Isothiocyanato trans-cyclohexylbiphenyl liquid crystal composition and its application

Abstract

The present invention discloses an isothiocyanato trans-cyclohexylbiphenyl liquid crystal composition and its application. The liquid crystal composition uses an isothiocyanato trans-cyclohexylbiphenyl liquid crystal compound as the first component, and the first component contains at least one compound represented by structural formula (I): wherein R1 is selected from an alkyl group containing 1 to 10 carbon atoms or an alkyl group containing an alkenyl group; X1 to X8 are each independently selected from -H, -CH3, -F or -Cl. The liquid crystal composition also includes a second component, and three or more components among a third component, a fourth component and a fifth component. The birefringence value (Δn) of the liquid crystal composition of the present invention is greater than 0.37, and its microwave frequency insertion loss is reduced, and the dielectric loss value (tanδε r,max ) are all less than 0.0065, the phase modulation amount (τ) is greater than 0.30, and the quality factor (μ) is higher than 50.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid crystal materials, and particularly relates to an isothiocyanato trans-cyclohexylbiphenyl liquid crystal composition and application thereof. Background Art

[0002] Microwave phase shifters are key components in the field of microwave communication technology and are widely used in radar systems, satellite antennas, communication systems, and other fields. Liquid crystal is a dielectric anisotropic material whose dielectric constant and birefringence change continuously with the change of the applied electric field and has low microwave absorption. Therefore, liquid crystal as a dielectric material for microwave phase shifters has the advantages of continuous adjustability of dielectric phase, excellent high-frequency and wide-band characteristics, low driving voltage, small size, and low cost. The research on liquid crystal for microwave devices began in the late 20th century and developed rapidly at the beginning of this century. Especially in recent years, it has received widespread attention from all over the world.

[0003] Liquid crystal materials are used as transmission media for microwave communication devices, and their own performance will directly affect the performance and use of microwave phase shifters. The molecular structure of liquid crystal materials for microwaves must meet the following conditions: ① Large dielectric anisotropy, high birefringence, wide nematic phase temperature range, low melting point and good low-temperature miscibility; ② Stable molecular structure, low polarizability, low or no microwave absorption, and low dielectric loss; ③ Low intermolecular force, low viscosity, and good viscoelastic coefficient (i.e., γ1 / K ii value); ④ The dielectric properties are stable and have little dependence on temperature, especially suitable for low temperature operation.

[0004] However, liquid crystal materials for display cannot be used at present due to their low birefringence, and existing liquid crystal materials for microwave use generally have the following problems: ① Because the Δn value is not large enough and the dielectric constant is small, the phase shift is insufficient; ② Due to the wave absorption and polarizability of the molecular structure groups, the dielectric loss is relatively large; ③ Due to the lack of low-melting point, high Δn value nematic liquid crystal compounds, the low-temperature performance of the liquid crystal material is affected and the outdoor working temperature is limited; ④ Due to the high viscosity of the high Δn value nematic liquid crystal compounds, the response time of the microwave device is longer, which affects the information transmission speed and the development of microwave communication devices.

[0005] Therefore, research and development of liquid crystal materials with high dielectric constant, low loss, fast response speed and low operating temperature that meet the performance requirements of microwave devices has become the key to the development of liquid crystal microwave devices. Only by breaking the technical bottleneck of the practical application of microwave liquid crystal materials can the defects of existing technologies be overcome. Summary of the invention

[0006] The object of the present invention is to provide an isothiocyanato trans-cyclohexylbiphenyl liquid crystal composition and its application, wherein the birefringence value (Δn) of the liquid crystal composition is greater than 0.37, the insertion loss of the microwave frequency is reduced, and the dielectric loss value (tan δεr , max ) are all less than 0.0065, the phase modulation amount (τ) is greater than 0.30, and the quality factor (μ) is higher than 50, which can meet the requirements of liquid crystal materials for microwave devices.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides an isothiocyanato trans-cyclohexylbiphenyl liquid crystal composition, which uses an isothiocyanato trans-cyclohexylbiphenyl liquid crystal compound as a first component, and the first component contains at least one compound represented by structural formula (I):

[0009]

[0010] Wherein, R1 is selected from an alkyl group containing 1 to 10 carbon atoms or an alkyl group containing an alkenyl group; X1 to X8 are each independently selected from -H, -CH3, -F or -Cl.

[0011] Compound (I) has low dielectric loss, low rotational viscosity, and a wide temperature range of nematic phase liquid crystal. After being purified and refined by recrystallization and electric field adsorption to obtain a high resistivity liquid crystal compound, it has low dielectric loss at 4 to 40 GHz and can be used as the main component of a high dielectric anisotropy, low dielectric loss (abbreviated as: high dielectric and low loss) nematic phase mixed liquid crystal material used in microwave devices.

[0012] Preferably, when X5 to X8 are as shown in structural formula (Ia-i), X1 to X4 are each independently selected from -H, -F or -Cl;

[0013]

[0014] Compound (I) is at least one or more selected from the following structural formulas (Ia-i), but is not limited thereto:

[0015]

[0016] Preferably, when X5 to X8 are as shown in formula (Ib-i), X1 to X4 are each independently selected from -H, -F, -Cl or -CH3;

[0017]

[0018] Compound (I) is at least one or more selected from the following structural formula (Ib-i), but is not limited thereto:

[0019]

[0020] Preferably, when X5 to X8 are as shown in structural formula (Ic-i), X1 to X4 are each independently selected from -H, -F, -Cl or -CH3;

[0021]

[0022] Compound (I) is at least one or more selected from the following structural formula (Ic-i), but is not limited thereto:

[0023]

[0024] In the technical solution of the present invention, the liquid crystal compound (I) is obtained by any synthesis method capable of producing the compound, and can also be obtained by the following synthesis route:

[0025]

[0026] The specific synthesis route is as follows: trans-alkylcyclohexylphenylboronic acid (i) and substituted p-bromoaniline (ii) are used as main raw materials, and trans-alkylcyclohexyl substituted benzidine (first intermediate A) is obtained through Suzuki coupling reaction; second intermediate B is obtained through diazotization bromination reaction; second intermediate B is reacted with butyl lithium and triethyl borate at low temperature to obtain trans-cyclohexylbiphenylboronic acid (third intermediate C), and then trans-alkylcyclohexyl substituted terphenylamine (fourth intermediate D) is obtained through secondary Suzuki coupling reaction with substituted p-bromoaniline (iii); and finally isothiocyanation reaction is carried out through thiophosgene to obtain liquid crystal compound (I).

[0027] The present invention purifies and removes ions by subjecting the prepared liquid crystal compounds (Ia-i), (Ib-i) and (Ic-i) with different structures to column chromatography, recrystallization, electric field adsorption and adsorption with a special adsorbent to obtain a high resistivity (ρ≥

[0028] 1.0×10 12 Ω·cm) and a liquid crystal compound (I) with a high charge retention rate, and then the composition is mixed and prepared and microwave dielectric performance is tested to obtain a nematic liquid crystal composition material with "high dielectric and low loss" that can meet the microwave K band.

[0029] In the technical solution of the present invention, the selected first component liquid crystal compound (I) has the following advantages: because the presence of a trans-cyclohexyl chair-type structural unit in the molecule increases the distance between molecules or steric hindrance, thereby reducing the intermolecular force and rotational viscosity, so that the liquid crystal molecules rotate faster in the electromagnetic field, reducing the microwave insertion loss caused by molecular rotational relaxation, that is, reducing the dielectric loss; at the same time, fluorine atoms, or chlorine atoms, or methyl groups are introduced at the side of the benzene ring, further reducing the aspect ratio of the molecule, increasing the intermolecular distance, reducing the intermolecular force, and effectively reducing the melting point of the compound, so that it has a wide temperature nematic liquid crystal phase and a lower rotational viscosity; in addition, the molecule contains a -NCS large polar group, which increases the π-electron conjugated system of the terphenyl, so that the molecule has a sufficiently large birefringence and molecular polarity (i.e., dielectric constant), increases the microwave phase tunability, improves the quality factor of the liquid crystal compound, and is also conducive to improving the high-frequency dielectric properties of the liquid crystal material.

[0030] In the technical solution of the present invention, the liquid crystal composition further comprises a liquid crystal composition composed of at least three components among the second component, the third component, the fourth component and the fifth component liquid crystal compounds.

[0031] Wherein, the second component is at least one of the liquid crystal compounds represented by formula II:

[0032]

[0033] In the structural formula (II), R2 is selected from a saturated alkyl group containing 2 to 7 carbon atoms or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H, -F or -Cl, and X6 and X7 are independently selected from -H, -F, -Cl, -CH3 or -C2H5; Ring A is selected from trans-cyclohexylene or phenylene; m, n are 0 or 1, and m+n≥1.

[0034] The second component includes any one or more of the following six types of polyphenylacetylene compounds of structural formula (IIa-i) to (IIf-i):

[0035]

[0036] The second component compound (II) has the following advantages: wide nematic phase temperature range, large molecular planar conjugated π-electron cloud density, high birefringence, low viscosity and melting point. For example, the melting point of 4(1)PPTUS in compound (IIc-i) is only 43.5℃, clearing point is 171.3℃, Δn=0.460(589.2nm,20℃), rotational viscosity γ1=455mPa.s; it is beneficial to improve the phase tunability of microwave phase shifter and improve the quality factor of the device. The preparation method of the selected isothiocyanato polyphenylacetylene liquid crystal compounds (IIa-i)~(IIf-i) is mainly derived from Chinese invention patents CN109852400B(2019.1.29), CN109943350B(2019.10.31), CN113528048A(2020.4.14), etc.

[0037] The third component is at least one of the liquid crystal compounds represented by formula III:

[0038]

[0039] In the structural formula (III), R3 is a saturated / unsaturated alkyl group containing 2 to 7 carbon atoms or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H, -F or -Cl; X7 is each independently selected from -H, -F, -Cl, -CH3 or -C2H5; Y is -NCS, -F, -OCF3 or a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms; and ring B is selected from trans-cyclohexylene or phenylene.

[0040] The third component includes any one or more of the following ten types of tetracyclic compounds of structural formula (IIIa-i) to (IIIj-i):

[0041]

[0042] The advantages of the third component are: stable molecular structure, high birefringence, and a wide nematic phase, which can effectively broaden the nematic phase width of the liquid crystal composition, increase the clearing point of the composition, effectively improve the phase tunability of the microwave device, reduce the dielectric loss of the liquid crystal composition, and improve the quality factor of the liquid crystal composition.

[0043] The preparation methods of liquid crystal compounds (IIa-i) to (IIj-i) are mainly derived from the Chinese invention patents of this group CN110746982B (2019.9.17), CN110776927B (2019.10.31), CN110746981B (2019.9.17), CN110760311B (2019.9.29), CN110699091B (2019.10.31), CN110776396B (2019.10.31), etc.

[0044] The fourth component is at least one of the liquid crystal compounds represented by formula IV:

[0045]

[0046] In structural formula (IV), R4 is a saturated alkyl group containing 2 to 7 carbon atoms or a dl-(±)-2-methylbutyl group; X1 to X2 are each independently selected from -H, -F, or -Cl; X8 is -H, -F or -CH3; Y1 is -NCS, -F or -OCF3; and ring C is selected from trans-cyclohexylene or phenylene.

[0047] The fourth component includes any one or more compounds of various tricyclic structure molecules such as the following structural formulas (IVa-i) to (IVf-i):

[0048]

[0049] The fourth component has the following advantages: stable molecular structure, good π-electron plane conjugation, low rotational viscosity and melting point of the molecule, and birefringence that meets the requirements of microwave phase shifters; for example, the melting point of 4(1)PGUS in compound (IVc-4) is only 38°C, the clearing point is 109°C, Δn=0.385 (589.2nm, 20°C), and the rotational viscosity γ1=245mPa.s; and it has good miscibility with other compounds, which is beneficial to reducing the high-frequency dielectric loss of the composition, improving the low-temperature performance of the composition and improving the quality factor.

[0050] The preparation technology of the selected liquid crystal compounds (IVa-n) to (IVf-n) is mainly derived from the Chinese invention patents CN110746983B (2019.10.31), CN110760311B (2019.10.31) and German Merck patent CN108603121A (2018.9.28) of this group.

[0051] The fifth component is at least one of the liquid crystal compounds represented by formula V:

[0052]

[0053] In structural formula (V), R5 is a saturated alkyl or unsaturated alkyl group containing 2 to 7 carbon atoms; R6 is selected from -F, -OCF3, -NCS, a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms; X9 is selected from -H, -F, -Cl or -CH3; ring D is a cyclohexylene ring or a phenylene ring; m and n are independently 0, 1 or 2, and m+n≥2.

[0054] The fifth component includes at least one compound of the following bicyclic structure molecules such as structural formula (Va-i) to (Vf-i):

[0055]

[0056] The advantages of the fifth component are: stable molecular structure, low molecular rotation viscosity and melting point, good solubility with other compounds, and can be used to reduce the rotation viscosity of liquid crystal compositions, increase response speed and improve low temperature performance. These bicyclic liquid crystal compounds are mainly derived from existing commercial liquid crystal compounds.

[0057] In the technical solution of the present invention, the total mass content of the first component (I) in the composition is about 5 to 50 wt%, preferably 15 to 35 wt%; wherein the mass content of each compound (Ii) or multiple compounds (Ii) in the composition is 1 to 20 wt%, preferably 5 to 15 wt%.

[0058] The mass content of the second component (II) in the composition is 5 to 35 wt%, preferably 10 to 25 wt%. The weight content of any compound (II-i) in the second component in the liquid crystal composition is 1 to 20 wt%, preferably 5 to 15 wt%;

[0059] The mass content of the third component (III) is 5-25 wt%, preferably 10-20 wt%. The weight percentage of any compound (III-i) in the third component in the liquid crystal composition is 1-20 wt%, preferably 5-15 wt%.

[0060] The mass content of the fourth component (IV) is 0-20 wt%, preferably 5-15 wt%. The content of any one compound (IV-i) in the fourth component in the composition is 0-15 wt%, preferably 5-10 wt%.

[0061] The mass content of the fifth component (V) is 0-10 wt%, preferably 3-8 wt%. The content of any one compound (Vi) in the fifth component in the composition is 0-8 wt%, preferably 3-6 wt%.

[0062] In the present invention, each component compound in the liquid crystal composition is purified and refined by electric field adsorption method [Chinese invention patent CN101760203B (2009)] to remove ions, so as to improve the resistivity and charge retention rate of the liquid crystal compound, and then mixed and prepared to obtain a high dielectric and low loss nematic liquid crystal composition that can meet the microwave K band. And the application of the above liquid crystal composition as a dielectric material of a microwave phase shifter component is provided.

[0063] The optical anisotropy or birefringence (Δn) value of the prepared liquid crystal composition is in the range of 0.37 to 0.41, the phase modulation amount (τ) in the microwave frequency band (4 to 40 GHz) is ≥0.300, and the dielectric constant (Δε r )≥0.95, maximum dielectric loss (tanδε r max) is less than 0.0060, and the quality factor (η) is greater than 50. It can be seen that the liquid crystal composition of the present invention increases the microwave phase modulation amount, reduces the microwave insertion loss, and further reduces the dielectric loss of the microwave device.

[0064] In addition, in order to improve the thermal stability of the liquid crystal composition, a small amount of thermal stabilizer may be added to the composition of the present invention, the amount of which accounts for 0.01 to 0.5 wt % of the total mass of the composition, preferably 0.05 to 0.15 wt %. The molecular structure of the stabilizer is as follows:

[0065]

[0066] The present invention also provides a microwave device, which comprises the liquid crystal composition.

[0067] The present invention also provides an application of the above-mentioned liquid crystal composition in a liquid crystal material medium of a microwave high-frequency device. The high-dielectric and low-loss nematic liquid crystal composition prepared above can meet the performance requirements of devices such as microwave phase shifters used in the K band, and can be used as a dielectric material for liquid crystal microwave phase shifter components.

[0068] The beneficial effects of the present invention are:

[0069] (1) The first component of the liquid crystal composition of the present invention is an isothiocyanato trans-cyclohexyl terphenyl liquid crystal compound (Formula I), which not only reduces the viscosity of the compound and broadens the temperature range of the nematic phase, but more importantly, improves the chemical stability of the liquid crystal material in high-frequency electromagnetic fields such as microwaves, reduces the polarization effect and absorption coefficient of microwaves on liquid crystal molecules, and reduces microwave (high-frequency) dielectric loss. When it is used as the main component and combined with liquid crystal compounds of other structures to form a mixed liquid crystal material, a "high dielectric and low loss" nematic liquid crystal material can be obtained.

[0070] (2) The birefringence value (Δn) of the liquid crystal composition of the present invention is greater than 0.37, the insertion loss of microwave frequency is reduced, and the dielectric loss value (tan δε r,max ) is less than 0.0060, the phase modulation amount (τ) is greater than 0.30, and the quality factor (μ) is higher than 50.

[0071] (3) The present invention adopts a low melting point liquid crystal component to reduce the low eutectic point of the liquid crystal composition, thereby meeting the outdoor low temperature working requirements of the microwave device and helping to solve the outdoor low temperature performance problem of the microwave device. DETAILED DESCRIPTION

[0072] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and the concept of the present invention will be fully conveyed to those skilled in the art, and the present invention will only be limited by the claims.

[0073] The abbreviations of the test items in the following embodiments and comparative examples are as follows:

[0074] △n is the optical anisotropy of the liquid crystal material, that is, the birefringence (589.2nm, 25℃); it means that after light passes through the liquid crystal material, it is refracted and scattered by the liquid crystal to form ordinary light and extraordinary light. The refractive index of ordinary light is represented by "no", and the refractive index of extraordinary light is represented by "ne", △n = n o -n e Microwave high-frequency devices require a Δn value ≥ 0.35. The higher the Δn value, the more conducive it is to improving the microwave phase shift.

[0075] Cr. is the melting point of the liquid crystal composition or the transition temperature from the solid state to the liquid crystal state; N. is the liquid crystal nematic phase transition temperature; Iso. is the clearing point temperature (°C) of the phase state of the liquid crystal composition;

[0076] mp is the eutectic point of the mixed liquid crystal material;

[0077] ρ is the resistivity of the liquid crystal material; γ1 is the rotational viscosity of the liquid crystal material;

[0078] △ε represents the dielectric constant of liquid crystal at low frequency (1KHz); Δε≡(ε || -ε ⊥ ); ∥ Represents the parallel component of the dielectric constant of liquid crystal at low frequency (1KHz); ε ⊥ It represents the vertical component of the dielectric constant of liquid crystal at low frequency (1KHz);

[0079] The dielectric anisotropy in the microwave range is defined as: Δε r ≡(ε r|| -ε r⊥ );△ε r The dielectric constant under microwave high frequency is generally required to be between 0.75 and 1.35; ε r⊥ is the vertical component of microwave high-frequency dielectric constant; ε r∥ is the parallel component of microwave high frequency dielectric constant;

[0080] tanδε r⊥ It is the dielectric loss expression of the vertical component of liquid crystal molecules under microwave high frequency; tanδε r∥ is the dielectric loss expression of the parallel component of liquid crystal molecules under microwave high frequency; τ is the phase modulatable coefficient of microwave frequency; η is the dielectric quality factor of microwave high frequency device;

[0081] The microwave phase tunability, or the phase tunability coefficient (τ) of the microwave frequency, is defined as: τ≡(Δε r / ε r|| ). It is the main parameter that reflects the phase tuning ability of liquid crystal materials to microwave frequencies, and generally requires τ ≥ 0.15; it can be seen that Δε r The larger it is, the more beneficial it is to increase the microwave phase shift amount.

[0082] The term "dielectric loss" refers to the loss of microwave frequency caused by the absorption of microwave frequency when microwaves are irradiated or pass through liquid crystal materials. It is the phenomenon that the liquid crystal material absorbs microwaves and causes the loss of microwave frequency. In liquid crystal materials, dielectric loss is usually manifested as parallel dielectric loss (tanδε r|| ) and vertical dielectric loss (tanδε r⊥ ),

[0083] The maximum dielectric loss of liquid crystal material is: tanδε r .max≡max{tanδε r⊥ , tanδε r||}. Among them, the parallel dielectric loss (tanδε r|| ) refers to the microwave frequency loss value along the molecular long axis direction in the liquid crystal material, which is usually small; the vertical dielectric loss (tanδε r⊥ ) refers to the loss value of microwave frequency along the short axis of the molecule in the liquid crystal material, which is usually larger. Therefore, physically, the maximum dielectric loss value of the liquid crystal material (tanδε r .max) often uses "tanδε r⊥ " value is used as a quantitative expression of microwave "dielectric loss". It is the main performance index parameter reflecting the liquid crystal material in the microwave field. Generally, the tanδε of the liquid crystal material is required to be r⊥ (or tanδεr .max) value ≤0.012 or less.

[0084] The "quality factor" (η, or FOM) mentioned in the term refers to the comprehensive evaluation result of the dielectric properties of liquid crystal as a microwave dielectric material, reflecting the performance and quality of liquid crystal materials in microwave devices. The material quality factor (η) is defined as: η≡τ / tanδε r max≈τ / tanδε r⊥ . Generally, η≥25 is required.

[0085] The term "high dielectric and low loss" liquid crystal material refers to a liquid crystal material with high dielectric anisotropy (Δε r ≥1.0), high optical anisotropy (△n≥0.37), low dielectric loss (tanδε r⊥ ≤0.0075 or 7.5E-03) of liquid crystal material.

[0086] The microwave dielectric properties of liquid crystal were tested by Chengdu Enchi Microwave Technology Co., Ltd. using the rectangular resonant cavity perturbation method. The test method is to introduce the liquid crystal into a polytetrafluoroethylene (PTFE) or quartz glass capillary; the inner diameter of the capillary is 1.5mm, the outer diameter is 2.78mm, and the effective length of the sample is 2.0cm; the filled capillary is introduced into the center of the cylindrical resonant cavity, and the resonant frequency is 10GHz to 35GHz; the vector network analyzer (N5227APNA microwave network analyzer, Keysight Technologies Inc.USA) is used for testing, and the magnetic field strength is 0.3T to 1.0T.

[0087] For ease of presentation, the compound structures appearing below are represented by the structural codes described in Table 1.

[0088] Table 1. Comparison table of structural codes of groups in compounds

[0089]

[0090]

[0091] Nematic liquid crystal is an organic substance that has both the fluidity of liquid and the orderliness and anisotropy of crystal. Under the action of external fields such as light, electricity, and magnetism, its molecules will undergo continuous deformation and flow, inducing periodic and continuous changes in its dielectric constant and refractive index, forming a strong nonlinear optical effect; nematic liquid crystal materials have received widespread attention in the scientific and technological community in recent years. Taking advantage of the low dielectric loss, continuously adjustable dielectric and optical anisotropy, and ultra-low energy consumption of nematic liquid crystal materials in the microwave K band (5-40GHz), it can be prepared into liquid crystal microwave phase shifters, which can realize microwave communication devices and greatly improve information conversion and communication capabilities.

[0092] The liquid crystal composition of the present invention uses an isothiocyanato trans-cyclohexylbiphenyl liquid crystal compound as the first component, and the first component contains at least one compound represented by structural formula (I):

[0093]

[0094] Wherein, R1 is selected from an alkyl group containing 1 to 10 carbon atoms or an alkyl group containing an alkenyl group; X1 to X8 are each independently selected from -H, -CH3, -F or -Cl.

[0095] The molecular structure of the liquid crystal compound (I) simultaneously contains trans-1,4-cyclohexane, terphenyl structure, -NCS, alkyl substituents, and F atoms or methyl groups. Among them, trans-1,4-cyclohexane replaces one of the benzene rings, reduces the π-electron conjugation system, is conducive to the efficient stacking of molecules and proper deformation in the electromagnetic field, so that the compound exhibits advantages such as lower dielectric loss, lower rotational viscosity, and wide temperature nematic phase. When they are applied to high dielectric anisotropic liquid crystal materials, they are conducive to reducing the dielectric loss of liquid crystal microwave devices, improving the phase modulation ability and increasing the quality factor of liquid crystal materials; the terphenyl structure has a large π-electron conjugation effect and structural stability, which is conducive to increasing the rigidity of the molecule and can increase the optical anisotropy (i.e., the birefringence Δn value) of the liquid crystal compound; the terminal group -NCS can increase the molecular dipole moment and molecular polarity to meet the phase modulatability (τ) of microwaves and the Δε required for low operating voltage. r Requirements: The alkyl substituent can increase the flexibility of its molecule and reduce the melting point of the liquid crystal compound. When it is applied to the liquid crystal composition, it is beneficial to reduce the co-solidification point of the composition so that it can adapt to the low temperature environment; the introduction of -F atoms or Cl atoms or -CH3 at the side of the benzene ring can broaden the molecular width and reduce the intermolecular force; therefore, this type of liquid crystal compound (I) has the advantages of low melting point, low viscosity, fast response speed, wide temperature nematic phase and low dielectric loss, and is the optimal component for improving the microwave dielectric properties of liquid crystal materials.

[0096] Liquid crystal compound (I) has at least one of the structural formulas (Ia-i), (Ib-i), and (Ic-i):

[0097]

[0098] Wherein, R1 is selected from an alkyl group containing 1 to 10 carbon atoms or a straight-chain alkyl group containing an alkenyl group; X1-X4 are each independently selected from -H, -F, -Cl or -CH3.

[0099] The structural codes, molecular structures, phase states and dielectric properties of compounds (Ia-i), (Ib-i) and (Ic-i) are listed in Table 2 below, but are not limited thereto:

[0100] Table 2. Comparison table of molecular structure, code and mesogenic properties of liquid crystal compound (I)

[0101]

[0102]

[0103]

[0104]

[0105] In the technical solution of the present invention, the liquid crystal composition further comprises three or more components among the second component, the third component, the fourth component and the fifth component;

[0106] The second component is at least one of the liquid crystal compounds represented by structural formula (II), the third component is at least one of the liquid crystal compounds represented by structural formula (III), and the fourth and fifth component compounds are at least one of the liquid crystal compounds represented by structural formulas (IV) and (V), respectively:

[0107]

[0108] Wherein, in the structural formula (II), R2 is selected from a saturated alkyl group containing 1 to 10 carbon atoms or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H or -F; X5 and X6 are independently selected from -H, -F, -Cl or -CH3; Ring A is selected from trans-cyclohexylene or phenylene; m, n are 0 or 1, and m+n≥1;

[0109] In the structural formula (III), R3 is a saturated alkyl group containing 1 to 10 carbon atoms, an unsaturated alkyl group or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H, -F or -Cl; X5 and X7 are each independently selected from -H, -F, -Cl, -CH3 or -C2H5; Y is -NCS, -F, -OCF3 or a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms;

[0110] In the structural formula (IV), R4 is a saturated straight-chain alkyl group containing 1 to 10 carbon atoms or dl-(±)-2-methylbutyl; X1 to X2 are each independently selected from -H, -F or -Cl; X8 is -H, -F or -CH3; Y1 is -NCS, -F or -OCF3; Ring B is selected from trans-cyclohexylene or phenylene;

[0111] In structural formula (V), R5 is a saturated alkyl group or an unsaturated straight-chain alkyl group containing 1 to 10 carbon atoms; R6 is selected from -F, -OCF3, -NCS or a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms; X9 is selected from -H, -F or -Cl; and ring C is a cyclohexylene ring or a phenylene ring.

[0112] The molecular structure of the liquid crystal compound (II) of the second component is as shown in Table 3, but is not limited thereto.

[0113] Table 3. Comparison table of molecular structures and codes in compound (II)

[0114]

[0115]

[0116] The molecular structure and structure code of the third component liquid crystal compound (III) are as shown in Table 4, but are not limited thereto:

[0117] Table 4. Molecular structure and code comparison table of the third component compound (III)

[0118]

[0119]

[0120] The molecular structure of the fourth component compound (IV) is shown in accordance with the structure and code described in Table 5, but is not limited thereto.

[0121] Table 5. Molecular structure and code comparison table of the fourth component compound (IV)

[0122]

[0123]

[0124] The molecular structure contained in the fifth component liquid crystal compound (V) is represented by the structure code described in Table 6, but is not limited thereto.

[0125] Table 6. Molecular structure and code comparison table of the fifth component compound (V)

[0126]

[0127] Each component compound of the liquid crystal composition of the present invention must be purified and refined by electric field adsorption or deionizing adsorbent to ensure high resistivity and high charge retention of the liquid crystal material; the purification treatment by electric field adsorption has been described above. Then, it is mixed and prepared according to a certain mass percentage to obtain a high dielectric and low loss nematic liquid crystal composition that can meet the microwave K band; in order to improve the thermal stability of the liquid crystal composition, a small amount of thermal stabilizer (ST-i) can also be added to the composition of the present invention, and its amount accounts for about 0.01 to 0.5wt% of the total mass of the composition, preferably 0.05 to 0.15wt%; see the specific description in the embodiment. In this way, a liquid crystal composition with lower dielectric loss and higher quality factor can be obtained, which can be used to make devices such as microwave phase shifters.

[0128] In addition, the present invention also proposes a microwave device, which uses a small amount of chiral dopant to adjust the alignment of liquid crystal composition molecules during the process of manufacturing microwave liquid crystal devices, so as to meet the working needs of devices such as microwave phase shifters. The specific structure of the chiral dopant is as follows:

[0129]

[0130] Example 1: Preparation of Liquid Crystal Composition M-1

[0131] The first component compound and the second component, third component, fourth component and fifth component liquid crystal compounds are respectively prepared into a liquid crystal composition according to a certain mass percentage. The specific method is as follows: each weighed compound is placed in a glass flask, and then placed in a clean oven for heating and melting; after each compound in the flask is melted, a magnetic rotor is placed, and then the mixture is stirred for 0.5 hours under a heating environment, filtered while hot and cooled to room temperature to obtain the liquid crystal composition M-1. The obtained liquid crystal composition is placed between the two substrates of a liquid crystal display to test the low-frequency dielectric properties of the liquid crystal. Its microwave dielectric properties are tested by the rectangular resonant cavity perturbation method by Chengdu Enchi Microwave Technology Co., Ltd. The test data are shown in Table 7:

[0132] Table 7. Composition and dielectric properties of liquid crystal composition (M-1)

[0133]

[0134]

[0135] Example 2: Preparation of Liquid Crystal Composition M-2

[0136] The first component, the second component, the third component, the fourth component and the fifth component liquid crystal compounds are mixed, and the specific method is the same as that of Example 1, thereby obtaining the liquid crystal composition M-2. The test data is shown in Table 8:

[0137] Table 8. Composition and dielectric properties of liquid crystal composition (M-2)

[0138]

[0139] Example 3: Preparation of Liquid Crystal Composition M-3:

[0140] Referring to the operation method of M-1 in Example 1, a liquid crystal composition M-3 was prepared. The test data is shown in Table 9:

[0141] Table 9. Composition and dielectric properties of mixed liquid crystal material (M-3)

[0142]

[0143]

[0144] Example 4: Preparation of Liquid Crystal Composition M-4:

[0145] Referring to the operation method of Example 1, a liquid crystal composition M-4 was prepared. Specific test data are shown in Table 10:

[0146] Table 10. Composition and dielectric properties of mixed liquid crystal material (M-4)

[0147]

[0148] Example 5: Preparation of Liquid Crystal Composition M-5:

[0149] Referring to the preparation method of Example 1, the liquid crystal composition M-5 was obtained. Specific test data are shown in Table 11:

[0150] Table 11. Composition and dielectric properties of mixed liquid crystal material (M-5)

[0151]

[0152]

[0153] Example 6: Preparation of Liquid Crystal Composition M-6

[0154] The liquid crystal composition M-6 was obtained by referring to the preparation method of Example 1. The specific dielectric performance test data thereof are shown in Table 12:

[0155] Table 12. Composition and dielectric properties of mixed liquid crystal material (M-6)

[0156]

[0157] Example 7: Preparation of Liquid Crystal Composition M-7

[0158] The liquid crystal composition M-7 was obtained by referring to the preparation method of Example 1. The composition content and dielectric properties of the composition are shown in Table 13:

[0159] Table 13. Composition and dielectric properties of mixed liquid crystal material (M-7)

[0160]

[0161] Example 8: Preparation of Liquid Crystal Composition M-8

[0162] Referring to the preparation method of Example 1, the liquid crystal composition M-8 was obtained. The composition content and dielectric properties of the composition are shown in Table 14:

[0163] Table 14. Composition and dielectric properties of mixed liquid crystal material (M-8)

[0164]

[0165] Example 9

[0166] Thermal stability test of liquid crystal composition:

[0167] Select the above liquid crystal compositions M-1 to M-6 and M-8 and add 0.05wt% to 0.15wt% of heat stabilizers ST-5, ST-6, ST-7, ST-8, ST-9, ST-10 and ST-12 respectively, accurately weigh and independently add to the above liquid crystal compositions M-1 to M-6 and M-8, heat to 60°C in a clean and dry environment, stir for 15 minutes, mix well, and cool to room temperature 25°C. Test its microwave dielectric properties after heating at room temperature (20°C), 60°C for 1 hour and 90°C for 1 hour. The test data are shown in Table 15 below:

[0168] Table 15. Dielectric properties of the liquid crystal composition after adding stabilizer at 19.1 GHz

[0169]

[0170] Example 10: Comparative composition D-1:

[0171] Comparative Example Composition D-1 is derived from the composition (Mixture N-14) in the example of US Patent US20190292458A (September 26, 2019, Merck, Germany). The data are shown in Table 16:

[0172] Table 16. Composition and dielectric properties of liquid crystal composition material comparative example (D-1)

[0173]

[0174] Example 11: Comparative Example Composition D-2:

[0175] Comparative Example Composition D-2 comes from "Composition M5 in Example 5" in Chinese Patent CN110746981A (2019.10.31, Wuhan University of Technology). The data is shown in Table 17:

[0176] Table 17. Composition and dielectric properties of liquid crystal composition material comparative example (D-2)

[0177]

[0178]

[0179] It can be seen from the performance parameter results of the liquid crystal compositions in the above embodiments that the liquid crystal compositions provided in the embodiments of the present invention have large optical anisotropy, low dielectric loss and large quality factor under microwaves, and can be used as liquid crystal materials in microwave communication devices, especially as nematic liquid crystal materials for microwave phase shifters. The liquid crystal compositions are nematic phase liquid crystal materials with high Δn value, low melting point, low dielectric loss and highly stable structure.

[0180] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A liquid crystal composition, characterized in that: The liquid crystal composition uses an isothiocyanato trans-cyclohexylbiphenyl liquid crystal compound as a first component, and the first component contains at least one compound represented by structural formula (I): wherein R1 is selected from an alkyl group containing 1 to 10 carbon atoms or an alkyl group containing an alkenyl group; X1 to X8 are each independently selected from -H, -CH3, -F or -Cl; the birefringence value (Δn) of the liquid crystal composition is greater than 0.37, the insertion loss of the microwave frequency is reduced, and the dielectric loss value (tanδε r,max ) are all less than 0.0065, the phase modulation (τ) is greater than 0.30, and the quality factor (μ) is higher than 50; The liquid crystal composition further comprises three or more components among a second component, a third component, a fourth component and a fifth component; The second component is at least one of the liquid crystal compounds represented by structural formula (II), the third component is at least one of the liquid crystal compounds represented by structural formula (III), and the fourth and fifth component compounds are at least one of the liquid crystal compounds represented by structural formulas (IV) and (V), respectively: Wherein, in the structural formula (II), R2 is selected from a saturated alkyl group containing 1 to 10 carbon atoms or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H or -F; X5 and X6 are independently selected from -H, -F, -Cl or -CH3; Ring A is selected from trans-cyclohexylene or phenylene; m, n are 0 or 1, and m+n≥1; In the structural formula (III), R3 is a saturated alkyl group containing 1 to 10 carbon atoms, an unsaturated alkyl group or a dl-(±)-2-methylbutyl group; X1 to X4 are each independently selected from -H, -F or -Cl; X5 and X7 are each independently selected from -H, -F, -Cl, -CH3 or -C2H5; Y is -NCS, -F, -OCF3 or a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms; In the structural formula (IV), R4 is a saturated straight-chain alkyl group containing 1 to 10 carbon atoms or dl-(±)-2-methylbutyl; X1 to X2 are each independently selected from -H, -F or -Cl; X8 is -H, -F or -CH3; Y1 is -NCS, -F or -OCF3; Ring B is selected from trans-cyclohexylene or phenylene; In structural formula (V), R5 is a saturated alkyl group or an unsaturated straight-chain alkyl group containing 1 to 10 carbon atoms; R6 is selected from -F, -OCF3, -NCS or a saturated / unsaturated alkyl group containing 1 to 5 carbon atoms; X9 is selected from -H, -F or -Cl; and ring C is a cyclohexylene ring or a phenylene ring.

2. The liquid crystal composition according to claim 1, characterized in that: Based on the total weight of the liquid crystal composition, the liquid crystal composition includes: 5-50wt% of the first component (I), 5-35wt% of the second component (II), 5-25wt% of the third component (III), 0-20wt% of the fourth component (IV), and 0-10wt% of the fifth component (V).

3. The liquid crystal composition according to claim 1, characterized in that: The first component (I) is selected from at least one compound of the following structural formulas (Ia-i), (Ib-i) and (Ic-i): Wherein, R1 is selected from a straight-chain alkyl group or an unsaturated straight-chain alkyl group containing 1 to 10 carbon atoms; X1 to X4 are each independently selected from -H, -F, -Cl or -CH3.

4. The liquid crystal composition according to claim 3, characterized in that: The structural formulas (Ia-i), (Ib-i), and (Ic-i) include but are not limited to:

5. The liquid crystal composition according to claim 1, characterized in that: The second component (II) includes at least one of the following structural formulas (II-1) to (II-6); the third component (II) includes at least one of the following structural formulas (III-1) to (III-10); the fourth component (IV) includes at least one of the following structural formulas (IV-1) to (IV-6); the fifth component (V) includes at least one of the following structural formulas (V-1) to (V-10); 6. The liquid crystal composition according to claim 1, characterized in that: Each component in the liquid crystal composition is a liquid crystal compound purified by electric field adsorption method, and its resistivity reaches 1.0×10 12 above.

7. The liquid crystal composition according to claim 1, characterized in that: A small amount of heat stabilizer may be added to the liquid crystal composition, and the amount thereof accounts for 0.01 to 0.5 wt % of the total mass of the liquid crystal composition.

8. A microwave device, characterized in that: The microwave device comprises the liquid crystal composition according to any one of claims 1 to 7.

9. Use of the liquid crystal composition according to any one of claims 1 to 7 in liquid crystal material medium of microwave high frequency devices.

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