CN115305060A - Two-phase transparent phase change material and preparation method thereof - Google Patents

Abstract

The invention provides a double-phase transparent composite phase change material which has high transparency in both a crystalline state and an amorphous state, and solves the problem that the transparency of the existing phase change material or composite phase change material is reduced in the crystalline state. The double-phase transparent composite phase change material comprises a core material which presents a transparent characteristic in an amorphous state; the core material is loaded in a transparent cavity, and in an amorphous state, the core material flowing in the crystalline state fills the cavity, so that most light rays can penetrate through the whole material to present a transparent effect; in the crystalline state, a transparent chamber forms a crystallization unit, and the size of a crystal grain formed after crystallization in one direction is less than 1000nm, so that after light is incident along the direction, most of light can penetrate through the barrier of a barrier with the thickness below the wavelength, and the light is rarely absorbed and consumed, thereby showing the transparent effect.

Description

Two-phase transparent phase change material and preparation method thereof

technical field

The invention belongs to the field of phase-change materials, and in particular relates to a double-phase transparent composite phase-change material.

Background technique

Phase change materials (Phase Change Materials, PCM) are a class of functional materials, which can keep the temperature constant for a certain period of time during the process of storing and releasing energy, so that the phase change materials can realize the functions of energy storage and temperature regulation, so that It is widely used in alleviating energy crisis and improving energy utilization efficiency.

Since crystalline materials form different boundaries during crystallization, severe scattering occurs during the penetration of visible light, resulting in a sharp drop in transparency. On the other hand, in some special optoelectronic application scenarios, transparency is an indispensable requirement. If the crystalline material can form a compound with good transparency under the premise of maintaining its own characteristics by adjusting the structure, it will greatly expand the application space of crystalline functional materials. A typical example is a crystalline phase change material, which disperses the crystalline phase into the filling material, so that the size of the crystalline phase is controlled at a submicron size where light can pass through, and a relatively uniform isotropic distribution is formed, which is expected to achieve thermal management of transparent devices.

Contents of the invention

The invention provides a two-phase transparent composite phase change material, which has high transparency both in the crystalline state and the non-crystalline state, and solves the problem that the transparency of the existing phase change materials or composite phase change materials decreases in the crystalline state.

The dual-phase transparent composite phase-change material described in this application includes a core material that exhibits transparency in an amorphous state; the core material is loaded in a transparent chamber, and the chamber is at least along one wall of a direction o1 The spacing between cells is less than 1000 nm (preferably less than 500 nm); multiple chambers form a porous network (Figure 1). In the amorphous state, due to the intrinsic optical properties of the cavity and the core material, and the fluid core material in the amorphous state fills the cavity, most of the light can pass through the material as a whole, showing a transparent effect; in the crystalline state , a transparent chamber constitutes a crystallization unit, so that the size of the crystal grains formed after crystallization in the direction o1 is less than 1000nm (preferably less than 500nm), after incident along the light of o1, most of the light can penetrate the thickness of the obstacle below the wavelength The light is rarely absorbed and consumed, and it also shows a transparent effect in the o1 direction.

As can be seen above, in directions other than direction o1, it can be less than 1000nm, and can also be greater than or equal to 1000nm (Fig. 2); when the transparent cavity is a relatively symmetrical structure, such as a sphere, the wall spacing in each direction is less than 1000nm (preferably is less than 500nm); when the transparent cavity is such as an ellipsoid structure, the length of its short side (direction o1) is less than 1000nm (preferably less than 500nm), and the length of the long side (direction o2) can be greater than 1000nm.

The core material applicable to the present invention can be:

(1) Polymer phase change materials, such as polyethylene glycol, polyester, polymer wax

(2) Organic small molecule phase change materials, such as paraffin and its derivatives, fatty acids and their derivatives

(3) Inorganic phase change materials, such as crystalline hydrated salts, molten salts

(4) Eutectic phase change materials, such as polyethylene glycol-paraffin

A transparent chamber suitable for use in the present invention may employ:

(1) Transparent polymers, such as epoxy resin, organic silica gel, transparent plastic, plexiglass

(2) Transparent inorganic materials, such as inorganic glass, inorganic ceramics, Si-O coating/gel

(3) Transparent natural chamber materials, such as transparent wood, foam

Whether in crystalline or amorphous materials, the appearance of cracks often leads to a large number of interfaces inside the material, and strong internal diffuse reflection occurs at these interfaces after light enters. A large amount of light is consumed and absorbed in the process of diffuse reflection, and cannot pass through the material, resulting in a decrease in transmittance. In a preferred solution of the present application, the cavity is interference-filled with the core material. For chambers with a certain size and quantity, the core material is always in an interference state during the filling process, so as to ensure that each chamber can be filled efficiently by the core material, which can effectively avoid most cracks and further ensure its transmittance.

The volume of the crystallization process shrinks. If there are gaps in each grid, it will be reflected in a large number of micro-voids in the macroscopic view, and there will be a certain amount of diffuse reflection inside. Therefore, the present application further provides a solution to the problem of light transmission: the degree of crystallization at the edge of the core material is less than 100%, and the amorphous filling void generation area at the edge can effectively suppress the generation of cracks when transforming from an amorphous state to a crystalline state (Fig. 3).

Specifically, the way to suppress the crystallization of the edge portion of the core material at least includes:

(1) There is an intermolecular force between the wall of the chamber and the edge of the core material. The inner wall of the shaped cavity restrains the edge of the core material through intermolecular force to inhibit its orientation;

(2) The core material fills the cavity with interference, on the one hand resisting the volume shrinkage during the crystallization process, and on the other hand suppressing its orientation through the extrusion force of the cavity wall on the edge part.

The present invention also relates to the preparation method of the above-mentioned two-phase transparent composite phase change material, one of which is: by loading the core material into the chamber of the transparent porous network material by means of physical adsorption or chemical adsorption, the composite phase change material is obtained. phase change material. The second is: obtain the composite phase change material by co-constructing the cavity and the core material.

For adsorption methods, suitable porous network materials can be:

(1) Inorganic porous materials, such as transparent Si-O porous coatings/gels

(2) Organic porous materials, such as transparent porous epoxy resin

(3) Bioporous materials, such as transparent wood

Applicable core materials can be:

(1) Polymer phase change materials, such as polyethylene glycol, polyester, polymer wax

(2) Organic small molecule phase change materials, such as paraffin and its derivatives, fatty acids and their derivatives

(3) Inorganic phase change materials, such as crystalline hydrated salts, molten salts

(4) Eutectic phase change materials; such as polyethylene glycol-paraffin

The adsorption method generally impregnates the porous network material in the solution or dispersion of the core material, for example:

The porous SiO ₂ airgel is impregnated in a sufficient amount of polyethylene glycol (PEG), and the porous SiO ₂ airgel adsorbs the PEG to form a stable transparent composite phase change material through the impregnation adsorption method.

In some preferred schemes, system pressure control is used to further increase its filling rate, for example:

For a stable structure that is not easy to deform, such as transparent wood, the porous cavity structure formed inside the transparent wood will not be deformed under a certain pressurized condition, and the vacuum impregnation method is used to fill and adsorb PEG, so that PEG can smoothly enter some smaller sizes. In the cavity, the overall filling rate is improved, so as to obtain a more stable transparent composite phase change material.

For the co-construction of the cavity and the core material, the cavity is mixed with the core material when the cavity is not formed, and the cavity precursor is formed into a small-sized cavity by cross-linking and other means, and the core material is located in the cavity. Cavities of desired size can be obtained by controlling the degree of crosslinking. In general, the crosslinking process of cavity precursors requires the participation of crosslinkers and initiators.

Therefore, the cavity precursor suitable for the co-construction method should have the ability to be cross-linked, and can be used:

(1) Organic polymers, such as epoxy resin (EP), silicone, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polymethyl methacrylate;

(2) Inorganic, such as transparent Si-O gel;

The core material suitable for the co-construction method cannot participate in the aforementioned crosslinking reaction, and the technician can choose from the following core materials according to the group situation and combined with known attempts in the field:

(1) Organic phase change materials, such as polyethylene glycol (PEG), paraffin, fatty acid;

(2) Crystalline hydrated salts, such as sodium sulfate decahydrate (Na ₂ SO ₄ ·10H ₂ O), ammonium aluminum sulfate dodecahydrate (NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O);

The following takes the epoxy resin cavity and polyethylene glycol core material as an example to illustrate the co-construction method:

(1) After adding 3-6 parts by weight of cross-linking agent into 30-60 parts by weight of epoxy resin, mix it with 40-70 parts by weight of polyethylene glycol, and heat and stir in an environment above the thermal melting temperature to obtain A homogeneously mixed solution of phase change components;

(2) Add 2-3 parts by weight of curing accelerator to 20-30 parts by weight of methyl hexahydrophthalic anhydride, stir to obtain a curing agent solution;

(3) The phase change component solution and the curing agent solution are mixed and stirred, and vacuum-dried at a constant temperature above the phase change temperature to remove air bubbles in the mixed solution.

The beneficial effects of the present invention are:

(1) By optimizing the cavity size, the light transmittance of the crystalline state is above 50%, and the enthalpy value of the melting/crystallization process of the crystal reaches the ideal enthalpy value (ideal enthalpy value = the proportion of the phase change core material to the overall mass of the composite) × more than 50% of the enthalpy value of the phase change core material).

(2) By optimizing the boundary of the core material, the light transmittance of the crystalline state is further increased to more than 60%, and the enthalpy value of the melting/crystallization process of the crystal is increased to more than 70% of the ideal enthalpy value.

Description of drawings

Fig. 1 is all directions less than 1000nm (preferably less than 500nm) porous structure cavity distribution and core material filling diagram;

Fig. 2 is only o1 direction less than 1000nm (preferably less than 500nm) porous structure cavity distribution and core material filling diagram;

Fig. 3 is the schematic diagram that the crystallization of edge part of core material is suppressed;

Fig. 4 is the surface SEM comparison of embodiment 2 and PEG (the crystalline material used in the composite material) at the phase transition temperature;

Fig. 5 is the phase dispersion of cryosection TEM when embodiment 2 is at the phase transition temperature;

Fig. 6 is the transmittance-wavelength change curve when embodiment 2 is up/down at the phase transition temperature;

Fig. 7 is the differential scanning calorimetry test result of embodiment 2.

Figure 8 is a diagram of the transparency effect of composite materials A, B, C, and D at the PEG phase transition temperature.

Detailed ways

The present invention will further illustrate the present invention through specific examples. The described embodiments are preferred embodiments of the present invention, and do not limit the content of the present invention. According to the actual needs of different application fields, corresponding component changes can be made. Modifications, substitutions and improvements within the spirit and principles of the present invention shall all be included within the protection scope of the present invention.

Example 1:

This embodiment provides a method for preparing a transparent porous-crystalline composite material at a melting temperature:

Step 1, preparation of porous chamber materials: prepare porous EP materials A, B, C, and D with a thickness of 1mm and a length and width of 3cm×3cm through a porogen, and the internal pore size of the porous EP materials A, B, and C At 200-800nm, the internal pore size of the porous EP material D is 1000-1500nm.

Step 2, preparation of excess liquid PEG: Put sufficient amount of PEG in a beaker and heat it in a water bath for 1 hour to a molten state of 70°C, so that the PEG is in a completely fluid state.

Step 3, surface treatment of the porous EP materials C and D: soak the porous EP material C in an aqueous solution of acrylic acid monomer to carboxylate the surface.

The porous EP material A and the surface carboxylated porous EP material C are filled with PEG: the porous EP is placed in excess PEG, and immersed for 6 hours at 80° C., so that the PEG fills the porous cavity.

Vacuum interference filling of porous EP material B and surface carboxylated porous EP material D: put porous EP in excess PEG, vacuum impregnate at 80°C for 6 hours, so that PEG is fully adsorbed and filled the porous chamber.

Step 4, composite material molding: Place A, B, C, and D in a constant temperature drying oven at 25°C for 2 hours to dry, so that the PEG in the chamber is fully crystallized, and a transparent porous-crystalline composite material with a thickness of 1 mm is obtained.

The transparency effects of A, B, C, and D composite materials at the PEG phase transition temperature (at this time, the phase transition crystallization component PEG is in the crystalline state) are shown in Figure 8. It can be seen from the figure that the effective Control can solve the transparency problem of phase change materials. Relevant characteristics and test results are shown in Table 1. Among them, the amorphous transparency and crystalline transparency are obtained by direct testing with a variable temperature PE lambda 950 UV spectrophotometer and a variable temperature integrating sphere module, and the PEG mass ratio is calculated by 1-porous The ratio of the chamber mass to the final sample mass is calculated. The measured enthalpy value is measured by a TA Q200 differential scanning calorimeter. The measured enthalpy value (J/g-PEG) is the measured enthalpy value/PEG mass ratio , the crystallinity was calculated by the ratio of the phase change enthalpy measured by differential scanning calorimetry to the ratio of the mass of PEG filling the porous chamber to the total mass of the sample × the theoretical enthalpy of PEG.

Table 1

Note: PEG is fluid in the amorphous state and cannot be measured for transparency, and it is theoretically close to 100% fully transparent.

After the phase change material PEG is compounded with the porous network skeleton, it still maintains the characteristics of its phase change material, and the average measured enthalpy (J/g-PEG) is 125, which has the phase change energy storage capacity of the phase change material.

After the phase change material PEG is compounded with small-sized porous network materials A, B, and C, it still maintains a transparency of more than 50%, but after being compounded with a large-scale porous network material D, its crystalline transparency is reduced to 0.2%, which is no different from pure PEG . Therefore, the transparency of the phase change material in the crystalline state can be guaranteed by constructing a network of small-sized cavities to accommodate the phase change material.

Furthermore, the transparency of the material in the crystalline state can be further improved by means of interference filling (B) and surface treatment (C). The extrusion force prevents their orderly arrangement to form crystals. The surface treatment is to prevent the orderly arrangement of crystals from the formation of crystals through the intermolecular force with the edge of the crystal.

Example 2:

This example provides a preparation method of a reversible light-transmitting energy storage shape-stable composite phase change material:

Step 1, functional solution preconfiguration: 40 parts by weight of EP-E51 solution after adding 4 parts by weight of toughening agent dibutyl phthalate is mixed with 60 parts by weight of solid polyethylene glycol PEG, at the PEG phase transition temperature Magnetic stirring and heating for 6 hours to obtain a uniform phase-change component solution with an encapsulation rate of 60%.

Step 2, configuration of curing agent solution: take 1 weight part of accelerator 2,4,6-tris(dimethylaminomethyl)phenol and add 10 weight parts of methyl hexahydrophthalic anhydride, fully magnetically stir for 2 hours to obtain dispersion Uniform hardener solution.

Step 3, defoaming treatment: the phase change component solution and the curing agent solution were mixed and electrically stirred for 1 hour, and then vacuum-dried at a constant temperature of 80°C for 2 hours to remove the bubbles in the mixed solution.

Step 4, mold forming: take out 2ml of the mixed liquid at high temperature and pour it into a 3cm×3cm silicone mold coated with a release agent, and self-level it into a sample with a specific shape. Curing at a constant temperature of 120°C for 6 hours to induce the movement of PEG and sufficient cross-linking of EP to form a uniform phase dispersion of submicron size, and cool down to obtain a solid shape-stable sample.

Step 5, demolding: cooling the solid shape-stable sample to a constant temperature near the hot-melt phase transition temperature and drying for 2 hours, then cooling naturally, and demoulding to obtain an optically transparent shape-stable phase-change material with a thickness of 1 mm.

Process the frozen section of the obtained product into thin pieces, place the obtained sample on a glass slide, wrap the sample with dripping water and heat it to 70°C (at the phase transition temperature), dissolve the water-soluble PEG component in the sample, and dry to remove moisture Then observe the chamber structure under SEM, as shown in Figure 4b. The surface microstructure of the pure PEG component in the crystalline state was taken for comparison, as shown in Figure 4a. It can be seen that the pore structure of the composite phase change material cannot be clearly observed at the 1um scale, and the pore structure is predicted to be much smaller than 100nm. In addition, the composite phase change material has a smooth, continuous and flat surface with almost no cracks, which can effectively reduce the occurrence of internal diffuse reflection, thereby improving light transmittance.

The TEM image of the frozen section after staining is shown in Figure 5. PEG is stained with ruthenium to form a dark area, and EP is a bright area. It can be seen that PEG/EP in the transparent composite phase change material has obvious submicron phase dispersion, which is conducive to large-scale Partial penetration of light.

The melting phase transition temperature is 49.8°C, the melting enthalpy is 61.2J/g, the condensation phase transition temperature is 22.3°C, and the condensation enthalpy is 60.8J/g. The light transmittance test results of the transparent composite phase change material samples are shown in Figure 7, which are the transmittances measured at 15°C and 70°C respectively. At the phase change temperature, the average transparency in the visible light band is about 72%. The average transparency in the visible light band is about 81%.

Example 3:

This example provides a preparation method of a reversible light-transmitting energy storage shape-stable composite phase change material:

Step 1, configuration of phase change component solution: mix 40 parts by weight of PDMS Dow Corning Sylgard 184 monomer B liquid with 60 parts by weight of solid paraffin, and heat with magnetic stirring at the phase change temperature for 6 hours to obtain a uniform encapsulation rate of 60%. Phase change component solutions.

Step 2, mixed solution configuration: Take 4 parts by weight of PDMS Dow Corning Sylgard 184 monomer B solution and add it to the phase change component solution, and fully electric stir for 1 hour to obtain a uniformly dispersed mixed solution.

Step 3, defoaming treatment: vacuum drying at constant temperature at 80° C. for 2 hours to remove the bubbles in the mixed solution.

Step 4, mold forming: take out 2ml of the mixed liquid at high temperature and pour it into a 3cm×3cm silicone mold coated with a release agent, and self-level it into a sample with a specific shape. Curing at a constant temperature of 120°C for 6 hours to induce the movement of paraffin and sufficient cross-linking of PDMS to form a uniform phase dispersion of submicron size, and cool down to obtain a solid shape stable sample.

Step 5, demolding: cooling the solid shape-stable sample to a constant temperature near the hot-melt phase transition temperature and drying for 2 hours, then cooling naturally, and demoulding to obtain an optically transparent shape-stable phase-change material with a thickness of 1 mm.

The obtained product has good phase change energy storage characteristics, the melting phase transition temperature is 62.5°C, the melting enthalpy is 70.2J/g, the condensation phase transition temperature is 54.2°C, and the condensation enthalpy is 69.8J/g. At the same time, it also exhibits good reversible optical transparency characteristics. The transmittance measured at 15°C and 70°C respectively, the average transparency of the visible light band at the phase transition temperature is about 61%, and the average transparency of the visible light band at the phase transition temperature About 74%.

Example 4:

This example provides a preparation method of a reversible light-transmitting energy storage shape-stable composite phase change material:

Step 1, configuration of phase change component solution: Mix 40 parts by weight of transparent organic silica gel with 60 parts by weight of Na ₂ SO ₄ ·10H ₂ O, and heat with magnetic stirring at the phase change temperature for 6 hours to obtain a uniform encapsulation rate of 60% solution of phase change components.

Step 2, mixed solution configuration: Take 2 parts by weight of defoaming agent, 3 parts by weight of leveling agent, and 10 parts by weight of silane coupling agent and add them to the phase change component solution in turn, and fully electric stir for 1 hour to obtain a uniformly dispersed mixed solution .

Step 3, defoaming treatment: vacuum drying at constant temperature at 80° C. for 2 hours to remove the bubbles in the mixed solution.

Step 4, mold forming: take out 2ml of the mixed liquid at high temperature and pour it into a 3cm×3cm silicone mold coated with a release agent, and self-level it into a sample with a specific shape. Curing at a constant temperature of 120°C for 6 hours, inducing the movement of Na ₂ SO ₄ ·10H ₂ O and fully cross-linking the organic silica gel to form a uniform phase dispersion of submicron size, and cooling down to obtain a solid shape stable sample.

Step 5, demolding: cooling the solid shape-stable sample to a constant temperature near the hot-melt phase transition temperature and drying for 2 hours, then cooling naturally, and demoulding to obtain an optically transparent shape-stable phase-change material with a thickness of 1 mm.

The obtained product has good phase change energy storage characteristics, the melting phase transition temperature is 62.5°C, the melting enthalpy is 70.2J/g, the condensation phase transition temperature is 54.2°C, and the condensation enthalpy is 69.8J/g. At the same time, it also exhibits good reversible optical transparency characteristics. The transmittance measured at 15°C and 70°C respectively, the average transparency of the visible light band at the phase transition temperature is about 61%, and the average transparency of the visible light band at the phase transition temperature About 74%.

Embodiment 2, 3, the comparison of the main component composition characteristics of the 4 products is shown in Table 2.

Table 2

Example 2 Example 3 Example 4 Main components (core material/chamber material) PEG/EP Paraffin/PDMS Na₂SO₄·10H₂O/organic silica gel Core material/chamber material ratio 6:4 6:4 6:4 Mass proportion of PCM components (%) 52.2 57.7 52.2 Amorphous transparency (%) 81 74 68 Crystal transparency (%) 72 61 55 Experimental enthalpy of pure PCM components 172.3 194.8 128.2 Measured enthalpy (J/g) 61.2 72.2 40.6 Measured enthalpy (J/g-PCM) 117.2 125.1 77.8 Crystallinity (%) 73.9 64.2 60.6

Claims (12)

1. The double-phase transparent composite phase change material is characterized by comprising a core material; the core material is phase-change material and is loaded in a transparent cavity, and the cavity is at least along one direction o ₁ Is less than 1000nm (preferably less than 500 nm); the plurality of chambers form a porous network.

2. The composite phase change material according to claim 1, wherein the wall spacing of the cavities in each direction is less than 1000nm (preferably less than 500 nm); or the chamber being in another direction o ₂ The wall surface interval of (2) is greater than or equal to 1000nm.

3. The composite phase change material of claim 1, wherein the core material is transparent in the amorphous state and is a polymeric phase change material, an organic small molecule phase change material, an inorganic phase change material, or a eutectic phase change material.

4. The composite phase change material of claim 1, wherein the core material is interference filled into the cavity.

5. The composite phase change material of claim 1, wherein the degree of crystallinity of the core material edges is less than 100%.

6. The phase change material of claim 1, wherein intermolecular forces exist between the chamber wall and the edge of the core material.

7. The composite phase change material of claim 5, wherein the core material is interference filled into the cavity.

8. The method for preparing the composite phase-change material according to claim 1, wherein the composite phase-change material is obtained by loading the core material into the cavity of the porous network material by physical adsorption or chemical adsorption.

9. The method of claim 8, wherein the porous network material is selected from the group consisting of inorganic porous materials, organic porous materials, and biological porous materials.

10. The method of claim 1, wherein the porous network precursor and the core material are uniformly mixed, and then the porous network precursor is induced to crosslink to form the cavity, and the core material is located in the cavity.

11. The method of claim 10, wherein the step of preparing the composition is carried out in a batch processThe porous network precursor is selected from: epoxy resins (EP), silicone, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA); the core material is selected from: polyethylene glycol (PEG), paraffin, fatty acid, sodium sulfate decahydrate (Na) ₂ SO ₄ ·10H ₂ O)。

12. The method of claim 11, comprising the steps of:

(1) Adding 3-6 parts by weight of cross-linking agent into 30-60 parts by weight of epoxy resin, mixing with 40-70 parts by weight of polyethylene glycol, and heating and stirring in an environment above the hot-melt phase-change temperature to obtain a phase-change component solution which is uniformly mixed;

(2) Adding 2-3 parts by weight of curing accelerator into 20-30 parts by weight of methylhexahydrophthalic anhydride, and stirring to obtain a curing agent solution;

(3) And mixing and stirring the phase change component solution and the curing agent solution, and carrying out vacuum drying treatment at a constant temperature above the phase change temperature to remove bubbles in the mixed solution.

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