can be inserted into the oriented azo dye molecules, so as to further induce the orientation of the azo dye molecules and increase the order parameter which can be as high as more than 0.7; after the photo-induced orientation process is finished, in the subsequent annealing process of the orientation layer film, due to the existence of cobalt ions in cobalt chloride, dye molecules such as BY and the like and Co are subjected to the action of the annealing temperature ²⁺ The metal ions form metal complexes by a complexation reaction. The formation of the complex is beneficial to the long-term stability of the dye molecule alignment layer, thereby further solving the problem that the dye molecules as the alignment layer are easily influenced by the environment such as temperature, illumination and the like and can not maintain the order for a long time.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: the composition can keep the excellent alignment quality of the optical alignment layer in the environment with a larger humidity range, and the optical alignment material composition prepared by the method has excellent performance, can better keep the excellent alignment quality of the prepared alignment layer film in the environment with a larger humidity range, and simultaneously realizes a better optical alignment process.

Drawings

FIG. 1 is a molecular structure diagram of an azo dye BY;

FIG. 2 is a schematic diagram of the molecule BY when a water molecule is inserted;

FIG. 3 shows the BY molecule and Co ²⁺ A complex reaction diagram of metal ions;

FIG. 4 shows the BY molecule and Co ²⁺ A metal ion complex diagram;

FIG. 5 is a BY amorphous film, and black dots are a BY diagram which is not completely dispersed;

FIG. 6 is a BY film showing the onset of crystal morphology;

FIG. 7 is a graph of the amorphous BY film with the dots representing cobalt chloride agglomerates;

FIG. 8 is a thin film diagram of BY.

Detailed Description

The technical solution of the present invention is further illustrated by the following examples.

Example 1

1) The dried azo dye powder, BY way of example, having a molecular structure shown in FIG. 1, anhydrous cobalt chloride, N, N-Dimethylformamide (DMF), was stored in an argon-filled glove box provided with an inert atmosphere and the water vapor inside was controlled to be within 0.5 ppm. The relative humidity RH was 50%.

2) The BY powder was dissolved in N, N-Dimethylformamide (DMF) at a concentration of 0.5 wt% and anhydrous cobalt chloride at a concentration of 0.05 wt%, and mixed uniformly.

3) The above solution was spin-coated on a glass substrate at 3000 rpm for 30 seconds using a spin coater. The glass substrate was preliminarily treated with ozone plasma in an ultraviolet ozone cleaner for 20 minutes in advance. Then dried at 90 ℃ for 30 minutes to effect solvent evaporation, resulting in a solid film about 15 nm thick, i.e., an alignment layer film. In the process, the anhydrous cobalt chloride undergoes hydration reaction to generate cobalt chloride hexahydrate.

4) Exposing the prepared alignment layer film substrate to 450nm linearly polarized light for 15 minutes, wherein the light intensity of the irradiation position is 20 mW/cm ² Randomly distributed BY molecules will tend to align perpendicular to the light polarization. In the process, the cobalt chloride hexahydrate releases crystal water due to the simultaneous illumination, and water molecules are inserted among the sequenced BY molecules, so that the sequencing reference quantity of the BY molecules is further increased, as shown in figure 2.

5) Annealing the oriented BY film substrate at 80 ℃ for 15 minutesPart of the BY molecules in this process are reacted with Co ²⁺ The metal ions form metal complexes through a complexation reaction as in fig. 3, and there may be the generation of metal complexes of type 1 and type 1.

The alignment layer film obtained in this example is an amorphous film, as shown in fig. 7, no crystal form is seen, and the polarization orientation can be performed smoothly, and the BY molecular order parameter after orientation is about 0.7.

Example 2

In an environment with a relative humidity RH of 60%, BY powder was dissolved in DMF at a concentration of 0.5 wt% and anhydrous cobalt chloride at a concentration of 0.08 wt%, and mixed uniformly. The above solution was spin-coated on a glass substrate at 3000 rpm for 30 seconds using a spin coater. The glass substrate was preliminarily treated with ozone plasma in an ultraviolet ozone cleaner for 20 minutes in advance. Then, the film was dried at 90 ℃ for 30 minutes to evaporate the solvent, and the rest of the procedure was the same as example 1 to obtain an alignment layer film.

The alignment layer film obtained in this example is an amorphous film, and can be smoothly polarized and oriented, and the BY molecular order parameter after orientation is about 0.7.

Comparative example 1

The BY powder was dissolved in DMF at a concentration of 0.5 wt% in an atmosphere with a relative humidity RH of 30% and mixed well. The above solution was spin-coated on a glass substrate at 3000 rpm for 30 seconds using a spin coater. The glass substrate was preliminarily treated with ozone plasma in an ultraviolet ozone cleaner for 20 minutes in advance. And then dried at 90 ℃ for 30 minutes to perform solvent evaporation, resulting in an alignment layer film.

The alignment layer film obtained in this comparative example is an amorphous film, and as shown in fig. 5, no crystalline form is observed, and the polarization orientation can be performed smoothly, and the BY molecular order parameter after orientation is about 0.7.

Comparative example 2

The BY powder was dissolved in DMF at a concentration of 0.5 wt% in an atmosphere with a relative humidity RH of 50% and mixed well. The above solution was spin-coated on a glass substrate at 3000 rpm for 30 seconds using a spin coater. The glass substrate was preliminarily treated with ozone plasma in an ultraviolet ozone cleaner for 20 minutes in advance. And then dried at 90 ℃ for 30 minutes to perform solvent evaporation, resulting in an alignment layer film.

The alignment layer film obtained in the comparative example starts to have a crystal form, as shown in fig. 6, the polarization orientation difficulty is increased, a larger exposure dose is required, and the BY molecular order parameter after orientation is about 0.3.

Comparative example 3

The BY powder was dissolved in DMF at a concentration of 0.5 wt% in an atmosphere with a relative humidity RH of 60% and mixed well. The above solution was spin-coated on a glass substrate at 3000 rpm for 30 seconds using a spin coater. The glass substrate was preliminarily treated with ozone plasma in an ultraviolet ozone cleaner for 20 minutes in advance. And then dried at 90 ℃ for 30 minutes to perform solvent evaporation, resulting in an alignment layer film.

In the alignment layer film obtained in the present comparative example, the crystalline forms of BY molecules are increased, as shown in fig. 8, the polarization orientation is difficult, the exposure dose is further increased, and the exposure time is prolonged, and no significant orientation is observed.

Claims

1. A cobalt chloride-modified azo dye photoalignment layer composition, comprising a hydrophilic azo dye compound and cobalt chloride.

2. The cobalt chloride-modified azo dye photoalignment layer composition according to claim 1, wherein the hydrophilic azo dye compound is brilliant yellow, SD1, CD1 or congo red.

3. The composition for a cobalt chloride-modified azo dye photoalignment layer according to claim 1, wherein the molar weight ratio of the cobalt chloride to the azo dye compound is 1 to 1.

4. The composition of claim 1, further comprising one or more of a viscosity modifier, an acrylate polymer liquid crystal, an initiator, or a photosensitizer.

5. A method for preparing a photoalignment layer of cobalt chloride-modified azo dye according to any of claims 1 to 4, wherein the method comprises the steps of dissolving a photoalignment material consisting of the composition according to any of claims 1 to 4 in an organic solvent by spin coating, slit coating, casting, ink-jet printing or printing, coating the solution on a substrate, annealing, and irradiating the photoalignment layer on the substrate with polarized ultraviolet light or blue light.

6. The method for preparing the cobalt chloride-modified azo dye photoalignment layer according to claim 5, wherein the organic solvent is one or more of DMF, absolute ethanol, ethylene glycol, benzyl alcohol or butyl cellosolve.

7. The method for preparing the cobalt chloride-modified azo dye photoalignment layer according to claim 5, wherein the organic solvent is a mixed solvent of anhydrous ethanol and DMF at a volume ratio of 5 to 10.

8. The method for preparing the cobalt chloride modified azo dye photoalignment layer according to claim 5, wherein the weight ratio of the azo dye compound to the organic solvent is 0.1-5%.

9. The method for preparing the cobalt chloride-modified azo dye photoalignment layer according to claim 5, wherein the substrate is a hard glass, an organic glass, an ITO glass substrate, a flexible PET or TAC film.

10. Use of the composition of claim 1 for preparing a photoalignment layer under the condition that the ambient relative humidity is 5-70%.