CN110092875A - A kind of preparation method of the pdlc film based on Liquid Crystal/Polymer composite system - Google Patents

Abstract

The invention provides a method for preparing a PDLC film based on a liquid crystal/polymer composite material system. The details are as follows: After mixing the liquid crystal, photopolymerizable monomer and photoinitiator uniformly according to a certain mass ratio, the mixture is poured into the liquid crystal cell by using the siphon principle, and the thickness of the liquid crystal cell is controlled at 10-30 μm by a plastic spacer. Then irradiate with ultraviolet light for 1 to 5 minutes at room temperature to form a polymer dispersed liquid crystal film. Then, the formed polymer-dispersed liquid crystal film is subjected to secondary photopolymerization in an electric field. The introduction of thiol monomer and vinyl ether monomer in the present invention greatly improves the photoelectric performance of the prepared PDLC film; by adjusting the mass ratio and polymerization conditions between acrylate, thiol and vinyl ether, the polymer mesh is adjusted The size of the liquid crystal and the size of the liquid crystal droplet have prepared a polymer-dispersed liquid crystal film with a smaller driving voltage, more energy-saving, and stable performance.

Description

A kind of preparation method of PDLC film based on liquid crystal/polymer composite material system

technical field

The invention belongs to the technical field of liquid crystal applications, and relates to a preparation method of a PDLC film based on a liquid crystal/polymer composite material system, specifically a polymer dispersed liquid crystal (Polymer Dispersed Liquid Crystal) prepared by an ultraviolet light curing system based on a liquid crystal/polymer composite material. Liquid Crystal, PDLC) film material method, the film material prepared can be widely used in liquid crystal display, smart glass, energy-saving building materials, automobile decoration and related fields.

Background technique

Polymer dispersed liquid crystal material is a composite material formed by uniformly dispersing nematic liquid crystal droplets in a polymer matrix. The optical axis of each liquid crystal droplet is in a preferred orientation, while the optical axes of different droplets are in a random orientation state. A nematic liquid crystal material with a dielectric anisotropy greater than zero (Δε>0) is poured between two substrates coated with an ITO (Indium-tinoxide, indium tin oxide) conductive layer to form a certain thickness of PDLC film , liquid crystal droplets with a diameter of about 1-4 μm are randomly distributed in the polymer network, and present a non-uniform arrangement. When the incident light enters the PDLC film without an electric field, because the effective refractive index of the light passing through the liquid crystal droplets is quite different from that of the polymer, the directors of a large number of liquid crystal droplets in the system are randomly distributed, resulting in the light passing through the liquid crystal. Multiple reflections and refractions occur on the interface with the polymer, so that the outgoing light is in a scattered state, and the appearance of the PDLC film is milky white and opaque; when a sufficiently strong external electric field is applied between the two substrates, the liquid crystal molecules are in a consistent arrangement, From bipolar arrangement to parallel arrangement, when the ordinary optical refractive index (n _o ) of the liquid crystal droplet matches the refractive index (n _p ) of the polymer matrix, the incident light is directly transmitted without reflection in the PDLC film , so that the light can be converted from the scattering state to the transmission state.

In the process of preparing PDLC by photopolymerization and phase separation, photopolymerization is a key step affecting the preparation of PDLC. Because the photopolymerization reaction is directly related to the microscopic morphology of the polymer network of the final PDLC film, which in turn affects the electro-optical properties of PDLC. Photopolymerization refers to the process in which the molecular weight of a compound increases due to the absorption of light, including further photocrosslinking of pre-generated macromolecules, some photoinitiated block copolymerization, and graft copolymerization. The photopolymerization initiating active species is produced by photochemical reactions, and the subsequent chain growth and chain termination processes are the same. Therefore, photopolymerization needs to absorb light energy only in the chain initiation stage. The characteristic of photopolymerization is that the activation energy required for the polymerization reaction is low, so it can occur in a large temperature range, especially easy to carry out low-temperature polymerization, which is better than chemical polymerization. Initiating polymerization is far superior. In the laboratory, pure polymers without initiator residues can be obtained by photopolymerization, which provides a very convenient means for various further studies. Photopolymerization has provided a powerful tool for the study of free radical polymerization kinetics and reaction history. In this sense, photopolymerization is a photoreaction with high quantum efficiency, so it has great practical value.

Current liquid crystal displays use polarizers for transmission and refraction of light, but the polarizers reduce the brightness and contrast of the display device. As an electro-optic display material, PDLC has incomparable advantages compared with traditional LCDs: no need for polarizers, high brightness, wide viewing angle, and bendability; no surface treatment of the substrate is required during its production process, and it is used in the production of TFT displays It will greatly improve the yield rate; and it is a solid film, which solves the problem of liquid crystal leakage, and the display device produced is thinner and the thickness is easier to control, which is beneficial to the production of large-area or flexible displays. Therefore, PDLC has broad application prospects in mobile phone display screens, large-area display advertising boards, wearable LCD screens, electronically controlled smart glass, etc., and has become a very active research frontier in the field of liquid crystals.

Contents of the invention

The object of the present invention is to provide a method for preparing a PDLC film based on a liquid crystal/polymer composite material system, and obtain a PDLC film with excellent electro-optic properties.

The preparation method of the PDLC film based on liquid crystal/polymer composite material system of the present invention comprises the following steps:

1) Mixing the liquid crystal material, the photopolymerizable monomer and the photoinitiator evenly, and making the mixture in a clear state at room temperature;

2) Pour the mixture in step 1) in a clear state into the liquid crystal cell through the siphon principle, and the mixture in the liquid crystal cell is irradiated with ultraviolet light in the first step to form a polymer dispersed liquid crystal film;

3) The polymer-dispersed liquid crystal film formed in step 2) is placed in an electric field for a second ultraviolet light irradiation, and polymerized to form a PDLC film of a liquid crystal/polymer composite material system.

According to the preparation method of the PDLC film of the present invention, wherein the photopolymerizable monomers include acrylates, thiols and vinyl ethers, preferably, the acrylates, mercaptans and The mass ratio of vinyl ethers is 27-32:0-8:0-8.

The acrylates include lauryl methacrylate (abbreviated as LMA) as a diluent and trimethylolpropane triacrylate (abbreviated as TMPTA) as a crosslinking agent; the mercaptan is tetrakis (3-mercapto propionate) pentaerythritol ester (abbreviated as PETMP), and the vinyl ether (abbreviated as C4V) can be purchased or synthesized in a laboratory.

Further, the mass ratio of the diluent to the crosslinking agent is 1:1-6:1, preferably 4:1. The mass of the photoinitiator is 3%-5% of the total mass of the photopolymerizable monomer; the mass ratio of the liquid crystal material to the photopolymerizable monomer is 70:30-50:50.

The liquid crystal material in the present invention can be any liquid crystal material known in the art, preferably, nematic liquid crystal SLC1717 is used. The photoinitiator of the present invention is preferably benzoin dimethyl ether (651).

According to the preparation method of the PDLC film of the present invention, wherein, step 2) the clearing point of the clear state is the critical temperature at which the homogeneous mixture of liquid crystal material and photopolymerizable monomer material changes from an anisotropic state to an isotropic state .

According to the preparation method of the PDLC film of the present invention, preferably, the thickness of the liquid crystal cell is 10-30 μm, wherein the liquid crystal cell is composed of glass coated with an indium tin oxide transparent electrode, and the thickness of the liquid crystal cell is Controlled by plastic spacers.

Preferably, the UV irradiation conditions for the first step in step 2) are: the light intensity is 1-5mw/cm ² , the wavelength is 365nm, and the irradiation time is 5-10 minutes; the UV irradiation conditions for the second step in step 3) It is: the light intensity is 10-30mw/cm ² , the wavelength is 365nm, and the irradiation time is 30-60 minutes. The electric field conditions in the second step of ultraviolet light irradiation polymerization are as follows: the field strength is 100-200V, and the electric field frequency is 100-1000HZ.

In the present invention, by introducing the diluent lauryl methacrylate, because of its long molecular chain, good flexibility, and a functionality of 1, the density of the polymer network mesh can be reduced to a certain extent, and the size of the mesh can be increased to make the liquid crystal micro The droplet becomes larger, which reduces the anchoring effect of the polymer network on the liquid crystal, thereby reducing the driving voltage of the PDLC. The first step of polymerization includes the self-polymerization of trimethylolpropane triacrylate and the copolymerization between trimethylolpropane triacrylate and mercaptan, and the second step of polymerization includes the reaction between vinyl ether (C4V) and mercaptan The copolymerization of PDLC film forms a vertical network. Due to the refractive index mismatch between the polymer matrix and the liquid crystal droplet in the film, and between the randomly oriented liquid crystal molecules in the liquid crystal droplet, the film presents a strong light scattering state, thereby increasing the contrast. A polymer liquid crystal dispersion film with high contrast and low driving voltage is formed through self-polymerization between acrylate monomers, copolymerization between acrylate and thiol, and polymerization between vinyl ether and thiol. At the same time, the phase separation process of the PDLC film material is controlled by using the compatibility of the monomer and the liquid crystal, so that it can form a PDLC film material with a suitable polymer network, thereby greatly improving the stability of the PDLC film material while ensuring the stability of the PDLC film material. Comprehensive electro-optical performance.

The advantage of the present invention is that the mercapto-acrylic ester system formed by one-step polymerization has a higher refractive index, more excellent water resistance, and better insulation than ordinary ultraviolet systems by introducing functional thiol monomers and vinyl ethers. Thermal effect, strong oxidation resistance, small amount of initiator, etc., and at the same time, the vertical anchoring formed by the two-step polymerization can greatly reduce the driving voltage of the PDLC film, so it can be adjusted by adjusting the mass ratio of acrylate, mercaptan and vinyl ether. The mass ratio between them and the appropriate polymerization conditions are selected to obtain a polymer-dispersed liquid crystal film with low driving voltage, high contrast and stable performance.

Description of drawings

Fig. 1 is the molecular structural formula of ultraviolet light polymerizable monomer of the present invention;

Fig. 2 is the scanning electron microscope picture of the macromolecule network of the polymer dispersed liquid crystal thin film material prepared by embodiment 1;

Fig. 3 is the voltage-transmittance curve of the polymer dispersed liquid crystal thin film material prepared by embodiment 1;

Fig. 4 is the comparison curve of the one-step polymerization and the saturation voltage after two-step polymerization of the polymer dispersed liquid crystal film material prepared by embodiment 1;

Fig. 5 is the scanning electron microscope picture of the macromolecule network of the polymer dispersed liquid crystal thin film material prepared by embodiment 2;

Fig. 6 is the voltage-transmittance curve of the polymer dispersed liquid crystal thin film material prepared by embodiment 2;

Fig. 7 is the comparison curve of the one-step polymerization and the saturation voltage after two-step polymerization of the polymer dispersed liquid crystal film material prepared by embodiment 2;

Fig. 8 is the scanning electron microscope picture of the macromolecule network of the polymer dispersed liquid crystal thin film material prepared by embodiment 3;

Fig. 9 is the voltage-transmittance curve of the polymer dispersed liquid crystal thin film material prepared by embodiment 3;

Fig. 10 is the comparison curve of the saturation voltage after the one-step polymerization and the two-step polymerization of the polymer dispersed liquid crystal thin film material prepared by embodiment 3;

Fig. 11 is the scanning electron microscope picture of the polymer network of the polymer dispersed liquid crystal thin film material prepared by embodiment 4;

Fig. 12 is the voltage-transmittance curve of the polymer dispersed liquid crystal thin film material prepared by embodiment 4;

Fig. 13 is a comparison curve of the saturation voltage after one-step polymerization and two-step polymerization of the polymer-dispersed liquid crystal film material prepared in Example 4.

Detailed ways

The preferred embodiments of the present invention are listed below, which are only used to explain the present invention rather than limit it.

Example 1

The photopolymerizable monomers selected were lauryl methacrylate, trimethylolpropane triacrylate and pentaerythritol tetrakis(3-mercaptopropionate). Mix the polymerizable monomer with the nematic liquid crystal SLC1717 at a mass ratio of 35.0:65.0. The mass ratio of lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate) and vinyl ether is 24.0:6.0:2.0:3.0. The mass of the photoinitiator benzoin dimethyl ether (651) is 3.0% of the total mass of the photopolymerizable monomers. After stirring evenly, the mixture is in a clear state at room temperature. The mixture is poured into a liquid crystal cell with a cell thickness of 20 μm by the siphon principle, and then irradiated by ultraviolet light with a light intensity of 2 mw/cm ² and a wavelength of 365 nm at room temperature for 5 Minutes, then at room temperature, the electric field intensity is 100V, the electric field frequency is 100HZ under the conditions of two-step polymerization, the ultraviolet light intensity is 15mw/cm ² , the wavelength is 365nm, and irradiated for 30 minutes to form the polymer dispersion of Example 1 liquid crystal film.

The microscopic morphology of the macromolecular network of the PDLC film is observed with a scanning electron microscope (as shown in Figure 2), and the electro-optic performance curve and saturation voltage of the PDLC film prepared above are measured with a liquid crystal comprehensive parameter tester (as shown in Figure 3 and Figure 4 Show).

The experimental results show that the prepared PDLC film has low driving voltage, large contrast, short on-state response time, uniform and dense polymer mesh, and good stability. Comparing the PDLC films formed by one-step polymerization and two-step polymerization, the driving voltage of the film after two-step polymerization is significantly reduced.

Example 2

The photopolymerizable monomers selected were lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), and vinyl ether. Mix the polymerizable monomer with the nematic liquid crystal SLC1717 at a mass ratio of 35.0:65.0. The mass ratio of lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate) and vinyl ether is 20.0:10.0:2.0:3.0. The mass of the photoinitiator benzoin dimethyl ether (651) is 3.0% of the total mass of the photopolymerizable monomers. After stirring evenly, the mixture is in a clear state at room temperature. The mixture is poured into a liquid crystal cell with a cell thickness of 20 μm by the siphon principle, and then irradiated by ultraviolet light with a light intensity of 2 mw/cm ² and a wavelength of 365 nm at room temperature for 8 Minutes, then at room temperature, the electric field intensity is 100V, and the electric field frequency is 100HZ under the conditions of two-step polymerization, the ultraviolet light intensity is 15mw/cm ² , the wavelength is 365nm, and irradiated for 30 minutes to form the polymer dispersion of Example 2 liquid crystal film.

The microscopic morphology of the macromolecular network of the PDLC thin film is observed with a scanning electron microscope (as shown in Figure 5), and the electro-optical performance curve and saturation voltage of the PDLC film prepared above are measured with a liquid crystal comprehensive parameter tester (as shown in Figure 6 and Figure 7 Show).

The experimental results show that with the increase of the content of trimethylolpropane triacrylate with three functional groups, the reaction rate is accelerated, and the liquid crystals are more prone to phase separation, and smaller-sized droplets are formed. Compared with Example 1, the driving voltage of the polymer-dispersed liquid crystal film material prepared in Example 2 is increased, the contrast is also increased correspondingly, the response time is reduced, the mesh of the polymer network is denser and more uniform, and it has good electro-optical properties. Compared with the driving voltage of the PDLC film formed by one-step polymerization, the driving voltage of the PDLC film formed by two-step polymerization decreased significantly.

Example 3

The photopolymerizable monomers selected were lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), and vinyl ether. Mix the polymerizable monomer with the nematic liquid crystal SLC1717 at a mass ratio of 35.0:65.0. The mass ratio of lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate) and vinyl ether is 23.0:5.0:2.0:5.0. The mass of the photoinitiator benzoin dimethyl ether (651) is 3.0% of the total mass of the photopolymerizable monomers. After stirring evenly, the mixture is in a clear state at room temperature. The mixture is poured into a liquid crystal cell with a cell thickness of 20 μm by the siphon principle, and then irradiated by ultraviolet light with a light intensity of 2 mw/cm ² and a wavelength of 365 nm at room temperature for 5 Minutes, then at room temperature, the electric field intensity is 100V, the electric field frequency is 100HZ under the conditions of two-step polymerization, the ultraviolet light intensity is 15mw/cm ² , the wavelength is 365nm, and irradiated for 30 minutes to form the polymer dispersion of Example 3 liquid crystal film.

The microscopic appearance of the macromolecular network of PDLC thin film is observed with scanning electron microscope (as shown in Figure 8), and the electro-optical performance curve and saturation voltage of the PDLC film of above-mentioned preparation are measured with liquid crystal comprehensive parameter tester (as shown in Figure 9, Figure 10 Show).

The experimental results show that since C4V is a molecule with a rigid structure, when the content of vinyl ether increases, the mesh of the polymer network of the formed PDLC film is denser, and the vertical anchoring energy is greater, making the liquid crystal molecules more dense. It is easy to arrange along the direction of the electric field. Compared with Embodiment 1 and Embodiment 2, the driving voltage of Embodiment 3 drops more obviously than the voltage of the PDLC film formed by one-time polymerization, which achieves the purpose of energy saving and environmental protection.

Example 4

The photopolymerizable monomers selected were lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), and vinyl ether. Mix the polymerizable monomer with the nematic liquid crystal SLC1717 at a mass ratio of 35.0:65.0. The mass ratio of lauryl methacrylate, trimethylolpropane triacrylate, pentaerythritol tetrakis(3-mercaptopropionate) and vinyl ether is 24.0:6.0:2.0:3.0. The mass of the photoinitiator benzoin dimethyl ether (651) is 3.0% of the total mass of the photopolymerizable monomers. After stirring evenly, the mixture is in a clear state at room temperature. The mixture is poured into a liquid crystal cell with a cell thickness of 20 μm by the siphon principle, and then irradiated with ultraviolet light with a light intensity of 2 mw/cm ² and a wavelength of 365 nm at room temperature for 10 Minutes, then at room temperature, the electric field intensity is 100V, and the electric field frequency is 100HZ under the conditions of two-step polymerization, the ultraviolet light intensity is 15mw/cm ² , the wavelength is 365nm, and irradiated for 30 minutes to form the polymer dispersion of Example 4 liquid crystal film.

The microscopic morphology of the polymer network of the PDLC film was observed with a scanning electron microscope (as shown in Figure 11), and the electro-optical performance curve of the PDLC film prepared above was measured with a liquid crystal comprehensive parameter tester (as shown in Figures 12 and 13).

The experimental results show that since one-step polymerization forms a PDLC film aligned perpendicular to the direction of the electric field, when the time of one-step polymerization increases, the density of the polymer network aligned perpendicular to the direction of the electric field increases, and the density of the polymer network aligned along the direction of the electric field decreases, so As a result, the driving voltage of the PDLC film increases, and compared with Example 1, the voltage drop of the PDLC film after two-step polymerization is not as obvious as that of Example 1.

Certainly, the present invention can also have multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the disclosure of the present invention, but these corresponding All changes and deformations should belong to the protection scope of the claims of the present invention.

Claims (10)

1. A method for preparing a PDLC film based on liquid crystal/polymer composite system, comprising the following steps: 1) Mixing the liquid crystal material, the photopolymerizable monomer and the photoinitiator evenly, and making the mixture in a clear state at room temperature; 2) Pour the mixture in step 1) in a clear state into the liquid crystal cell through the siphon principle, and the mixture in the liquid crystal cell is irradiated with ultraviolet light for the first time to form a polymer-dispersed liquid crystal film; 3) The polymer-dispersed liquid crystal film formed in step 2) is placed in an electric field for a second ultraviolet light irradiation, and polymerized to form a PDLC film of a liquid crystal/polymer composite material system. 2 . The method for preparing a PDLC film according to claim 1 , wherein the photopolymerizable monomers include acrylates, mercaptans and vinyl ethers. 3 . 3. The method for preparing a PDLC film according to claim 2, characterized in that: the mass ratio of the acrylates, mercaptans and vinyl ethers is between 27-32:0-8:0-8. 4. according to the preparation method of the described PDLC film of claim 2 or 3, it is characterized in that: described acrylic acid ester comprises lauryl methacrylate as diluent and trimethylolpropane triacrylate as crosslinking agent ; The thiol is four (3-mercaptopropionic acid) pentaerythritol ester. 5 . The method for preparing a PDLC film according to claim 4 , wherein the mass ratio of the diluent to the crosslinking agent is 1:1˜6:1. 6. The method for preparing a PDLC film according to any one of claims 1-5, wherein the liquid crystal material is a nematic liquid crystal SLC1717, and the photoinitiator is benzoin dimethyl ether. 7. according to the preparation method of any described PDLC film in the claim 1-5, it is characterized in that: the quality of described photoinitiator is 3%～5% of the total mass of photopolymerizable monomer; The mass ratio of the photopolymerizable monomer and the photopolymerizable monomer is 70:30˜50:50. 8. according to the preparation method of the arbitrary described PDLC film of claim 1-5, it is characterized in that: the clearing point of step 2) described clear state is the homogeneous mixture of liquid crystal material and photopolymerizable monomer material from anisotropic The critical temperature at which the state changes to an isotropic state. 9. The method for preparing a PDLC film according to any one of claims 1-5, characterized in that: the thickness of the liquid crystal cell is 10-30 μm, wherein the liquid crystal cell is made of a transparent electrode coated with indium tin oxide Composed of glass, the thickness of the liquid crystal cell is controlled by plastic spacers. 10. The method for preparing a PDLC film according to any one of claims 1-5, characterized in that: in step 2), the conditions for the first ultraviolet light irradiation are: the light intensity is 1-5mw/cm ² , and the wavelength is 365nm , the irradiation time is 5 to 10 minutes; the electric field intensity in step 3) is 100 to 200V, the electric field frequency is 100 to 1000HZ, and the ultraviolet light irradiation intensity in the second step in step 3) is 10 to 30mw/cm ² , The wavelength is 365nm, and the irradiation time is 30-60 minutes.