Preparation and characterization of chalcone liquid crystal elastomer using polarized light orientation

Abstract

The application discloses a preparation and characterization of a chalcone liquid crystal elastomer using polarized light orientation, and belongs to the technical field of liquid crystal elastomers. The preparation steps are as follows: liquid crystal monomers, light-responsive liquid crystal monomers containing chalcone, a chain extender and a crosslinking agent are dissolved in a solvent and ultrasonically mixed uniformly, then poured into a polytetrafluoroethylene mold, a catalyst is added, and the first crosslinking is initiated under light-proof conditions to obtain a pre-crosslinked liquid crystal polymer film. Then, the pre-crosslinked film is placed under a specific shape photomask for different angle polarized light orientation programming. After the programming is completed, the second crosslinking is initiated under light-proof conditions to obtain a liquid crystal elastomer. The material endows the liquid crystal elastomer with bidirectional shape memory characteristics. In addition, after the material is programmed under different shape photomasks and different angle polarized light orientation, the liquid crystal elastomer can exhibit different complex shape two-dimensional to three-dimensional thermal actuation behaviors.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid crystal elastomers, and relates to preparation and characterization of a chalcone liquid crystal elastomer using polarized light orientation. BACKGROUND

[0002] Liquid crystal elastomers are a class of stimuli-responsive materials that exhibit both liquid crystal and elastomeric properties, in which the phase transition of liquid crystal units can lead to large deformation of the anisotropic polymer network. By designing the arrangement of liquid crystal units, the mechanical response of liquid crystal elastomers can be programmed to achieve complex shape deformation with controllable actuation stress, providing potential for artificial muscles, bionic devices and soft robots. Therefore, precise control of the arrangement of liquid crystal units in liquid crystal elastomers is crucial to achieve the desired actuation behavior. So far, strategies including mechanical stretching orientation, shear orientation, and external electric / magnetic field orientation have been developed. However, when these strategies are used to program uniform orientation distribution to display simple deformation modes such as uniaxial contraction, bending and twisting, they are very effective. But to achieve free design of orientation distribution with high spatial resolution, two-dimensional to three-dimensional deformation, which undoubtedly increases the difficulty of potential application fields.

[0003] The combination of surface orientation and 3D printing technology realizes the spatial control of liquid crystal elastomers, but is limited in the resolution and universality of macroscopic shape. Developing a photo-orientation method can provide an effective way to control the spatial orientation of liquid crystal elastomers, thus realizing three-dimensional complex deformation. This method can adjust the orientation arrangement of molecules in a small range of microns without direct contact with the material, providing new possibilities for the development of liquid crystal devices with high-resolution pattern structures. Although photo-orientation methods based on azobenzene (azo) group photoisomerization have been reported, it lacks an in-situ photo-orientation strategy to enrich the design method, because the previously reported photo-orientation methods must be first applied to the orientation layer of the liquid crystal cell, and then the processed cell is used as a mold to obtain a liquid crystal elastomer with a designed orientation distribution of liquid crystal units. SUMMARY

[0004] The purpose of the present application is to provide a preparation of a chalcone liquid crystal elastomer using polarized light orientation.

[0005] The present application firstly proposes an effective strategy for in-situ photo-programming of liquid crystal elastomer by integrating chalcone intermediates, which can undergo directional [2+2] cycloaddition under linear polarized light, thereby inducing liquid crystal units to align perpendicular to the polarization direction in exposed areas, while the intermediates remain unchanged in unexposed areas; based on this mechanism, light can be in-situ written into patterned anisotropy in liquid crystal elastomer materials, thereby facilitating the design and implementation of complex three-dimensional deformation.

[0006] The second object of the present application is to provide a chalcone liquid crystal elastomer oriented by polarized light.

[0007] Technical scheme: The preparation method of the chalcone liquid crystal elastomer oriented by polarized light provided by the present application has the following preparation steps:

[0008] Step (1): The prepared base liquid crystal monomer, light-responsive liquid crystal monomer, chain extender and crosslinking agent are dissolved in a solvent in proportion and ultrasonically mixed uniformly, and then poured into a polytetrafluoroethylene mold; then a catalyst is added to initiate the first crosslinking under light-proof conditions, thereby obtaining a pre-crosslinked liquid crystal polymer film;

[0009] Step (2): The pre-crosslinked liquid crystal polymer film prepared in step (1) is placed under a specific shape photomask, and then the polymer film is oriented and programmed by polarized light of different angles; after the programming is completed, the second crosslinking is initiated in a light-proof environment, and the liquid crystal elastomer capable of two-dimensional to three-dimensional shape change under thermal stimulation, i.e. the chalcone liquid crystal elastomer oriented by polarized light, is obtained after the second crosslinking is completed.

[0010] Further, in step (1), the base liquid crystal monomer includes main chain liquid crystal monomer or side chain liquid crystal monomer.

[0011] Further, in step (1), the light-responsive liquid crystal monomer is suitable for two kinds of base liquid crystal systems, including system one and system two.

[0012] Among them, system one uses main chain liquid crystal monomer, which includes four solutes of main chain liquid crystal monomer, light-responsive liquid crystal monomer, chain extender and crosslinking agent, and the main chain liquid crystal monomer, light-responsive liquid crystal monomer, chain extender and crosslinking agent are RM257 or RM82, M-Cha, DODT and PETMP respectively;

[0013] In system two, main chain liquid crystal monomer and side chain liquid crystal monomer are used, specifically including four solutes of main chain liquid crystal monomer, side chain liquid crystal monomer, light-responsive liquid crystal monomer and crosslinking agent, and the main chain liquid crystal monomer, side chain liquid crystal monomer, light-responsive liquid crystal monomer and crosslinking agent are PMHS, MBB, M-Cha and 11UB respectively; this system does not need to use a chain extender.

[0014] Further, in system one, the molar ratio of main chain liquid crystal monomer RM257 or RM82: photoresponsive liquid crystal monomer M-Cha: chain extender DODT: crosslinking agent PETMP is 0.97-0.85: 0.03-0.15: 0.85-0.95: 0.02-0.08 in terms of the amount of substance.

[0015] In system two, the molar ratio of main chain liquid crystal monomer PMHS: side chain liquid crystal monomer MBB: photoresponsive liquid crystal monomer M-Cha: crosslinking agent 11UB is 1: 0.7-0.9: 0.01-0.1: 0.05-0.15.

[0016] Further, in system one, the solvent used is dichloromethane, and the mass ratio of each solute to the solvent in system one is 100:1; in addition, for the preparation of a thin film with a size of 2x2 cm 2 , the total amount of solute used is 100 mg, and the solute content is increased or decreased proportionally with the change of the area of the thin film;

[0017] In system two, the solvent used is toluene, and the mass ratio of each solute to the solvent in system two is 150:1; in addition, for the preparation of a thin film with a size of 2x2 cm 2 , the total amount of solute used is 150 mg, and the solute content is increased or decreased proportionally with the change of the area of the thin film.

[0018] Further, in system one, the catalyst used is dipropylamine or other amine-based basic reagent;

[0019] In system two, the catalyst used is Kastle reagent; the catalyst provides an alkaline environment for the entire crosslinking system, promoting crosslinking and film formation.

[0020] Further, the one-time crosslinking condition in system one is a light-free environment, and crosslinking is carried out at room temperature for 12-16 hours;

[0021] The one-time crosslinking condition in system two is a light-free environment, and crosslinking is carried out at 60°C for 3-4 hours.

[0022] Further, in step (2), the time for polarization light orientation programming is 0.5-1 hour.

[0023] Further, in step (2), the secondary crosslinking condition in system one is a light-free environment, and crosslinking is carried out at room temperature for 10-14 hours;

[0024] The secondary crosslinking condition in system two is a light-free environment, and crosslinking is carried out at 50°C for 24-48 hours.

[0025] Furthermore, the characterization of a chalcone liquid crystal elastomer prepared by the preparation method using polarized light orientation shows that the liquid crystal elastomer programmed by polarized light orientation is in a flat state at room temperature, undergoes a specific deformation along the direction perpendicular to the polarized light orientation after heating, and returns to the initial flat state after the thermal stimulus is removed.

[0026] By adding photomasks with different patterns during the polarization orientation programming process to perform complex programming, the elastomer film can achieve two-dimensional to three-dimensional complex shape modes under heating conditions (that is, the liquid crystal elastomer programmed by polarization orientation can change to two-dimensional to three-dimensional complex shape under thermal stimulation along the direction perpendicular to the polarization orientation).

[0027] Furthermore, the liquid crystal elastomer is in a flat initial state before being heated, and after being heated, it will undergo a specific deformation along the direction perpendicular to the polarization light orientation. After the stimulus is removed, it will return to the initial state.

[0028] Furthermore, after pre-programming photomasks with different patterns, it is possible to achieve complex deformation modes from two-dimensional to three-dimensional shapes.

[0029] This invention utilizes some applications of in-situ optically writable anisotropic chalcone-containing liquid crystal elastomers, such as the ability of the material of this invention to achieve two-dimensional to three-dimensional shape changes under thermal stimulation.

[0030] Beneficial effects: Compared with the prior art, the features of this invention are: 1. The manufacturing process is simple, and no large equipment is required to manufacture liquid crystal elastomers; 2. It is intelligent and can achieve pre-programming of different deformation shapes under remote control of polarized light; 3. High spatial resolution of material orientation distribution can be achieved by using polarized light pre-programming; 4. The developed chalcone liquid crystal molecules are bonded to the liquid crystal elastomer, and their photocrosslinking characteristics give the material excellent photoorientation behavior. Attached Figure Description

[0031] Figure 1 This is a flowchart of the operation of the present invention;

[0032] Figure 2 These are internal component structure diagrams of two different systems in this invention;

[0033] Figure 3 This is a schematic diagram illustrating the thermal actuation behavior of a chalcone-containing liquid crystal elastomer after polarization orientation programming at different angles, and the thermal actuation behavior after polarization orientation programming at different angles under photomasks of different shapes, according to embodiments of the present invention. Detailed Implementation

[0034] In order to more clearly illustrate the technical solutions of the present application, the technical solutions of the present application are further described in detail below in combination with the drawings:

[0035] The preparation method of the chalcone liquid crystal elastomer using polarized light orientation according to the present application comprises the following steps:

[0036] (1) Dissolve main chain liquid crystal monomers or side chain liquid crystal monomers, light responsive liquid crystal monomers, crosslinking agents, etc. in a solvent, and ultrasonically treat to obtain a transparent solution;

[0037] (2) Pour the transparent solution into a polytetrafluoroethylene mold, then add a catalyst, and place in a light-proof environment to perform pre-crosslinking to obtain a liquid crystal elastomer film;

[0038] (3) Place the pre-crosslinked liquid crystal elastomer film under a specific shape of a photomask, then use polarized light of different angles to perform orientation programming on the polymer film, and after light orientation for 0.5-1 hours, place the polymer film in a light-proof environment to complete secondary crosslinking of the film, and then obtain a liquid crystal elastomer capable of changing from two-dimensional to three-dimensional shape under thermal stimulation.

[0039] Example 1:

[0040] (1) Light-induced remodeling without external force is a new processing method of crosslinked polymers with exchangeable linkages. With the spatial selectivity of light, this process can be applied to the microprocessing of various complex three-dimensional structures;

[0041] (2) By controlling the polarization direction and irradiation point of linearly polarized ultraviolet light, different arrangement directions of liquid crystals can be induced in the film. This strategy improves the light-induced actuation freedom of the liquid crystal elastomer film, and can be applied in soft light actuators;

[0042] (3) The thermal actuation behavior of the liquid crystal elastomer film makes the film exhibit different shapes at room temperature and heated state, thereby expressing different information. With this, the technology can be applied in information storage and anti-counterfeiting.

[0043] Example 2:

[0044] (1) Liquid crystal performance test of the polymer film: use a differential scanning calorimeter to test the liquid crystal interval of the film; use a polarizing microscope to observe the visual light and dark changes of the single domain film before and after rotating by 45° to determine whether it is oriented; use a small-angle X-ray scattering instrument to test the polymer film to determine the orientation degree of the single domain liquid crystal film;

[0045] (2) : Thermal actuation test: Firstly, simple thermal bending behavior, the polymer film is polarized light oriented along four different angles 0°, 45°, 90°, 135°, the oriented and completed secondary cross-linked polymer film can be thermal bending along the perpendicular to the polarized light orientation angle under heating condition, and can be returned to the flat initial state under cooling condition; Secondly, thermal actuation behavior test for complex two-dimensional to three-dimensional shape change, firstly, the polymer film is placed under a specific shape of photomask, and then the polymer film is polarized light oriented along the photomask at different angles, the oriented and completed secondary cross-linked polymer film can be actuated along the angle perpendicular to the orientation direction under heating condition, thereby showing complex two-dimensional to three-dimensional shape change, for example, from flat film to wave shape or showing the shape of English letters.

Claims

1. A method for preparing a chalcone liquid crystal elastomer oriented with polarized light, characterized by, The preparation steps are as follows: Step (1): the prepared base liquid crystal monomer, light response liquid crystal monomer, chain extender and crosslinking agent are dissolved in a solvent in proportion, and ultrasonic mixing is uniformly mixed, and then poured into a polytetrafluoroethylene mold; then a catalyst is added, and the first crosslinking is initiated under light-proof conditions, thereby obtaining a pre-crosslinked liquid crystal polymer film; The base liquid crystal monomers include main chain liquid crystal monomers or side chain liquid crystal monomers; The light response liquid crystal monomers are suitable for two kinds of base liquid crystal systems, including system one and system two; In system one, main chain liquid crystal monomers are used, which include four solutes of main chain liquid crystal monomers, light response liquid crystal monomers, chain extenders and crosslinking agents, and the main chain liquid crystal monomers, light response liquid crystal monomers, chain extenders and crosslinking agents are RM257 or RM82, M-Cha, DODT and PETMP respectively; In system two, main chain liquid crystal monomers and side chain liquid crystal monomers are used, which specifically include four solutes of main chain liquid crystal monomers, side chain liquid crystal monomers, light response liquid crystal monomers and crosslinking agents, and the main chain liquid crystal monomers, side chain liquid crystal monomers, light response liquid crystal monomers and crosslinking agents are PMHS, MBB, M-Cha and 11UB respectively; In system one, the molar ratio of RM257 or RM82:M-Cha:DODT:PETMP is 0.97-0.85:0.03-0.15:0.85-0.95:0.02-0.08; In system two, the molar ratio of PMHS:MBB:M-Cha:11UB is 1:0.7-0.9:0.01-0.1:0.05-0.15; In system one, the solvent used is dichloromethane, and the mass ratio of each solute to the solvent in system one is 100:1; and the content of the solute used is increased or decreased proportionally corresponding to the change of the area of the liquid crystal polymer film; In system two, the solvent used is toluene, and the mass ratio of each solute to the solvent in system two is 150:1; and the content of the solute used is increased or decreased proportionally corresponding to the change of the area of the liquid crystal polymer film; In system one, the catalyst used is dipropylamine or other amine alkaline reagent; In system two, the catalyst used is Kast catalyst; The first crosslinking condition in system one is a light-proof environment, and the crosslinking is carried out at room temperature for 12-16 hours; The first crosslinking condition in system two is a light-proof environment, and the crosslinking is carried out at 60°C for 3-4 hours; Step (2): the prepared pre-crosslinked liquid crystal polymer film is placed under a photomask, and then the polymer film is oriented and programmed by polarized light at different angles, and after the programming is completed, the second crosslinking is initiated in a light-proof environment, and after the second crosslinking is completed, a liquid crystal elastomer which changes from two-dimensional to three-dimensional shape under thermal stimulation is prepared, that is, a chalcone liquid crystal elastomer oriented by polarized light; The time of the polarized light orientation programming is 0.5-1 hour; The second crosslinking condition in system one is a light-proof environment, and the crosslinking is carried out at room temperature for 10-14 hours; The second crosslinking condition in system two is a light-proof environment, and the crosslinking is carried out at 50°C for 24-48 hours.

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