CN113698518B - Liquid crystal elastomer material based on liquid metal nano droplets - Google Patents

Abstract

The invention discloses a liquid crystal elastomer material based on liquid metal nano-droplets and a preparation method and application thereof. Liquid metal nano-droplets are introduced into the liquid crystal elastomer matrix material, and there is a dynamic interaction between the sulfur element in the molecular chain and the liquid metal, which can realize the uniform distribution of liquid metal nano-droplets in the liquid crystal elastomer. Secondary crosslinking, the liquid metal nanodroplet-based liquid crystal elastomer material (LM‑LCE) was finally prepared. The mechanical properties, especially the fatigue resistance, of the composite liquid crystal elastomer material are greatly improved, which can effectively promote the liquid crystal elastomer-based soft actuator material and its long-term industrial applications.

Description

A liquid crystal elastomer material based on liquid metal nanodroplets

technical field

The invention relates to the field of liquid crystal elastomers, in particular to a liquid crystal elastomer material with ultra-high fatigue resistance, which is formed by compounding liquid metal nano-droplets and a liquid crystal elastomer base material.

Background technique

Liquid crystal elastomers (LCEs), as unconventional types of polymeric materials that combine the anisotropy of mesogens and the entropic elasticity of elastomers, can be made in response to external stimuli such as heat, light, humidity, electricity, and magnetic fields Reversible deformation. This excellent two-way shape memory function makes LCE materials have potential applications in soft actuators, sensors, micromechanical systems, soft robotics, etc. However, the unsatisfactory mechanical properties of conventional LCE materials, especially the moderate driving stress and poor fatigue resistance, have become the fundamental obstacles hindering the practical industrial application of LCE materials. There is an urgent desire to develop new LCE materials with simultaneous large driving stroke, high driving stress and excellent fatigue resistance, but this remains a formidable challenge.

To improve the mechanical properties of LCE materials, most of the previous research efforts have focused on introducing new molecular structures, crystallization treatments, interpenetrating networks and adding nanofillers to enhance the driving stress, elastic modulus and working ability; however, the Fatigue resistance was selectively ignored. The fatigue resistance of LCE materials is a key factor for their industrial application, and little research has been done on the long-term durability of LCEs in the past 40 years. In fact, this disadvantage arises from an inherent defect of the LCE structural network: in order to obtain a high driving strain, the LCE material is always lightly cross-linked. This low crosslink density means that some polymer chains may not be chemically crosslinked, so during actuation, the uncrosslinked polymer chains will suffer irreversible slippage and the physical association of the associated polymer chains will suffer If damaged, some parts of the molecular network will be damaged and the internal structure of the polymer will be permanently damaged, resulting in poor fatigue resistance.

To improve the fatigue resistance of LCE materials, the traditional research method is to incorporate many reinforcing materials such as gold nanoparticles, carbon nanotubes and carbon fibers into the LCE matrix to introduce additional physical associations to enhance the chain-like network of LCEs, but The desired effect was not achieved, which may be caused by phase separation due to the absence of interaction between the reinforcement material and the LCE matrix.

The document Proc.Natl.Acad.Sci.U.S.A.2019, 116, 21438 reported a method of introducing a liquid metal method into a liquid crystal elastomer, and prepared an electrically driven liquid crystal elastomer material. It uses a liquid crystal monomer of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene. The disadvantage is that there are too many liquid metals introduced, and the size of the liquid metal droplets is too large, about hundreds of microns, and the clearing point of the liquid crystal elastomer is high, exceeding 60 ℃, and the mechanical properties of the liquid crystal elastomer have not been obtained. It is very large, and the literature does not report on the fatigue resistance of liquid crystal elastomers.

The literature Soft Matter, 2020, 16, 5878 also reported a method of introducing liquid metal into a liquid crystal elastomer, thereby preparing a conductive composite liquid crystal elastomer material. It uses a liquid crystal monomer of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene. The liquid metal is dispersed in the liquid crystal elastomer with micron size, and the electrical conductivity of the composite liquid crystal elastomer is realized, but the mechanical properties of this new composite liquid crystal elastomer have not been well improved, and the fatigue resistance has not been reported. . At present, there are composite materials of liquid crystal elastomer and liquid metal, but in order to achieve the electrical conductivity of the composite material, their liquid metal is above the micron size, and there is no major improvement in the mechanical properties of the liquid crystal elastomer composite material.

SUMMARY OF THE INVENTION

Technical problem: The purpose of the present invention is to provide a liquid crystal elastomer material based on liquid metal nano-droplets, the liquid crystal elastomer material has ultra-high fatigue resistance, and solves the problem of insufficient service life of traditional liquid crystal elastomer materials during practical application. problem, and provide a preparation method of this material.

Technical solution: The liquid crystal elastomer material based on liquid metal nano-droplets of the present invention is made of liquid crystal monomers. The directions are arranged in an orderly manner to form a molecular main chain, and the liquid metal is broken into nano-scale droplets and then has a dynamic interaction with the sulfur element in the molecular main chain to be uniformly and stably dispersed in the liquid crystal elastomer matrix.

The liquid crystal monomer is 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate.

The liquid metal is a gallium indium tin alloy, and the mass ratio of gallium, indium and tin is 0.62-0.8:0.25-0.1:0-0.13.

The mass ratio of the liquid metal mass to the liquid crystal monomer is 5%-8%.

The preparation method of the liquid crystal elastomer material based on liquid metal nano-droplets of the present invention is as follows:

Step 1. The liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate, chain extension agent 2,2-oxybis (ethane-1-thiol), cross-linking agent pentaerythritol tetrakis (3-mercaptopropionate) and liquid metal for water removal treatment;

Step 2. Place all the materials in step 1 in anhydrous dichloromethane, and then place them in a brown bacterial strain bottle under the condition of flowing nitrogen, and fully stir to form a uniform solution;

Step 3. get catalyst dipropylamine and be dissolved in methylene chloride, then join in the solution in the above-mentioned brown bacterial strain bottle;

Step 4. Ultrasonic treatment with an ultrasonic breaker for 1-1.5 hours to break the liquid metal into nanometers, and to achieve uniform mixing of the above mixture;

Step 5. Pour the above mixture into a polytetrafluoroethylene tank, and then put it into an oven at 36°C-45°C for 1-1.5h;

Step 6. Cool the polytetrafluoroethylene tank in step 5 to room temperature to prepare an unoriented liquid metal nano-droplet-based liquid crystal elastomer material LM-LCE film;

Step 7. Cut the above-mentioned unoriented LM-LCE film into a long strip, stretch and keep it fixed at room temperature to obtain a stretched and oriented long strip of liquid metal nano-droplet-based liquid crystal elastomer material LM-LCE film ;

Step 8. Put the stretched and oriented elongated LM-LCE film prepared in step 7 into an oven, keep at 36°C-45°C for 8-11 hours, and then naturally cool to room temperature to obtain an oriented structure. Liquid metal nanodroplets-based liquid crystal elastomer material LM-LCE film.

in,

The liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate has the following structural formula :

Described crosslinking agent pentaerythritol tetrakis (3-mercaptopropionate), structural formula is as follows:

Described chain extender 2,2-oxygen bis (ethane-1-thiol), structural formula is as follows:

Described catalyst dipropylamine, structural formula is as follows:

The amount ratio of the above-mentioned liquid crystal monomer, chain extender and crosslinking agent in step 1 is: liquid crystal monomer Y2003: chain extender DMDE: crosslinking agent PETMP=1:20:22-1:10:12;

The mass ratio of liquid metal to liquid crystal monomer chain extender and crosslinking agent is: liquid metal: (liquid crystal monomer+chain extender+crosslinking agent)=1:20-1:12.

The chain extender 2,2-oxybis(ethane-1-thiol) in step 1 was replaced by 3,6-dithio-1,8-octanediol.

In step 4, the power of ultrasonication of the ultrasonic crusher was set to 360W.

In the step 7, the unoriented LM-LCE film is cut into a long strip and stretched at room temperature, stretched to 2-2.7 times the original length and kept fixed.

The liquid crystal elastomer based on liquid metal nano-droplets of the present invention has super fatigue resistance, solves the problems of low durability and insufficient service life of conventional liquid crystal elastomers in the actual application process, and has great applications in artificial muscles and other fields. great potential applications.

Beneficial effects: The present invention provides a liquid crystal elastomer based on liquid metal nano-droplets. Compared with the prior art, the present invention has the following beneficial effects:

① The liquid crystal elastomer based on liquid metal nano-droplets prepared by the present invention, the liquid crystal monomer used is 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyl) oxy)hexyl)oxy)benzoate. It has excellent strain properties of liquid crystal elastomers, and exhibits excellent reversible deformation under thermal stimulation or ultraviolet light stimulation, and the size ratio of its original size and isotropic phase reaches 2.22;

② The liquid crystal elastomer based on liquid metal nano-droplets prepared by the present invention has the excellent toughness of the liquid crystal elastomer. The dynamic thermodynamic test shows that the elongation at break of the liquid metal nano-droplet-based liquid crystal elastomer of the present invention reaches 1010.87% at room temperature, and the toughness reaches 18.31 MJ/m ³ , which is higher than the related performance of the traditional liquid crystal elastomer. 1 order of magnitude;

③ The liquid crystal elastomer based on liquid metal nano-droplets prepared by the present invention has a linear viscoelastic region of 72% in the dynamic thermomechanical analyzer test; under the condition that it is repeatedly stretched to 70% of the original length and released , can withstand more than 10,000 stretching cycles without significant decline in mechanical properties. It is 2 orders of magnitude higher than traditional liquid crystal elastomers and hundreds of times that of traditional liquid crystal elastomers.

④ The liquid crystal elastomer based on liquid metal nano-droplets prepared by the present invention exhibits super fatigue resistance far higher than that of ordinary liquid crystal elastomers. It can help realize the industrial application of liquid crystal elastomers, such as in the field of biomimetic materials such as artificial muscles.

In the composite material of the present invention, the liquid metal is dispersed in the liquid crystal elastomer at the nanometer level. The composite material is non-conductive, but the clearing point of the composite material is significantly reduced, and the mechanical properties are significantly improved, especially the fatigue resistance.

Description of drawings

Figure 1 is a graph showing the relationship between shrinkage stress and strain of the prepared liquid metal nanodroplet-based liquid crystal elastomer in a dynamic thermomechanical analyzer cycle test;

FIG. 2 is a graph showing the storage modulus and the relationship between elasticity and strain of the prepared liquid metal nanodroplet-based liquid crystal elastomer tested in a dynamic thermomechanical analyzer.

Detailed ways:

First, the liquid crystal monomer, chain extender, cross-linking agent, catalyst and liquid metal are ultrasonically pulverized and mixed uniformly. Under the condition of thermal polymerization, a liquid metal nanodroplet-based liquid crystal elastomer (LM-LCE) was prepared. The liquid crystal monomer is 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate (Y2003) , the chain extender is 2,2-oxybis(ethane-1-thiol) (DMDE), the crosslinking agent is pentaerythritol tetrakis (3-mercaptopropionate) (PETMP), and the liquid metal is gallium indium tin alloy (The mass ratio is 0.62:0.25:0.13).

The liquid metal nanodroplet-based liquid crystal elastomer prepared by this method has ultra-high fatigue resistance, and the liquid crystal elastomer composite can withstand an unprecedented linear viscoelastic region of 72%, 10,000 stretching cycles (maximum 70% deformation), 2,000 continuous actuation deformations and a tensile deformation with a maximum value above 1000%. In addition, this LM-doped LCE composite exhibits large reversible deformation (max: 55%), high actuation stress (max: 1.13 MPa), fully reversible thermal/light actuation function and a Under the condition of excellent self-healing ability. The mechanical properties, especially the fatigue resistance, of the composite liquid crystal elastomer material are greatly improved, which can effectively promote the liquid crystal elastomer-based soft actuator material and its long-term industrial applications.

The present invention will be further described below in conjunction with specific examples.

I Preparation of liquid-crystalline elastomers based on liquid metal nanodroplets

According to the following ratios: the mass ratio of liquid crystal monomer Y2003, chain extender DMDE and crosslinking agent PETMP is 1:20:22; the mass ratio of liquid metal to liquid crystal monomer, chain extender and crosslinking agent is 1:20 . Weigh the relevant monomers, chain extenders, cross-linking agents, catalysts and liquid metals and add them to a 10 mL brown strain bottle; add dichloromethane; use an ultrasonic breaker for sonication for 1 h to make the above mixture evenly mixed; The solution was poured into a polytetrafluoroethylene (PTFE) mold, and then placed in an oven at 40 °C for 1.5 h; then the obtained pre-crosslinked LM-LCE-5 sample was carefully taken out from the PTFE mold; After cutting, it was stretched to about 270% of its original strength and kept fixed; after being placed in an oven and kept at 40 °C for 10 h, the LM-LCE sample was obtained.

The liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate has the following structural formula :

Described crosslinking agent pentaerythritol tetrakis (3-mercaptopropionate), structural formula is as follows:

Described chain extender 2,2-oxygen bis (ethane-1-thiol), structural formula is as follows:

Described catalyst dipropylamine, structural formula is as follows:

II Stress-strain, toughness, reversible deformation, maximum actuating stress, linear viscoelastic region, UV drive, shrinkage force and self-healing tests of liquid metal nanodroplet-based liquid crystal elastomers prepared;

① Stress-strain test: Use a universal tensile tester (SANS E42.503) to perform stress-strain test at room temperature.

②Toughness determination: Integrate the stress-strain curve measured in ①, and calculate the area enclosed by the curve and the X-axis of the abscissa, which is the toughness.

③Reversible deformation test: use a dynamic thermodynamic mechanical analyzer (DMAQ850, TA company), in the isostress mode, cycle heating and cooling, and record the length (L) of the film at a certain time in the direction of the stretching orientation and the film The ratio of the shortest length (L _iso ) in the isotropic state and the number of cycles.

④Maximum actuating stress test: Using a dynamic thermodynamic mechanical analyzer (DMAQ850, TA Company), the shrinkage force test during the heating process was performed in the iso-strain mode.

⑤ Linear viscoelastic region test: Using a dynamic thermodynamic mechanical analyzer (DMAQ850, TA Company), in the oscillation mode, test the maximum linear viscoelastic region of the liquid metal nano-droplet-based liquid crystal elastomer.

⑥Ultraviolet light driving test: Use a 365nm ultraviolet light source to irradiate the LM-LCE film in a natural sagging state, and record the change of the length of the sample with the time of ultraviolet light irradiation.

⑦Self-healing test: Cut the LM-LCE film sample, then splicing it, and after placing it at 40°C for 10 hours, observe the self-healing effect with a metallographic microscope and a scanning electron microscope, and use a universal tensile tester (SANS E42.503) Perform post-repair stress-strain testing.

Embodiment 1: The specific preparation steps of liquid crystal elastomer based on liquid metal nano-droplets are as follows:

Weigh liquid crystal monomer Y2003 (592.5mg, 1.1mmol), chain extender 2,2'-oxybis(ethane-1-thiol) (138.2mg, 1.0mmol), crosslinker pentaerythritol tetrakis (3- mercaptopropionate) (24.4mg, 0.05mmol) and liquid metal (39.7mg) were added to a 10mL brown strain bottle; 6.00μL catalyst dipropylamine was dissolved in dichloromethane (1.8mL), and then added into the above-mentioned brown strain bottle; ultrasonically treat the above-mentioned mixture for 1 h with an ultrasonic crusher; pour the obtained solution into a polytetrafluoroethylene (PTFE) mold (3 cm long × 2 cm wide × 1 cm deep), It was then placed in an oven at 40 °C for 1.5 h; the resulting pre-crosslinked LM-LCE-5 sample was then carefully taken out from the PTFE mold; it was cut and stretched to about 270% of its original strength, and Keep it fixed; put it in an oven and keep it at 40 °C for 10 h to get the LM-LCE-5 sample.

Example 2: Stress-strain, toughness, reversible deformation, maximum actuating stress, linear viscoelastic region, ultraviolet light drive, shrinkage force and self-healing test of the prepared liquid metal nanodroplet-based liquid crystal elastomer;

①Stress-strain test: Using a universal tensile tester (SANS E42.503), the stress-strain test at different temperatures was carried out in the iso-strain mode, and the maximum elongation at break was measured to be 1010.87%.

②Toughness determination: Integrate the stress-strain curve measured in ①, calculate the area enclosed by the curve and the abscissa X-axis, the result is: 18.31MJ/m ³ .

③Reversible deformation test: use a dynamic thermodynamic mechanical analyzer (DMAQ850, TA company), in the isostress mode, cycle heating and cooling, and record the length (L) of the film at a certain time in the direction of the stretching orientation and the film The ratio of the shortest length (L _iso ) in the isotropic state, the maximum ratio was measured to be 2.22, and the number of fully reversible deformation cycles reached 2000.

(4) Shrinkage stress test during the heating process: Use a dynamic thermodynamic mechanical analyzer (DMA Q850, TA Company) to perform the shrinkage force test during the heating process in the iso-strain mode. The temperature was raised from 30°C to 80°C, and then cooled from 80°C to 30°C, and the maximum shrinkage stress was measured to be 1.13MPa.

⑤ Linear viscoelastic region test: Using a dynamic thermodynamic mechanical analyzer (DMAQ850, TA company), in the oscillation mode, test the maximum linear viscoelastic region of the liquid crystal elastomer based on liquid metal nano-droplets, and the set frequency is 1HZ Under the condition of , the maximum linear viscoelastic region is 72%.

⑥Ultraviolet light drive test: Use a 365nm ultraviolet light source to irradiate the LM-LCE film in a natural sagging state, and record the film in the direction of the stretching orientation at a certain moment under the irradiation of 0.4W/cm ² of ultraviolet light. The ratio of the length (L) of the film to the shortest length of the film in the isotropic state (L _iso ), the maximum ratio was measured to be 2.22.

⑦Self-healing test: Cut the LM-LCE film sample, then splicing it, and after placing it at 40°C for 10 hours, observe the self-healing effect with a metallographic microscope and a scanning electron microscope, and use a universal tensile tester (SANS E42.503) Perform post-repair stress-strain testing. The test results show that the self-healing efficiency of the liquid crystal elastomer composite material is 80%.

The above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention. It should be pointed out that for those skilled in the art, without departing from the basis and principle of the present invention, it is also possible to make Several equivalent replacements and improvements, these technical solutions after equivalent replacements and improvements to the claims of the present invention, all fall within the protection scope of the present invention.

Claims (5)

1. A liquid crystal elastomer material based on liquid metal nano-droplets, characterized in that the liquid crystal elastomer material is formed by polymerizing a liquid crystal monomer, and after the polymerization, the liquid crystal monomer is in the form of a mesogen in the molecular chain, All of them are arranged in order along the stretching direction to form a molecular main chain, and the liquid metal is broken into nano-scale droplets and then has a dynamic interaction with the sulfur element in the molecular main chain to be uniformly and stably dispersed in the liquid crystal elastomer matrix; The liquid crystal monomer, chain extender, crosslinking agent, catalyst and liquid metal are subjected to ultrasonic pulverization, and then mixed uniformly; under the condition of thermal polymerization, a liquid crystal elastomer based on liquid metal nano-droplets is prepared; The liquid crystal monomer is 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate; The liquid metal is gallium indium tin alloy, and the mass ratio of gallium, indium and tin is 0.62-0.8:0.25-0.1:0-0.13; The mass ratio of the liquid metal mass to the liquid crystal monomer is 5%-8%; The liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate has the following structural formula:

Described crosslinking agent pentaerythritol tetrakis (3-mercaptopropionate), structural formula is as follows:

Described chain extender 2,2-oxygen bis (ethane-1-thiol), structural formula is as follows:

Described catalyst dipropylamine, structural formula is as follows:

The quantity ratio of the above-mentioned liquid crystal monomer, chain extender and crosslinking agent is: liquid crystal monomer: chain extender: crosslinking agent=1:20:22-1:10:12; The mass ratio of liquid metal to liquid crystal monomer, chain extender and crosslinking agent is: liquid metal: (liquid crystal monomer+chain extender+crosslinking agent)=1:20-1:12. 2. a preparation method of liquid crystal elastomer material based on liquid metal nano-droplets as claimed in claim 1, is characterized in that, preparation process is as follows: Step 1. The liquid crystal monomer 4-((6-(acryloyloxy)hexyl)oxy)phenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate, chain extension agent 2,2-oxybis (ethane-1-thiol), cross-linking agent pentaerythritol tetrakis (3-mercaptopropionate) and liquid metal for water removal treatment; Step 2. Place all the materials in step 1 in anhydrous dichloromethane, and then place them in a brown bacterial strain bottle under the condition of flowing nitrogen, and fully stir to form a uniform solution; Step 3. get catalyst dipropylamine and be dissolved in methylene chloride, then join in the solution in the above-mentioned brown bacterial strain bottle; Step 4. Ultrasonic treatment with an ultrasonic breaker for 1-1.5 hours to break the liquid metal into nanometers, and to achieve uniform mixing of the above mixture; Step 5. Pour the above mixture into a polytetrafluoroethylene tank, and then put it into an oven at 36°C-45°C for 1-1.5h; Step 6. Cool the polytetrafluoroethylene tank in step 5 to room temperature to prepare an unoriented liquid metal nano-droplet-based liquid crystal elastomer material LM-LCE film; Step 7. Cut the above-mentioned unoriented LM-LCE film into a long strip, stretch and keep it fixed at room temperature to obtain a stretched and oriented long strip of liquid metal nano-droplet-based liquid crystal elastomer material LM-LCE film ; Step 8. Put the stretched and oriented elongated LM-LCE film prepared in step 7 into an oven, keep at 36°C-45°C for 8-11 hours, and then naturally cool to room temperature to obtain an oriented structure. Liquid metal nanodroplets-based liquid crystal elastomer material LM-LCE film. 3. The method for preparing a liquid metal nano-droplet-based liquid crystal elastomer material according to claim 2, wherein the chain extender 2,2-oxybis(ethane-1-thiol) in step 1 is composed of 3,6-Dithio-1,8-octanediol substitution. 4. The method for preparing a liquid crystal elastomer material based on liquid metal nano-droplets as claimed in claim 2, characterized in that in step 4, the power of ultrasonication of the ultrasonic crusher is set to 360W. 5. The method for preparing a liquid crystal elastomer material based on liquid metal nano-droplets as claimed in claim 2, wherein in the step 7, the unoriented LM-LCE film is cut into a long strip and stretched at room temperature, Extend to 2-2.7 times its original length and keep it fixed.

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