CN117304945A - Liquid crystal composition and liquid crystal grating - Google Patents

Abstract

The present application provides a liquid crystal composition, including at least one compound of general formula (1), and at least one compound of general formula (2) and a compound of general formula (3). The liquid crystal composition provided by this application has a higher extraordinary light refractive index ne, a stable smectic phase at low temperatures, better compatibility with polymer monomers, and a wide range from normal temperature to low temperature. In the smectic phase state, the liquid crystal molecules have a very regular arrangement, which can make the holographic polymer dispersed liquid crystal grating liquid crystal phase temperature range include the working range of the grating, and the liquid crystal area has better stability . In addition, this application also provides a liquid crystal grating.

Description

Liquid crystal composition and liquid crystal grating

Technical field

This application belongs to the field of liquid crystal technology, and specifically relates to a liquid crystal composition and a liquid crystal grating.

Background technique

In recent years, liquid crystal materials have been widely used in the display industry and phase optical elements. Televisions, computer monitors, and mobile phone displays use various optical anisotropies and dielectric anisotropies of liquid crystal materials to achieve display functions. Liquid crystal materials are mixed with polymerizable monomers under the conditions of photosensitizer and UV irradiation to form mosaic polymer-dispersed liquid crystals (PDLC), which are also widely used in the direction of dimming films.

At the same time, holographic volume gratings and optical waveguide devices formed by liquid crystal materials and polymerizable material monomers under the irradiation of photosensitizers and coherent light sources have also been widely studied and tested. Fabrication of optical waveguides may include material systems that allow recording of holographic optical elements within the waveguide. For example, in a holographic polymer dispersed liquid crystal (HPDLC) mixture, two coherent laser beams can be irradiated into this liquid mixture to record, for example, the volume phase. During the recording process, the monomers polymerize and the mixture undergoes photopolymerization-induced phase separation, forming liquid crystal-rich regions filled with liquid crystal droplets, liquid crystal-poor regions interspersed with transparent polymers, and alternating liquid crystal-rich and liquid crystal-poor regions. The striped surface that forms the grating. The resulting grating, often referred to as a switchable Bragg grating (SBG), has all the properties commonly associated with volume or Bragg gratings, plus a higher refractive index modulation range and diffraction efficiency over a continuous range (diffraction efficiency) compared to Bragg gratings. The ratio of incident light to the desired direction) the ability to power up a tuned grating.

The optical waveguide devices described above can be used in a range of display and sensor applications. Waveguides containing one or more grating layers encoding multiple optical functions can be implemented using various waveguide structures and material systems in many applications, such as near-eye displays for augmented reality (AR) and virtual reality (VR). Compact head-up displays (HUDs) and helmet-mounted displays or head-mounted displays (HMDs) for road transport, aviation and military applications, as well as for biometrics and lidar, etc.

Currently, the liquid crystal compositions used for holographic polymer dispersed liquid crystal gratings do not have a high extraordinary light refractive index ne, resulting in low diffraction efficiency of the holographic grating. Some liquid crystal compositions with a high extraordinary light refractive index ne also There is a high crystallization temperature Tcn, which causes the holographic volume grating to have high diffraction efficiency but also has the risk of grating anomalies, and the risk is very high.

Contents of the invention

The purpose of this application is to provide a liquid crystal composition and a liquid crystal grating to improve at least part of the above technical problems.

In a first aspect, embodiments of the present application provide a liquid crystal composition, including:

At least one of the compounds of general formula (1); and

At least one of the compounds of general formula (2); and

At least one of the compounds of general formula (3);

The compound of general formula (1) is:

The compound of general formula (2) is:

The compound of general formula (3) is:

Among them, R ₁ , R ₂ and R ₃ are independently selected from a carbon chain of 8-12 carbon atoms, and the carbon atoms can be replaced by Si; X ₁ , X ₂ and X ₃ are independently selected from CN, NCS, F Or any one of C≡C-CN;

In the compound of general formula (1), the compound of general formula (2) and the compound of general formula (3), 2,3,5,6 on the benzene ring adjacent to R ₁ or R ₂ or R3 Carbon atoms can be replaced by nitrogen atoms, and any H atoms on the benzene ring can be replaced by F.

In some embodiments, the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 1% to 50%.

Preferably, the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 2% to 40%.

In some embodiments, the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition is 1% to 40%.

Preferably, the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition is 1% to 30%. In some embodiments, the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 20% to 95%.

Preferably, the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 25% to 85%.

In some embodiments, the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 5% to 30%; the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition The percentage is 1% to 20%; the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 30% to 80%.

Preferably, X ₁ , X ₂ and X ₃ are all CN.

In a second aspect, embodiments of the present application also provide a liquid crystal grating, which includes the above-mentioned liquid crystal composition.

The liquid crystal composition and liquid crystal grating provided by this application have a higher extraordinary light refractive index ne, a stable smectic phase at low temperatures, and better compatibility with polymer monomers in the range from normal temperature to low temperature. There is a wide smectic phase state in the smectic phase state. In the smectic phase state, the liquid crystal molecules have a very regular arrangement state, which can make the holographic polymer dispersed liquid crystal grating liquid crystal phase temperature range include the working range of the grating, and the liquid crystal area has a more Good stability.

These and other aspects of the application will be more clearly understood in the following description of the embodiments.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

This application proposes a liquid crystal composition, which includes at least one compound of general formula (1), at least one compound of general formula (2), and at least one compound of general formula (3).

That is, the liquid crystal composition contains the compound of general formula (1), the compound of general formula (2), and the compound of general formula (3) at the same time. It should be noted that the compound of general formula (1) included in the liquid crystal composition may be one or more, and similarly, the compound of general formula (2) may be one or more; the compound of general formula (3) may be one or more. It can be understood that in this application, multiple means two or more than two, that is, at least two.

The compound of general formula (1) is:

Among them, R ₁ is selected from a carbon chain with 8-12 carbon atoms, that is, a carbon chain with 8-12 carbon atoms, and in the compound of general formula (1), 2,3 on the benzene ring adjacent to R ₁ ,5,6 carbon atoms can be replaced by nitrogen (N) atoms, and any H (hydrogen) atom on the benzene ring can be replaced by F (fluorine). It can be understood that when an F atom replaces an H atom, it can be mono-substituted. , or multiple substitutions, which are not limited here. In this application, the 2, 3, 5, and 6 carbon atoms on the benzene ring refer to other carbon atoms on the benzene ring except for the para-substituted group.

In some embodiments, R ₁ can be selected from a carbon chain of 9-12 carbon atoms, and R ₁ can be an alkyl group or an alkoxy group, which can reduce the degree of unsaturation in the liquid crystal composition and improve the stability of the molecule to ultraviolet rays. properties and thermal stability. In some embodiments, R ₁ can also be an alkyl or alkoxy group containing side chains. The side chains can shorten the chain length, effectively reduce the polarity of the molecule, increase the refractive index, and at the same time reduce the unsaturation in the liquid crystal composition. degree, improving the stability of the molecule to UV rays and heat. It should also be noted that the carbon atom in the R ₁ group can be substituted by a silicon atom. When a silicon atom replaces a carbon atom, it can be either mono-substituted or poly-substituted, which is not limited here.

Among them, R ₁ can be a linear chain structure, such as a linear carbon chain of 9-12 carbon atoms, so that under a longer linear structure, the liquid crystal has a wider smectic phase temperature, and at low temperatures (such as -25℃~5℃) is no longer a nematic phase and can better meet the appearance and optical properties of liquid crystal polymer dispersed liquid crystal holographic volume gratings.

The mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition can be, for example, 1%-50%. For example, the mass ratio of the compound of general formula (1) in the liquid crystal composition can be 1%, 5%, or 10%. , 20%, 30%, 40%, 50%, etc. Preferably, the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition can be controlled to 2%-40%, such as 8%, 12%, 25%, 28%, 35%, etc., where Without limitation, by controlling the proportion of the compound of general formula (1) in the liquid crystal composition, the birefringence of the liquid crystal composition can be more accurately controlled, thereby obtaining a liquid crystal composition that better meets the needs. More preferably, the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition can be controlled to 5%-30%, such as 5%-10%, 5%-25%, 10%-20 %, etc., are not limited here.

Among them, X ₁ can be selected from CN, NCS, F and C≡C-CN and other groups. Preferably, X ₁ can be CN.

It can be understood that the above-mentioned various compounds are only exemplary and should not be understood as limitations on the compounds of general formula (1).

The compound of general formula (2) is:

In some embodiments, wherein R ₂ is selected from a carbon chain of 8-12 carbon atoms, that is, a carbon chain having 8-12 carbon atoms, and in the compound of general formula (2), it is adjacent to the cyclohexyl group The 2, 3, 5, and 6 carbon atoms on the benzene ring can be replaced by nitrogen (N) atoms, and any H (hydrogen) atom on the benzene ring can be replaced by F (fluorine). It is understandable that the F atom replaces H When an atom is used, it can be either mono-substituted or poly-substituted, and is not limited here.

In some embodiments, _R2 may be selected from alkyl or alkoxy groups of 9-12 carbon atoms. R ₂ can be an alkyl group or an alkoxy group, which can reduce the degree of unsaturation in the liquid crystal composition and improve the stability of the molecule to ultraviolet rays and heat. In some embodiments, R ₂ can also be an alkyl or alkoxy group containing side chains. The side chains can shorten the chain length, effectively reduce the polarity of the molecule, increase the refractive index, and at the same time reduce the unsaturation in the liquid crystal composition. degree, improving the stability of the molecule to UV rays and heat. It should also be noted that the carbon atom in the R ₂ group can be replaced by a silicon atom. When the silicon atom replaces the carbon atom, it can be either single or poly-substituted, which is not limited here.

Among them, R ₂ can be a linear chain structure, such as a linear carbon chain of 9-12 carbon atoms, so that under a longer linear chain structure, the liquid crystal has a wider smectic phase temperature, and at low temperatures (such as -25℃~5℃) is no longer a nematic phase and can better meet the appearance and optical properties of liquid crystal polymer dispersed liquid crystal holographic volume gratings.

The mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition can be, for example, 1%-40%. For example, the mass ratio of the compound of general formula (2) in the liquid crystal composition can be 1%, 5%, or 10%. , 20%, 30%, 40%, etc. Preferably, the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition can be controlled to 1%-30%, such as 4%, 8%, 10%, 12%, 25%, 28%, etc. , is not limited here. By controlling the proportion of the compound of general formula (2) in the liquid crystal composition, the birefringence of the liquid crystal composition can be more accurately controlled, thereby obtaining a liquid crystal composition that better meets the needs. More preferably, the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition can be controlled to 1%-20%, such as 5%-10%, 5%-15%, 10%-20 %, etc., are not limited here.

Among them, X ₂ can be selected from CN, NCS, F and C≡C-CN and other groups. Preferably, X ₂ can be CN.

When one or more of the above-mentioned compounds of general formula (2) are added to the liquid crystal composition, it is beneficial to improve the diffraction efficiency of the liquid crystal composition. It can be understood that the above-mentioned various compounds are only exemplary and should not be understood as limitations on the compounds of general formula (2).

The compound of general formula (3) is:

Among them, R ₃ is selected from a carbon chain with 8-12 carbon atoms, that is, a carbon chain with 8-12 carbon atoms, and in the compound of general formula (3), 2,3 on the benzene ring adjacent to R ₁ ,5,6 carbon atoms can be replaced by nitrogen (N) atoms, and any H (hydrogen) atom on the benzene ring can be replaced by F (fluorine). It can be understood that when an F atom replaces an H atom, it can be mono-substituted. , or multiple substitutions, which are not limited here. In this application, the 2, 3, 5, and 6 carbon atoms on the benzene ring refer to other carbon atoms on the benzene ring except for the para-substituted group.

In some embodiments, R ₃ may be selected from alkyl or alkoxy groups of 9 to 12 carbon atoms. R ₃ can be an alkyl group or an alkoxy group, which can reduce the degree of unsaturation in the liquid crystal composition and improve the stability of the molecule to ultraviolet rays and heat. In some embodiments, R ₃ can also be an alkyl or alkoxy group containing side chains. The side chains can shorten the chain length, effectively reduce the polarity of the molecule, increase the refractive index, and at the same time reduce the unsaturation in the liquid crystal composition. degree, improving the stability of the molecule to UV rays and heat. It should also be noted that the carbon atom in the R ₃ group can be replaced by a silicon atom. When the silicon atom replaces the carbon atom, it can be either single or poly-substituted, and is not limited here.

Among them, R ₃ can be a linear chain structure, such as a linear carbon chain of 9-12 carbon atoms, so that under a longer linear chain structure, the liquid crystal has a wider smectic phase temperature, and at low temperatures (such as -25℃~5℃) is no longer a nematic phase and can better meet the appearance and optical properties of liquid crystal polymer dispersed liquid crystal holographic volume gratings.

The mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition can be, for example, 20%-95%. For example, the mass ratio of the compound of general formula (3) in the liquid crystal composition can be 20%, 30%, or 40%. , 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. Preferably, the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition can be controlled to 25%-85%, such as 25%, 28%, 35%, 45%, 50%, 55%, etc. , is not limited here. By controlling the proportion of the compound of general formula (3) in the liquid crystal composition, the birefringence of the liquid crystal composition can be more accurately controlled, thereby obtaining a liquid crystal composition that better meets the needs. More preferably, the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition can be controlled to 30%-80%, such as 30%-40%, 45%-65%, 35%, 40% %, 45%, etc. are not limited here.

Among them, X ₃ can be selected from CN, NCS, F and C≡C-CN and other groups. Preferably, X ₃ can be CN.

When one or more of the above-mentioned compounds of general formula (3) are added to the liquid crystal composition, it is beneficial to improve the diffraction efficiency of the liquid crystal composition. It can be understood that the above-mentioned various compounds are only exemplary and should not be understood as limitations on the compounds of general formula (3).

It should be noted that the above-mentioned compound of general formula (1) can be combined with any one or more compounds of general formula (2) and any one or more compounds of general formula (3) to obtain a liquid crystal composition. This is not limited.

In some embodiments, the liquid crystal composition may also include other additives, such as anti-ultraviolet agents, antioxidants, chiral agents, etc. In addition, the liquid crystal composition may also include antistatic agents or defoaming agents, etc. No limitation is made here. The anti-ultraviolet agent can be, for example, benzophenones or benzotriazole compounds, and the antioxidant can be, for example, BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), TBHQ (tert-butylated hydroquinone), etc. Examples of chiral agents include oxazolidinones, 8-phenylmenthol, and the like. The defoaming agent may be, for example, a silicone defoaming agent, ethylene oxide, propylene oxide, or the like. Antistatic agents may be, for example, ethoxylated aliphatic alkyl amines, sodium alkyl sulfonates, etc.

The mass percentage of the added amount of the additive to the total mass of the liquid crystal composition is preferably less than or equal to 1%. The added amount and type of the additive do not affect the properties of the liquid crystal composition.

The liquid crystal composition proposed in this application is specifically introduced below through examples.

The liquid crystal composition provided by the present invention can be prepared using well-known techniques in the art. For example, it can be prepared by the following method: mixing each component in the liquid crystal composition evenly by stirring or ultrasonic mixing. The liquid crystal compositions in the following examples were mixed by stirring to obtain a homogeneous composition, and then their physical and chemical properties were tested.

As shown in Table 1, the component ratios of the liquid crystal compositions in each embodiment and comparative example are specifically shown below, where the following data are all weight percentages:

Table 1 Ingredients of the liquid crystal compositions in each embodiment and comparative example

The liquid crystal compositions obtained in Examples 1-4 and Comparative Examples 1-4 were tested and the following parameters were measured:

Tcs(℃) represents the temperature when the liquid crystal changes from crystalline to smectic phase; Tcn(℃) represents the temperature when liquid crystal changes from crystalline to nematic phase; Tsn(℃) represents the temperature when liquid crystal changes from smectic phase to nematic phase. The temperature; n _e represents the refractive index of extraordinary light in the liquid crystal.

The measured data are shown in Table 2:

Table 2 Measurement results of Examples 1-4 and Comparative Examples 1-4

The liquid crystal compositions in Comparative Examples 1-4 are liquid crystal compounds in the prior art. It can be seen that the liquid crystal compositions obtained in Examples 1-4 have a high refractive index n _e of extraordinary light and maintain the In the case of extraordinary light refractive index n _e , it has a stable smectic phase at low temperature (-25°C ~ -20°C), so it can have better compatibility with polymer monomers, Example 1 -4 The Tsn temperature of the liquid crystal composition obtained is between 7°C and 13°C. Therefore, in the low temperature region, compared with other liquid crystal compositions in the prior art, it has a wider smectic phase range and can maintain stable Smectic phase. In the smectic phase, the liquid crystal molecules have a very regular arrangement, which allows the subsequent preparation of the holographic polymer dispersed liquid crystal grating. The liquid crystal phase temperature range can completely cover the working range of the grating.

The liquid crystal composition provided in this embodiment adopts a long carbon chain structure. The long carbon chain liquid crystal composition enables the liquid crystal to have a wider smectic phase temperature. It no longer belongs to the nematic phase at low temperatures, but this smectic phase It can meet the appearance and optical properties of liquid crystal polymer dispersed liquid crystal holographic volume gratings. In this way, the phase change of liquid crystal with smectic phase as the temperature increases is solid crystal - smectic phase - nematic phase - liquid state, and the liquid crystal composition can remain stable in the smectic phase, which can make the hologram formed by subsequent preparation The liquid crystal phase temperature range of polymer dispersed liquid crystal gratings can completely cover the working range of the grating.

One of the uses of the above-mentioned liquid crystal composition is to make optical components, such as making liquid crystal gratings, where the liquid crystal grating can be a holographic polymer dispersed liquid crystal grating (HPDLC) or other types of gratings, etc., which are not mentioned here. Make limitations.

This application also provides a liquid crystal grating, which includes the above-mentioned liquid crystal composition. In addition, the liquid crystal grating also includes a polymer, wherein the polymer can be an acrylate monomer, and more specifically, it can be a cross-linked multifunctional acrylate. Monomers, such as the following polymer monomers:

Pentaerythritol Triacrylate Phenyl methacrylate

Polydipentaerythritol hexaacrylate

1,6-diacryloyloxyhexane

When preparing a liquid crystal grating, materials for preparing a liquid crystal grating are first prepared. Specifically, a polymer monomer and a liquid crystal composition are mixed to form a uniform solution, in which the polymer monomer serves as a solvent and the liquid crystal composition serves as a solute. Among them, photoinitiators, co-initiators, chain extenders, surfactants, etc. can also be added, which are not limited here.

The stability of the liquid crystal grating material system depends on the mutual solubility of the polymer monomer and the liquid crystal composition. If the mutual solubility is good, the liquid crystal grating material system can continue to form a clear liquid state. If the mutual solubility is poor, it may Crystallization occurs, which reduces the stability of the liquid crystal grating and shortens its service life.

The liquid crystal compositions obtained in the aforementioned Comparative Examples 1-4 and Examples 1-4 were mixed with the same polymer monomers to prepare a liquid crystal grating material system. The polymer monomers were pentaerythritol triacrylate, and polymerized The mass ratio of the monomer and the liquid crystal composition is the same.

The prepared materials for preparing liquid crystal gratings were stored for a long time at room temperature of 20°C to observe whether crystallization occurred. The observation results are shown in Table 3:

Table 3 Recording table of crystallization results of liquid crystal grating material system

It can be seen from the data in Table 3 that the liquid crystal grating material system obtained in Examples 1-4 did not crystallize during the 30-day experimental period, while the liquid crystal grating material system obtained in Comparative Examples 1-4 In about a week, the crystallization phenomenon began to occur, and the experimental results showed that the liquid crystal grating material system obtained in Examples 1-4 has a longer service life.

The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included in the protection scope of this application.

Claims (10)

1. A liquid crystal composition, characterized in that it includes: At least one of the compounds of general formula (1); as well as At least one of the compounds of general formula (2); as well as At least one of the compounds of general formula (3); The compound of general formula (1) is: The compound of general formula (2) is: The compound of general formula (3) is: Among them, R ₁ , R ₂ and R ₃ are independently selected from a carbon chain of 8-12 carbon atoms, and the carbon atoms can be replaced by Si; X ₁ , X ₂ and X ₃ are independently selected from CN, NCS, F Or any one of C≡C-CN; In the compound of general formula (1), the compound of general formula (2) and the compound of general formula (3), 2,3,5,6 on the benzene ring adjacent to R ₁ or R ₂ or R3 Carbon atoms can be replaced by nitrogen atoms, and any H atoms on the benzene ring can be replaced by F. 2. The liquid crystal composition according to claim 1, characterized in that the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 1% to 50%. 3. The liquid crystal composition according to claim 2, characterized in that the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 2% to 40%. 4. The liquid crystal composition according to claim 1, wherein the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition is 1% to 40%. 5. The liquid crystal composition according to claim 4, wherein the mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition is 1% to 30%. 6. The liquid crystal composition according to claim 1, wherein the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 20% to 95%. 7. The liquid crystal composition according to claim 6, wherein the mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 25% to 85%. 8. The liquid crystal composition according to any one of claims 2 to 7, characterized in that the mass percentage of the compound of general formula (1) in the total mass of the liquid crystal composition is 5% to 30%; The mass percentage of the compound of general formula (2) in the total mass of the liquid crystal composition is 1% to 20%; The mass percentage of the compound of general formula (3) in the total mass of the liquid crystal composition is 30% to 80%. 9. The liquid crystal composition according to claim 1, wherein X ₁ , X ₂ and X ₃ are all CN. 10. A liquid crystal grating, characterized in that the liquid crystal grating includes the liquid crystal composition according to any one of claims 1-9.