Liquid crystal composition and light adjusting device thereof

Abstract

The present application relates to a liquid crystal composition, the liquid crystal composition includes one or more double mesogenic compounds of general formula I, one or more chiral compounds and one or more nematic liquid crystal compounds of general formula II. The present application also relates to a light modulation device having at least two stable states, at least one of which is a transparent state that substantially transmits incident light, and at least one of which is a haze state that substantially scatters incident light, the transparent state and the haze state being switchable by an external electric field without the need for continuous energization, the transparent state being clear and highly transparent, and the scattering state being privacy shielding. The present application optimizes the components of the liquid crystal composition, so that the light modulation device has higher haze in the shielding state, and can reduce the thickness of the liquid crystal cell when achieving the same shielding effect, thereby reducing the driving voltage and being more energy-saving. At the same time, it reduces the failure rate of device preparation, reduces the amount of liquid crystal used, reduces the cost, and improves the value of the liquid crystal light modulation device in practical application.NCS-MG1-X1-MG2-NCS I

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid crystals, in particular to a liquid crystal bimeric composition comprising a bimeric compound with NCS group and its derived bistable liquid crystal composition and the application of the liquid crystal composition in light modulation devices such as light valve, switchable window, switchable glasses, switchable rearview mirror and the like. BACKGROUND

[0002] In recent years, with the improvement of people's demand for quality of life and energy saving and environmental protection, light modulation glass has been widely concerned and studied due to its more convenient, comfortable and energy saving characteristics. The bistable intelligent light modulation glass composed of cholesteric liquid crystal composition material is one of the important light modulation technologies. The important feature of cholesteric liquid crystal composition bistable light modulation glass technology is that it can maintain more than two stable optical states under zero electric field conditions, and uses a short pulse of seconds for state switching, thereby greatly saving the electric energy consumed by driving. The shielding state (i.e. optical FC state) of the bistable light modulation glass is the stable state of the bistable light modulation under zero field conditions. It not only can minimize the propagation of parallel light to protect the privacy of the user, but also can reduce the light transmittance and adjust the ambient light. The haze of FC state is generally used to represent the degree of light scattering and the efficiency of parallel light propagation. As we all know, the haze is related to the anisotropy of refractive index (i.e. Δn, hereinafter referred to as Δn) of the liquid crystal composition, pitch and cell thickness, especially the square of the Δn of the liquid crystal.

[0003] Bimeric material refers to a liquid crystal compound containing two relatively independent liquid crystal mesogenic groups in the molecule. Due to its special molecular structure, the elastic constant of the liquid crystal composition can be adjusted in the liquid crystal composition, thereby changing the uniformity of the molecular plane arrangement of the liquid crystal composition, reducing the texture defects, and thus reducing the haze of the device containing the liquid crystal composition in the transmittance state, and increasing the haze in the haze state. For example, the Δn of the bimeric material and its composition disclosed in patents CN109825309A and CN110467926A is relatively low, so the cell thickness needs to be increased to compensate for the optical scattering effect. Therefore, not only the amount of material is increased, but also the driving voltage is greatly increased, resulting in increased energy consumption, and the proportion of breakdown of the light modulation device is greatly increased.

[0004] Therefore, it is urgent to develop a liquid crystal composition and its light modulation device to solve the above limitations. SUMMARY

[0005] We find that NCS and its derivative dimers and compositions made therefrom can improve the Δn of cholesteric bistable composition to a great extent, thereby increasing the FC haze of the dimming glass, making the privacy protection effect more obvious, while reducing the pitch (cell thickness) of the dimming device and the driving voltage.

[0006] By optimizing the structure and content of the bimesogenic compound, a cholesteric liquid crystal composition containing at least one bimesogenic compound of bis-terminal isothiocyanate is obtained, and then the liquid crystal composition is matched with specific interface conditions to make a high-haze bistable dimming device.

[0007] To achieve the purpose of the present application, the present application provides a liquid crystal composition, which comprises:

[0008] one or more bimesogenic compounds of general formula I:

[0009] NCS-MG1-X1-MG2-NCS I;

[0010] one or more chiral compounds; and

[0011] one or more nematic liquid crystal compounds of general formula II:

[0012]

[0013] wherein:

[0014] MG1 and MG2 each independently represent a mesogenic unit, and the mesogenic unit is selected from the group consisting of mesogenic units of general formula III:

[0015]

[0016] wherein H1-H7 each independently represent a ring structure, and the ring structure is selected from the group consisting of

[0017] wherein 1-4 H atoms in the ring structure can each independently be replaced by halogen, CN, or an alkyl group having 1-7 carbon atoms, at least one -CH2- in the alkyl group can be replaced by -CHO-, -CO-, -COO- or -OCO-, and at least one H atom in the alkyl group can be replaced by F or Cl;

[0018] A1-A5 each independently represent -OCOO-, -OCH2-, -CH2O-, -CF2O-, -(CH2)2-, -(CH2)4-, -C≡C-, -CH=CH-, -CF2CF2-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or a single bond; p, q and r are 0 or 1;

[0019] X1is selected from the group consisting of radicals of general formula IV:

[0020]

[0021] wherein Y1and Y2each independently represent -O-, -CH=CH-, -CF2O-, -OCF2-, -CF2CF2- or a single bond;

[0022] R1and R2each independently represent -H, -F, -Cl, -NCS, -OCF3, -CF3, -CN or a chain alkyl group having 1 to 25 carbon atoms, wherein one or more H atoms in the chain alkyl group having 1 to 25 carbon atoms can each independently be substituted with a halogen, and one or more non-adjacent -CH2- in the chain alkyl group having 1 to 25 carbon atoms can each independently be replaced with -O-, -CH=CH-, -CH=CF- or -CF=CF-;

[0023] R 10 is a hydrogen atom, R 11 is a hydrogen atom or a chain alkyl group having 1 to 5 carbon atoms;

[0024] m is 0, 1 or 2, n is 1, 2 or 3, o is 1 or 2, and m+n+o is not more than 5, and s is an integer from 1 to 12.

[0025] In some embodiments of the present application, the liquid crystal composition further comprises one or more compounds of general formula V:

[0026] R3-MG3-X2-MG4-R4 V;

[0027] wherein R3and R4each independently represent H, F, Cl, CN, NO2 or a chain alkyl group having 1 to 25 carbon atoms, wherein one or more H atoms in the chain alkyl group having 1 to 25 carbon atoms can each independently be substituted with a halogen or CN, and one or more non-adjacent -CH2- in the chain alkyl group having 1 to 25 carbon atoms can each independently be replaced with -O-, -S-, -NH-, -N(CH3)-, -CO-, -COO-, -OCO-, -OCOO-, -SCO-, -COS-, -CH=CH-, -CH=CF-, -CF=CF- or -C≡C-, in such a way that two -O- are not adjacent to each other;

[0028] MG3and MG4each independently represent a mesogenic moiety, the mesogenic moiety being selected from the group consisting of mesogenic moieties of general formula III; and

[0029] X2is selected from the group consisting of radicals of general formula IV.

[0030] In some embodiments of the present application, mesogenic groups MG1-MG4 each independently comprise at least 2 six-membered rings.

[0031] In some embodiments of the present application, mesogenic groups MG1-MG4 are each independently selected from the group consisting of and mirror image structures thereof, wherein 1-4 H atoms in the six-membered rings can each independently be replaced by halogen, CN or an alkanediyl group having 1-7 C atoms, at least one -CH2- in said alkanediyl group can be replaced by -CHO-, -CO-, -COO- or -OCO-, and at least one H atom in said alkanediyl group can be replaced by F or CI.

[0032] In some embodiments of the present application, the nematic liquid crystalline compound of general formula II is selected from one or more compounds of general formula VI and / or general formula VII:

[0033]

[0034] wherein R5, R6and R7each independently represent -H, -F, -CI, -NCS, -OCF3, -CF3or an alkanediyl group having 1-25 C atoms, one or more non-adjacent -CH2- in said alkanediyl group having 1-25 C atoms can each independently be replaced by -0-, -CH=CH-, -CH=CF- or -CF=CF-;

[0035] A6and A8each independently represent -OCOO-, -OCH2-, -CH2O-, -CF2O-, -(CH2)2-, -(CH2)4-, -C≡C-, -CH=CH-, -CF2CF2-, -CF=CF-, -CH=CH-COO-, -OCO-CH=CH- or a single bond;

[0036] H8, H9, H 10 , H 11 and H 12 each independently represent a cyclic structure, the cyclic structure being selected from the group consisting of

[0037] ;

[0038] a is 1, 2, 3 or 4, b is 0, 1 or 2, c is 1 or 2, and a+b+c is not more than 5;

[0039] d is 0, 1, 2, 3 or 4, and

[0040] e is an integer not less than 2.

[0041] In some embodiments of the present application, the compound of general formula I is selected from the group consisting of:

[0042]

[0043]

[0044]

[0045] In some embodiments of the present application, the chiral compound is selected from one or more of the following compounds:

[0046]

[0047]

[0048] In some embodiments of the present application, the nematic liquid crystal compound is selected from the group consisting of:

[0049]

[0050]

[0051]

[0052]

[0053] In some embodiments of the present application, the compound of general formula I is in the range of 10% to 40% of the total mass of the liquid crystal composition, further preferably, the compound of general formula I is in the range of 15% to 35% of the total mass of the liquid crystal composition, and even further preferably, the compound of general formula I is in the range of 20% to 30% of the total mass of the liquid crystal composition.

[0054] In some embodiments of the present application, the helical pitch P of the liquid crystal composition is in the range of 0.2 μm to 4 μm; further preferably, the helical pitch P of the liquid crystal composition is in the range of 0.8 μm to 2 μm.

[0055] In some embodiments of the present application, the chiral compound is in the range of 1% to 20% of the total mass of the liquid crystal composition.

[0056] In some embodiments of the present application, the compound of general formula II is in the range of 40% to 85% of the total mass of the liquid crystal composition; further preferably, the compound of general formula II is in the range of 50% to 70% of the total mass of the liquid crystal composition.

[0057] In some embodiments of the present application, the liquid crystal composition further comprises one or more dye compounds.

[0058] The present application also provides a light-adjusting device comprising the liquid crystal composition of the present application, which has at least two stable states, including at least one transmissive state that allows the incident light to pass through substantially and at least one haze state that allows the incident light to scatter substantially, and the transmissive state and the haze state can be switched by an external electric field without continuous power supply, the transmissive state has high clarity and high transmittance, and the haze state has privacy shielding. The transmissive state is switched by a first voltage, and the haze state is switched by a second voltage.

[0059] In some embodiments of the present application, the haze of the transmissive state of the light-adjusting device is not more than 10%.

[0060] In some embodiments of the present application, the haze of the haze state of the light-adjusting device is not less than 80%.

[0061] In another aspect, to achieve the above-mentioned purposes, the present application also provides a novel liquid crystal light-adjusting device, which meets the needs by the combination of the liquid crystal composition, the device structure, and the driving mode.

[0062] In some embodiments of the present application, the liquid crystal light-adjusting device comprises a first transparent conductive substrate, a second transparent conductive substrate, and a liquid crystal layer arranged between the first transparent conductive substrate and the second transparent conductive substrate, the first transparent conductive substrate comprises a first transparent substrate and a first transparent conductive layer arranged adjacent to one side of the liquid crystal layer, the second transparent conductive substrate comprises a second transparent substrate and a second transparent conductive layer arranged adjacent to one side of the liquid crystal layer, the liquid crystal layer comprises a liquid crystal composition, the liquid crystal composition is a cholesteric liquid crystal composition, the cholesteric liquid crystal composition has a pitch P < 4 μm, the cholesteric liquid crystal composition comprises an elastic constant regulator; the liquid crystal layer changes the arrangement state of the liquid crystal molecules in the liquid crystal layer under the voltage applied between the first transparent conductive substrate and the second transparent conductive substrate, the change of the arrangement state of the liquid crystal molecules in the liquid crystal layer leads to the change of the propagation characteristics including transmission, scattering, reflection, etc. of the light incident on the liquid crystal layer, the arrangement state of the liquid crystal molecules has at least two stable states that remain substantially stable after the voltage is removed, at least one of the stable states is a transmissive state, the transmissive state allows the light incident on the liquid crystal layer to pass through, at least one of the stable states is a shielding state, the shielding state allows the light incident on the liquid crystal layer to scatter. The transmissive state has a haze not more than 10%, the haze state has a haze not less than 80%, and the absolute change of the haze of the haze state within 5 min is not more than 10%.

[0063] The planar state liquid crystal molecules are arranged in a substantially uniform manner with a helical structure, and have a low light scattering for incident light, so that the liquid crystal light modulation device exhibits a high transmittance state mainly in the form of light transmission. The liquid crystal molecules in the haze state exist in the form of domains. Due to the strong torque and elastic effect of the liquid crystal molecules, the sudden application of an electric field can make the liquid crystal form a plurality of orientation-chaotic molecular domains. In each molecular domain, the liquid crystal molecules still have a substantially ordered helical arrangement, and the orientation between the molecular domains is substantially disordered. After the external electric field is removed, the disordered molecular arrangement in the form of multiple domains can be maintained for a long time, forming a stable focal conic state of the liquid crystal molecular arrangement. The multi-domain structure of the liquid crystal molecules can strongly scatter the incident light.

[0064] As described above, the liquid crystal molecules in the haze state exist in the form of multiple domains. The liquid crystal molecules in the domains are substantially ordered, and the domains are disordered. The scattering state can be stably maintained under the action of suitable interface conditions. The interface conditions, driving conditions and material properties are the key to the haze and stability of the haze state. From the material properties, the existence state of the domain and the birefringence of the liquid crystal composition are the key factors affecting the haze and stability of the haze state. The existence state of the domain is closely related to the chiral compound, and the existence of the chiral compound is the basis for the formation of the helical structure. It is found that when the pitch is greater than or equal to 2 μm, the initial haze of the haze state gradually decreases with the increase of the pitch, and the stability of the haze state gradually decreases, resulting in a significant decrease in the haze of the haze state after a certain period of time. It is also found that when the pitch is too large, it will be difficult to form a domain structure, and therefore the stable scattering state cannot be formed, and the haze state is finally lost. In order to achieve the purpose of the present application, the pitch P of the liquid crystal composition must be less than 4 μm. The size of the pitch P can be adjusted by the content of the chiral compound, which follows the formula P = 1 / (HTP*c), wherein HTP is the helical twist ability of the chiral compound, and c is the mass concentration of the chiral compound in the liquid crystal composition. Under suitable interface and driving conditions and pitch, the focal conic texture of the FC state can be stably maintained. Under the action of the electric field, the liquid crystal molecules quickly form a metastable multi-domain state at the moment of switching to the FC state, and then under the joint action of the interface conditions, the metastable state will gradually tend to be stable, and the haze of the haze state will also be maintained at a certain level, and can be stably maintained for a long time. It is found that under suitable driving conditions and interface conditions, the haze of the FC state tends to be stable after 5 minutes, and this stable state can be maintained for a long time. In order to facilitate evaluation, we define the haze stability as the absolute change in haze between the haze at least 5 minutes after switching to the FC state and the initial haze at the moment of switching.

[0065] As known to those skilled in the art, the optical and electrical properties of the composition, such as Δn, haze and driving voltage, have physical additive characteristics, i.e. the properties of the composition are physically added to the properties of the components and the contents thereof, such as (Where i represents the ith component, xi represents the content of the ith component). Replacing the components of the composition with materials having higher Δn can directly increase the Δn of the composition. Meanwhile, there is the following relationship between the physical properties, Hf = k * Δn 2 * (Hf is the FC state haze of the liquid crystal, k is the coefficient, d is the cell thickness of the liquid crystal), that is, the increase of Δn of the composition can increase the haze of the FC state of the liquid crystal cell, and the cell thickness can be thinned without reducing the haze. The direct effect of reducing the cell thickness is to reduce the amount of liquid crystal used in the liquid crystal cell per unit area, thereby reducing the use cost of the liquid crystal. According to the calculation formula of the driving voltage: (“Liquid Crystal Device Foundation”, P323, Yang Dengke, Wu Shicong), the decrease of the cell thickness will also reduce the driving voltage, thereby reducing the energy consumption.

[0066] The beneficial effects of the present application are that the present application provides a liquid crystal dimming device, through the component-optimized liquid crystal composition, the dimming device has higher haze in the shielding state, and the liquid crystal cell thickness can be reduced to achieve the same shielding effect, thereby reducing the driving voltage and being more energy-saving. At the same time, the yield of device preparation is reduced, the amount of liquid crystal used is reduced, the cost is reduced, and the value of the liquid crystal dimming device in practical application is improved. DETAILED DESCRIPTION

[0067] In the following description, for the purpose of explanation and complete understanding of the present application, a large number of specific details are set forth. However, it is apparent to those skilled in the art that the present application can be implemented without these specific details. In other examples, well-known structures and devices are shown in block diagrams. In this regard, the illustrative example embodiments are merely for illustration and do not limit the present application. Therefore, the scope of protection of the present application is not limited by the above specific embodiments, but only by the scope of the appended claims.

[0068] In the following examples, each component can be synthesized by a known method or obtained by a commercial route. These synthesis techniques are conventional, and each liquid crystal compound obtained is tested to meet the standard of electronic compounds.

[0069] In the present application and especially in the following examples, the group structures in the liquid crystal composition are coded; Table 1 shows the group structures and codes for the liquid crystal composition and the bimesogenic compound.

[0070] Table 1 Group structure code of liquid crystal composition

[0071]

[0072]

[0073] wherein "5PPN" corresponds to the structure according to the naming convention of Table 1:

[0074]

[0075] "n=3" corresponds to the structure according to the naming convention of Table 1: -C3H7.

[0076] (1) Preparation of liquid crystal composition

[0077] The liquid crystal composition was prepared according to the proportion of each component compound specified in the following examples. The preparation of the liquid crystal composition was carried out according to the conventional method in the art. First, each component compound was weighed according to the corresponding mass percentage, the liquid crystal composition was placed in a glass sample bottle, a magnetic stirrer was added, and it was placed on a heated magnetic stirrer. The liquid crystal composition in the sample bottle was heated and stirred until it completely dissolved to form an isotropic transparent solution. At this time, the temperature has reached the clearing point of the liquid crystal composition. Maintain this temperature and continue heating and stirring for 60 minutes to ensure uniform mixing of the sample. Stop heating and continue stirring for 2 hours.

[0078] (2) Structure of light modulation device

[0079] The liquid crystal light modulation device comprises a first transparent conductive substrate and a second transparent conductive substrate, the first transparent conductive substrate and the second transparent conductive substrate are parallel to each other and oppositely arranged to form a liquid crystal cell, the thickness of the liquid crystal cell is 15 μm and 20 μm, the supporting structure is a spherical polystyrene spacer, which accounts for 0.2 wt.% of the liquid crystal composition. The transparent conductive substrate is ITO transparent conductive glass, the alignment layer is VA type, and the orientation is carried out by rubbing orientation method. The liquid crystal layer filled in the liquid crystal cell between the first transparent conductive substrate and the second transparent conductive substrate comprises the above-mentioned liquid crystal composition, and the liquid crystal composition can contain dichroic dye, and the dichroic content is selected according to the requirement of transmittance.

[0080] (3) Haze measurement method

[0081] The liquid crystal composition was vacuum filled into a VA liquid crystal cell with a thickness of 15 μm and 20 μm, respectively. After sealing, the liquid crystal light modulation device was placed in a constant temperature of 25°C for more than 30 minutes, and then tested. First, turn on the WGT-S type haze meter, and start testing after the light source is stable for 30 minutes. The pulse voltage is used to drive it to planar state and focal conic state, respectively, and then the transmittance and haze are measured by WGT-S haze meter, and the phenomenon is observed visually.

[0082] The embodiments of the present application and its objectives are described and illustrated by way of examples below. These examples are merely exemplary and illustrative, but not restrictive. In the present application and especially in the following examples, the present application is beneficial in that the present application provides a liquid crystal dimming device, through the component-optimized liquid crystal composition, the dimming device has higher haze in the shielding state, reduces the liquid crystal cell thickness while achieving the same shielding effect, thereby reducing the driving voltage, more energy-saving. At the same time, reduce the failure rate of device preparation, reduce the amount of liquid crystal used, reduce the cost, improve the value of liquid crystal dimming device in practical application.

[0083] Comparative Example 1

[0084]

[0085] Example 1

[0086]

[0087] Example 2

[0088]

[0089] Example 3

[0090]

[0091] Example 4

[0092]

[0093] Example 5

[0094]

[0095] Example 6

[0096]

[0097] Example 7

[0098]

[0099] Example 8

[0100]

[0101] Example 9

[0102]

[0103] Example 10

[0104]

[0105] Example 11

[0106]

[0107] Comparative Example 2

[0108]

[0109] Example 12

[0110]

[0111] Example 13

[0112]

[0113] Examples 1-4, by adding isothiocyanate-terminated bimesogenic compounds, compared with Comparative Example 1, the haze of the light modulation device made of the liquid crystal composition of the present application in the shielding state is significantly increased; Examples 5-11, by adding isothiocyanate-terminated bimesogenic compounds and various nematic liquid crystal compounds, chiral compounds, good use effect can be achieved; Examples 12-13, compared with Comparative Example 2, the haze of the 15 μm light modulation device made of the liquid crystal composition of the present application in the shielding state is significantly increased, compared with Comparative Example 1, the 15 μm liquid crystal cell reduces the driving voltage compared with the 20 μm liquid crystal cell in the case of achieving the same shielding effect, is more energy-saving, and due to the reduction of the cell thickness, the amount of liquid crystal used is reduced, thereby reducing the cost and improving the value of the liquid crystal light modulation device in practical application.

[0114] While several example embodiments have been described in detail above, the disclosed embodiments are merely exemplary and not limiting, as numerous other modifications, rearrangements, and / or alternatives will occur to one skilled in the art upon reading the above description without departing from the novel teachings and advantages of the disclosure. Therefore, all such modifications, rearrangements, and / or alternatives are intended to be included within the scope of the disclosure as defined by the appended claims.

Claims

1. A liquid crystal composition, comprising: One or more bichemical compounds of formula I accounting for 20% to 40% of the total mass of the liquid crystal composition: NCS-MG1-X1-MG2-NCS I; One or more chiral compounds accounting for 1% to 20% of the total mass of the liquid crystal composition; and One or more nematic liquid crystal compounds of formula II accounting for 40% to 70% of the total mass of the liquid crystal composition: in: MG1 and MG2 are each independently represented wherein 1-4 H atoms in the six-membered ring can be independently substituted by halogen; H1-H3 each independently represent in 1-4 H atoms in can be independently replaced by halogen; A1 and A2 each independently represent -CF2O-, -C≡C- or a single bond; X1 is selected from the group consisting of groups of formula IV: wherein Y1 and Y2 each independently represent -O- or a single bond; R1 represents a chain alkyl group having 1 to 25 carbon atoms, wherein one or more non-adjacent -CH2- groups in the chain alkyl group having 1 to 25 carbon atoms can be independently replaced by -O-; R2 represents -F, -NCS or -CN; R 10 is a hydrogen atom, R 11 It is a hydrogen atom or a chain alkyl group having 1 to 5 carbon atoms; m is 0, 1 or 2, n is 1, 2 or 3, o is 1 or 2, and m+n+o is not greater than 5; s is an integer from 1 to 12.

2. The liquid crystal composition according to claim 1, wherein the liquid crystal composition further comprises one or more compounds of formula V: R3-MG3-X2-MG4-R4 V; in, R3 and R4 represent CN; MG3 and MG4 are each independently represented and X2 is selected from the group consisting of groups of formula IV.

3. The liquid crystal composition according to claim 1, wherein the compound of formula I is selected from the group consisting of: n is a positive integer from 1 to 25; n is a positive integer from 1 to 25; n is a positive integer from 1 to 12; n is a positive integer from 1 to 12; n is a positive integer from 1 to 25; n is a positive integer from 1 to 12; n is a positive integer from 1 to 25; n is a positive integer from 1 to 25; n is a positive integer from 1 to 25; and n is a positive integer from 1 to 25.

4. The liquid crystal composition according to claim 1, wherein The helical pitch P of the liquid crystal composition is 0.2-4 μm. 5 . The liquid crystal composition according to claim 1 , further comprising one or more dye compounds.

6. A dimming device, characterized in that: The dimming device includes a first transparent conductive substrate, a second transparent conductive substrate, and a liquid crystal layer disposed between the first transparent conductive substrate and the second transparent conductive substrate, wherein the liquid crystal layer comprises the liquid crystal composition according to any one of claims 1 to 5.

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