A method of preparing a liquid crystal elastomer foam doped with boron nitride

Abstract

The application provides a preparation method of a liquid crystal elastomer foam doped with boron nitride, comprising the following steps: 1) preparation of a NaCl salt template; 2) preparation of a liquid crystal elastomer monomer solution: a liquid crystal elastomer monomer solution is prepared by adding a sufficient amount of a toluene solution into 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methyl benzene RM257 as a liquid crystal unit; 3) formation of a liquid crystal elastomer network; 4) preparation of a pre-crosslinked liquid crystal elastomer foam; 5) deformation programming of the liquid crystal elastomer foam: the pre-crosslinked liquid crystal elastomer foam is placed into the template for constant compression, and secondary crosslinking is performed using ultraviolet light under the constant compression state to form a secondary crosslinking network; at this time, the liquid crystal elastomer foam has a thermoreversible deformation characteristic, which is manifested as expansion at a temperature rise and shrinkage at a temperature drop, and the process cycle is reversible; and 6) preparation of a liquid crystal elastomer / heat-conducting BN composite foam.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation technology of a liquid crystal elastomer foam doped with boron nitride, which can be used in the fields of intelligent thermal management such as weapon equipment, precision electronics, space flexible robots and automatic temperature changing space and belongs to the field of high polymer functional composite materials. BACKGROUND

[0002] The intelligent heat conduction composite material with temperature sensing breaks through the fixed mode of traditional thermal control materials, and focuses on developing intelligent high-efficiency heat conduction function integrated components with accurate temperature sensing and automatic temperature adjusting functions, such as weapon equipment, precision electronics, space flexible robots, automatic temperature changing space and the like, so that a thermal control system suitable for extremely complex environments is finally constructed.

[0003] The intelligent regulation and control of the heat conduction performance of the heat conduction material under complex space environments is a core problem affecting the intelligent regulation and control of the heat conduction system, so that the thermal control system of weapon equipment and precision electronics needs to utilize resistance / capacitance type sensing or the difference between thermal expansion and cold contraction to obtain the key structure of accurate temperature sensing and stability under different environments, utilize the structural response of the material under complex environments to realize the control of the heat conduction performance of the material, and finally improve the autonomous intelligent regulation and control function of the heat conduction material under complex environments. The heat conduction composite material technology with accurate temperature sensing and intelligent regulation is proposed, the traditional preparation technology based on the heat conduction material is overturned, and the thermal control demand of the environment temperature sensing and intelligent heat conduction under complex environments is met in principle.

[0004] The core of the heat conduction composite material with accurate temperature sensing and intelligent regulation is a composite functional structure composed of a polymer matrix and high-heat-conducting fillers. From the molecular perspective, a polymer with resilience and interfacial adhesion is respectively prepared, the morphological change of the polymer under temperature is realized, then the polymer is respectively filled into high-heat-conducting fillers with different morphological structures, the morphological change and heat conduction performance of the polymer under different environmental temperatures are characterized, the intelligent regulation and control of the heat conduction performance of the heat conduction composite material are realized. Finally, the assembly of the material is selectively realized according to the equipment demand, and the demand of the core structure of the composite material for the intelligent thermal control technology under extreme environments is met in technology. SUMMARY

[0005] The application aims to provide a method for preparing a liquid crystal elastomer foam. The material prepared by the application has the characteristics of resilience and high heat conduction, and is used to meet the thermal control demand of the environment temperature sensing and intelligent heat conduction under complex environments. The technical scheme of the application is as follows:

[0006] A preparation method of a liquid crystal elastomer foam doped with boron nitride, comprising the following steps:

[0007] 1) Preparation of NaCl salt template: Screen the NaCl particles, load into the mold and compact, wet the NaCl particles in the temperature control box, take out and dry, get the NaCl salt template fused into a block;

[0008] 2) Configuration of liquid crystal elastomer monomer solution: Take 1,4-bis-[4-(3-acryloyloxypropoxy) benzoyloxy]-2-methyl benzene RM257 as the liquid crystal unit, 2,2'-(1,2-ethylenedioxy) bisethanethiol EDDET containing bimer capto group as the spacer, and pentaerythritol tetra(3-mercapto propionate) PETMP containing tetra-mercapto group as the crosslinking agent, and add the substances in the sufficient amount of toluene solution in the amount ratio of RM257:EDDET:PETMP=80-120:1.5-2.5:1 to prepare the liquid crystal elastomer monomer solution;

[0009] 3) Formation of liquid crystal elastomer network: Take appropriate amount of 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone HHMP as a photoinitiator, and di-n-propylamine as a catalyst, and stir at room temperature to form the liquid crystal elastomer network;

[0010] 4) Preparation of pre-crosslinked liquid crystal elastomer foam: The liquid crystal elastomer solution is pressed into the gap of the NaCl salt template to form a three-dimensional skeleton by vacuum-assisted pouring; the solvent toluene is removed, and then the pre-crosslinked liquid crystal elastomer foam is obtained by immersing in water to remove the internal NaCl salt template and repeatedly changing water until it floats on the water surface;

[0011] 5) Deformation programming of liquid crystal elastomer foam: The pre-crosslinked liquid crystal elastomer foam is placed in the mold for constant compression, and then secondary crosslinking is performed using ultraviolet light under constant compression to form a secondary crosslinking network; at this time, the liquid crystal elastomer foam has the characteristics of thermally reversible deformation, which is manifested as expansion at elevated temperature and contraction at reduced temperature, and the process cycle is reversible;

[0012] 6) Preparation of liquid crystal elastomer / thermally conductive BN composite foam: The appropriate amount of thermally conductive filler boron nitride (BN) powder is pressed into the pores of the liquid crystal elastomer foam, and annealing treatment is performed to obtain the liquid crystal elastomer / thermally conductive BN composite foam.

[0013] The thermally conductive composite material prepared by the template method according to the material thermal expansion and contraction process can accurately perceive and intelligently adjust the environmental temperature, which is different from the traditional preparation technology based on thermally conductive materials. The prepared material has the characteristics of intelligent perception and viscosity, resilience, and high thermal conductivity, and is expected to be used in the fields of intelligent thermal management of human body, artificial intelligence, electronic information, etc. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a schematic diagram of the material preparation process.

[0015] Figure 2 Interface phonon transport analog map. DETAILED DESCRIPTION

[0016] The preferred embodiments of the present application are given to further illustrate the present application and are not meant to limit the scope of the present application.

[0017] 1) Preparation of NaCl template: Sieve NaCl particles, select particles with particle size between 0.45-0.60 mm, load into the mold and compact, then wet the NaCl particles in the temperature control box, then take out and dry in the air oven for 1 h to obtain a sintered NaCl salt template.

[0018] 2) Preparation of liquid crystal elastomer foam: Prepare a liquid crystal elastomer monomer solution, with 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) as the liquid crystal unit, 2,2'-(1,2-ethylenedioxy)bisethanethiol (EDDET) containing bimer capto group as the spacer, and pentaerythritol tetra(3-mercapto propionate) (PETMP) containing tetra-mercapto group as the crosslinking agent, with the mass ratio of RM257:EDDET:PETMP=100:2:1 in sufficient amount of toluene solution, and with appropriate amount of 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (HHMP) as the photoinitiator and di-n-propylamine as the catalyst, stirring at room temperature for 10 h to prepare the liquid crystal elastomer network. The liquid crystal elastomer solution with the formed liquid crystal elastomer network is pressed into the gap of the NaCl salt template to form a three-dimensional skeleton by vacuum-assisted infusion. Dry the solvent toluene in an oven at 100°C, then immerse the sample in distilled water to remove the internal NaCl salt template, and repeat the water change until the sample floats on the water surface to obtain the liquid crystal elastomer foam.

[0019] 3) Deformation programming of liquid crystal elastomer foam: The first crosslinking network is formed in the previous step, and there are still excess acrylate groups in the system. The pre-crosslinked liquid crystal elastomer foam is placed in a quartz glass mold for constant compression to 30% of the original height, and secondary crosslinking is carried out under constant compression using ultraviolet light. The wavelength of the ultraviolet light is 365 nm, the intensity is 500 mw / cm 2 , and the time is 20 minutes. The remaining acrylate groups are further crosslinked by ultraviolet light to form a secondary crosslinking network. At this time, the foam has the property of thermoreversible deformation, showing expansion with heating and contraction with cooling, and the process is reversible.

[0020] 4) Liquid crystal elastomer / thermally conductive BN composite foam preparation: The appropriate amount of thermally conductive filler, boron nitride (BN) powder, was pressed into the liquid crystal elastomer foam pores by vacuum filling. The sample was placed in a tube furnace, heated to 500℃ at a rate of 20℃ / min, and held for 2h. Then, annealing treatment was performed at a cooling rate of 10℃ / min, and the final material was obtained.

[0021] The above has made an exemplary description of the present application, it should be explained that, without departing from the core of the present application, any simple modification, modification or other equivalent replacement which can not cost the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A method for preparing a liquid crystal elastomer foam doped with boron nitride, comprising the following steps: 1) Preparation of NaCl salt template: sieving NaCl particles, loading into a mold and compacting, wetting the NaCl particles in a temperature-controlled box, removing and drying to obtain a NaCl salt template fused into a block; 2) Preparation of liquid crystal elastomer monomer solution: using 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene RM257 as a liquid crystal unit, 2,2'-(1,2-ethylenedioxy)bisethane thiol EDDET containing bimer capto group as a spacer, and tetra(3-mercapto propionic acid) pentaerythritol ester PETMP containing tetra-mercapto group as a crosslinking agent, adding the liquid crystal elastomer monomer solution in sufficient amount of toluene solution with a molar ratio of RM257:EDDET:PETMP=80-120:1.5-2.5:1, to obtain the liquid crystal elastomer monomer solution; 3) Formation of liquid crystal elastomer network: using an appropriate amount of 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone HHMP as a photoinitiator and di-n-propylamine as a catalyst, stirring at room temperature to form a liquid crystal elastomer network; 4) Preparation of pre-crosslinked liquid crystal elastomer foam: pressing the liquid crystal elastomer solution into the gap of the NaCl salt template to form a three-dimensional skeleton by vacuum-assisted infusion; removing the solvent toluene, then soaking in water to remove the internal NaCl salt template, and repeatedly changing the water until it floats on the water surface, thereby obtaining a pre-crosslinked liquid crystal elastomer foam; 5) Deformation programming of liquid crystal elastomer foam: placing the pre-crosslinked liquid crystal elastomer foam into a mold for constant compression, and using ultraviolet light for secondary crosslinking under constant compression to form a secondary crosslinking network; at this time, the liquid crystal elastomer foam has a thermally reversible deformation characteristic, showing expansion with heating and contraction with cooling, and the process is reversible; 6) Preparation of liquid crystal elastomer / thermal conductive BN composite foam: pressing an appropriate amount of thermal conductive filler boron nitride (BN) powder into the pores of the liquid crystal elastomer foam, and annealing to obtain a liquid crystal elastomer / thermal conductive BN composite foam.

2. The production method according to claim 1, wherein The particle size of the NaCl particles in step 1) is between 0.45 and 0.60 mm.

3. The production method according to claim 1, wherein Step 5) The wavelength of the UV light was 365 nm, the intensity was 500 mw / cm2and the time was 20 minutes. 2 , the intensity was 500 mw / cm2and the time was 20 minutes.

4. The production method according to claim 1, wherein In step 6), an appropriate amount of thermal conductive filler boron nitride (BN) powder is pressed into the pores of the liquid crystal elastomer foam by vacuum filling, placed in a tube furnace, heated to 500°C at a rate of 20°C / min, held for 2h, and then annealed at a rate of 10°C / min to obtain a liquid crystal elastomer / thermal conductive BN composite foam.

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