CN115785668B - Light response dynamic liquid crystal elastomer driver material and preparation method thereof - Google Patents

Abstract

The invention discloses a light response dynamic liquid crystal elastomer driver material and a preparation method thereof. The liquid crystal elastomer is prepared by coordination and crosslinking of a polymer and metal ions. The liquid crystal elastomer has the capability of low-temperature and high-temperature shaping, and the driving performance can be obtained after shaping. In addition, the resulting driver material has solid state plasticity, light or heat responsive driving characteristics, and good mechanical properties, and reversible driving strain is 1% -80%. The preparation method of the liquid crystal elastomer driver is simple and effective, and no photo-thermal response additive is needed to be added in the preparation process.

Description

A light-responsive dynamic liquid crystal elastomer actuator material and preparation method thereof

Technical Field

The invention relates to a liquid crystal elastomer driver material belonging to the technical field of polymer materials, and in particular to a light-responsive dynamic liquid crystal elastomer driver material and a preparation method thereof.

Background Art

Liquid crystal elastomer actuators are a type of intelligent polymer material that can respond to external stimuli and produce reversible deformation. Traditional liquid crystal elastomer actuators can only respond to external temperature changes, which is obviously not conducive to their application. Light is a relatively green stimulus source and has the significant advantage of being able to operate controllably in both time and space. By introducing inorganic photothermal conversion fillers into the polymer network, the liquid crystal elastomer actuator can obtain light responsiveness and thus obtain the ability of light-controlled driving. However, this preparation method is usually accompanied by the agglomeration of photothermal fillers, which affects the driving performance and mechanical properties of the actuator. Although a relatively uniform liquid crystal elastomer polymer network can be prepared by developing and introducing organic light-absorbing additives, the exudation and potential toxicity of organic photothermal additives have a great impact on the application scenarios of the actuator. In addition, traditional liquid crystal elastomer actuators based on stable covalent cross-linking usually do not have shape plasticity, self-healing and reprocessing, which is also unfavorable to their application prospects.

Therefore, it is an urgent problem to prepare light-responsive liquid crystal elastomer actuators with uniform structure and dynamic properties by simple and effective means.

Summary of the invention

To solve the deficiencies of the prior art, the present invention provides a light-responsive dynamic liquid crystal elastomer actuator material and a preparation method thereof. The actuator material has a simple preparation method, a uniform dynamic polymer network, and excellent light-responsive driving performance and mechanical properties.

The technical solution adopted by the present invention is:

1. A photoresponsive dynamic liquid crystal elastomer actuator material

The liquid crystal elastomer actuator material is prepared by cross-linking the polymer described in formula (I) with metal ions;

The polymer is a catechol-terminated copolymer of 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene and 3,6-dioxa-1,8-octanedithiol, which is denoted as RM257-Dopa.

The chemical structure of the polymer is shown in formula (I):

The number average molecular weight of the polymer is 1,000-50,000.

The coordination mode between the polymer and the metal ion in the polymer network is one or both of double coordination and triple coordination.

In terms of mass fractions, the mass fraction of the polymer is 90-99.9 parts, and the mass fraction of the metal ion is 0.1-10 parts.

The metal ions are one or more of ferric ions, ferrous ions, ruthenium ions, aluminum ions, copper ions, nickel ions, zinc ions, titanium ions, calcium ions, magnesium ions, vanadium ions, manganese ions, and cobalt ions.

Liquid crystal elastomer actuator materials have solid-state plasticity, light or heat responsive driving characteristics and good mechanical properties, with a reversible driving strain of 1%-80%.

2. A method for preparing the light-responsive dynamic liquid crystal elastomer actuator material

1) dissolving the polymer in a solvent, and then adding a solution containing metal ions to obtain a precursor solution;

2) adding an alkaline solution to the precursor solution, stirring and mixing to obtain a liquid crystal elastomer solution;

3) injecting the liquid crystal elastomer solution into molds of different shapes, and demolding after the solvent evaporates to obtain an initial liquid crystal elastomer;

4) placing the initial liquid crystal elastomer in a first solvent and a second solvent in sequence for purification and then drying completely to obtain a purified liquid crystal elastomer;

5) giving the purified liquid crystal elastomer any preset shape by external force and placing it at 20-250° C. for 30 seconds to 10 days to obtain a pre-liquid crystal elastomer;

6) After cooling the pre-liquid crystal elastomer, a liquid crystal elastomer actuator material is obtained.

In the above 1), the mass fraction of the polymer is 90-99.9 parts, the mass fraction of the metal ion is 0.1-10 parts, and the mass fraction of the alkaline solution is 0.1-20 parts.

In the above 1), the mass ratio of the solvent to the polymer is 1:1-40:1.

In the above 1), the solvent used to dissolve the polymer is one or more of dichloromethane, chloroform, tetrahydrofuran, ethyl acetate, dioxane, toluene, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the solvent used to prepare the metal ion-containing solution is one or more of methanol, ethanol, isopropanol, n-butanol, glycerol, ethylene glycol, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and water;

In the above 2), the alkaline substance for preparing the alkaline solution is one or more of triethylamine, potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide, pyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene;

4), the first solvent and the second solvent are one or more of methanol, ethanol, isopropanol, ethyl acetate, dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide and N,N-dimethylacetamide; the solvent 2 is one or more of methanol, ethanol, isopropanol, ethyl acetate, dichloromethane, chloroform and tetrahydrofuran.

3. A soft robot

The liquid crystal elastomer driver material is prepared or the liquid crystal elastomer driver material prepared by the method is prepared.

The liquid crystal elastomer actuator involved in the present invention has a structurally uniform polymer network and can exhibit good light-responsive driveability, plasticity, self-healing property and reprocessability without using any photothermal additives and reversible bond exchange catalysts.

Liquid crystal elastomer materials are prepared by direct coordination and cross-linking of linear polymers with specific functional groups (i.e., catechol groups) and metal ions. The preparation process is simple and easy to control, and does not involve high temperature, high pressure or other harsh reaction conditions. Structurally, the repeating units of the linear polymers used contain liquid crystal units that can produce order-disorder transitions and flexible chain extension molecules. At the same time, both ends of the polymer are capped by catechol groups. The catechol groups can form coordination structures with metal ions (especially iron ions). The formed catechol-iron complexes, catechol-ruthenium complexes, catechol-cobalt complexes, etc. have strong absorption in the visible and near-infrared light regions, giving the polymer network a good photothermal effect. In addition, coordination bonds such as catechol-iron, catechol-ruthenium, and catechol-cobalt are thermosensitive, which can cause the polymer network to rearrange under direct heating or photothermal action, showing properties such as plasticity, self-healing, and processability.

The beneficial effects of the present invention are as follows:

1. The liquid crystal elastomer driver material provided by the present invention has a structurally uniform polymer network, which can exhibit photoresponsive drivability, plasticity, self-healing and reprocessability without the presence of additional photothermal additives, thereby solving the shortcomings of most currently reported photoresponsive liquid crystal elastomer materials that use photothermal additives, such as agglomeration, toxicity and high risk of exudation, making it have obvious advantages over most currently reported liquid crystal elastomer drivers.

2. The liquid crystal elastomer driver material provided by the present invention has a simple preparation process, and the process of forming a cross-linked network does not involve harsh reaction conditions. It is adaptable to a variety of production and processing methods, such as casting, 3D printing, etc., and shows a high application prospect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydrogen nuclear magnetic resonance ( ¹ H NMR) graph of the polymer used in Example 1. FIG.

FIG. 2 is a differential scanning calorimetry (DSC) temperature rise and temperature drop curve of the polymer used in Example 1.

FIG. 3 is a Raman spectrum of the liquid crystal elastomer material prepared in Example 1.

FIG. 4 is a scanning electron microscope (SEM) and an energy dispersive X-ray spectroscopy (EDS) element distribution image of the fracture surface of the liquid crystal elastomer material prepared in Example 1.

FIG. 5 is a tensile stress-strain curve of the liquid crystal elastomer material prepared in Example 1.

FIG6 is a photothermal response diagram of the liquid crystal elastomer material prepared in Example 1.

FIG. 7 is a stress relaxation curve diagram of the liquid crystal elastomer material prepared in Example 1 at different temperatures.

FIG8 is a reversible driving curve and a display diagram of the liquid crystal elastomer actuator prepared in Example 1.

DETAILED DESCRIPTION

The present invention is described in more detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

Embodiments of the present invention are as follows:

Example 1

Weigh 0.5g of a polymer with a number average molecular weight of 5360 and dissolve it in 12ml of chloroform. After it is fully dissolved, add 625μl of a 0.1mol/l methanol solution of ferric chloride and mix evenly. Subsequently, slowly add 935μl of a 0.2mol/l methanol solution of potassium hydroxide to the above solution and mix thoroughly. After pouring the obtained liquid crystal elastomer solution into a polytetrafluoroethylene mold, evaporate the solvent at 30°C until it is completely dry. The obtained coordinated cross-linked initial liquid crystal elastomer is placed in 50ml of a mixed solvent of N,N-dimethylformamide/methanol with a volume ratio of 7/3 for purification, and then taken out and placed in 50ml of methanol for secondary purification. Finally, the obtained liquid crystal elastomer material is completely dried in vacuum at 30°C to obtain a purified liquid crystal elastomer, which has photoresponsive dynamics. The purified liquid crystal elastomer obtained is axially stretched to a strain of 150%, placed at 120°C for 5 minutes, and then slowly cooled to room temperature to obtain a liquid crystal elastomer actuator material with light-responsive contraction/elongation drive. The final liquid crystal elastomer actuator material has driving characteristics.

FIG1 is a ¹ H NMR spectrum of the polymer used in this embodiment. FIG2 is a DSC heating and cooling curve of the polymer used in this embodiment. It can be seen that the phase transition temperature from order to disorder of the polymer during the heating process is 42.3°C. FIG3 is a Raman spectrum of the liquid crystal elastomer material prepared in this embodiment. The characteristic peaks at 530, 585 and 634 cm ^-1 of Raman shift shown in the figure indicate that the catechol groups on the polymer coordinate with the iron ions and serve as crosslinking points to construct a polymer network. FIG4 (a) and (b) are respectively SEM and EDS element distribution diagrams of the fracture surface of the liquid crystal elastomer material prepared in this embodiment. It can be seen that the polymer network structure is uniform and the iron ions are evenly distributed in the polymer network. FIG5 is a tensile stress-strain curve of the liquid crystal elastomer actuator material prepared in this embodiment. It can be seen from the figure that the polymer can exhibit excellent mechanical properties. At room temperature, its tensile strength is 6.25±0.13MPa and its fracture strain is 325±10%. FIG6 is a photothermal response diagram of the liquid crystal elastomer material prepared in this embodiment. It can be seen that under near-infrared light of 0.8W/ ^cm2 808nm, the polymer surface can quickly heat up and exceed 100°C within 5s, showing excellent photothermal conversion performance. The dynamic characteristics of the network are characterized by the stress relaxation behavior of the polymer. FIG7 is a stress relaxation curve of the liquid crystal elastomer material prepared in this embodiment at different temperatures. It can be seen that when the temperature rises from 90°C to 140°C, the coordination bond exchange of the polymer network is significantly accelerated, so that the stress relaxation degree and speed of the polymer within the test time increase rapidly, indicating that the polymer network has good dynamic characteristics. FIG8 is a reversible drive curve and display diagram of the liquid crystal elastomer actuator prepared in this embodiment. It can be seen that when the temperature is cyclically raised and lowered between 0°C and 80°C, the polymer exhibits obvious contraction and elongation drive, and the drive strain is about 33%. As can be seen from the inset in FIG8, the lengths of the strip actuators at 0°C and 80°C are 3.3cm and 2.5cm, respectively.

Example 2

Weigh 0.3g of a polymer with a number average molecular weight of 5360 and dissolve it in 12ml of chloroform. After it is fully dissolved, add 850μl of a 0.1mol/l methanol solution of ferric chloride and mix it evenly. Subsequently, slowly add 1180μl of a 0.2mol/l methanol solution of potassium hydroxide to the above solution and mix it thoroughly. After casting the obtained liquid crystal elastomer into a polytetrafluoroethylene mold, evaporate the solvent at 30°C until it is completely dry. The obtained coordinated cross-linked initial liquid crystal elastomer is placed in 50ml of a 7/3 volume ratio of N,N-dimethylformamide/methanol mixed solvent for purification, and then taken out and placed in 50ml of methanol for secondary purification. Finally, the obtained liquid crystal elastomer material is completely dried in vacuum at 30°C to obtain a purified liquid crystal elastomer. After the obtained purified liquid crystal elastomer is axially stretched to a strain of 150%, it is placed at 120°C for 10min, and then slowly cooled to room temperature to obtain a liquid crystal elastomer actuator material with light-responsive contraction/elongation drive. The driving strain of the obtained actuator is about 28%.

Example 3

Weigh 0.5g of a polymer with a number average molecular weight of 8380 and dissolve it in 12ml of chloroform. After fully dissolved, add 380μl of 0.1mol/l ferric chloride methanol solution and 160μl of 0.1mol/l aluminum chloride methanol solution and mix them evenly. Subsequently, slowly add 745μl of 0.2mol/l potassium hydroxide methanol solution to the above solution and mix them thoroughly. After casting the obtained liquid crystal elastomer into a polytetrafluoroethylene mold, evaporate the solvent at 30°C until it is completely dry. The obtained coordinated cross-linked initial liquid crystal elastomer is placed in 50ml of a 7/3 volume ratio of N,N-dimethylformamide/methanol mixed solvent for purification, and then taken out and placed in 50ml of methanol for secondary purification. Finally, the obtained liquid crystal elastomer material is completely dried in vacuum at 30°C to obtain a purified liquid crystal elastomer. After the obtained purified liquid crystal elastomer is folded and bent, it is left to stand at 30°C for 3 days to prepare a liquid crystal elastomer actuator material with light-responsive reversible bending drive, and the driving strain is about 46%.

Example 4

Weigh 1.0g of a polymer with a number average molecular weight of 46200 and dissolve it in 15ml of chloroform. After fully dissolved, add 50μl of a 0.1mol/l methanol solution of ferric chloride and 10μl of a 0.1mol/l methanol solution of ruthenium chloride and mix them evenly. Subsequently, slowly add 90μl of a 0.2mol/l methanol solution of potassium hydroxide to the above solution and mix them thoroughly. After casting the obtained liquid crystal elastomer into a polytetrafluoroethylene mold, evaporate the solvent at 30°C until it is completely dry. The obtained coordinated cross-linked initial liquid crystal elastomer is placed in 50ml of a 7/3 volume ratio of N,N-dimethylformamide/methanol mixed solvent for purification, and then taken out and placed in 50ml of methanol for secondary purification. Finally, the obtained liquid crystal elastomer material is completely dried in vacuum at 30°C to obtain a purified liquid crystal elastomer. After the obtained purified liquid crystal elastomer is folded and bent, it is left to stand at 30°C for 3 days to prepare a liquid crystal elastomer actuator material with light-responsive reversible bending drive, and the driving strain is about 76%.

Example 5

Weigh 0.68g of a polymer with a number average molecular weight of 1650 and dissolve it in 15ml of dichloromethane. After it is fully dissolved, add 4200μl of 0.1mol/l ferric chloride tetrahydrofuran solution and mix well. Subsequently, slowly add 1810μl of 0.6mol/l potassium hydroxide methanol solution to the above solution and mix thoroughly. After casting the obtained liquid crystal elastomer into a polytetrafluoroethylene mold, evaporate the solvent at 30°C until it is completely dry. The obtained coordinated cross-linked initial liquid crystal elastomer is placed in 50ml of a 7/3 volume ratio of N,N-dimethylformamide/methanol mixed solvent for purification, and then taken out and placed in 50ml of methanol for secondary purification. Finally, the obtained liquid crystal elastomer material is completely dried in vacuum at 30°C to obtain a purified liquid crystal elastomer. After the obtained purified liquid crystal elastomer is folded and bent, it is allowed to stand at 110°C for 20min to prepare a liquid crystal elastomer actuator material with light-responsive reversible bending drive, and the driving strain is about 17%.

Claims (8)

1. The light response dynamic liquid crystal elastomer driver material is characterized in that the light response dynamic liquid crystal elastomer driver material is prepared by coordination and crosslinking of a polymer shown in a formula (I) and metal ions;

（I）；

The mass portion of the polymer is 90-99.9 portions and the mass portion of the metal ion is 0.1-10 portions;

the number average molecular weight of the polymer is 1000-50000.

2. A light responsive dynamic liquid crystal elastomeric driver material as in claim 1, wherein: the coordination mode of the polymer and the metal ion in the polymer network is one or two of double coordination mode and triple coordination mode.

3. A light responsive dynamic liquid crystal elastomeric driver material as in claim 1, wherein: the metal ion is one or more of iron ion, ferrous ion, ruthenium ion, aluminum ion, copper ion, nickel ion, zinc ion, titanium ion, calcium ion, magnesium ion, vanadium ion, manganese ion and cobalt ion.

4. A method of preparing a light responsive dynamic liquid crystal elastomeric driver material as claimed in any one of claims 1 to 3, comprising the steps of:

1) Dissolving a polymer in a solvent, and then adding a solution containing metal ions to obtain a precursor solution;

2) Adding an alkaline solution into the precursor solution, and uniformly stirring and mixing to obtain a liquid crystal elastomer solution;

3) Injecting the liquid crystal elastomer solution into moulds with different shapes, and demoulding after the solvent is volatilized to obtain an initial liquid crystal elastomer;

4) Sequentially placing the initial liquid crystal elastomer in a first solvent and a second solvent for purification, and then drying completely to obtain a purified liquid crystal elastomer;

5) The purified liquid crystal elastomer is endowed with any preset shape through the action of external force, and then is placed at 20-250 ℃ for 30 seconds-10 days, so as to obtain a pre-liquid crystal elastomer;

6) After cooling the pre-liquid crystal elastomer, a liquid crystal elastomer driver material is obtained.

5. The method for preparing a light-responsive dynamic liquid crystal elastomer driver material according to claim 4, wherein the polymer is 90-99.9 parts by mass, the metal ion is 0.1-10 parts by mass, and the alkaline solution is 0.1-20 parts by mass.

6. The method for preparing a light-responsive dynamic liquid crystal elastomer driver material according to claim 4, wherein in the step 1), the mass fraction ratio of the solvent to the polymer is 1:1-40:1.

7. The method for preparing a light-responsive dynamic liquid crystal elastomer driver material according to claim 4, wherein the solvent used for dissolving the polymer in 1) is one or more of dichloromethane, chloroform, tetrahydrofuran, ethyl acetate, dioxane, toluene, N-dimethylformamide, N-dimethylacetamide and dimethylsulfoxide; the solvent used for preparing the metal ion-containing solution is one or more of methanol, ethanol, isopropanol, N-butanol, glycerol, ethylene glycol, tetrahydrofuran, N-dimethylformamide, N-dimethylacetamide and water;

In the step 2), alkaline substances for preparing alkaline solution are one or more of triethylamine, potassium hydroxide, sodium methoxide, potassium methoxide, pyridine, 1, 8-diazabicyclo [5.4.0] undec-7-ene and 1,5, 7-triazabicyclo [4.4.0] dec-5-ene;

4) Wherein the first solvent is one or more of methanol, ethanol, isopropanol, ethyl acetate, dichloromethane, chloroform, tetrahydrofuran, N-dimethylformamide and N, N-dimethylacetamide; the second solvent is one or more of methanol, ethanol, isopropanol, ethyl acetate, dichloromethane, chloroform and tetrahydrofuran.

8. A soft robot comprising the liquid crystal elastomer driver material of any one of claims 1-3 or the liquid crystal elastomer driver material of any one of claims 4-7.