Nanofiber-based shape memory aerogel as well as preparation method and application thereof

Abstract

The invention belongs to the field of intelligent materials, and discloses nanofiber-based shape memory aerogel as well as a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: adding 4, 4-diaminodiphenyl ether and 1, 2, 4, 5-pyromellitic dianhydride into N, N-dimethylformamide to prepare a polyamide acid solution; carrying out electrostatic spinning by taking the polyamide acid solution as a spinning solution to obtain a polyamide acid nanofiber membrane; cutting the polyamide acid nanofiber membrane into fibers with micron lengths, and carrying out amidation treatment to obtain polyimide nanofibers; the preparation method comprises the following steps: adding polyimide nanofibers, high-molecular-weight polyethylene glycol diacrylate and low-molecular-weight polyethylene glycol diacrylate into water, uniformly dispersing, and then adding ammonium persulfate and tetramethylethylenediamine to obtain a first mixed solution; performing freeze polymerization reaction on the first mixed solution, and performing freeze drying after the reaction is finished to obtain the nanofiber-based shape memory aerogel. The aerogel has excellent mechanical properties and shape memory properties, and can be widely applied to the industry.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of intelligent materials, and relates to a nanofiber-based shape memory aerogel as well as a preparation method and application thereof. BACKGROUND

[0002] As a new intelligent material, the shape memory polymer aerogel material maintains the ability of shape memory materials to fix their own shape under certain conditions and to recover when exposed to specific stimuli (light, heat, electricity, moisture and magnetic field), and also inherits the characteristics of super-light and porosity, thus having important application prospects in many fields.

[0003] Polyethylene glycol is one of the most promising organic phase change materials due to its high latent heat of phase change, strong adaptability of phase change temperature and greenness without pollution. It is often used as a shape memory material and mainly plays a role of molecular switch in the shape memory material. However, the polyethylene glycol-based shape memory polymer has obvious defects, that is, the mechanical properties and thermal properties of the material are low in a pure / original polymer system, and there is a liquid leakage phenomenon after the aerogel is made, which limits the application of this kind of material in the field of shape memory aerogel.

[0004] In order to solve this problem, researchers found that the shape memory aerogel can be effectively prepared by directly loading polyethylene glycol on the aerogel skeleton structure through immersion. This method solves the problems of poor mechanical properties and low adhesion of polyethylene glycol-based aerogel, but the shape memory aerogel still has the problems of low porosity, low response rate and serious damage to the structure of the aerogel.

[0005] Therefore, it is necessary to develop a shape memory polymer aerogel material with excellent mechanical properties and shape memory properties. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a nanofiber-based shape memory aerogel as well as a preparation method and application thereof, which has excellent mechanical properties and shape memory properties.

[0007] In a first aspect of the present application, a preparation method of a nanofiber-based shape memory aerogel is provided, which comprises the following steps:

[0008] S1.4,4-diamino diphenyl ether and 1,2,4,5-benzene tetracarboxylic dianhydride are added into N,N-dimethylformamide and reacted in a nitrogen environment to obtain a polyamic acid solution;

[0009] S2. The polyamic acid solution is used as a spinning solution for electrospinning to obtain a polyamic acid nanofiber membrane;

[0010] S3. cutting the polyamide acid nanofiber membrane into micron-length fibers and performing imidization treatment to obtain polyimide nanofibers;

[0011] S4. adding the polyimide nanofibers, high-molecular-weight polyethylene glycol diacrylate and low-molecular-weight polyethylene glycol diacrylate into water to uniformly disperse, then adding ammonium persulfate and tetramethyl ethylenediamine, stirring to uniformly mix to obtain a first mixed solution;

[0012] S5. performing a freeze polymerization reaction on the first mixed solution, and freeze-drying after the reaction is completed to obtain a nanofiber-based shape memory aerogel.

[0013] In some embodiments of the present application, in step S1, the use amount ratio of 4,4-diamino diphenyl ether, 1,2,4,5-benzene tetracarboxylic dianhydride and N,N-dimethylformamide is 12 mmol:12 mmol:(20-40) mL.

[0014] In some embodiments of the present application, the electrospinning condition is that the spinning speed is 0.5 ml / h, the spinning voltage is 18 kV, the collection roller rotation speed is 50 rad / min, and the receiving distance is 15 cm.

[0015] In some embodiments of the present application, in step S3, the imidization treatment is specifically a gradient temperature rising reaction in the range of 100℃-300℃.

[0016] In some specific embodiments of the present application, the imidization treatment is specifically a reaction at 100℃ for 1h, then a reaction at 200℃ for 1h, and then a reaction at 300℃ for 2h.

[0017] In some embodiments of the present application, the weight average molecular weight of the high-molecular-weight polyethylene glycol diacrylate is greater than 1000, and the weight average molecular weight of the low-molecular-weight polyethylene glycol diacrylate is less than 1000.

[0018] In some embodiments of the present application, the preparation method of the high-molecular-weight polyethylene glycol diacrylate is that an acryloyl chloride solution is slowly added to a solution containing high-molecular-weight polyethylene glycol and potassium carbonate to obtain a second mixed solution, and the second mixed solution is placed in a nitrogen atmosphere for reaction at room temperature to obtain the high-molecular-weight polyethylene glycol diacrylate.

[0019] In some embodiments of the present application, the solvent of the acryloyl chloride solution is anhydrous dichloromethane.

[0020] In some embodiments of the present application, the method for preparing the solution containing high molecular weight polyethylene glycol and potassium carbonate comprises: pouring high molecular weight polyethylene glycol, potassium carbonate and anhydrous dichloromethane into a three-necked flask with nitrogen blowing, and stirring until the high molecular weight polyethylene glycol is completely dissolved to obtain the solution containing high molecular weight polyethylene glycol and potassium carbonate.

[0021] In some embodiments of the present application, the weight average molecular weight of the high molecular weight polyethylene glycol is greater than 1000.

[0022] In some embodiments of the present application, the method for preparing the high molecular weight polyethylene glycol diacrylate comprises: slowly dropping an acryloyl chloride solution into the solution containing high molecular weight polyethylene glycol and potassium carbonate to obtain a second mixed solution, and placing the second mixed solution in a nitrogen atmosphere at room temperature for reaction, and preparing the high molecular weight polyethylene glycol diacrylate by vacuum filtration, rotary evaporation, extraction and vacuum drying.

[0023] In some embodiments of the present application, in the second mixed solution, the molar ratio of acryloyl chloride, high molecular weight polyethylene glycol and potassium carbonate is 5:1:5.

[0024] In some embodiments of the present application, in step S4, the mass ratio of the high molecular weight polyethylene glycol diacrylate to the low molecular weight polyethylene glycol diacrylate is 7:3.

[0025] In some embodiments of the present application, in step S4, the mass ratio of the polyimide nanofiber to the high molecular weight polyethylene glycol diacrylate is (7-14):100.

[0026] In some embodiments of the present application, in step S5, the freezing polymerization of the first mixed solution is specifically: first freezing a part of the mixed solution in liquid nitrogen for 2-3 min, and then freezing the whole in a zero temperature condition for 36-60 h.

[0027] The second aspect of the present application provides a nanofiber-based shape memory aerogel prepared by the above preparation method.

[0028] The third aspect of the present application provides an application of the above nanofiber-based shape memory aerogel in a thermal response material.

[0029] Compared with the prior art, the high-molecular polyethylene glycol diacrylate is obtained by modifying the high-molecular polyethylene glycol, the acrylate group has high reactivity, in the mixed solution of the high-molecular polyethylene glycol diacrylate and the low-molecular weight polyethylene glycol diacrylate, the polyimide nanofiber is mixed, the acrylate groups of the high-molecular polyethylene glycol diacrylate and the low-molecular weight polyethylene glycol diacrylate form a stable three-dimensional network structure PEGDA through cross-linking reaction, the cross-linking effectively fixes the polyimide nanofiber at a specific position, so that the polyimide nanofiber forms more 'network nodes' with the polyethylene glycol diacrylate cross-linking network inside the aerogel, the rigidity and ductility of the polyethylene glycol diacrylate aerogel inside are increased, and better shape memory and recovery performance of the aerogel are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0030] These and / or other aspects and advantages of the present application will become apparent and be more readily understood through consideration of the following description, taken in conjunction with the accompanying drawings, in which:

[0031] Figure 1 A process schematic diagram of a preparation method of a nanofiber-based shape memory aerogel provided by the present application;

[0032] Figure 2 Fourier transform infrared spectrograms and nuclear magnetic resonance hydrogen spectrograms of PEGDA4000 prepared in the present embodiment 1;

[0033] Figure 3 Optical photos of PINF / PEGDA-1, PINF / PEGDA-2 and PINF / PEGDA-3;

[0034] Figure 4 SEM photos of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2 and PINF / PEGDA-3 aerogel cross sections;

[0035] Figure 5 Radial compression stress-strain curves of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2 and PINF / PEGDA-3 aerogel;

[0036] Figure 6 DSC data of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3 and PINF;

[0037] Figure 7 Macroscopic photos of shape memory processes of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2 and PINF / PEGDA-3;

[0038] Figure 8 Scanning electron microscope images of PINF / PEGDA-2 in initial state (a), compressed state (b) and recovered state (c) prepared in Example 1 of the present application;

[0039] Figure 9 Thermodynamic curves (a) of PINF / PEGDA-2 prepared in Example 1 of the present application in shape memory process, temperature-time and strain-time curves (b) in a single temperature cycle, and temperature-time, stress-time and strain-time curves (c) in three temperature cycle periods. DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be further specifically explained below by means of examples in combination with the accompanying drawings. In the description, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present application with reference to the accompanying drawings is intended to explain the general inventive concept of the present application, and should not be understood as a limitation of the present application.

[0041] It should be noted that the terms used in the present application are generally the terms commonly used by those skilled in the art, and if they are inconsistent with the commonly used terms, the terms in the present application shall prevail.

[0042] As shown in Figure 1 , the embodiment of the first aspect of the present application provides a preparation method of nanofiber-based shape memory aerogel, comprising the following steps:

[0043] S1.4,4-diamino diphenyl ether and 1,2,4,5-benzene tetracarboxylic dianhydride are added to N,N-dimethylformamide and reacted in a nitrogen environment to obtain a polyamic acid solution;

[0044] S2. The polyamic acid solution is used as a spinning solution for electrospinning to obtain a polyamic acid nanofiber membrane (PAA nanofiber membrane);

[0045] S3. The polyamic acid nanofiber membrane is cut into micrometer-length fibers and subjected to imidization treatment to obtain polyimide nanofibers (PINF);

[0046] S4. The polyimide nanofibers (PINF), high molecular weight polyethylene glycol diacrylate (PEGDA 4000 ) and low molecular weight polyethylene glycol diacrylate (PEGDA 700 ) are uniformly dispersed in water, and then ammonium persulfate (APS) and tetramethyl ethylenediamine (TEMED) are added and stirred until uniformly mixed to obtain a first mixed solution;

[0047] S5. The first mixed solution is subjected to a freezing polymerization reaction, and after the reaction is completed, freeze-drying is performed to obtain a nanofiber-based shape memory aerogel.

[0048] The embodiment of the present application obtains high molecular polyethylene glycol diacrylate by modifying high molecular polyethylene glycol, so that the high molecular polyethylene glycol has a higher reactive acrylate group. Then, the high molecular polyethylene glycol diacrylate and the low molecular weight polyethylene glycol diacrylate are mixed into the polyimide nanofiber. The acrylate groups of the high molecular polyethylene glycol diacrylate and the low molecular weight polyethylene glycol diacrylate form a stable three-dimensional network structure PEGDA through cross-linking reaction. This cross-linking effectively fixes the polyimide nanofiber at a specific position, so that the polyimide nanofiber forms more 'network nodes' with the polyethylene glycol diacrylate cross-linking network inside the aerogel, increases the rigidity and ductility of the polyethylene glycol diacrylate aerogel inside, and promotes the aerogel to have better shape memory and recovery performance.

[0049] In some embodiments of the present application, the amount ratio of 4,4-diamino diphenyl ether, 1,2,4,5-benzene tetracarboxylic dianhydride and N,N-dimethylformamide in step S1 is 12 mmol:12 mmol:(20-40) mL.

[0050] In some embodiments of the present application, the electrospinning condition is that the spinning speed is 0.5 ml / h, the spinning voltage is 18 kV, the collection roller rotation speed is 50 rad / min, and the receiving distance is 15 cm.

[0051] In some embodiments of the present application, the imidization treatment in step S3 is specifically a gradient temperature rising reaction in the range of 100-300 DEG C. The imidization treatment in the gradient temperature rising manner can make the reaction more uniform.

[0052] In some specific embodiments of the present application, the imidization treatment is specifically that first reacting at 100 DEG C for 1 h, then reacting at 200 DEG C for 1 h, and then reacting at 300 DEG C for 2 h.

[0053] In some embodiments of the present application, the weight average molecular weight of the high molecular weight polyethylene glycol diacrylate is greater than 1000 (for example, PEGDA 4000 ), and the weight average molecular weight of the low molecular weight polyethylene glycol diacrylate is less than 1000 (for example, PEGDA 700 ).

[0054] In some embodiments of the present application, the preparation method of the high molecular weight polyethylene glycol diacrylate is: slowly adding an acryloyl chloride solution into a solution containing high molecular weight polyethylene glycol and potassium carbonate to obtain a second mixed solution, and reacting the second mixed solution at room temperature under a nitrogen atmosphere to obtain the high molecular weight polyethylene glycol diacrylate. This step is used for modifying the high molecular weight polyethylene glycol to make it have a higher reactive acrylate group, and at the same time, improve the mechanical properties of the polymer.

[0055] In some embodiments of the present application, the solvent of the acryloyl chloride solution is anhydrous dichloromethane.

[0056] In some embodiments of the present application, the preparation method of the solution containing high molecular weight polyethylene glycol and potassium carbonate is: pouring high molecular weight polyethylene glycol, potassium carbonate and anhydrous dichloromethane into a three-necked flask with nitrogen, and stirring until the high molecular weight polyethylene glycol is completely dissolved to obtain the solution containing high molecular weight polyethylene glycol and potassium carbonate.

[0057] In some embodiments of the present application, the weight average molecular weight of the high molecular weight polyethylene glycol is greater than 1000, for example, PEG 4000 .

[0058] In some embodiments of the present application, the preparation method of the high molecular weight polyethylene glycol diacrylate is: slowly adding an acryloyl chloride solution into a solution containing high molecular weight polyethylene glycol and potassium carbonate to obtain a second mixed solution, and reacting the second mixed solution at room temperature under a nitrogen atmosphere, and then preparing the high molecular weight polyethylene glycol diacrylate through vacuum filtration, rotary evaporation, extraction and vacuum drying.

[0059] In some embodiments of the present application, in the second mixed solution, the molar ratio of acryloyl chloride, high molecular weight polyethylene glycol and potassium carbonate is 5:1:5.

[0060] In some embodiments of the present application, in step S4, the mass ratio of the polyimide nanofiber to the high molecular weight polyethylene glycol diacrylate is (7-14):100.

[0061] In some embodiments of the present application, in step S4, the mass ratio of the high molecular weight polyethylene glycol diacrylate to the low molecular weight polyethylene glycol diacrylate is 7:3.

[0062] In some embodiments of the present application, in step S5, the first mixed solution is subjected to a freeze polymerization reaction, specifically: first, a part of the first mixed solution is frozen in liquid nitrogen for 2-3 min, and then the whole is frozen in a zero temperature condition for 36-60 h.

[0063] If directly and quickly frozen, cross-linking is not complete, the aerogel shrinks seriously in the drying process, and the mechanical property of the aerogel is affected, in the embodiment of the present application, the purpose of partial freezing and then overall freezing is to enable the material to be completely cross-linked.

[0064] In some embodiments of the present application, step S5 is specifically: a part of the first mixed solution is frozen in liquid nitrogen for 2-3 min, that is, a part is in a low-temperature environment and a part is in a normal-temperature environment, to form ice crystals; and then the material is transferred to a subzero temperature condition to slowly occur cross-linking reaction.

[0065] Embodiments of the second aspect of the present application provide the nanofiber-based shape memory aerogel prepared by the above preparation method.

[0066] Embodiments of the third aspect of the present application provide an application of the above nanofiber-based shape memory aerogel in a thermal response material.

[0067] Embodiment 1

[0068] (1) 40 g of PEG 4000 , 6.91 g of potassium carbonate (K2CO3) and 200 ml of anhydrous dichloromethane (CH2Cl2) were poured into a three-necked flask with nitrogen and stirred at room temperature for 1 h until the PEG 4000 was completely dissolved, and this solution was named as A. Then 4.06 ml of acryloyl chloride was added to 40 ml of CH2Cl2 to prepare a B solution. Then the B solution was slowly added to the A solution, and the reaction was carried out at room temperature for 48 h under a nitrogen atmosphere. After the reaction was completed, K2CO3 was removed by vacuum filtration, and the solution was concentrated to 40 ml by using a rotary evaporator. Finally, the concentrated solution was poured into anhydrous ether (ice bath) for extraction, the precipitate was collected, and the precipitate was dried in a vacuum oven at 35℃ until the weight of the precipitate no longer changed to obtain PEGDA 4000 white powder. Figure 2 The Fourier transform infrared spectrum and the nuclear magnetic resonance hydrogen spectrum of the PEGDA 4000 ; Figure 2 (a) of the PEGDA 4000 and the Fourier infrared transform spectrum of PEG 4000 , it can be found that, compared with the infrared spectrum of PEG 4000 , the modified PEGDA 4000 has a clear C=O stretching vibration peak at 1720 cm -1 . Figure 2 (b) is the PEGDA 4000PEGDA. The results of the infrared spectrum and the nuclear magnetic resonance hydrogen spectrum proved the successful preparation of PEGDA. 4000

[0069] (2) A three-neck flask was added 20 ml of N,N-dimethylformamide (DMF), 2.4 g of 4,4-diamino diphenyl ether (ODA) was added to the container and stirred for 0.5 h until completely dissolved, then 2.6 g of 1,2,4,5-benzene tetra carboxylic dianhydride (PMDA) was reacted for 6 h under nitrogen atmosphere at 4°C, after the reaction was completed, 13.5 ml of DMF solution was added and ultrasonically stirred for 2 h under the same conditions, to obtain polyamide acid (PAA) spinning solution. The PAA nanofiber membrane was prepared using an electrospinning machine, and the spinning process was as follows: the spinning speed was 0.5 ml / h, the spinning voltage was 18 kV, the collection roller speed was 50 rad / min, and the receiving distance was 15 cm, to obtain the PAA nanofiber membrane. The PAA nanofiber membrane was cut into micron-length fibers using a homogenizer, and the PAA fibers were amidated (graded temperature treatment from low to high: first 100°C for 1 h, then 200°C for 1 h, then 300°C for 2 h, and then cooling), to obtain polyimide nanofiber (PINF).

[0070] (3) 3.15 g of PEGDA 4000 , 1.35 g of PEGDA 700 , and 0.3 g of PINF were added to 30 ml of deionized water and stirred at room temperature for 2 h. Then 1 ml of ammonium persulfate (APS) (4 wt%) solution and 100 μl of tetramethyl ethylenediamine (TEMED) were added to the mixed solution, and the mixture was stirred vigorously for 30 s to mix completely, and the mixed solution was transferred to a cuboid mold, and the bottom of the mold was immersed in liquid nitrogen to directionally freeze the mixed solution. Finally, the mold was placed in a refrigerator at -10°C to freeze polymerize for 48 h, and after the freeze polymerization was completed, freeze-drying was performed for 60 h to obtain a nanofiber-based shape memory aerogel 1, denoted as PINF / PEGDA-2.

[0071] Example 2

[0072] Steps (1) and (2) were the same as in Example 1, and step (3) was as follows:

[0073] 2.1 g of PEGDA 4000 , 0.9 g of PEGDA 700 ​and 0.3 g PINF were added into 30 ml deionized water and stirred at room temperature for 2 h. Then 1 ml APS (4 wt%) solution and 100 μΐ TEMED were added into the mixed solution and stirred vigorously for 30 s to make them fully mixed. The mixed solution was quickly transferred into a cuboid mold and the mixed solution in the mold was directionally frozen by immersing the bottom of the mold into liquid nitrogen. Finally, the mold was put into a refrigerator at -10 °C for 48 h of cryopolymerization and then freeze-dried for 60 h after the completion of the cryopolymerization to obtain a nanofiber-based polyethylene glycol diacrylate shape memory aerogel, denoted as PINF / PEGDA-1.

[0074] Example 3

[0075] Step (1) and Step (2) were the same as Example 1, and Step (3) was as follows:

[0076] 4.2 g PEGDA 4000 , 1.8 g PEGDA 700 and 0.3 g PINF were added into 30 ml deionized water and stirred at room temperature for 2 h. Then 1 ml APS (4 wt%) solution and 100 μΐ TEMED were added into the mixed solution and stirred vigorously for 30 s to make them fully mixed. The mixed solution was quickly transferred into a cuboid mold and the mixed solution in the mold was directionally frozen by immersing the bottom of the mold into liquid nitrogen. Finally, the mold was put into a refrigerator at -10 °C for 48 h of cryopolymerization and then freeze-dried for 60 h after the completion of the cryopolymerization to obtain a nanofiber-based polyethylene glycol diacrylate shape memory aerogel, denoted as PINF / PEGDA-1.

[0077] Comparative Example 1

[0078] This comparative example 1 provides a preparation method of a polyethylene glycol diacrylate shape memory aerogel, and the specific steps are as follows:

[0079] (1) 40 g PEG 4000 , 6.91 g K2CO3 and 200 ml anhydrous CH2Cl2 were poured into a three-necked flask with nitrogen and stirred at room temperature for 1 h until PEG 4000 was completely dissolved, and this solution was named as solution A. Then 4.06 ml acryloyl chloride was added into 40 ml CH2Cl2 to prepare solution B. Then solution B was slowly added dropwise into solution A, and the reaction was carried out at room temperature for 48 h under a nitrogen atmosphere. After the completion of the reaction, K2CO3 was removed by vacuum filtration, and the solution was concentrated to 40 ml by using a rotary evaporator. Finally, the concentrated solution was poured into anhydrous ether (ice bath) for extraction, and the precipitate was collected and dried in a vacuum oven at 35 °C until the weight of the precipitate no longer changed to obtain PEGDA 4000 white powder.

[0080] (2) 3.15 g PEGDA4000 and 1.35 g PEGDA 700 The mixture solution was stirred at room temperature for 2 h. Then 1 ml APS (4 wt%) solution and 100 μl TEMED were added into the mixture solution, which was stirred vigorously for 30 s to make it fully mixed. The mixture solution was quickly transferred into a cuboid mold, and the mixture solution in the mold was directionally frozen by a block of iron soaked in liquid nitrogen at the bottom. Finally, the mold was put in a refrigerator at -10 °C to freeze polymerize for 48 h, and then freeze-dried for 60 h to obtain aerogels with directional channel structure, which was denoted as PEGDA.

[0081] Figure 3 The optical photos of PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3. It can be seen that the aerogels of PINF / PEGDA with different ratios prepared by the above method are shaped regularly, and the color of the PINF / PEGDA aerogels gradually changes from yellow to white with the increase of the content of PEGDA.

[0082] Figure 4 The cross-section SEM images of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3 aerogels. Figure 4 In the figure, a figure (low magnification) and a' figure (high magnification) are the cross-section scanning electron microscope images of PEGDA prepared by Comparative Example 1; b figure (low magnification) and b' figure (high magnification) are the cross-section scanning electron microscope images of PINF / PEGDA-1 prepared by Example 2; c figure (low magnification) and c' figure (high magnification) are the cross-section scanning electron microscope images of PINF / PEGDA-2 prepared by Example 1; d figure (low magnification) and d' figure (high magnification) are the cross-section scanning electron microscope images of PINF / PEGDA-3 prepared by Example 3. It can be seen from the figure that Figure 4 It can be seen that there are many closed and incomplete places in the PEGDA aerogel, the channels of the PINF / PEGDA-2 aerogel in the axial direction are relatively dense, the pore size is small (25-40 μm), the pore wall is thick (500-700 nm), and a three-dimensional interconnected channel structure is presented, which is more complete than the channel structure of the PEGDA aerogel, and the dimensional stability of the aerogel is better. However, with the increase of the content of PEGDA, the pore size of the PINF / PEGDA aerogel decreases (from 60 μm to 15 μm), and the channels of the aerogel in PINF / PEGDA-3 appear a certain degree of collapse and closure.

[0083] Test Example 1

[0084] The compression performance of the aerogels prepared by the method shown in Comparative Example 1, Example 1, Example 2 and Example 3 was tested using a Modle E43 universal material testing machine. The compression rate of the material instrument was set to 5 mm / min. After the test, the force-displacement curve of the material was obtained, and the compression stress-strain curve was calculated as shown in Figure 5 .

[0085] Figure 5 The radial compression stress-strain curves of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3 aerogels are shown in Figure 5 It can be seen that the compression stress of PEGDA aerogel in the longitudinal direction is 200.4 kPa. The introduction of PINF increases the compression stress of PINF / PEGDA aerogel, and the compression stress of PINF / PEDGA-2 is 1058.92 kPa. With the increase of PEGDA content, the maximum stress of the aerogel is significantly increased, such as at the compression strain of 60% of the aerogel, the maximum stress of PINF / PEGDA-1 (225.67 kPa) is much lower than that of PINF / PEGDA-3 (1958.88 kPa).

[0086] Test Example 2

[0087] Differential scanning calorimetry (DSC) test: about 10 mg of different component aerogel samples were weighed into the test crucible, the sample temperature was raised to 100°C at a rate of 5°C / min and kept for 5 min to eliminate the thermal history of the sample, then the sample temperature was cooled to -20°C at a rate of -5°C / min, and finally the sample was heated to 100°C at the same heating rate, and the experiment was carried out in a nitrogen atmosphere.

[0088] Figure 6DSC data of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3 and PINF. PINF is the polyimide nanofiber sample prepared in step (2) of Example 1. It can be seen that the PEGDA aerogel without PINF has a melting temperature (Tm) of 58℃ and a crystallization temperature (Tc) of 38℃. The PINF / PEGDA-2 aerogel with the same PEGDA concentration has a Tm of 55℃ and a Tc of 34℃, which is lower than that of the PEGDA aerogel. In order to further explore the relationship between the initial concentration of PEGDA and the phase change behavior, PINF / PEGDA aerogels with different concentrations were tested. The Tm and Tc of PINF / PEGDA-1 aerogel are about 56℃ and 37℃, and the Tm and Tc of PINF / PEGDA-3 aerogel are about 51℃ and 31℃. With the increase of the initial concentration of PEGDA, the Tm and Tc of the aerogel show a downward trend. The DSC results prove that the PINF / PEGDA and PEGDA aerogels have obvious crystallization-melting phase transition, which retains the possibility of achieving excellent thermal response shape memory performance.

[0089] Figure 7 Macroscopic photos of the shape memory process of PEGDA, PINF / PEGDA-1, PINF / PEGDA-2, PINF / PEGDA-3. In the initial state, all aerogels are cubic blocks. Using a tablet press, the sample is compressed to 30% of the initial height at 80℃ environment, and cooled at room temperature to fix the shape of the aerogel. Finally, the sample is placed back into the 80℃ environment, and the recovery state of the aerogel is observed. As can be seen from the figure, the PEGDA aerogel cannot achieve rebound, indicating that it does not have significant shape memory performance. The PINF / PEGDA-2 aerogel prepared with PINF aerogel skeleton as template has excellent shape memory performance, indicating that PINF significantly enhances the shape memory of the PEGDA aerogel. The scanning electron microscope images of PINF / PEGDA-2 in the initial state (a), compressed state (b) and recovery state (c) are shown in FIG. 6. Figure 8

[0090] Test Example 3

[0091] Select compression fixture, DMA control force mode, and cylindrical sample.

[0092] ​The shape memory function of the PINF / PEGDA-2 aerogel was quantitatively studied using a dynamic mechanical analyzer (DMA). The test process was as follows: first, a stress of 0.8 kPa was applied to the sample to ensure that the sample and the clamp were tightly fitted, and then the sample was heated to 80°C at a heating rate of 10°C / min, and was allowed to stand for 10 min to eliminate the thermal history of the sample. Then, a stress of 1 MPa was applied to the sample at 80°C, and the temperature of the sample was lowered to 20°C by passing cold nitrogen gas to fix the shape under the stress. After standing for 5 min, the stress was removed to obtain a temporary shape. Finally, the sample was heated to 80°C at a heating rate of 10°C / min and was kept at 80°C for 10 min. The above steps were repeated 3 times. During the dynamic test, the instrument recorded the data of time, temperature, force and deformation in real time. The stress and strain data were calculated according to the original size of the sample and the stress cross-sectional area. The shape fixing rate (R f ) and the shape recovery rate (R r ) of the shape memory aerogel can be calculated according to formulas (1) and (2), respectively.

[0093]

[0094] wherein ε f(N) is the strain of the sample after eliminating the thermal history in the initial stage, ε d(N) is the strain corresponding to the pre-deformation shape of the sample obtained after the test temperature was lowered to 20°C, ε f(N) is the strain of the sample after the stress was removed at 20°C, and ε p(N) is the strain of the sample after being heated to 80°C and kept at 80°C for 10 min. The strain data in different stages were obtained by calculation after the DMA test.

[0095] The test results of the PINF / PEGDA-2 dynamic mechanical analyzer are shown in FIG. 1. Figure 9 Figure 9 In FIG. 1, (a) is the thermodynamic curve of the PINF / PEGDA-2 prepared in this embodiment 1 in the shape memory process. After three cycles, the thermodynamic curve can still be closed, indicating that the aerogel has excellent shape memory performance. Meanwhile, under the action of a force of 1 MPa, the aerogel has a deformation of 62%, showing excellent thermal deformation performance. (b) is the temperature-time and strain-time curves in a single temperature cycle. From the strain data in each stage, the R f = 100% and R r ​= 99.8%. Meanwhile, the sample needed only 12 s to recover from 62% strain to 0% strain after the temperature was again raised to 80 °C, showing the fast response speed of the aerogel. (c) The figure is the temperature-time, stress-time and strain-time curves in three temperature cycle periods. It can be seen from the figure that the stress-time and strain-time curves of the aerogel remain essentially unchanged during the three cycles; by calculation, the R f R r remained at 100% and 99.8%, indicating that the PINF / PEGDA-2 aerogel has excellent shape memory stability.

[0096] While some embodiments of the general inventive concept have been shown and described, one of ordinary skill in the art will appreciate variations that can be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing nanofiber-based shape memory aerogel, characterized in that: The preparation method comprises the following steps: S1. 4,4-diaminodiphenyl ether and 1,2,4,5-pyromellitic dianhydride were added to N,N-dimethylformamide and reacted in a nitrogen atmosphere to obtain a polyamic acid solution; S2. The polyamic acid solution was used as a spinning solution for electrospinning to obtain a polyamic acid nanofiber membrane; S3. The polyamic acid nanofiber membrane is cut into micron-length fibers, and subjected to imidization treatment to obtain polyimide nanofibers; S4. The polyimide nanofibers, high molecular weight polyethylene glycol diacrylate and low molecular weight polyethylene glycol diacrylate were added to water and dispersed evenly, and then ammonium persulfate and tetramethylethylenediamine were added and stirred until uniformly mixed to obtain a first mixed solution; S5. The first mixed solution is subjected to freeze polymerization reaction, and freeze-dried after the reaction is completed to obtain a nanofiber-based shape memory aerogel.

2. The preparation method according to claim 1, characterized in that In step S1, the usage ratio of 4,4-diaminodiphenyl ether, 1,2,4,5-pyromellitic dianhydride and N,N-dimethylformamide is 12 mmol:12 mmol:(20-40) mL.

3. The preparation method according to claim 1, characterized in that In step S3, the imidation treatment is specifically: a gradient temperature reaction is performed within the range of 100°C-300°C.

4. The preparation method according to claim 1, characterized in that The weight average molecular weight of the high molecular weight polyethylene glycol diacrylate is greater than 1000, and the weight average molecular weight of the low molecular weight polyethylene glycol diacrylate is less than 1000.

5. The preparation method according to claim 1, characterized in that The preparation method of the high molecular weight polyethylene glycol diacrylate comprises: slowly adding an acryloyl chloride solution dropwise to a solution containing high molecular weight polyethylene glycol and potassium carbonate to obtain a second mixed solution; and placing the second mixed solution in a nitrogen atmosphere to react at room temperature to prepare the high molecular weight polyethylene glycol diacrylate.

6. The preparation method according to claim 1, characterized in that In step S4, the mass ratio of the polyimide nanofibers to the high molecular weight polyethylene glycol diacrylate is (7-14):

100.

7. The preparation method according to claim 1, characterized in that In step S4, the mass ratio of high molecular weight polyethylene glycol diacrylate to low molecular weight polyethylene glycol diacrylate is 7:

3.

8. The preparation method according to claim 1, characterized in that In step S5, the first mixed solution is subjected to a freeze polymerization reaction, specifically: a portion of the mixed solution is first frozen in liquid nitrogen for 2 to 3 minutes, and then the entire mixed solution is placed in a sub-zero temperature condition and frozen for 36 hours to 60 hours.

9. A nanofiber-based shape memory aerogel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nanofiber-based shape memory aerogel according to claim 9 in thermal responsive materials.

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