Electric heating type liquid crystal elastomer artificial muscle and preparation method thereof

Abstract

The invention relates to an electric heating type liquid crystal elastomer artificial muscle and a preparation method thereof, belongs to the technical field of intelligent high polymer materials, and solves the technical problems that the liquid crystal elastomer artificial muscle in the prior art is easy to harden and embrittle due to excessive filler and is weak in deformability. The electric heating type liquid crystal elastomer artificial muscle comprises two layers of liquid crystal elastomer films and an electric heating element, the electric heating element is arranged between the two layers of liquid crystal elastomer films; the raw materials of the liquid crystal elastomer film comprise a liquid crystal unit, a chain extender, a cross-linking agent and a catalyst. Wherein the liquid crystal unit is 1, 4-bis-[4-(3-acryloyloxy propoxy) benzoyloxy]-2-methyl benzene. Joule heat generated by the electric heating element can activate the liquid crystal elastomer, deformation of the liquid crystal elastomer is not limited, and therefore the liquid crystal elastomer has the advantages of being high in deformability, controllable in heating mode and time, programmable in driving and the like; and a self-sensing function is also realized, and the shape change can be monitored and regulated in real time according to the resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent polymer materials. Specifically, the present invention relates to an electrothermal liquid crystal elastomer artificial muscle and a preparation method thereof. Background Art

[0002] Artificial muscles refer to materials or devices that change shape after being stimulated by external physical or chemical stimuli. They show broad application prospects in soft robots, self-sensing systems, and biomedical devices. Currently, the intelligent soft materials used to prepare artificial muscles include shape memory polymers, hydrogels, dielectric elastomers, liquid crystal elastomers, etc. Among them, liquid crystal elastomers are composed of liquid crystal units and polymer networks, and have both the anisotropy of liquid crystal units and the entropic elasticity of polymer networks. Compared with traditional intelligent soft materials, liquid crystal elastomers have the characteristics of strong reversible deformation ability, high power density, excellent mechanical properties, anisotropic contraction, etc., showing great potential in the field of artificial muscles.

[0003] Liquid crystal elastomers are generally driven to deform by photochemical effects, environmental heating, photothermal effects, and electrothermal effects. Electricity, as one of the most commonly used energy sources in human society, has the advantages of convenience, cleanliness, low cost, and high adjustability compared to stimuli such as heat and light. It is the preferred driving energy source for modern devices. Integrating electric heating elements into liquid crystal elastomers, designing and regulating heating modes and heating sequences, provides great convenience for the driving control of liquid crystal elastomers. At present, there are a variety of heating elements, including conductive nanoparticles such as graphite, carbon black, and carbon nanotubes, which are used as fillers and dispersed in liquid crystal elastomer precursor solutions. These nanoparticles have excellent electrical and thermal conductivity, thereby realizing the electrothermal drive of liquid crystal elastomers. Taylor H.Ware et al. added carbon nanotubes to liquid crystal elastomers, and electrical stimulation can be used to trigger the deformation of liquid crystal elastomers. In addition, Luo Dan's research group at the Southern University of Science and Technology prepared a liquid crystal elastomer actuator doped with graphite and carbon black. When a DC voltage of 150V is applied, the temperature of the liquid crystal elastomer increases under the action of Joule heat and shows a reversible actuation strain of 40%. However, when the content of conductive nanoparticles is high, the liquid crystal elastomer becomes stiff and brittle, limiting the material's ability to deform. Summary of the invention

[0004] In view of the above problems, the present invention provides an electrothermal liquid crystal elastomer artificial muscle and a preparation method thereof, which solves the technical problems in the prior art that the liquid crystal elastomer artificial muscle has too much filler and tends to become hard and brittle and has weak deformation ability.

[0005] The present invention provides an electrothermal liquid crystal elastomer artificial muscle, comprising two layers of liquid crystal elastomer films and an electrothermal element; the electrothermal element is arranged between the two layers of liquid crystal elastomer films;

[0006] The raw materials of the liquid crystal elastomer film include liquid crystal primitives, chain extenders, cross-linking agents and catalysts;

[0007] The liquid crystal element is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene.

[0008] Optionally, the chain extender is 3,6-dioxa-1,8-octanedithiol.

[0009] Optionally, the cross-linking agent is pentaerythritol tetrakis(3-mercaptopropionate).

[0010] Optionally, the catalyst is di-n-propylamine.

[0011] Optionally, the molar ratio of the liquid crystal unit to the chain extender is 7-2:6-1.

[0012] Optionally, the molar ratio of the crosslinking agent to the chain extender is 0-1:1-10.

[0013] Optionally, the mass of the catalyst accounts for 1% to 3% of the total mass of the liquid crystal unit, the chain extender and the cross-linking agent.

[0014] Another aspect of the present invention further discloses a method for preparing an electrothermal liquid crystal elastomer artificial muscle, which is used to prepare the aforementioned electrothermal liquid crystal elastomer artificial muscle, and the specific steps are:

[0015] Step 1, preparing a liquid crystal elastomer film;

[0016] Step 2, placing an electric heating element on the surface of the first layer of liquid crystal elastomer film;

[0017] Step 3, preparing a second layer of liquid crystal elastomer film on the electric heating element;

[0018] Step 4: multiple layers of liquid crystal elastomer films and multiple layers of electric heating elements are provided, and the liquid crystal elastomer films and the electric heating elements are alternately stacked.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] (1) The electric heating element contained in the electrothermal liquid crystal elastomer artificial muscle of the present invention can generate Joule heat that can activate the liquid crystal elastomer and will not restrict the deformation of the liquid crystal elastomer, thereby showing the characteristics of strong deformation ability, controllable heating mode and time, and programmable drive.

[0021] (2) The electrothermal liquid crystal elastomer artificial muscle of the present invention also has a self-sensing function, and can monitor and control shape changes in real time according to the size of the resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1This is a photo of the electrothermal liquid crystal elastomer artificial muscle prepared in Example 1 of the present invention;

[0023] Figure 2 This is a graph showing the relationship between input voltage and temperature of the electrothermal liquid crystal elastomer artificial muscle prepared in Example 1 of the present invention;

[0024] Figure 3 This is a graph showing the relationship between input voltage and bending angle of the electrothermal liquid crystal elastomer artificial muscle prepared in Example 1 of the present invention;

[0025] Figure 4 This is a reversible bending cycle diagram of the electrothermal liquid crystal elastomer artificial muscle prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In addition, the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0027] A specific embodiment of the present invention, as Figure 1-Figure 4 , discloses an electrothermal liquid crystal elastomer artificial muscle, comprising two layers of liquid crystal elastomer films and an electrothermal element; the electrothermal element is arranged between the two layers of liquid crystal elastomer films.

[0028] Furthermore, the raw materials of the liquid crystal elastomer film include liquid crystal primitives, chain extenders, cross-linking agents and catalysts.

[0029] Furthermore, the liquid crystal element is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene (RM257); the chain extender is 3,6-dioxa-1,8-octanedithiol (EDDET); the crosslinker is pentaerythritol tetrakis(3-mercaptopropionic acid)ester (PETMP); and the catalyst is di-n-propylamine (DPA).

[0030] Further, the structural formula of 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene (RM257) is:

[0031]

[0032] Further, the structural formula of 3,6-dioxa-1,8-octanedithiol (EDDET) is:

[0033]

[0034] Further, the structural formula of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) is:

[0035]

[0036] Further, the structural formula of di-n-propylamine (DPA) is:

[0037]

[0038] The molar ratio of the liquid crystal unit to the chain extender is 7-2:6-1, preferably 7:5.

[0039] The molar ratio of the crosslinking agent to the chain extender is 0-1:1-10, preferably 1:5.

[0040] The mass of the catalyst accounts for 1% to 3% of the total mass of the liquid crystal unit, the chain extender and the cross-linking agent, and preferably 2%.

[0041] Furthermore, the electric heating element is a serpentine wire or liquid metal.

[0042] Another aspect of the present invention discloses a method for preparing an electrothermal liquid crystal elastomer artificial muscle, which comprises the following specific steps:

[0043] Step 1, preparing a liquid crystal elastomer film;

[0044] Specifically, the liquid crystal elastomer is used to prepare a liquid crystal elastomer film by compression molding or direct ink writing 3D printing.

[0045] Furthermore, the preparation method of the liquid crystal elastomer is:

[0046] The liquid crystal unit, chain extender, cross-linking agent and catalyst are dissolved in an organic solvent, mixed evenly and reacted fully at room temperature to obtain a liquid crystal elastomer ink, and a liquid crystal elastomer film is prepared by direct ink writing 3D printing or compression molding.

[0047] Furthermore, the liquid crystal element is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene (RM257); the chain extender is 3,6-dioxa-1,8-octanedithiol (EDDET); the crosslinker is pentaerythritol tetrakis(3-mercaptopropionic acid)ester (PETMP); and the catalyst is di-n-propylamine (DPA).

[0048] The molar ratio of the liquid crystal unit to the chain extender is 7-2:6-1, preferably 7:5.

[0049] The molar ratio of the crosslinking agent to the chain extender is 0-1:1-10, preferably 1:5.

[0050] The catalyst is used in an amount of 1% to 3% of the molar amount of the acrylic ester liquid crystal monomer, preferably 2%.

[0051] Step 2, placing an electric heating element on the surface of the first layer of liquid crystal elastomer film;

[0052] The electric heating element is a serpentine wire (copper or stainless steel) or liquid metal (gallium-indium alloy).

[0053] Step 3, preparing a second layer of liquid crystal elastomer film on the electric heating element;

[0054] Step 4: multiple layers of liquid crystal elastomer films and multiple layers of electric heating elements are provided, and the liquid crystal elastomer films and the electric heating elements are alternately stacked.

[0055] In order to illustrate the effectiveness of the method proposed in the present invention, the above technical solution of the present invention is described in detail below through a specific embodiment, and the specific implementation steps are as follows:

[0056] A method for preparing an electrothermal liquid crystal elastomer artificial muscle comprises the following steps:

[0057] (1) 10.30 g of liquid crystal element RM257, 2.74 g of chain extender EDDET and 0.13 g of catalyst DPA were mixed evenly and reacted fully to obtain liquid crystal elastomer ink, and a first layer of single-domain liquid crystal elastomer film was prepared by direct ink writing 3D printing method at a printing temperature of 40°C;

[0058] (2) 3D printing a liquid metal (gallium-indium alloy) modified with sodium alginate on the surface of the first layer of liquid crystal elastomer film, and placing copper foil at both ends for connecting to an external power supply;

[0059] (3) using the liquid crystal elastomer ink prepared in step (1), 3D printing a multi-domain liquid crystal elastomer film on the surface of the liquid metal for encapsulation, with the printing temperature being 140° C.;

[0060] (4) Finally, a sandwich-structured electrothermal liquid crystal elastomer artificial muscle is obtained.

[0061] Performance Testing

[0062] (1) Effect of input voltage on the temperature of liquid crystal elastomer artificial muscle

[0063] Different constant DC voltages were input into the electrothermal liquid crystal elastomer artificial muscle, and the highest temperature of the liquid crystal elastomer was recorded using a thermometer. The results are as follows: Figure 2 As shown in Figure 2, the temperature of the surface of the liquid crystal elastomer increases with the increase of the applied voltage, and when the voltage is 1.5V, the maximum temperature can reach 131.2℃.

[0064] (2) Effect of input voltage on the bending angle of liquid crystal elastomer artificial muscle

[0065] Due to the mismatch between the shrinkage rates of the two layers of single-domain and multi-domain liquid crystal elastomers, the artificial muscle bends toward the contracted single-domain liquid crystal elastomer when heated. The bending angle increases with the increase of input voltage. When the voltage is 1.5V, the maximum bending angle can reach 270.1°. The results are shown in Figure 2. Figure 3 shown.

[0066] (3) Cyclic performance test of liquid crystal elastomer artificial muscle

[0067] The liquid crystal elastomer artificial muscle was tested by a 240s power-on and 240s power-off cycle for 30 times. The results are as follows Figure 4 The bending angle of the artificial muscle remains basically unchanged within 30 power-on and power-off cycles, which proves that the electrically controlled liquid crystal elastomer artificial muscle prepared by the present invention has good stability.

[0068] (4) Comparative test between the prior art and the present application

[0069] Taylor H.Ware et al. added carbon nanotubes to liquid crystal elastomers, and electrical stimulation can be used to trigger the deformation of liquid crystal elastomers (Advanced Functional Materials, 2019, 29, 1905063). However, due to the addition of conductive nanoparticles, the shrinkage rate of its electrically controlled liquid crystal elastomer artificial muscle is greatly reduced to only 3%. The electrically controlled liquid crystal elastomer artificial muscle of this application has strong deformation ability, and the maximum bending angle can reach 270.1°, which greatly improves the actuation performance.

[0070] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. An electrothermal liquid crystal elastomer artificial muscle, characterized in that: It includes two layers of liquid crystal elastic body films and an electric heating element; the electric heating element is arranged between the two layers of liquid crystal elastic body films; The raw materials of the liquid crystal elastomer film include liquid crystal primitives, chain extenders, cross-linking agents and catalysts; The liquid crystal element is 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene.

2. The electrothermal liquid crystal elastomer artificial muscle according to claim 1, characterized in that: The chain extender is 3,6-dioxa-1,8-octanedithiol.

3. The electrothermal liquid crystal elastomer artificial muscle according to claim 1, characterized in that: The crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionate).

4. The electrothermal liquid crystal elastomer artificial muscle according to claim 1, characterized in that: The catalyst is di-n-propylamine.

5. The electrothermal liquid crystal elastomer artificial muscle according to claim 1, characterized in that: The molar ratio of the liquid crystal unit to the chain extender is 7-2:6-1.

6. The electrothermal liquid crystal elastomer artificial muscle according to claim 5, characterized in that: The molar ratio of the crosslinking agent to the chain extender is 0-1:1-10.

7. The electrothermal liquid crystal elastomer artificial muscle according to claim 6, characterized in that: The mass of the catalyst accounts for 1% to 3% of the total mass of the liquid crystal base element, the chain extender and the cross-linking agent.

8. A method for preparing an electrothermal liquid crystal elastomer artificial muscle, for preparing the electrothermal liquid crystal elastomer artificial muscle according to any one of claims 1 to 7, comprising the following specific steps: Step 1, preparing a liquid crystal elastomer film; Step 2, placing an electric heating element on the surface of the first layer of liquid crystal elastomer film; Step 3, preparing a second layer of liquid crystal elastomer film on the electric heating element; Step 4: multiple layers of liquid crystal elastomer films and multiple layers of electric heating elements are provided, and the liquid crystal elastomer films and the electric heating elements are alternately stacked.

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