WO2024000274A1 - Dual-phase transparent phase change material and preparation method therefor - Google Patents

Abstract

The present invention provides a dual-phase transparent composite phase change material which has high transparency in both a crystalline state and a non-crystalline state, and solves the problem of existing phase change materials or composite phase change materials having reduced transparency in a crystalline state. The dual-phase transparent composite phase change material of the present application comprises a core material that exhibits transparent characteristics in a non-crystalline state. The core material is loaded in transparent chambers, and in a non-crystalline state, the flowing core material in the crystalline state fills the chambers, such that most light may traverse the entirety of the material, achieving a transparent effect. In a crystalline state, one transparent chamber constitutes one crystalline unit, and the size of grains formed after crystallization is less than 1000 nm in one direction; therefore, when light is incident along said direction, most of the light may penetrate the barrier of an obstruction having a thickness below the wavelength, resulting in minimal light absorption and consumption, achieving a transparent effect.

Description

Dual-phase transparent phase change material and preparation method thereof Technical field

The invention belongs to the field of phase change materials, and specifically relates to dual-phase transparent composite phase change materials.

Background technique

Phase change materials (PCM) are a type of functional material that can maintain a constant temperature within a certain period of time during the process of storing and releasing energy, allowing the phase change material to achieve energy storage and temperature control functions, thereby enabling It is widely used in alleviating energy crisis and improving energy efficiency.

Since crystalline materials form different boundaries during the crystallization process, severe scattering occurs during visible light penetration, resulting in a sharp decrease in transparency. On the other hand, in some special optoelectronic application scenarios, transparency is an indispensable requirement. If the structure of crystalline materials can be controlled to form a compound with good transparency while maintaining its own characteristics, it will greatly expand the application space of crystalline functional materials. Typical examples include crystalline phase change materials, which disperse the crystalline phase into filler materials so that the size of the crystalline phase is controlled to a sub-micron size through which light can pass, 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 dual-phase transparent composite phase change material, which has high transparency in both crystalline and amorphous states, and solves the problem of reduced transparency in the crystalline state of existing phase change materials or composite phase change materials.

The dual-phase transparent composite phase change material described in this application includes a core material that exhibits transparent characteristics in an amorphous state; the core material is loaded in a transparent chamber, and the wall of the chamber is at least along one direction o1. The spacing between them is less than 1000nm (preferably less than 500nm); multiple chambers form a porous network (Fig. 1). In the amorphous state, due to the intrinsic optical properties of the cavity and core material, as well as the fluidity of the core material filling the cavity in the amorphous state, most of the light can pass through the entire material, 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 the light is incident along o1, most of the light can penetrate obstacles with thickness below the wavelength. The light is rarely absorbed and consumed due to the blocking, and it also shows a transparent effect in the o1 direction.

It can be seen from the above that in directions other than direction o1, it can be less than 1000nm or greater than or equal to 1000nm (Figure 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, for example, 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.

Core materials suitable for use in the present invention may be:

(1) Polymer phase change materials, such as polyethylene glycol, polyester, and 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 salt, molten salt

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

Transparent chambers suitable for use in the present invention may be:

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

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

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

Whether in crystalline or amorphous materials, the occurrence 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 during the diffuse reflection process and cannot pass through the material, causing the transmittance to decrease. In a preferred solution of the present application, the cavity is interference-filled with the core material. For cavities of a certain size and quantity, the core material is always in an interference state during the filling process, thereby ensuring that each cavity can be efficiently filled with the core material, effectively avoiding most cracks, and further ensuring its transmittance.

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

Specifically, ways to inhibit crystallization at the edge of the core material include at least:

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

(2) The interference filling of the cavity by the core material resists the volume shrinkage during the crystallization process on the one hand, and on the other hand suppresses its orientation through the squeezing force of the cavity wall on the edge portion.

The present invention also relates to a method for preparing the above-mentioned dual-phase transparent composite phase change material. One method is to load the core material into a cavity of a transparent porous network material through physical adsorption or chemical adsorption to obtain the composite. Phase change materials. The second is to 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, and 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 salt, molten salt

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

By adsorption method, the porous network material can generally be immersed in the solution or dispersion of the core material, for example:

The porous SiO ₂ aerogel is immersed in a sufficient amount of polyethylene glycol (PEG). Through the impregnation adsorption method, the porous SiO ₂ aerogel absorbs PEG to form a stable transparent composite phase change material.

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

For stable structures that are not easily deformed, such as transparent wood, the porous cavity structure formed inside the transparent wood will not deform under certain pressurized conditions. The vacuum impregnation method is used to fill and adsorb PEG, so that PEG can smoothly enter some smaller sizes. In the chamber, the overall filling rate is increased, thereby obtaining a more stable transparent composite phase change material.

The method of co-building the cavity and the core material is to mix it with the core material when the cavity is not formed, and use cross-linking and other means to make the cavity precursor form a small-sized cavity, while the core material is located in the cavity. By controlling the degree of cross-linking, the cavity of the desired size can be obtained. Generally, the cross-linking process of cavity precursors requires the participation of cross-linking agents 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), organic silica gel, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), and polymethyl methacrylate;

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

The core materials suitable for the co-construction method cannot participate in the aforementioned cross-linking reaction. Technical personnel can choose from the following core materials according to the group conditions and the well-known attempts in the field:

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

(2) Crystalline hydrated salts, such as sodium sulfate decahydrate (Na ₂ SO ₄ ·10H ₂ O), ammonia 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) Add 3-6 parts by weight of cross-linking agent to 30-60 parts by weight of epoxy resin, mix with 40-70 parts by weight of polyethylene glycol, and heat and stir in an environment above the hot melt phase change temperature to obtain Mix the phase change component solution evenly;

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

(3) Mix and stir the phase change component solution and the curing agent solution, and perform vacuum drying at a constant temperature above the phase change temperature to remove 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 mass to the overall mass of the composite × phase change core material enthalpy value) more than 50%.

(2) Through core material boundary optimization, 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

Figure 1 is a schematic diagram of the cavity distribution and core material filling of a porous structure with dimensions less than 1000nm (preferably less than 500nm) in all directions;

Figure 2 is a schematic diagram of the cavity distribution and core material filling of a porous structure with only the o1 direction less than 1000nm (preferably less than 500nm);

Figure 3 is a schematic diagram showing that the edge part of the core material is suppressed from crystallization;

Figure 4 is a surface SEM comparison of Example 2 and PEG (crystalline material used in composite materials) at the phase transition temperature;

Figure 5 is the phase dispersion of frozen section TEM in Example 2 at the phase transition temperature;

Figure 6 is a transmittance-wavelength change curve of Example 2 when the phase transition temperature is above/low;

Figure 7 is the differential scanning calorimetry test result of Example 2.

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

Detailed ways

The present invention is further explained through specific embodiments. The above-described embodiments are preferred embodiments of the present invention and do not limit the content of the present invention. Corresponding component changes can be made to meet the actual needs of different application fields. Modifications, substitutions and improvements within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Example 1:

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

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

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

Step 3: Surface treatment of porous EP materials C and D: soak porous EP material C in acrylic acid monomer aqueous solution to carboxylize its surface.

The porous EP material A and the surface carboxylated porous EP material C were filled with PEG: the porous EP was added to excess PEG and immersed at 80°C for 6 hours, so that the PEG filled the porous cavity.

The porous EP material B and the surface carboxylated porous EP material D were subjected to vacuum interference filling: the porous EP was added to excess PEG, and vacuum immersed at 80°C for 6 hours, so that the PEG could fully adsorb and fill the porous chamber.

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

The transparent effect of A, B, C, and D composite materials at the PEG phase transition temperature (when the phase transition crystal component PEG is in the crystalline state) is shown in Figure 8. It can be seen from the figure that the effective Control can solve the transparency problem of phase change materials. The relevant characteristics and test results are shown in Table 1. Among them, the amorphous transparency and crystalline transparency are directly measured by the variable temperature PE lambda 950 UV spectrophotometer and the variable temperature integrating sphere module. The PEG mass proportion is calculated through 1-porous The ratio of the chamber mass to the final sample mass is calculated. The measured enthalpy value is measured by the TA Q200 differential scanning calorimeter. The measured enthalpy value (J/g-PEG) is the measured enthalpy value/PEG mass ratio. , the crystallinity is calculated by calculating the ratio of the phase change enthalpy of the differential scanning calorimetry test to the proportion 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 a fluid in the amorphous state and the transparency cannot be measured. Theoretically, it is close to 100% transparent.

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

After the phase change material PEG is combined with the small-sized porous network materials A, B, and C, it still maintains a transparency of more than 50%. However, after being combined with the large-pore network material D, its crystalline transparency is reduced to 0.2%, which is the same as pure PEG. . Therefore, the transparency of the phase change material in the crystalline state can be ensured by constructing a small-sized cavity network to accommodate the phase change material.

Furthermore, the transparency of the material in the crystalline state can be further improved through interference filling (B), surface treatment (C) and other methods. Interference filling can not only effectively avoid most cracks, but also based on the impact of the cavity wall on the edge of the crystal. The squeezing force prevents their orderly arrangement to form crystals. Surface treatment prevents their orderly arrangement to form crystals through intermolecular forces with the edge of the crystal.

Example 2:

This embodiment provides a method for preparing a reversibly transparent energy storage shape-stable composite phase change material:

Step 1, pre-configuration of functional solution: Mix 40 parts by weight of EP-E51 solution after adding 4 parts by weight of toughening agent dibutyl phthalate and 60 parts by weight of solid polyethylene glycol PEG, at the PEG phase transition temperature Heating with magnetic stirring for 6 hours, a phase change component solution with a uniform encapsulation rate of 60% was obtained.

Step 2, curing agent solution configuration: add 1 part by weight of the accelerator 2,4,6-tris(dimethylaminomethyl)phenol to 10 parts by weight of methylhexahydrophthalic anhydride, and stir thoroughly with magnetic force for 2 hours to obtain dispersion. Homogeneous hardener solution.

Step 3. Degassing treatment: Mix the phase change component solution and the curing agent solution with electric stirring for 1 hour, and vacuum dry at a constant temperature of 80°C for 2 hours to remove bubbles in the mixed solution.

Step 4, mold forming: Take out 2ml of the mixture at high temperature and pour it into a 3cm × 3cm silicone mold pre-coated with release agent, and self-level into a sample with a specific shape. Curing at a constant temperature of 120°C for 6 hours induces the movement of PEG and full cross-linking of EP to form a uniform phase dispersion of sub-micron size, and then cools down to obtain a solid shape-stable sample.

Step 5, demoulding: Cool the solid shape-stable sample to a temperature near the hot-melt phase change temperature and dry at a constant temperature for 2 hours, then naturally cool and demould to obtain a 1 mm thick optically transparent shape-stable phase change material.

The obtained product is cryo-sectioned into thin pieces, and the obtained sample is placed on a glass slide. The sample is wrapped with drops of water and heated to 70°C (phase transition temperature) to dissolve the water-soluble PEG component in the sample, and dried to remove the moisture. The chamber structure was then observed 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 hole structure cannot be clearly observed in the composite phase change material at the 1um scale, and the hole 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 increasing the light transmittance.

The TEM image of the frozen section after dyeing is shown in Figure 5. PEG is dyed 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 beneficial to large-scale Partial light penetration.

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 sample are shown in Figure 7, which are the transmittance measured at 15°C and 70°C respectively. The average transparency in the visible light band is about 72% at the phase change temperature. The average transparency in the visible light band is about 81%.

Example 3:

This embodiment provides a method for preparing a reversibly transparent energy storage shape-stable composite phase change material:

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

Step 2, Mixed solution preparation: Add 4 parts by weight of PDMS Dow Corning Sylgard 184 Monomer B solution into the phase change component solution, and stir fully with electric power for 1 hour to obtain a uniformly dispersed mixed solution.

Step 3, deaeration treatment: vacuum dry at a constant temperature of 80°C for 2 hours to remove bubbles in the mixed solution.

Step 4, mold forming: Take out 2ml of the mixture at high temperature and pour it into a 3cm × 3cm silicone mold pre-coated with release agent, and self-level into a sample with a specific shape. Curing at a constant temperature of 120°C for 6 hours induces the movement of paraffin and fully cross-links PDMS to form a uniform phase dispersion of submicron size, and then cools down to obtain a solid shape-stable sample.

Step 5, demoulding: Cool the solid shape-stable sample to a temperature near the hot-melt phase change temperature and dry at a constant temperature for 2 hours, then naturally cool and demould to obtain a 1 mm thick optically transparent shape-stable phase change material.

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

Example 4:

This embodiment provides a method for preparing a reversibly transparent energy storage shape-stable composite phase change material:

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

Step 2, mix 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 sequence, and stir fully with electric power for 1 hour to obtain a uniformly dispersed mixed solution. .

Step 3, deaeration treatment: vacuum dry at a constant temperature of 80°C for 2 hours to remove bubbles in the mixed solution.

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

Step 5, demoulding: Cool the solid shape-stable sample to a temperature near the hot-melt phase change temperature and dry at a constant temperature for 2 hours, then naturally cool and demould to obtain a 1 mm thick optically transparent shape-stable phase change material.

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

A comparison of the main components and characteristics of the products of Examples 2, 3, and 4 is shown in Table 2.

Table 2

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

Claims (12)

1. A dual-phase transparent composite phase change material, characterized in that it includes a core material; the core material is a phase change material loaded in a transparent chamber, and the distance between the walls of the chamber at least along one direction _o1 is less than 1000nm (Preferably less than 500nm); Multiple chambers form a porous network.
2. The composite phase change material according to claim 1, characterized in that the wall spacing of the chamber along all directions is less than 1000nm (preferably less than 500nm); or the wall spacing of the chamber along another direction _o2 The spacing is greater than or equal to 1000nm.
3. The composite phase change material according to claim 1, characterized in that the core material is transparent in the amorphous state and is a polymer phase change material, an organic small molecule phase change material, an inorganic phase change material, or a eutectic. Phase change materials.
4. The composite phase change material according to claim 1, wherein the core material interference-fills the cavity.
5. The composite phase change material according to claim 1, characterized in that the crystallinity degree of the edge of the core material is less than 100%.
6. The phase change material according to claim 1, characterized in that there is an intermolecular force between the chamber wall and the edge of the core material.
7. The composite phase change material according to claim 5, characterized in that the core material interference-fills the cavity.
8. The method for preparing a composite phase change material according to claim 1, wherein the composite phase change material is obtained by loading the core material into a cavity of a porous network material through physical adsorption or chemical adsorption. .
9. The preparation method according to claim 8, characterized in that the porous network material is selected from inorganic porous materials, organic porous materials, and biological porous materials.
10. The method for preparing a composite phase change material according to claim 1, characterized in that after the porous network precursor and the core material are uniformly mixed, cross-linking of the porous network precursor is initiated to form the cavity, and the core material is The material is located in the cavity.
11. The preparation method according to claim 10, characterized in that the porous network precursor is selected from: epoxy resin (EP), organic silica gel, polydimethylsiloxane (PDMS), polymethylmethacrylate (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 preparation method according to claim 11, characterized in that it includes the following steps:

    (1) Add 3-6 parts by weight of cross-linking agent to 30-60 parts by weight of epoxy resin, mix with 40-70 parts by weight of polyethylene glycol, and heat and stir in an environment above the hot melt phase change temperature to obtain Mix the phase change component solution evenly;

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

    (3) Mix and stir the phase change component solution and the curing agent solution, and perform vacuum drying at a constant temperature above the phase change temperature to remove bubbles in the mixed solution.

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