Patent Application
20250043182
The present disclosure belongs to the technical field of liquid crystal (LC) materials, and specifically relates to a twist-bend nematic LC dimer-based material and use thereof, and an LC-based cholesteric heliconical (CH) material and use thereof.
Twist-bend nematic (NTB) liquid crystal (LC) is a new type of nematic LC materials discovered in the past decade, and is composed of bent LC dimer molecules. This material has a nanoscale periodic heliconical structure and is a photonic material with a broad application potential. NTB LC materials have the advantages of high response speed, wide viewing angle, low voltage driving, and low power consumption, thus showing broad application prospects in the fields of LC displays, optical communications, laser modulators, and biosensors.
Research on the NTB LC materials began in 2010, and the NTB phase was discovered in various bent LC dimer compounds containing flexible methylene spacers, such as 1,7-bis(4-cyanobiphenyl-4-yl) heptane (CB7CB). An LC dimer-based material that constitutes an NTB LC phase has an extremely-low bending elastic constant K33, which is highly different from that of conventional long rod-shaped LC materials. In recent years, the NTB LC materials have received increasing attention, involving material synthesis, property characterization, theoretical simulation, and applications. A temperature range of the NTB LC phase is closely related to its chemical structure. Typically, this phase only exists at relatively high temperatures with a narrower temperature range, greatly limiting its application in device fabrication. Ideally, this phase needs to be stable at ambient temperature.
At present, there are opportunities to reduce the temperature range of the NTB phase by designing specific molecular structures, such as introducing S bond(s) and introducing pyrene-based functional group(s) into the molecular structure. Alternatively, a vitrified NTB can be formed through a rapid cooling process. However, although the above methods can achieve an NTB phase at low temperature or ambient temperature, this state is extremely unstable and may crystallize after a few hours of storage, and still cannot realize practical applications.
Through specific molecular structure design, such as functional modification on the structure of LC dimer, introduction of some specific functional groups such as sulfur bonds and pyrene, and changing a structural symmetry of the LC dimer molecule, the temperature range of the NTB phase is optimized to obtain an NTB phase with a relatively broad temperature range, and even the NTB phase can be achieved at ambient temperature. However, the above molecular design scheme mainly faces the following three problems. First, although current materials can reach low temperature or ambient temperature, the above material system of NTB phase is extremely unstable, and crystallization can occur after a sample is stored for a few hours or days. Second, the scheme has difficulties in molecular design, long chemical synthesis cycle, and high difficulty in purification. Third, there is a high uncertainty of the molecular design, making it impossible to obtain a synthesized molecule with a satisfactory NTB phase, and even the synthesized molecules cannot form an NTB phase.
A vitrified NTB phase can be obtained through some specific processes such as rapid liquid nitrogen refrigeration or specific LC dimer molecular design. Depending on the molecular structure, a glass transition temperature of the LC dimer can be at an extremely-low temperature approximately to 0° C. or above ambient temperature. Still, this vitrified NTB phase is also extremely unstable, manifesting in two aspects. On one hand, this phase cannot respond normally to an external electric field. Moreover, once an electric field is applied to the phase or a large temperature change occurs, this vitrified NTB phase may undergo structural collapse and then crystallization begins from the NTB LC phase. On the other hand, this NTB phase at ambient temperature is still not stable for a long time, and the crystallization can occur after a few days of storage.
One of the prominent application scenarios of NTB LC materials is the construction of an LC-based cholesteric heliconical (CH) structure. This is an extremely promising photonic superstructure that has attracted great attention in recent years due to its wide dynamic range reflection band modulation performance driven by low electric fields. CH structure is a special chiral nematic LC state. When a material system meets an abnormally low bending elastic constant (K33<1 pN), the CH structure can be constructed with the help of an external electric field. Distinguished from the conventional cholesteric helical structure, where the LC molecules are helical arrangement and at an right-angle to the helical direction, in the CH structure, LC molecules spontaneously and helically arrange to form a one-dimensional periodic heliconical structure along a direction of the electric field, and this structure forms a specific oblique angle θ with a direction of the heliconical axis, where a pitch of the heliconical structure is called a pitch P. This special molecular assembly behavior enables the oblique angle θ and pitch P in the CH structure to achieve a wide range of reversible modulation according to changes in electric field intensity, thus manifesting as spectral modulation within a wide dynamic range controlled by low electric fields. This spectral modulation range can start from a near-ultraviolet band, cover an entire visible light band, and then extend to a near-infrared band, with a total spectral modulation range of not less than 600 nm. Moreover, this electric field modulation behavior has almost no spectral distortion. In comparison, the electric field modulation behavior of traditional cholesteric right-angle helical structures generally face bottlenecks such as narrow spectral modulation range (<50 nm), high driving voltage, and spectral distortion. Accordingly, the unique electric field modulation of the CH structure has also inspired a series of innovative photonic technologies based on the CH structure, including spectral filtering, tunable laser microcavities, information encryption, nonlinear optics, and dynamically-adjustable planar optics applications.
Currently, the most significant issue facing the CH structure in promoting industrial applications is the crystallization instability of a material system based on the CH structure at ambient temperature. The material system of the CH structure generally includes three parts: 1) a most necessary LC dimer-based material for providing an ultra-low bending elastic constant necessary to build the CH; 2) a conventional nematic LC material for further modifying physical parameters of the material system such as a cholesteric phase temperature range, optical and dielectric anisotropy; and 3) a chiral additive for providing an initial chiral environment and a helical twisting power (HTP).
The LC dimer-based material with an NTB phase has an ultra-low bending elastic constant due to its unique molecular configuration, and serves as a necessary condition for the formation of CH. However, the LC dimer-based material has a nematic phase that generally shows an extremely high temperature range and an extremely narrow temperature domain. For example, the most typical LC dimer-based material, CB7CB, has a nematic phase that exists at 104° C. to 117° C., which greatly limits its application scenarios. The nematic temperature of the LC dimer-based material can be reduced while the phase range can be broadened through molecular design. However, there is still a long way to go before reaching ambient temperature. Meanwhile, the molecular design always has long research and development cycles as well as high research and development risks, and faces difficulties in the design, synthesis, and purification of novel molecules. In addition, a traditional nematic LC materials (such as 4-cyano-40-pentylbiphenyl (5CB), and E7) can be mixed with the LC dimer-based material to effectively reduce the nematic temperature and broaden the phase range of the material system, thereby covering ambient temperature and maintaining the ultra-low bending elastic constant. Although the LC dimer-based material has an excellent miscibility with the traditional nematic LC materials, the resulting material system is highly unstable at ambient temperature and generally crystallizes within a few hours, leading to structural collapse. This is mainly due to the instability of LC dimer-based materials at low temperatures, and there is still no substantial molecular design or process optimization to solve the above problem.
In view of the above deficiencies in the prior art, an object of the present disclosure is to provide a twist-bend nematic (NTB) liquid crystal (LC) dimer-based material and use thereof, and an LC-based cholesteric heliconical (CH) material and use thereof.
To achieve the above object, the present disclosure provides the following technical solutions:
In a first aspect of the present disclosure, provided is an ambient-temperature stable non-crystalline NTB LC dimer-based material, being at least one selected from the group consisting of CBnCB, CBnOCB, and CBOnOCB, with n independently being positive integer of 3 to 15, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, where
In some embodiments, the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 30% to 75% of CB7CB, 15% to 45% of CB9CB, and 5% to 25% of CB11CB; where
In some embodiments, the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 40% to 60% of CB7CB, 20% to 40% of CB9CB, and 10% to 20% of CB11CB.
In some embodiments, the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 60% of the CB7CB, 20% of the CB9CB, and 20% of the CB11CB; alternatively,
the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 40% of the CB7CB, 40% of the CB9CB, and 20% of the CB11CB.
In some embodiments, the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 50% of the CB7CB, 35% of the CB9CB, and 15% of the CB11CB; alternatively,
the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 55% of the CB7CB, 30% of the CB9CB, and 15% of the CB11CB.
In a second aspect of the present disclosure, provided is an ambient-temperature stable non-crystalline LC-based CH material, consisting of the following components by mass percentage: 35% to 55% of an LC dimer-based material, 40% to 60% of a nematic LC monomer material, and 0.1% to 10% of a chiral molecule; where
the LC dimer-based material is CBnCB, with n being a positive integer of 3 to 15, such as 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, and the CBnCB, and the CBnCB has a structure as follows:
In some embodiments, the nematic LC monomer material is selected from the group consisting of 5CB, 8CB, 7OCB, E7, TEB300, SLC1717, SLC9023, and HTD028200-200, where
In some embodiments, the chiral molecule is selected from the group consisting of CB15, R811, S811, R2011, S2011, R1011, S1011, R5011, and S5011.
In some embodiments, the CB15 has a structure as follows:
The chiral molecule is purchased commercially, and suppliers can be selected from companies such as Jiangsu Hecheng Advanced Materials Co., Ltd, China, Shijiazhuang Slichem Display Material Co., Ltd, China, Yantai Xianhua Technology Group Co., Ltd, China, and Merck Germany.
In some embodiments, the LC dimer-based material consists of the following components by mass percentage: 30% to 75% of the CB7CB, 15% to 45% of the CB9CB, and 5% to 25% of the CB11CB; where
In some embodiments, the ambient-temperature stable non-crystalline LC-based CH material consists of the following components by mass percentage: 40% to 50% of the LC dimer-based material, 45% to 55% of the nematic LC monomer material, and 1% to 5% of the chiral molecule.
In some embodiments, the ambient-temperature stable non-crystalline LC-based CH material consists of the following components by mass percentage: 45% of the LC dimer-based material, 52% of the nematic LC monomer material, and 3% of the chiral molecule.
In some embodiments, the LC dimer-based material consists of the following components by mass percentage: 40% to 60% of the CB7CB, 20% to 40% of the CB9CB, and 10% to 20% of the CB11CB.
In some embodiments, the LC dimer-based material consists of the following components by mass percentage: 60% of the CB7CB, 20% of the CB9CB, and 20% of the CB11CB; alternatively,
the LC dimer-based material consists of the following components by mass percentage: 40% of the CB7CB, 40% of the CB9CB, and 20% of the CB11CB.
In some embodiments, the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 50% of the CB7CB, 35% of the CB9CB, and 15% of the CB11CB; alternatively,
the ambient-temperature stable non-crystalline NTB LC dimer-based material consists of the following components by mass percentage: 55% of the CB7CB, 30% of the CB9CB, and 15% of the CB11CB.
In the present disclosure, the LC dimer-based material can provide the required ultra-low bending elastic constant and suppress crystallization. The nematic LC monomer material can reduce the nematic temperature range and modify the physical parameters of the material system. The chiral molecule can construct an initial chiral environment to form a chiral nematic phase; based on differences in the helical twisting power (HTP) of chiral molecules and the left and right rotation of chirality, specific chiral molecules can be selected and the content of chiral molecules can be adjusted.
In a third aspect of the present disclosure, provided is use of the ambient-temperature stable non-crystalline NTB LC dimer-based material of any one of the above technical solutions or the ambient-temperature stable non-crystalline LC-based CH material of any one of the above technical solutions in preparation of a display panel and a display device.
By adopting the foregoing technical solutions, the present disclosure achieves the following advantages and beneficial effects.
The present disclosure provides an ambient-temperature stable non-crystalline NTB LC dimer-based material. In the present disclosure, the ambient-temperature stable non-crystalline NTBLC dimer-based material has a simple monomer composition and a simple preparation process. By mixing a variety of LC dimer-based materials with different degrees of molecular bending and central flexibility in specific proportions, a supercooling capability of the material system is significantly enhanced with the help of intermolecular interactions and molecular chain entanglement. As a result, a stable, reliable, and non-crystalline NTB phase is achieved at ambient temperature. The material sample maintains an NTB phase region over a wide temperature range without any crystallization for at least 300 days. The present disclosure is of great significance to the development of LC dimer-based materials, the in-depth research on NTB LC phase, and the development in the field of modern photonics.
In the ambient-temperature stable non-crystalline NTB LC dimer-based material of the present disclosure, an overall stability of the material system can be effectively improved according to different dimer component ratios; the ambient-temperature stable non-crystalline NTB LC dimer-based material has an NTB phase over a wide temperature range, from ambient temperature to approximately 100° C.
In the present disclosure, the ambient-temperature stable non-crystalline NTB LC dimer-based material can meet long-term storage requirements. Even if the NTB phase is stored at ambient temperature for not less than 300 days, no crystallization is observed. The material system exhibits an excellent stability, far exceeding that of other material systems.
The present disclosure further provides an ambient-temperature stable non-crystalline LC-based CH material. The ambient-temperature stable non-crystalline LC-based CH material of the present disclosure has an overall chiral nematic temperature range covering the ambient temperature (25° C.). The material system is extremely stable and does not show any crystallization even if it is stored for not less than 1 year at ambient temperature. The material system has an extremely-low bending elastic constant, with K33<0.4 pN at ambient temperature. The physical parameters of the material system, including dielectric constant and elastic constant, can remain stable and do not fluctuate with storage. The physical parameters of the material system do not change significantly even after being stored for one year.
In the present disclosure, the ambient-temperature stable non-crystalline LC-based CH material exhibits wide dynamic selective reflection modulation driven by a low electric field (<2 V/μm), and has a reflection band range modulation range from 430 nm to 1,050 nm, exceeding 600 nm. The modulation of the broad spectrum of this electric field still shows an extremely strong stability. After the material system has been stored for one year, the reflection spectral bands corresponding to the electric field intensity almost show a one-to-one correspondence, with no obvious difference.
Currently, existing material systems have a relatively high nematic temperature range, generally not less than 100° C. The nematic temperature range of the ambient-temperature stable non-crystalline LC-based CH material of the present disclosure covers the ambient temperature.
Currently, existing material systems are extremely unstable at ambient temperature and generally crystallize rapidly within a few hours, causing the structure to collapse and completely fail. In the present disclosure, the ambient-temperature stable non-crystalline LC-based CH material is extremely stable, and no crystallization occurs even if it is stored at ambient temperature for not less than 1 year.
In the ambient-temperature stable non-crystalline LC-based CH material of the present disclosure, a variety of relatively conventional LC dimers CB7CB, CB9CB, CB11CB and other homologues are mixed in specific proportions. In this way, through a synergy between molecules and the complexity of molecular conformation caused by an entanglement effect of molecular chains, the stability of the material system is effectively improved, thereby inhibiting crystallization.
The present disclosure further provides use of the ambient-temperature stable non-crystalline NTB LC dimer-based material of the above technical solution or the ambient-temperature stable non-crystalline LC-based CH material of the above technical solution in preparation of a display panel and a display device. The present disclosure solves the bottleneck problem that has limited the application of CH structures for a long time, and is a key technological breakthrough that promotes engineering and even mass production of CH structures.
To describe the technical solutions in embodiments of the present disclosure or in the prior art more clearly, the accompanying drawings required for the embodiments are briefly described below. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and those of ordinary skill in the art may still derive other accompanying drawings from these accompanying drawings without creative efforts.
In order to further illustrate the present disclosure, the applicant will further describe the technical solution of the present disclosure in detail below with reference to the accompanying drawings and specific examples, such that those skilled in the art can clearly understand the present disclosure. However, the following examples should not be construed to limit the scope of the claims of the present disclosure to any extent.
In the examples of the present disclosure, preparation methods of the CBnCB, the CBnOCB, and the CBOnOCB can be found in the literature: Liq. Cryst., 2017, 44, 127-146, which is incorporated herein by reference.
In the examples of the present disclosure, the reagents used were as follows:
The CBnCB material was synthesized according to a synthesis route as follows:
Adipoyl chloride and 4-bromobiphenyl were added dropwise to a suspension of aluminum trichloride/dichloromethane and stirred, and a resulting reaction mixture was added into water and shaken to be uniform with dichloromethane. A remaining aqueous suspension was filtered, an obtained solid was washed thoroughly with water and recrystallized from toluene. Triethylsilane was added dropwise to α,ω-bis(4′-bromobiphenyl-4-yl)butane and stirred in a solution of trifluoroacetic acid and dichloromethane. A resulting reaction mixture was left to reach ambient temperature and stirred for 48 h, then a resulting white solid was filtered off, washed with water and recrystallized from toluene. A mixture of α,ω-bis(4′-bromobiphenyl-4-yl)hexane, cuprous cyanide, and dry N-methylpyrrolidone was stirred at 200° C. for 4 h, and then cooled to 80° C., and added with ferric chloride and hydrochloric acid. A resulting mixture was stirred for another 30 min, cooled overnight, added with water, and shaken to be uniform with dichloromethane. A resulting organic layer was washed with water, dried over CaCl2 and the solvent was removed, and the remaining product was finally recrystallized from toluene.
An ambient-temperature stable non-crystalline NTB LC dimer-based material consisted of the following components by mass percentage: 60% of CB7CB, 20% of CB9CB, and 20% of CB11CB, and was named sample S7.
During determination, each of the above components was weighed according to the above ratio, stirred evenly for 2 h at 130° C., and mixed evenly to obtain a product, which was then subjected to determination. The following examples and comparative examples were all conducted according to this method.
An ambient-temperature stable non-crystalline NTB LC dimer-based material consisted of the following components by mass percentage: 40% of CB7CB, 40% of CB9CB, and 20% of CB11CB, and was named sample S8.
An ambient-temperature stable non-crystalline NTB LC dimer-based material consisted of the following components by mass percentage: 50% of CB7CB, 35% of CB9CB, and 15% of CB11CB, and was named sample S9.
An ambient-temperature stable non-crystalline NTB LC dimer-based material consisted of the following components by mass percentage: 55% of CB7CB, 30% of CB9CB, and 15% of CB11CB, and was named sample S10.
A material used CB7CB as a single component and was named sample S1.
A material used CB9CB as a single component and was named sample S2.
A material used CB11CB as a single component and was named sample S3.
An LC material consisted of the following components by mass percentage: 60% of CB7CB and 40% of CB9CB, and was named sample S4.
An LC material consisted of the following components by mass percentage: 60% of CB7CB and 40% of CB11CB, and was named sample S5.
An LC material consisted of the following components by mass percentage: 60% of CB9CB and 40% of CB11CB, and was named sample S6.
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-1, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-4, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-7, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-8, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-9, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-10, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-11, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample S-1, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample S-2, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample S-2, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-1, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-2, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-3, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-4, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; and
A material was named sample D-5, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-6, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-7, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-8, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-9, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-10, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample D-11, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample T-2, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample T-3, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; and
A material was named sample T-5, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
A material was named sample T-6, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
An ambient-temperature stable non-crystalline LC-based CH material was named sample T-12, and consisted of the following components by mass percentage: 45% of an LC dimer-based material, 52% of a nematic LC monomer material, and 3% of a chiral molecule; where
3 groups of samples S1, S2, and S3 were heated to 130° C. to melt into isotropic state. At this temperature, the samples were separately poured into an LC cell (size: 15*18 mm2, thickness 12 μm) with surface parallel alignment direction, and placed in a precision temperature-controlled hot stage. The samples were slowly cooled down at 3° C./min to observe phase transition of the samples. The results are shown in
The three LC dimer-based materials CB7CB, CB9CB, and CB11CB were weighed according to the proportions in samples S4, S5, S6, S7, S8, S9, and S10 and placed in sample bottles for mixing. A magnetic stirrer was added to each sample bottle and the samples were separately stirred evenly at 130° C. for 2 h until mixed to be uniform. At this temperature, the samples were separately poured into an LC cell (size: 15*18 mm2, thickness 12 μm) with surface parallel alignment direction, and placed in a precision temperature-controlled hot stage. The samples were slowly cooled down at 3° C./min to observe phase transition of the samples. The phase transitions of samples S4, S5, S6, S7, and S8 are highly similar to those of samples S1, S2, and S3, that is, they transformed from isotropic state to conventional N phase state at around 120° C., and from N phase state to NTB phase state at around 105° C. The NTB phase state of samples S4, S5, S6, S7, and S8 could all be supercooled to ambient temperature of 25° C.
The temperature range and ambient temperature stability of the NTB phase state of the material were characterized by polarized optical microscope (POM) and X-ray diffraction (XRD). The samples S4, S5, S6, S7, and S8 were stored at ambient temperature, and their stability and crystallization were monitored through the POM. The NTB phase state could be confirmed by the images of POM, and the results are shown in
In order to further confirm the stability of the above material system, the above samples S4, S5, S6, S7, and S8 were further analyzed by XRD method. The results are shown in
The differential scanning calorimeter (DSC) analysis data results are shown in
The comparative experimental results of the crystallization stability of the material systems prepared according to Examples 5 to 6 and Comparative Examples 7 to 19 are shown in Table 1:
The experimental steps for sample preparation and crystallization stability test were as follows: all the above samples were each stirred at 130° C. for 2 h and poured into a commercial LC test empty box. The LC empty box was composed of two pieces of transparent glass coated with ITO electrodes, with a size of 18×15 mm2 and an internal spacing of 12 μm. The samples were then slowly cooled to ambient temperature of 25° C. at 5° C./min. In order to eliminate the potential energy inside the material, a square wave electric field signal with a voltage of 10 V and a frequency of 1 kHz was applied to the samples for 10 min. The samples were then stored in a constant-temperature-humidity chamber (25° C., 50%), and the crystallization of the samples was observed every day.
The crystallization time of a sample is defined as a time interval from the completion of sample preparation to the moment when crystallization of the sample is first discovered. The crystallization of the sample could be roughly measured by visual observation and verified by POM. As shown in
As shown in Table 1, when the mass percentage of the nematic LC monomer 5CB reaches 52%, the material system exhibits a chiral nematic phase state at ambient temperature of 25° C. Depending on the composition and content of the LC dimer-based material CBnCB in the material systems, the material systems exhibit differentiated crystallization times. When the material ratio in the present disclosure is satisfied, the material system exhibits an ultra-stable crystallization stability.
It could be proved from the data in Table 1 that when the material system only includes a single LC dimer-based material CBnCB, such as Comparative Examples 7 to 9, the material system is extremely unstable and crystallization occurs after only a few hours (samples S-1, S-2, and S-3). When the material system includes two LC dimer-based materials CBnCB, the stability of the material system is improved, for example, Comparative Examples 10 to 20. The sample prepared in Comparative Example 15 has the best stability and could last for 20 days without crystallization. However, the crystallization stability of the system is closely related to the content of CBnCB, and most of the material components still have a poor stability. When the material system includes 3 kinds of LC dimer-based materials CBnCB, the stability of the material system is abnormally improved. Sample T-1 prepared according to Example 5 and sample T-4 prepared according to Example 6 do not crystallize for 400 days, showing a significantly enhanced stability. Comparative Examples 21, 22, and 25 crystallize on days 38, 4, and 5, respectively, which is due to the higher concentration of individual CBnCB in the system. This high concentration results in a material system with a stability close to that of a single dimer (such as sample S-1, S-2, and S-3), which was extremely unstable and prone to crystallization. Comparative Examples 23 and 24 crystallize on days 200 and 120, respectively, which might be due to the fact that the complex interactions between molecules are not enough to establish an optimal balance to prevent crystallization. As a result, the percentage content and ratio of the three LC dimer-based materials in the present disclosure are crucial to the crystallization behavior.
The improvement in crystallization stability is due to the interaction between a variety of LC dimer-based materials and is not limited to the nematic LC monomer materials they cooperated with. Even if the nematic LC monomer material 5CB in material sample T-1 is replaced with other nematic LC monomer materials, this strong crystallization stability remains unchanged. The specific results are shown in Table 2:
In the present disclosure, the ambient-temperature stable non-crystalline LC-based CH material has an ultra-high crystallization stability and a long-term stability of physical parameters. Sample T-1 prepared according to Example 5 was filled into a commercial LC box (size: 15*18 mm2, thickness 12 μm) containing an ITO electrode, to determine dielectric constants (a parallel dielectric constant ε//, a perpendicular dielectric constant ci, and a relative dielectric constant Δε), a splay elastic parameter K11, and a bending elastic parameter K33 by a capacitance-voltage method. In this method, the LC was induced from a planar arrangement to a vertical arrangement by applying an AC signal with a frequency of 1 kHz. A capacitance of the sample was monitored as a function of the applied voltage, which was varied from 0.1 V to 8.5 V with intervals of 30 s. According to the theoretical fitting test of the dependence of capacitance on voltage, a relative dielectric constant and elastic parameters could be extracted. The dielectric constant and elastic parameters were tested using a commercial LC comprehensive parameter tester (ALCT-IV1, INSTEC, USA). The results are shown in
Furthermore, in order to verify the stability of sample T-1 of the ambient-temperature stable non-crystalline LC-based CH material of the present disclosure, the electric field-driven reflection band modulation performance of the CH structure constructed by the same was analyzed. The reflection spectrum of sample T-1 during a one-year storage period was tested with electric field driving, and the results are shown in
As a comparison, the electric field-driven reflection band of a CH structure constructed with an unstable material system (such as sample D-6 prepared according to Comparative Example 15) was tested. The results are shown in
In the present disclosure, the ambient-temperature stable non-crystalline LC-based CH material could form an LC-based CH structure. This structure is a special helical structure formed under the driving of electric field. The reflection spectrum corresponding to the structure driven by an electric field changes with the intensity of the electric field, showing a wide dynamic range (450 nm to 1,050 nm) of tunability in the reflection spectrum. Therefore, the existence of the LC-based CH structure is confirmed from the reflection spectrum data in
To further illustrate the above issues, the following POM data is provided, and the results are shown in
Although the embodiments of the present disclosure have been shown and described, and the present disclosure has been described in detail, these are only some, but not all, of the embodiments of the present disclosure. It will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present disclosure. Other embodiments can be obtained without inventive step, and all belong to the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310908652.4 | Jul 2023 | CN | national |
| 202310908656.2 | Jul 2023 | CN | national |
This application is a national stage application of International Patent Application No. PCT/CN2023/124384, filed on Oct. 13, 2023, which claims priorities of the Chinese Patent Application No. CN202310908656.2, filed with China National Intellectual Property Administration on Jul. 24, 2023, and the Chinese Patent Application No. CN202310908652.4, filed with China National Intellectual Property Administration on Jul. 24, 2023. The disclosure of the three applications is incorporated by references in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2023/124384 | 10/13/2023 | WO |
