An electrothermal liquid crystal elastomer artificial muscle and a preparation method thereof

Abstract

The present application relates to a kind of electric heating type liquid crystal elastomer artificial muscle and its preparation method, belong to intelligent polymer material technical field, solve the technical problem that weak deformation capacity of liquid crystal elastomer artificial muscle filler in prior art is too much to be hard and brittle easily.The electric heating type liquid crystal elastomer artificial muscle of the present application includes two layers of liquid crystal elastomer film and electric heating element;Electric heating element is set between two layers of liquid crystal elastomer film;The raw material of liquid crystal elastomer film includes liquid crystal base element, chain extender, crosslinking agent and catalyst;Wherein, liquid crystal base element is 1,4- Bis-[4-(3-acryloyloxy propoxy) benzoyloxy]-2-methyl benzene.The joule heat generated by electric heating element can activate liquid crystal elastomer, and will not limit the deformation of liquid crystal elastomer, so as to show the characteristics such as strong deformation ability, controllable heating mode and time, programmable drive;Also have self-sensing function, can be monitored and regulated shape change in real time according to the size of resistance.

Description

Technical Field

[0001] This invention belongs to the field of intelligent polymer materials technology. Specifically, this invention relates to an electrothermal liquid crystal elastomer artificial muscle and its preparation method. Background Technology

[0002] Artificial muscles are materials or devices that change shape upon exposure to external physical or chemical stimuli, showing broad application prospects in soft robotics, self-sensing systems, and biomedical devices. Currently, smart soft materials used to fabricate artificial muscles include shape memory polymers, hydrogels, dielectric elastomers, and liquid crystal elastomers. Among these, liquid crystal elastomers, composed of liquid crystal units and a polymer network, combine the anisotropy of liquid crystal units with the entropic elasticity of the polymer network. Compared to traditional smart soft materials, liquid crystal elastomers exhibit strong reversible deformation capabilities, high power density, excellent mechanical properties, and anisotropic contraction, demonstrating enormous potential in the field of artificial muscles.

[0003] Liquid crystal elastomers (LCEs) are typically driven to deform through photochemical effects, environmental heating, photothermal effects, and electrothermal effects. Electricity, as one of the most commonly used energy sources in human society, offers advantages over heat and light stimuli, including convenience, cleanliness, low cost, and high adjustability, making it the preferred driving energy source for modern equipment. Integrating electrothermal elements into LCEs and designing and controlling the heating mode and sequence greatly facilitates the driving control of LCEs. Currently, various heating elements, including conductive nanoparticles such as graphite, carbon black, and carbon nanotubes, are used as fillers dispersed in the LCE precursor solution. These nanoparticles possess excellent electrical and thermal conductivity, thus enabling electrothermal actuation of the LCE. Taylor H. Ware et al. added carbon nanotubes to LCEs, allowing for the triggering of LCE deformation using electrical stimulation. Furthermore, Luo Dan's research group at Southern University of Science and Technology prepared LCE actuators doped with graphite and carbon black. Applying a 150V DC voltage caused the LCE to heat up under Joule heating, exhibiting a 40% reversible actuated strain. However, when the content of conductive nanoparticles is high, the liquid crystal elastomer will become hard and brittle, limiting the material's deformation ability. Summary of the Invention

[0004] In view of the above problems, the present invention provides an electrothermal liquid crystal elastomer artificial muscle and its preparation method, which solves the technical problems of existing liquid crystal elastomer artificial muscles being prone to hardening and brittleness due to excessive filler and having weak deformation ability.

[0005] This invention provides an electrothermal liquid crystal elastomer artificial muscle, comprising two layers of liquid crystal elastomer film and an electrothermal element; the electrothermal element is disposed between the two layers of liquid crystal elastomer film;

[0006] The raw materials for liquid crystal elastomer films include liquid crystal building blocks, chain extenders, crosslinking agents, and catalysts;

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

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

[0009] Optionally, the crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) ester.

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

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

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

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

[0014] Another aspect of the present invention 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 as follows:

[0015] Step 1: Prepare a liquid crystal elastomer film;

[0016] Step 2: Place an electrothermal element on the surface of the first layer of liquid crystal elastomer film;

[0017] Step 3: Prepare a second liquid crystal elastomer film on the electrothermal element;

[0018] Step 4: Set up a multilayer liquid crystal elastomer film and a multilayer electrothermal element, with the liquid crystal elastomer film and electrothermal element stacked alternately.

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

[0020] (1) The electrothermal element contained in the electrothermal liquid crystal elastomer artificial muscle of the present invention generates Joule heat that can activate the liquid crystal elastomer and does not restrict the deformation of the liquid crystal elastomer, thereby exhibiting characteristics such as 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, which can monitor and control shape changes in real time according to the resistance. Attached Figure Description

[0022] Figure 1Photograph of the electrothermal liquid crystal elastomer artificial muscle prepared in Example 1 of this invention;

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

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

[0026] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0027] A specific embodiment of the present invention, such as Figures 1-4 An electrothermal liquid crystal elastomer artificial muscle is disclosed, comprising two liquid crystal elastomer films and an electrothermal element; the electrothermal element is disposed between the two liquid crystal elastomer films.

[0028] Furthermore, the raw materials for liquid crystal elastomer films include liquid crystal building blocks, chain extenders, crosslinking agents, and catalysts.

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

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

[0031]

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

[0033]

[0034] Furthermore, the structural formula of pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP) is as follows:

[0035]

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

[0037]

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

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

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

[0041] Furthermore, the 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, the specific steps of which are as follows:

[0043] Step 1: Prepare a liquid crystal elastomer film;

[0044] Specifically, liquid crystal elastomer films are prepared by using compression molding or direct ink writing 3D printing.

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

[0046] Liquid crystal building blocks, chain extenders, crosslinking agents, and catalysts are dissolved in an organic solvent, mixed uniformly at room temperature, and allowed to react fully to obtain liquid crystal elastomer ink. Liquid crystal elastomer films are then prepared using direct ink writing 3D printing or compression molding.

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

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

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

[0050] The catalyst comprises 1% to 3% of the molar amount of the acrylate liquid crystal monomer, preferably 2%.

[0051] Step 2: Place an electrothermal element on the surface of the first layer of liquid crystal elastomer film;

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

[0053] Step 3: Prepare a second liquid crystal elastomer film on the electrothermal element;

[0054] Step 4: Set up a multilayer liquid crystal elastomer film and a multilayer electrothermal element, with the liquid crystal elastomer film and electrothermal element stacked alternately.

[0055] To illustrate the effectiveness of the method proposed in this invention, the following detailed description of the above technical solution is provided through a specific embodiment. The specific implementation steps are as follows:

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

[0057] (1) Mix 10.30g of liquid crystal unit RM257, 2.74g of chain extender EDDET and 0.13g of catalyst DPA evenly and react fully to obtain liquid crystal elastomer ink, and use direct ink writing 3D printing method to prepare the first layer of single-domain liquid crystal elastomer film at a printing temperature of 40℃.

[0058] (2) Sodium alginate-modified liquid metal (gallium indium alloy) was 3D printed on the surface of the first layer of liquid crystal elastomer film, and copper foil was placed at both ends for connecting to an external power source.

[0059] (3) Using the liquid crystal elastomer ink prepared in step (1), a multi-domain liquid crystal elastomer film was 3D printed on the liquid metal surface for encapsulation at a printing temperature of 140℃.

[0060] (4) Finally, an electrothermal liquid crystal elastomer artificial muscle with a sandwich structure is obtained.

[0061] Performance testing

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

[0063] Different constant DC voltages were applied to an 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, the temperature of the liquid crystal elastomer surface increases with increasing applied voltage, reaching a maximum temperature of 131.2℃ when the voltage is 1.5V.

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

[0065] The mismatch between the contraction rates of the single-domain and multi-domain liquid crystal elastomers causes the artificial muscle to bend towards the contracting single-domain liquid crystal elastomer side when heated. The bending angle increases with increasing input voltage; at 1.5V, the maximum bending angle reaches 270.1°, as shown in the figure. Figure 3 As shown.

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

[0067] The liquid crystal elastomer artificial muscle was subjected to a 240s on-state and 240s off-state cycle test, with 30 cycles. The results are as follows. Figure 4 As shown, the bending angle of the artificial muscle remained essentially unchanged during 30 cycles of power on and off, demonstrating that the electrically controlled liquid crystal elastomer artificial muscle prepared in this invention has good stability.

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

[0069] Taylor H. Ware et al. incorporated carbon nanotubes into liquid crystal elastomers, enabling deformation to be triggered by electrical stimulation (Advanced Functional Materials, 2019, 29, 1905063). However, due to the addition of conductive nanoparticles, the contraction rate of their electrically controlled liquid crystal elastomer artificial muscle was significantly reduced to only 3%. In contrast, the electrically controlled liquid crystal elastomer artificial muscle of this application exhibits strong deformability, with a maximum bending angle of 270.1°, greatly improving its actuation performance.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrothermal liquid crystal elastomer artificial muscle, characterized in that, The invention includes two layers of liquid crystal elastomer film and an electrothermal element, which are 3D printed. The liquid crystal elastomer film is prepared by direct ink writing 3D printing. The electrothermal element is placed between the two layers of liquid crystal elastomer film by 3D printing. The Joule heat generated by the electrothermal element is used to activate the liquid crystal elastomer. The raw materials for liquid crystal elastomer films consist of liquid crystal modules, chain extenders, and catalysts; The liquid crystal unit is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene; the chain extender is 3,6-dioxa-1,8-octanedithiol; and the catalyst is di-n-propylamine. The molar ratio of liquid crystal building blocks to chain extender is 7:5; The specific steps for preparing the electrothermal liquid crystal elastomer artificial muscle are as follows: Step 1: Prepare a liquid crystal elastomer film; Step 2: 3D print an electrothermal element on the surface of the first layer of liquid crystal elastomer film; Step 3: Prepare a second liquid crystal elastomer film on the electrothermal element; Step 4: Set up a multilayer liquid crystal elastomer film and a multilayer electrothermal element, with the liquid crystal elastomer film and electrothermal element stacked alternately.

2. The electrothermal liquid crystal elastomer artificial muscle according to claim 1, characterized in that, The mass of the catalyst accounts for 1% to 3% of the total mass of the liquid crystal unit and the chain extender.

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