CN115960360A - Material with pressure clamping effect and preparation method and application thereof - Google Patents
Material with pressure clamping effect and preparation method and application thereof Download PDFInfo
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention provides a press-clamping effect material which is a PEG/PET solid-solid phase change copolymer material, wherein the press-clamping effect material comprises PET serving as a carrier framework material and PEG serving as a phase change material, and the mass ratio of the PET to the PEG is (1). The PEG/PET material has huge latent heat of phase change and entropy change in the phase change process, has huge pressure heat entropy change and relatively higher sensitivity of phase change to a pressure field, can reach huge isothermal entropy change value and pressure heat entropy change under small pressure, and has potential application value in the aspect of pressure heat refrigeration technology. The PEG with different molecular weights and the PEG with different proportions are combined to generate copolymerization reaction to realize the regulation of phase transition temperature and other thermal properties, so that the PEG/PET system becomes a controllable pressure heat material system, and the PEG/PET system has potential application value in the aspects of meeting the refrigeration technical requirements under various conditions, optimizing the refrigeration efficiency and the like.
Description
Technical Field
The invention relates to a material with a pressure card effect, a preparation method and application thereof
Background
The refrigeration technology in the modern society is more and more widely applied, and the refrigeration energy consumption is more than 15 percent of the total energy consumption, which is equivalent to 450 multiplied by 10 per year 6 Ton of CO 2 And (4) discharging the amount. The working gas freon of the currently commonly used vapor compression refrigeration technology has a strong ozone consumption effect, and the carnot cycle efficiency can only reach 25%. The refrigeration technology which can achieve both environmental protection and high-efficiency energy conservation is important, and meanwhile, the selection of the refrigeration working medium cannot be ignored.
Solid state refrigeration technology based on thermal effects is a particular concern and is considered to be a more environmentally friendly, more efficient alternative to gas compression based refrigeration technology. The solid phase-change material can generate entropy change and temperature change under the driving of a magnetic field, an electric field, axial force or isostatic pressure, namely magnetic card (thermal), electric card (thermal), elastic card (thermal) and pressure card (thermal) effects, which are collectively called solid thermal effect. The thermal effect of the solid state first order phase change provides the possibility of controlling the exchange of latent heat by an external field, with refrigeration energy efficiencies of up to 75%.
Among the solid state thermal effects currently studied, the magnetocaloric and electrocaloric effects are well studied. The use of the magnetocaloric effect often requires a large magnetic field to drive, which is not easily achieved in practical use; meanwhile, the magnetic material of the refrigeration working medium usually contains rare earth elements in nature, which increases the use cost to a certain extent. The refrigerating temperature span of the electrothermal effect is usually limited, and the electrothermal effect often occurs at a temperature different from the ambient temperature, so that the practical application is limited; the polar material of the refrigeration working medium needs to be driven by an electric field, and a complex material synthesis process is also needed to reduce the blocking leakage current.
Compared with magnetic cards, elastic cards and electric card effects, the research on the card pressing effect is still in the starting stage, so that the research on novel card pressing materials and the clarification of the card pressing effect mechanism are the main research directions in the current stage. The autoclaving effect refers to a physical phenomenon in which a material generates exothermic or endothermic behavior due to pressure. Mechanical heat effect driven by mechanical force, particularly piezothermal effect, generally exists in the first-stage phase-change material, but the material is not required to have magnetic or electric polarization property, so that the phase change driven by an external field is easier and more convenient to realize; meanwhile, the autoclave material is easy to prepare, and the packaging process enables the autoclave material not to be limited to the shape of the material. The research on the piezothermal effect is indispensable for the refrigeration technology pursuing green sustainable development.
The giant pressure thermal effect usually occurs near the first order phase transition of the material, which is driven by pressure to generate thermal response when proper pressure is applied near the phase transition temperature of the material. In current research, the autoclave effect is generally evaluated based on isothermal entropy change or adiabatic temperature change under pressure. In recent years, the piezothermal effect of many materials has been reported, exhibiting excellent refrigeration performance and distinctive field-induced phase change. Such as MnCoGe 0.99 In 0.01 、MnCoGeB 0.03 、(MnNiSi) 0.62 (FeCoGe) 0.38 、(Ni 50 Mn 31.5 Ti 18.5 ) 99.8 B 0.2 Isoalloyed materials, (NH) 4 ) 2 SO 4 、(NH 4 ) 2 NbOF 5 、(NH 4 ) 2 SnF 6 、(NH 4 ) 2 MoOF 4 Iso-inorganic salt and super-ionic conductor AgI, caF 2 Can reach more than 50 J.Kg under a certain pressure -1 ·K -1 Isothermal entropy change of (a). TRIS [ (NH) 2 )C(CH 2 OH) 3 ]、PG[(CH 3 )C(CH 2 OH) 3 ]、AMP[(NH 2 )(CH 3 )C(CH 2 OH) 2 ]、NPG[(CH 3 ) 2 C(CH 2 OH) 2 ]The novel plastic crystal autoclave material has more excellent autoclave performance, the isothermal autoclave entropy change of the material is higher than that of the inorganic material by one order of magnitude, and the maximum isothermal autoclave entropy change can reach 680 J.Kg -1 ·K -1 Left and right. The discovery of the plastic-crystalline material plays an essential role in the development process of the piezothermal effect due to the considerable piezothermal effect.
Suitable solid materials for commercial use are subject to cost and toxicity concerns, as well as phase change with large latent heat at the desired operating temperature. For example, the plastic crystal material generates huge isothermal entropy change after undergoing first-order phase change under pressure, so that the plastic crystal material becomes a candidate material with excellent autoclave effect. However, refrigeration technology that is efficient and feasible in practical applications necessarily requires materials with high sensitivity to applied external fields while having large latent heat. The above materials like MnCoGe 0.99 In 0.01 The alloy can obtain 52 J.kg under the pressure of 3kbar -1 ·K -1 Pressure-heat entropy change of; inorganic Compound (NH) 4 ) 2 SO 4 Although 60 J.Kg can be achieved under the pressure of 1kbar -1 ·K -1 The entropy change value of the material is not comparable to that of a plastic crystal material; the highest isothermal pressure thermal entropy change of the plastic crystal material such as TRIS which is in particular concerned can reach 682 J.Kg -1 ·K -1 But in applications a high pressure of about 50kbar is required due to its large thermal hysteresis. The application of high pressure is as difficult to achieve in practical applications as a high magnetic field. Therefore, a phase change material with large latent heat driven by small pressure is expected to be applied in practical application.
Disclosure of Invention
Therefore, the invention aims to provide a novel high-performance autoclave material system and a preparation method and application thereof.
The inventor of the invention discovers through intensive research that the PEG/PET copolymer with solid-solid phase change prepared by a physical modification method is a typical first-order phase change material, the phase change process is accompanied by larger phase change latent heat and entropy change, and the entropy change of the phase change process can reach-430 J.Kg to the maximum -1 ·K -1 . Compared with plastic crystal material with huge entropy change, the phase change of the PEG/PET copolymer is more sensitive to the action of a pressure field, and the reversible entropy change is 41 J.Kg under the pressure of 1kbar -1 ·K -1 . The maximum pressure-driven phase change rate can reach 10.7K/kbar, and the maximum reversible entropy change can be achieved under the small pressure drive of 3 kbar. The giant piezothermal effect under small pressure is shown for the first time, and the sensitivity to a pressure field is also superior to that of most of the giant piezothermal materials reported before. By regulating the molecular weight of PEG, the phase transition temperature and entropy change of the PEG/PET copolymer can be effectively regulated, and the optimization of the performance of the autoclave material is realized.
The invention prepares PEG/PET solid-solid phase change copolymer materials with different PEG molecular weights by taking polyethylene terephthalate (PET) as a framework material and polyethylene glycol (PEG) as a phase change material and fixing the solid-liquid phase change material PEG on the carrier framework PET by a physical modification method. Two ends of the PEG molecule are bound on the rigid PET molecular chain by hydrogen bonds or other intermolecular forces, so that the PEG molecule cannot be separated from the binding and cannot freely translate, and the PEG cannot be converted from a solid state into a liquid state at a melting point; however, the PEG molecules bound at two ends can still rotate or vibrate, and can form an amorphous state or a crystalline state along with the change of temperature, so that solid-solid phase transformation occurs. The PEG with different molecular weights is subjected to eutectic reaction in the PEG/PET copolymer to cause the synergistic effect of eutectic addition, so that the PEG/PET copolymer becomes a novel solid-solid phase change material with higher phase change enthalpy and controllable phase change temperature. The material has simple preparation method and low cost, can reach huge isothermal entropy change value under small pressure, and is a pressure-heating refrigeration working medium with great potential.
Unless otherwise indicatedTo illustrate, the term PEG as used herein is a commercial chemical Composition HO (CH) 2 CH 2 O) n H (n =13 to 454); PET is a commercial chemical composition of (C) 10 H 8 O 4 ) m (m =52 to 104).
As used herein, "molecular weight" is relative molecular weight.
In the invention, since PET is used as a carrier skeleton and PEG is a phase change material, the abbreviation of the PEG/PET material only shows the molecular weight of the PEG, and the PEG/PET material with the PEG relative molecular weight of 4000 is marked as PEG4000/PET; the molecular weight of PEG is shown by the molecular weight and proportion of PEG of two or more than two kinds of combined (PEG 1+ PEG 2)/PET materials, for example, the PEG/PET material generated by mixing PEG with the molecular weight of 4000 and 20000 is marked as (a PEG4000+ b PEG 20000)/PET, wherein a and b are the relative mass parts of PEG4000 and PEG20000 respectively.
The purpose of the invention is realized by the following technical scheme.
The invention provides a pressure-blocking effect material which is a PEG/PET solid-solid phase change copolymer material and comprises polyethylene terephthalate as a carrier framework material and polyethylene glycol as a phase change material, wherein the mass ratio of the polyethylene terephthalate to the polyethylene glycol is (1).
According to the material with the pressure clamping effect, provided by the invention, hydroxyl in PEG molecules and hydroxyl at the ends of PET molecules form hydrogen bond connection so as to retain the crystal characteristics of PEG.
According to the material with the effect of pressure-seizing provided by the invention, the mass ratio of PET to PEG is preferably 1.
According to the material with the pressure-card effect provided by the invention, the molecular weight of PEG can be 600-20000, and the relative molecular weight of PET can be 10000-20000.
The invention provides a pressure-card effect material, wherein the entropy change of the phase change process is 300 J.Kg -1 ·K -1 ～500J·Kg -1 ·K -1 。
The invention provides a material with the effect of pressure and seizing, wherein the material is 0.Maximum isothermal entropy change induced by 1GPa (GPa) 300 J.Kg -1 ·K -1 ～500J·Kg -1 ·K -1 。
The invention provides a material with the effect of pressure clamping, wherein the pressure-driven phase change rate is 76-105 KGPa -1 。
The invention also provides a preparation method of the material with the effect of pressing cards, which comprises the following steps:
1) Respectively dissolving PEG and PET in an organic solvent to obtain a PEG solution and a PET solution;
2) And mixing the PEG solution and the PET solution according to the mass ratio of the PEG to the PET, carrying out copolymerization reaction at 180-200 ℃, and cooling to obtain the material with the pressure-sensitive adhesive effect.
According to the preparation method provided by the invention, preferably, the organic solvent in step 1) is dimethyl sulfoxide. Preferably, the step 1) includes: preparing PEG solution from PEG and dimethyl sulfoxide according to the mass ratio of 1; preparing PET and dimethyl sulfoxide into a PET solution according to the mass ratio of 1.
Preferably, the step 1) may further include: before preparing the solution, drying the raw material PEG by using a silica gel drying agent until the weight is constant; and putting the PET in an oven, and drying for more than 4 hours at the temperature of between 100 and 120 ℃ until the weight is constant.
Preferably, the step 2) may further include: washing and filtering the product of the polymerization reaction, then placing the product in a vacuum drying oven, and drying the product in vacuum for 1 to 48 hours at a temperature of between 80 and 120 ℃.
The invention also provides the application of the material with the effect of pressing cards or the material with the effect of pressing cards obtained by the preparation method in the technology of hot pressing refrigeration.
Compared with the prior art, the invention has the following obvious advantages: firstly, the PEG/PET material is easy to prepare and the raw material is low in price. Meanwhile, on one hand, the PEG/PET material prepared by the inventor is a typical first-order phase change material, the phase change causes huge phase change latent heat and entropy change, and the entropy change in the phase change process can reach-430 J.Kg -1 ·K -1 . Compared with the plastic crystal material with huge entropy change reported in the pastThe PEG/PET phase-change material is more sensitive to the action of a pressure field, and the reversible entropy change is-41 J.Kg under the pressure of 1kbar -1 ·K -1 The pressure-driven phase change speed is 10.7K/kbar, and the maximum reversible entropy change (430 J.Kg) can be achieved under the small pressure drive of 3kbar -1 ·K -1 ). The giant piezothermal effect under small pressure is shown for the first time, and the sensitivity to a pressure field is also superior to all the giant piezothermal materials reported previously. On the other hand, the inventor finds that the entropy change is the largest in the phase change process when the molecular weight of pure PEG is 10000 through a calorimetric test result; PEG with different molecular weights can generate synergistic effect after being properly combined, the entropy change is larger than that when the PEG is used alone, and the phase transition temperature can also receive synergistic effect. Therefore, the phase transition temperature and entropy change of the autoclave material can be effectively regulated and controlled by regulating and controlling the molecular weight of PEG, and the optimization of the performance of the autoclave material is realized. The PEG/PET system material has the advantages of adjustable phase change and huge autoclave effect, and has great potential application value in autoclave refrigeration technology.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIGS. 1A to 1C are SEM scanning electron micrographs of PET6000/PET obtained in example 1 and room temperature XRD results thereof.
FIGS. 2A to 2E are heat flow curves at normal pressure of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET obtained in examples 1 to 5 in sequence, and arrows indicate the processes of temperature rise and temperature decrease.
FIGS. 3A to 3E are heat flow curves of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET prepared in examples 1-5 in sequence under different pressures, and arrows indicate the processes of temperature rise and temperature fall.
FIGS. 4A to 4E are entropy change curves of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET obtained in examples 1 to 5 in sequence under different pressures.
FIG. 5 is the isothermal entropy change curves resulting from the pressure of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET obtained in examples 1-5, wherein P represents the pressure and the arrows represent the pressurization and depressurization process.
FIG. 6 shows adiabatic temperature curves of the pressures of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET obtained in examples 1-5. In the figure P represents the pressure and the arrows indicate the pressurization and depressurization process.
FIG. 7 shows reversible isothermal entropy curves caused by pressures of PEG6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET and (1/2PEG4000 + 1/2PEG 20000)/PET obtained in examples 1-5. In the figure P represents the pressure and the arrows indicate the pressurization and depressurization process.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, and the examples are given only for illustrating the present invention and not for limiting the scope of the present invention.
Examples 1 to 23
The materials and equipment used in the examples are illustrated below:
1) Polyethylene glycol and dimethyl sulfoxide (DMSO, molecular formula C) 2 H 6 OS) is purchased from chemical reagents of national medicine group, and the purity is not lower than 98%.
2) The purity of the polyethylene terephthalate is not less than 98 percent, and the polyethylene terephthalate is purchased from the element mall official network under the flag of Suzhou Star science and technology Limited.
3) The magnetic stirrer used for the preparation of PEG/PET was purchased from Beijing Laegwey technologies, inc. model number of magnetic stirrer C-MAG HS7 Control.
4) The instrument source used by the scanning electron microscope is the complex nano science instrument (Shanghai) limited company, feina China, and the model is phenom proX; the measuring instrument used for the room temperature XRD was a Rigaku-SmartLab variable temperature X-ray diffractometer manufactured by Japan science;
5) The entropy change and the autoclaving effect in the phase transition process are measured by a SETARAM microcalorimeter (i.e. differential scanning calorimeter under pressure DSC) produced by kepu technologies, france.
The molecular weights of PEG used in the examples of the present invention are 600, 2000, 4000, 6000, 8000, 10000, 12000, 20000, respectively, and the molecular weight of PET is 15000, and the molecular weights and synthesis temperature conditions of PEG used in each example are specifically listed in Table 1.
The preparation method comprises the following steps:
1) Drying the raw material PEG by a silica gel drying agent until the weight is constant; putting PET in an oven, and drying at 110 ℃ for more than 4 hours until the weight is constant;
2) Weighing PET and PEG with different molecular weights according to the mass ratio. Preparing PEG and dimethyl sulfoxide into a solution according to the mass ratio of 1; preparing PET and dimethyl sulfoxide into a solution according to the mass ratio of 1;
3) Mixing the two solutions in the step 2) at 200 ℃ according to the mass ratio of PEG to PET being 95;
4) And (4) putting the copolymer obtained by filtering in the step 3) into a vacuum drying oven, and performing vacuum drying for 24 hours at 100 ℃ to obtain the PEG/PET copolymer.
TABLE 1
| Example numbering | Molecular weight of PEG | PEG/PET copolymer |
| 1 | 6000 | PEG6000/PET |
| 2 | 10000 | PEG10000/PET |
| 3 | 20000 | PEG20000/PET |
| 4 | 4000，20000 | (2/3PEG4000+1/3PEG20000)/PET |
| 5 | 4000，20000 | (1/2PEG4000+1/2PEG20000)/PET |
| 6 | 2000 | PEG2000/PET |
| 7 | 4000 | PEG4000/PET |
| 8 | 8000 | PEG8000/PET |
| 9 | 2000，20000 | (1/2PEG2000+1/2PEG20000)/PET |
| 10 | 2000，20000 | (2/3PEG2000+1/3PEG20000)/PET |
| 11 | 2000，20000 | (1/3PEG2000+2/3PEG20000)/PET |
| 12 | 4000，20000 | (1/3PEG4000+2/3PEG20000)/PET |
| 13 | 6000，20000 | (1/2PEG6000+1/2PEG20000)/PET |
| 14 | 6000，20000 | (2/3PEG6000+1/3PEG20000)/PET |
| 15 | 6000，20000 | (1/3PEG6000+2/3PEG20000)/PET |
| 16 | 2000，10000 | (1/2PEG2000+1/2PEG10000)/PET |
| 17 | 2000，10000 | (2/3PEG2000+1/3PEG10000)/PET |
| 18 | 2000，10000 | (1/3PEG2000+2/3PEG10000)/PET |
| 19 | 4000，10000 | (1/2PEG4000+1/2PEG10000)/PET |
| 20 | 4000，10000 | (2/3PEG4000+1/3PEG10000)/PET |
| 21 | 4000，10000 | (1/3PEG4000+2/3PEG10000)/PET |
| 22 | 600，4000，10000 | (1/6PEG600+1/6PEG4000+2/3PEG1000)/PET |
| 23 | 600，6000，10000 | (1/6PEG600+1/6PEG6000+2/3PEG1000)/PET |
And (3) performance testing and characterization:
1) Morphological analysis of copolymer
The morphological characteristics of the obtained sample are measured by a Scanning Electron Microscope (SEM), and a diffraction pattern at room temperature is given by an X-ray diffractometer. Typically, fig. 1A to 1C show SEM images and diffraction patterns thereof of example 1. It can be seen that the synthesized PEG/PET sample showed no phase separation and the copolymer morphology appeared as a uniform continuous structure. In the solid copolymer, PET and PEG have similar polarity and good compatibility. The hydroxyl in the PEG molecule and the hydroxyl at the end of the PET molecule form hydrogen bond connection, and the crystal property of the PEG is reserved.
2) Measurement of thermodynamic Properties at atmospheric pressure
The entropy change of the phase change process of the sample is measured by using a differential scanning calorimeter. Typically, FIGS. 2A-2E show the materials obtained in examples 1-5 (PEG 6000/PET, PEG10000/PET, PEG 20000/PET), (2) at a ramping rate of 1K/minHeat flow curves of/3PEG4000 + 1/3PEG 20000)/PET, (1/2PEG4000 + 1/2PEG 20000)/PET). At a heating rate of 1K/min, the measured heat flow curve shows: PEG6000/PET has phase change near 329K, and the entropy change in the phase change process is calculated to be 368 J.Kg -1 ·K -1 Thermal hysteresis 24K; PEG10000/PET has phase change near 335K, and the entropy change in the phase change process is calculated to be 425.5 J.Kg -1 ·K -1 Thermal hysteresis 22K; PEG20000/PET has phase change near 327K, and the entropy change in the phase change process is calculated to be 384 J.Kg -1 ·K -1 Thermal hysteresis 25K; (2/3 PEG4000+1/3PEG 20000)/PET has phase change near 324K, and the entropy change of the phase change process is calculated and found to be 376J-Kg -1 ·K -1 Thermal hysteresis 21K; (1/2PEG4000 + 1/2PEG 20000)/PET has phase change near 324K, and the calculation shows that the entropy change of the phase change process is 402.3 J.Kg -1 ·K -1 The thermal hysteresis was 19.7K. The materials have huge phase change entropy change, but the thermal hysteresis is less than most of reported entropy changes and is more than 100 J.Kg -1 ·K -1 Macro-autoclave materials (e.g., TRIS, thermal hysteresis 75K AMP 60K).
3) Measurement of the effect of pressure and heat
Measuring a heat flow curve and specific heat under different pressures by using a Differential Scanning Calorimeter (DSC) under the pressure, and calculating an entropy curve under different pressures so as to calculate the pressure-heat entropy change, the adiabatic temperature change under the pressure, the reversible pressure-heat entropy change and the reversible adiabatic temperature change. Typically, FIGS. 3A-3E show the heat flow curves of examples 1-5 (PEG 6000/PET, PEG10000/PET, PEG20000/PET, (2/3 PEG4000+1/3PEG 20000)/PET, (1/2 PEG4000+1/2PEG 20000)/PET at different pressures as determined by pressure DSC.
The heat flow curve shows that pressure can drive the phase transition temperature to move towards the high temperature region. Compared with the normal pressure, the phase change temperature of PEG6000/PET in the temperature rising process is shifted by about 9K and the phase change temperature in the temperature lowering process is shifted by about 10K under the pressure of 0.1GPa (the pressure-driven phase change rate in the temperature rising process is 87K-GPa) -1 The temperature reduction process is 101 K.GPa -1 ) (ii) a The phase change temperature of PEG10000/PET can move about 9K in the temperature rising process and about 10K in the temperature lowering process by the pressure of 0.1GPa (pressure driving)The temperature rise process of the phase change rate is 87 K.GPa -1 The temperature reduction process is 95 K.GPa -1 ) (ii) a The pressure of 0.1GPa can cause the phase transition temperature of PEG20000/PET in the temperature rise process to move by about 10K and the phase transition temperature in the temperature decrease process to move by about 8K (the pressure-driven phase transition rate temperature rise process is 96K-GPa) -1 The temperature reduction process is 76 K.GPa -1 ) (ii) a The pressure of 0.1GPa can cause the phase change temperature of (2/3 PEG4000+1/3PEG 20000)/PET temperature rise process to move by about 10K, and the phase change temperature of the temperature reduction process to move by about 11K (the pressure-driven phase change rate temperature rise process is 97K Gpa. GPa) -1 The temperature reduction process is 105 KGPa -1 ) (ii) a The pressure of 0.1GPa can cause the phase change temperature of (1/2PEG4000 + 1/2PEG 20000)/PET temperature rise process to move by about 10K, and the phase change temperature of the temperature reduction process to move by about 10K (the pressure-driven phase change rate temperature rise process is 97K-GPa) -1 The temperature reduction process is 104 K.GPa -1 ) The phase transition process of these samples is shown to be sensitive to pressure-driven induction, which is superior to most reported giant piezothermal materials, such as: the rates of AMP, TRIS and PG pressure-driven phase change in the cooling process are respectively about 85 +/-27 and 15 +/-6 K.GPa -1 ，94±3K·GPa -1 The phase change rate of AMP, TRIS and PG pressure drive in temperature rise process is about 64 + -4 and 37 + -2 K.GPa respectively -1 ，79±2K·GPa -1 。
According to the heat flow curves measured under different pressures in fig. 3A to fig. 3E, the entropy change curves (as shown in fig. 4A to fig. 4E) with temperature changes under different pressures are calculated, and the entropy change curves are subtracted by an indirect measurement method to obtain isothermal entropy change and adiabatic temperature change (as shown in fig. 5 and fig. 6) caused by the pressures. In the phase change process: the maximum isothermal entropy change of PEG6000/PET is about 380 J.Kg -1 ·K -1 The maximum isothermal entropy change of PEG10000/PET is 435 J.Kg -1 ·K -1 The maximum isothermal entropy change of PEG20000/PET is about 408 J.Kg -1 ·K -1 The maximum isothermal entropy change of (2/3PEG4000 + 1/3PEG 20000)/PET is about 383 J.Kg -1 ·K -1 The maximum isothermal entropy change of (1/2PEG4000 + 1/2PEG 20000)/PET is about 402 J.Kg -1 ·K -1 . The maximum pressure thermal entropy change of PEG6000/PET is about 360 J.Kg under the pressure of 0.1GPa -1 ·K -1 The maximum entropy change of PEG10000/PET is about 400 J.Kg -1 ·K -1 PEG20000/PET has a maximum entropy of about 390 J.Kg -1 ·K -1 The maximum entropy change of pressure and heat of (2/3 PEG4000+1/3PEG 20000)/PET is about 357 J.Kg -1 ·K -1 The maximum pressure-heat entropy change of (1/2PEG4000 + 1/2PEG 20000)/PET is about 373 J.Kg -1 ·K -1 Almost reaches the intrinsic phase transition entropy change value of the material, and is superior to the reported thermal entropy change of a plurality of thermal materials under 0.1 GPa. To account for the irreversible entropy change caused by hysteresis, a reversible isothermal entropy change curve is calculated, as shown in FIG. 7. It can be found that the reversible entropy change of PEG6000/PET is about 32 J.Kg at a pressure of 0.1GPa -1 ·K -1 The reversible entropy change of PEG10000/PET is about 34 J.Kg -1 ·K -1 The reversible entropy change of PEG20000/PET is about 14 J.Kg -1 ·K -1 The reversible entropy change of (2/3 PEG4000+1/3PEG 20000)/PET is about 31 J.Kg-1. K-1, and the reversible entropy change of (1/2 PEG4000+1/2PEG 20000)/PET is about 41 J.Kg -1 ·K -1 . The wide thermal hysteresis and the driving capability of weak pressure to phase change of NPG, AMP, TRIS and the like reported before enable reversible entropy change of the materials to be almost zero at small pressure of 0.1 GPa. The material of the invention has certain reversible entropy change under the small pressure of 0.1 GPa.
By combining the above results, it can be determined that: (1) The PEG/PET (the molecular weight of PEG is respectively 600, 2000, 4000, 6000, 8000, 10000, 12000 and 20000, the molecular weight of PET is 15000) material has huge pressure-heat entropy change and high sensitivity of phase change to pressure fields, and can reach huge isothermal entropy change value and pressure-heat entropy change under small pressure. (2) For PEG/PET materials corresponding to PEG with different molecular weights, huge thermal compression effect is shown under the pressure of 0.1 GPa. The PEG with the proper molecular weight is selected to adjust the phase change temperature to be near the room temperature in consideration of the combination of the PEG with different molecular weights and the PEG with different proportions, so that the application of the pressure heat material as a room temperature refrigerating working medium is promoted.
Claims (10)
1. The material with the function of blocking by pressing is a PEG/PET solid-solid phase change copolymer material, and comprises PET as a carrier framework material and PEG as a phase change material, wherein the mass ratio of the PET to the PEG is (1-25).
2. The electrocaloric effect material of claim 1, wherein hydroxyl groups in the PEG molecule form hydrogen bonds with hydroxyl groups at the ends of the PET molecule to preserve the crystalline properties of PEG.
3. The material according to claim 1 or 2, wherein the mass ratio of PET to PEG is 1.
4. The piezocard effect material according to any one of claims 1 to 3 wherein the molecular weight of PEG is between 500 and 25000 and the relative molecular mass of PET is between 10000 and 20000.
5. The piezocard effect material according to any of claims 1 to 4, wherein the entropy change of the phase change process thereof is higher than 300J-Kg -1 ·K -1 。
6. The piezocard effect material of any one of claims 1 to 5 wherein its maximum isothermal entropy variation induced by a pressure of 0.1GPa is higher than 300J-Kg -1 ·K -1 。
7. The chuck-pressing effect material of any one of claims 1 to 6, wherein the pressure-driven phase transition rate is 76-105K-GPa -1 。
8. A process for the preparation of the presscard effect material according to any one of claims 1 to 7, comprising the following steps:
1) Respectively dissolving PEG and PET in an organic solvent to obtain a PEG solution and a PET solution;
2) And mixing the PEG solution and the PET solution according to the mass ratio of the PEG to the PET, carrying out copolymerization reaction at 180-200 ℃, and cooling to obtain the material with the pressure card effect.
9. The production method according to claim 8, wherein the organic solvent in step 1) is dimethyl sulfoxide;
preferably, the step 1) includes: preparing PEG solution from PEG and dimethyl sulfoxide according to the mass ratio of 1; preparing PET and dimethyl sulfoxide into a PET solution according to the mass ratio of 1;
preferably, the step 1) further comprises: before preparing the solution, drying the raw material PEG by using a silica gel drying agent until the weight is constant; and putting PET in a drying oven, and drying at 100-120 ℃ for more than 4 hours until the weight is constant;
preferably, the step 2) further comprises: washing and filtering the product of the polymerization reaction, then placing the product in a vacuum drying oven, and drying the product in vacuum for 1 to 48 hours at a temperature of between 80 and 120 ℃.
10. Use of the piezocard effect material according to any one of claims 1 to 7 or of the piezocard effect material prepared by the preparation process according to claim 8 or 9 in an autoclave refrigeration technology.
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