阅读说明：本技术 一种力学性能可转变的动态相变凝胶及其制备方法 (Dynamic phase change gel with transformable mechanical properties and preparation method thereof ) 是由 杨伟 赵星 彭丽梅 柯凯 包睿莹 杨鸣波 于 2021-01-18 设计创作，主要内容包括：本发明涉及一种力学性能可转变的动态相变凝胶及其制备方法,属于功能复合材料领域。本发明提供一种动态相变凝胶,所述动态相变凝胶以相变材料和能够形成三维网络结构的前驱体为原料,所述前驱体以熔融的相变材料为凝胶介质原位聚合交联形成三维交联网络结构,所得三维交联网络结构则对相变材料原位封装形成所述动态相变凝胶。本发明相变材料中通过原位聚合交联的方式引入三维网络结构从而得到力学性能可转变的动态相变凝胶,原位形成的交联网络既可防止相变材料熔融后的泄露问题又能保证复合材料整体的力学均匀性；所得动态相变凝胶在相变前后能够发生10～5级别的可逆模量改变,由此可通过外界刺激按需调节相变凝胶的模量和刚度。(The invention relates to a dynamic phase change gel with transformable mechanical properties and a preparation method thereof, belonging to the field of functional composite materials. The invention provides a dynamic phase-change gel, which takes a phase-change material and a precursor capable of forming a three-dimensional network structure as raw materials, wherein the precursor takes a molten phase-change material as a gel medium to form a three-dimensional cross-linked network structure through in-situ polymerization and cross-linking, and the obtained three-dimensional cross-linked network structure encapsulates the phase-change material in situ to form the dynamic phase-change gel. The phase-change material of the invention is introduced with a three-dimensional network structure in an in-situ polymerization crosslinking mode to obtain dynamic phase-change gel with convertible mechanical properties, and the in-situ formed crosslinking network can prevent the phase-change materialThe leakage problem after the materials are melted can also ensure the integral mechanical uniformity of the composite material; the obtained dynamic phase-change gel can generate 10 times before and after phase change 5 The grade of reversible modulus changes, so that the modulus and rigidity of the phase-change gel can be adjusted as required by external stimuli.)

1. The dynamic phase-change gel is characterized in that a phase-change material and a precursor capable of forming a three-dimensional network structure are used as raw materials, the precursor is in-situ polymerized and crosslinked to form a three-dimensional crosslinked network structure by taking a molten phase-change material as a gel medium, and the obtained three-dimensional crosslinked network structure encapsulates the phase-change material in situ to form the dynamic phase-change gel.

2. The dynamic phase change gel of claim 1, wherein the phase change material is polyethylene glycol.

3. The dynamic phase change gel according to claim 1 or 2, wherein the precursor capable of forming a three-dimensional network structure is a substance capable of forming a three-dimensional network structure under the action of thermal initiation or photoinitiation.

4. The dynamic phase change gel according to any one of claims 1 to 3, wherein the precursor capable of forming a three-dimensional network structure is prepared by the following method: at normal temperature, the monomer, the cross-linking agent, the initiator and the water are fully and evenly mixed to prepare the water-based polyurethane elastomer; wherein the monomer is acrylic acid or acrylamide, the crosslinking agent is N, N-methylene bisacrylamide or other divinyl crosslinking agents, and the initiator is an inorganic peroxide or organic peroxide initiator or a photoinitiator; preferably, the initiator is ammonium persulfate;

further, the mass ratio of the cross-linking agent to the monomer is 2-5%; the mass ratio of the initiator to the monomer is 0.5-3%; the mass ratio of water to the monomer is 30-50%.

5. The dynamic phase-change gel according to any one of claims 1 to 4, wherein the mass ratio of the phase-change material to the precursor capable of forming a three-dimensional network structure is as follows: 100: 20 to 40.

6. The dynamic phase change gel according to any one of claims 1 to 5, wherein the three-dimensional cross-linked network is polyacrylic acid or polyacrylamide.

7. The method for preparing the dynamic phase change gel according to any one of claims 1 to 6, wherein the method comprises the following steps: selecting a phase-change material and a precursor capable of forming a three-dimensional network structure as raw materials, taking a molten phase-change material as a gel medium, and gelling the molten phase-change material and the precursor capable of forming the three-dimensional network structure to generate a three-dimensional cross-linked network structure in situ, thereby preparing the dynamic phase-change gel.

8. The method for preparing dynamic phase-change gel according to claim 6, wherein when the phase-change material is polyethylene glycol and the three-dimensional cross-linked network is polyacrylic acid or polyacrylamide, the method for preparing dynamic phase-change gel comprises: melting the phase-change material at 70-90 ℃; preparing a three-dimensional network precursor liquid; slowly adding the three-dimensional network precursor liquid into the melted phase-change material, and stirring and mixing at 60-80 ℃; then the mixed solution which is uniformly mixed is gelatinized at the temperature of 60-90 ℃;

further, the method for preparing the three-dimensional network precursor solution comprises the following steps: at normal temperature, mixing a monomer, a cross-linking agent, an initiator and water, and then carrying out ultrasonic treatment to obtain the three-dimensional network precursor liquid.

9. The dynamic phase change gel is used as a thermal interface material, a shape memory driver or a high-temperature early warning sensor, and is the dynamic phase change gel as claimed in any one of claims 1 to 5, or is the dynamic phase change gel prepared by the method as claimed in claim 7 or 8.

10. A method for preventing leakage of a phase-change material after melting is characterized by comprising the following steps: the method comprises the steps of taking a molten phase-change material as a medium, introducing a precursor capable of forming a three-dimensional network structure, and carrying out in-situ polymerization and crosslinking on the precursor to generate a three-dimensional crosslinking network through gelation, so that in-situ packaging of the phase-change material by the three-dimensional crosslinking network structure is realized, and further, leakage of the phase-change material after melting is prevented.

Technical Field

The invention relates to a dynamic phase change gel with transformable mechanical properties and a preparation method thereof, belonging to the field of functional composite materials.

Background

Compared with the traditional rigid electronic or soft material, the dynamic material with transformable mechanical properties (transformation of modulus and transformation of rigidity) can adapt to a more complex external environment, and has great potential application value in the field of intelligent flexible materials. The most direct transformation of mechanical properties is represented by the transformation of material rigidity. Currently, the rigidity transformation of the material under external stimulation is mainly realized through the following modes:

1. the electro-fluid or magnetic fluid changes viscosity under a high electric field or magnetic field, and further changes the macroscopic mechanical state of the material, but often requires rigid accessories such as an electromagnet or a high-voltage capacitor.

2. Reversible dynamic covalent or non-covalent bonds, the strength of the bonds can influence the mechanical properties of the material, and the reversible bonds can be used for realizing the mechanical transformation of the material under specific stimulation. However, these dynamic bond strategies typically depend on complex molecular design and chemical modifications.

3. The glass transition of the polymer, which utilizes the glass transition characteristics of the polymer, can realize the modulus change of the material under the thermal stimulation, and is widely applied because the glass transition only involves the thermal stimulation. But the glass transition is generally only capable of giving rise to a modulus of 10²Cannot meet the requirements of more complex fields.

Compared with glass transition, the crystalline polymer can generate rigidity change to a greater extent in the crystallization-melting or melting-crystallization transition process, so that the method has a greater prospect in the aspect of realizing macroscopic mechanical property transition of the composite material, but the construction of a mechanical property transition material based on polymer phase transition is rare at present.

The crystalline polymer is transformed into liquid state and then leaks, which is a main reason for limiting the application of the transformation of mechanical properties. Leakage is currently addressed primarily by blending with high melting or cross-linked polymers, microencapsulation, and the like. However, these methods have problems of complicated preparation or poor packaging effect, etc., and cause mechanical non-uniformity of the composite material.

Disclosure of Invention

Aiming at the defects, the invention aims to provide a dynamic phase-change gel with transformable mechanical properties (the mechanical properties can be transformed, namely the material can be regulated and controlled according to the requirements of different application scenes under the external stimulation, for example, the transformation from soft to hard or from hard to soft can be realized) and a preparation method thereof, namely, a three-dimensional network structure is introduced into a phase-change material in an in-situ polymerization crosslinking mode to obtain the dynamic phase-change gel with transformable mechanical properties, and the crosslinked network formed in situ can not only prevent the leakage problem of the phase-change material after melting, but also ensure the overall mechanical uniformity of the composite material; the obtained dynamic phase-change gel can generate 10 times before and after phase change⁵The order of reversible modulus changes, whereby the modulus and stiffness of the phase-change gel can be adjusted as desired by external stimuli (light or thermal stimuli).

The technical scheme adopted by the invention is as follows:

the first technical problem to be solved by the present invention is to provide a dynamic phase change gel, wherein the dynamic phase change gel uses a phase change material and a precursor capable of forming a three-dimensional network structure as raw materials, the precursor uses a melted phase change material as a gel medium to form a three-dimensional cross-linked network structure through in-situ polymerization and cross-linking, and the obtained three-dimensional cross-linked network structure encapsulates the phase change material in situ to form the dynamic phase change gel.

Further, the phase change material is polyethylene glycol (PEG). Preferably, the number average molecular weight of the polyethylene glycol is 800-20000.

Further, the precursor capable of forming a three-dimensional network structure is a substance capable of forming a three-dimensional network structure under the action of thermal initiation or photoinitiation.

Further, the precursor capable of forming the three-dimensional network structure is prepared by adopting the following method: at normal temperature, the monomer, the cross-linking agent, the initiator and water are fully and uniformly mixed (mixing and then ultrasonic treatment can be adopted) to prepare the modified polyurethane material; wherein the monomer is acrylic acid or acrylamide, the crosslinking agent is N, N-methylene bisacrylamide or other divinyl crosslinking agents, and the initiator is an inorganic peroxide or organic peroxide initiator or a photoinitiator; preferably, the initiator is ammonium persulfate.

Further, in the preparation process of the precursor capable of forming the three-dimensional network structure, the mass ratio of the cross-linking agent to the monomer is 2-5%, preferably 5%; the mass ratio of the initiator to the monomer is 0.5-3%; the mass ratio of water to the monomer is 30-50%, preferably 30%; that is, the preferable mass ratio of the monomer, the crosslinking agent, the initiator and the water is 100: 5: 2: 30.

further, the mass ratio of the phase-change material to the precursor capable of forming the three-dimensional network structure is as follows: 100: 20 to 40. If the content of the three-dimensional network is too small, a complete three-dimensional network cannot be formed in the in-situ polymerization crosslinking process, so that the gelation process cannot be completed; if the content of the three-dimensional network is too high, the crystal-melting or melting-crystal transformation characteristics of the intrinsic phase-change material are greatly influenced, and the mechanical transformation process of the phase-change gel is further influenced; therefore, in order to ensure the completion of the gelation process and not influence the mechanical transformation of the phase-change gel, the mass ratio of the three-dimensional network to the intrinsic phase-change material is limited to 20-40%.

Further, the three-dimensional cross-linked network is polyacrylic acid (PAA) or Polyacrylamide (PAM).

In the invention, the phase-change gel can be achieved by thermal initiation or photo-initiation polymerization, wherein a thermal initiator is required to be added in the thermal initiation process, and a photo-initiator is required to be added in the photo-initiation process.

The second technical problem to be solved by the present invention is to provide a preparation method of the above dynamic phase change gel, wherein the preparation method comprises: selecting a phase-change material and a precursor capable of forming a three-dimensional network structure as raw materials, taking a molten phase-change material as a gel medium, and carrying out gelation on the precursor capable of forming the three-dimensional network structure and the molten phase-change material to generate a three-dimensional cross-linked network structure in situ, thereby preparing the dynamic phase-change gel.

Further, when the phase change material is polyethylene glycol and the three-dimensional cross-linked network is polyacrylic acid (PAA) or Polyacrylamide (PAM), the preparation method of the dynamic phase change gel comprises the following steps: melting the phase-change material at 70-90 ℃; preparing a three-dimensional network precursor liquid; slowly adding (dropwise adding) the three-dimensional network precursor liquid into the melted phase-change material, and stirring and mixing at 60-80 ℃; and gelatinizing the uniformly mixed solution at 60-90 ℃.

Further, the method for preparing the three-dimensional network precursor liquid comprises the following steps: at normal temperature, mixing a monomer, a cross-linking agent, an initiator and water, and then carrying out ultrasonic treatment to obtain the three-dimensional network precursor liquid. In the invention, the three-dimensional network precursor liquid needs to be slowly added into the molten phase-change material because the following reasons exist: the temperature of the three-dimensional network precursor liquid is low, and if the three-dimensional network precursor liquid is rapidly added into the melted phase-change material, the phase-change material is crystallized due to contact with cold substances, so that the phase separation of the uniform mixed liquid is caused. The reason why the gelation temperature is set to 60 ℃ to 90 ℃ is that: too low a temperature will result in incomplete gelling, while too high a temperature will tend to form aggregates.

The third technical problem to be solved by the present invention is to indicate the use of the above dynamic phase change gel: can be used as thermal interface material, shape memory driver or high-temperature early warning sensor.

The fourth technical problem to be solved by the present invention is to provide a method for preventing leakage of a phase change material after melting, wherein the method comprises: the method comprises the steps of taking a molten phase-change material as a medium, introducing a precursor capable of forming a three-dimensional network structure, and carrying out in-situ polymerization and crosslinking on the precursor to generate a three-dimensional crosslinking network through gelation, so that in-situ packaging of the phase-change material by the three-dimensional crosslinking network structure is realized, and further, leakage of the phase-change material after melting is prevented.

The invention has the beneficial effects that:

the dynamic phase change gel with convertible mechanical property of the method has the following advantages:

(1) the polymer three-dimensional cross-linked network is introduced into the phase-change material, so that the phase-change material can be effectively prevented from leaking after being melted.

(2) The three-dimensional network is formed by in-situ crosslinking by taking the melted phase-change material as a medium, is prepared in one step, does not need subsequent independent packaging of the phase-change material, and has the advantages of simple process, low cost, uniform product mechanics and the like.

(3) Due to the temperature-responsive physical state change characteristic of the phase-change material, the phase-change gel can be mechanically transformed under the temperature stimulation by using the phase-change material as a gel medium; the obtained phase-change gel can generate 10 times before and after phase change⁵The reversible modulus of the grade changes.

(4) The crystallization degree of the phase-change material can be regulated and controlled by changing the content of the three-dimensional cross-linked network of the polymer, so that the mechanical transformation degree of the phase-change gel can be regulated and controlled.

Drawings

FIG. 1 is a graph showing the crystallization process observed for the phase change gels obtained in examples one, two, three, and one; as can be seen from FIG. 1, in the prepared phase-change gel, as the content of the three-dimensional network of the polymer increases, the crystallization rate of the phase-change gel gradually decreases.

FIG. 2 is a graph showing the crystal ratios of the phase change gels obtained in the first, second, third and first comparative examples; as can be seen from fig. 2, in the prepared phase-change gel, as the content of the three-dimensional network of the polymer increases, the crystallization of the phase-change gel is gradually inhibited, and therefore, the content of the three-dimensional network can be used to regulate the degree of crystallization.

FIG. 3 is a digital photograph showing the shape stability of the phase-change gel obtained in the first embodiment, the second embodiment and the third embodiment; as can be seen from FIG. 3, the three-dimensional network in the prepared phase-change gel can well prevent PEG from leaking at high temperature.

FIG. 4 is a graph showing the temperature scanning modulus changes of the phase change gels obtained in the first, second and third embodiments; as can be seen from FIG. 4, the phase-change gel obtained by the present invention can achieve a large degree of modulus transformation under temperature stimulation.

Detailed Description

The invention provides a preparation method of dynamic phase change gel with transformable mechanical properties. The method adopts an in-situ polymerization crosslinking method, uses a phase-change material (such as PEG-4000) in a molten state as a gel medium, and forms a polymer (such as polyacrylic acid PAA) three-dimensional network by in-situ polymerization crosslinking. The method can save the processes of preparing a single three-dimensional framework, impregnating the phase-change material and the like, thereby greatly reducing the cost. Meanwhile, the PAA and the PEG have good compatibility, so that the overall mechanical uniformity of the obtained phase-change gel is ensured. In phase change gels, the three-dimensional crosslinked network of polymers can prevent leakage of PEG after melting. The melt-crystallization or crystallization-melting transition of PEG can cause a macroscopic mechanical transition of phase change gels, and this transition is reversible.

The following examples are given to illustrate the present invention and should not be construed as limiting the invention in any way, and those skilled in the art will appreciate that the invention is not limited thereto or thereby by the following examples.

EXAMPLES preparation of a dynamic phase Change gel with switchable mechanical Properties

The dynamic phase-change gel with transformable mechanical properties is prepared by the following steps:

(1) preparation of molten intrinsic phase change material PEG: placing the phase change material PEG which is solid at normal temperature into a container, and then standing at the temperature of 80 ℃ for melting to obtain a molten intrinsic phase change material; the melting time is 1h-6 h; keeping PEG above 60 deg.C before use to prevent crystallization;

(2) preparing a three-dimensional network precursor solution: mixing a monomer, a cross-linking agent, an initiator and water in proportion at normal temperature, and performing ultrasonic treatment to obtain a three-dimensional network precursor solution; the monomer is acrylic acid AA, the cross-linking agent is N, N-methylene bisacrylamide MBA, and the initiator is ammonium persulfate APS; wherein the cross-linking agent accounts for 5 percent of the mass ratio of the monomer; the mass ratio of the initiator to the monomer is 2 percent; the mass ratio of water to the monomer is 30 percent;

(3) preparing a mixed solution of three-dimensional network precursor liquid/molten phase-change material: slowly adding the prepared three-dimensional network precursor liquid in the step (2) into the melted phase-change material in the step (1) (in the process, the phase-change material needs to be kept at the temperature of more than 60 ℃ to avoid crystallization), controlling the mass ratio of the three-dimensional network precursor liquid to the intrinsic phase-change material to be 20%, and ultrasonically removing bubbles after stirring to obtain a three-dimensional network precursor liquid/melted phase-change material mixed liquid;

(4) preparing dynamic phase change gel: standing the uniform mixed solution obtained in the step 3) at a temperature of 80 ℃ for gelation to obtain dynamic phase change gel with transformable mechanical properties; gelation time 30 min.

In the phase-change gel prepared by the method, the three-dimensional cross-linked network can inhibit PEG crystallization to a certain extent; as can be seen from fig. 1 and 2, compared to pure phase change material PEG (pure phase change material is used as comparative example one), the phase change gel prepared by the present invention shows a reduced crystallization rate and crystallization degree, so that the crystallization process, i.e., the mechanical transformation process, of the phase change gel can be controlled by the in-situ three-dimensional network.

Due to the constraining effect of the three-dimensional network, PEG does not exhibit leakage problems after melting; FIG. 3 shows that the phase change gel still did not leak any liquid at 80 ℃ for 1 h.

The melting process of PEG from low temperature to high temperature and the crystallization process from high temperature to low temperature are both accompanied by macroscopic mechanical transformation of the phase-change gel, and the PEG has a physical state change (from liquid state to solid state or from solid state to liquid state), which causes a huge transformation on mechanical properties such as modulus (figure 4) of the phase-change gel.

EXAMPLES preparation of two dynamic phase Change gels with switchable mechanical Properties

The dynamic phase-change gel with transformable mechanical properties is prepared by the following steps:

(1) preparation of molten intrinsic phase change material PEG: placing the phase change material PEG which is solid at normal temperature into a container, and then standing at the temperature of 80 ℃ for melting to obtain a molten intrinsic phase change material; the melting time is 1h-6 h; keeping PEG above 60 deg.C before use to prevent crystallization;

(2) preparing a three-dimensional network precursor solution: mixing a monomer, a cross-linking agent, an initiator and water in proportion at normal temperature, and performing ultrasonic treatment to obtain a three-dimensional network precursor solution; the monomer is acrylic acid AA, the cross-linking agent is N, N-methylene bisacrylamide MBA, and the initiator is ammonium persulfate APS; wherein the cross-linking agent accounts for 5 percent of the mass ratio of the monomer; the mass ratio of the initiator to the monomer is 2 percent; the mass ratio of water to the monomer is 30 percent;

(3) preparing a mixed solution of three-dimensional network precursor liquid/molten phase-change material: slowly adding the prepared three-dimensional network precursor liquid in the step (2) into the phase-change material melted in the step (1) (in the process, the phase-change material needs to be kept at the temperature of more than 60 ℃ to avoid crystallization), controlling the mass ratio of the three-dimensional network precursor liquid to the intrinsic phase-change material to be 30%, and ultrasonically removing bubbles after stirring to obtain a three-dimensional network precursor liquid/melted phase-change material mixed liquid;

(4) preparing dynamic phase change gel: standing the uniform mixed solution obtained in the step 3) at a temperature of 80 ℃ for gelation to obtain dynamic phase change gel with transformable mechanical properties; gelation time 30 min.

Example preparation of three mechanical Property transformable dynamic phase Change gel

The dynamic phase-change gel with transformable mechanical properties is prepared by the following steps:

(1) preparation of molten intrinsic phase change material PEG: placing the phase change material PEG which is solid at normal temperature into a container, and then standing at the temperature of 80 ℃ for melting to obtain a molten intrinsic phase change material; the melting time is 1h-6 h; keeping PEG above 60 deg.C before use to prevent crystallization;

(2) preparing a three-dimensional network precursor solution: mixing a monomer, a cross-linking agent, an initiator and water in proportion at normal temperature, and performing ultrasonic treatment to obtain a three-dimensional network precursor solution; the monomer is acrylic acid AA, the cross-linking agent is N, N-methylene bisacrylamide MBA, and the initiator is ammonium persulfate APS; wherein the cross-linking agent accounts for 5 percent of the mass ratio of the monomer; the mass ratio of the initiator to the monomer is 2 percent; the mass ratio of water to the monomer is 30 percent;

(3) preparing a mixed solution of three-dimensional network precursor liquid/molten phase-change material: slowly adding the prepared three-dimensional network precursor liquid in the step (2) into the phase-change material melted in the step (1) (in the process, the phase-change material needs to be kept at the temperature of more than 60 ℃ to avoid crystallization), controlling the mass ratio of the three-dimensional network precursor liquid to the intrinsic phase-change material to be 40%, and ultrasonically removing bubbles after stirring to obtain a three-dimensional network precursor liquid/melted phase-change material mixed liquid;

(4) preparing dynamic phase change gel: standing the uniform mixed solution obtained in the step 3) at a temperature of 80 ℃ for gelation to obtain dynamic phase change gel with transformable mechanical properties; gelation time 30 min.