CN114804712A

CN114804712A - Phase change microcapsule, preparation and application

Info

Publication number: CN114804712A
Application number: CN202210338802.8A
Authority: CN
Inventors: 蒋金洋; 琚思懿; 王立国; 王凤娟; 辛忠毅
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2022-04-01
Filing date: 2022-04-01
Publication date: 2022-07-29
Anticipated expiration: 2042-04-01
Also published as: CN114804712B

Abstract

The invention discloses a phase change microcapsule, preparation and application thereof. The preparation method comprises the following steps: adding molten metal into a solution containing a surfactant, and obtaining a stable metal microsphere suspension under the synergistic action of high-speed stirring and strong ultrasound; and transferring the suspension to a three-neck flask, adding a silicon dioxide precursor, adjusting the pH value, and stirring for reaction to obtain the silicon dioxide-coated gallium phase-change microcapsule. The phase change microcapsule prepared by the method has the advantages of controllable particle size, large energy storage density, strong heat conductivity, good mechanical property and the like, has good compatibility with building materials, and can be used for regulating and controlling the hydration heat release rate and heat release quantity of cement.

Description

Phase-change microcapsule, preparation and application

Technical Field

The invention relates to a phase change material and preparation thereof, in particular to a phase change microcapsule, preparation and application thereof.

Background

As a traditional building material, the concrete has been used for nearly two hundred years, and is an engineering material with the largest consumption and the widest application space in the modern production and construction. Concrete belongs to a poor thermal conductor, the internal temperature is rapidly increased due to a large amount of heat generated by hydration of cement at the initial stage of pouring, the temperature difference between the inside and the surface is overlarge, and a concrete matrix cannot freely stretch and deform due to the constraints of external environment, foundation, pouring structure boundary and the like, so that temperature cracks are generated on the surface, and the service life and the use safety of a building are threatened.

The phase-change material has good thermophysical properties, can absorb or release heat in the phase-change process, is beneficial to adjusting and controlling the environmental temperature, and is an effective and simple measure for controlling the early temperature crack formation of concrete. Generally, when the phase-change material is mixed into the gel material, the phase-change material is subjected to encapsulation treatment such as microcapsule wrapping, porous material adsorption, melt blending and the like. However, the phase-change material prepared by the existing treatment method still has the problems of limited energy storage density, low thermal conductivity, easy leakage in the phase-change process and the like, and has limited hydration and heat release effects on the regulating water and the regulating water. In addition, the large strength and rigidity difference between the phase change material and the cementing material inevitably has negative influence on the mechanical properties of the building material.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide a phase change microcapsule and application thereof, and solves the problems of limited energy storage density, low thermal conductivity and easy leakage in the phase change process of a phase change material.

The invention also aims to provide a preparation method of the phase-change microcapsule, which solves the problems of complex operation, poor dispersion uniformity and low dispersion efficiency of the existing low-melting-point metal dispersion technology.

The technical scheme is as follows: the microcapsule comprises a core material and a shell, wherein the shell wraps the core material, the shell is formed by silicon dioxide, and the core material is formed by gallium.

The preparation method of the phase-change microcapsule comprises the following steps:

adding a surfactant into a mixed solution of deionized water and ethanol, heating and stirring until the surfactant is fully dissolved to prepare a dispersant solution;

heating a proper amount of gallium to a molten state;

mixing the prepared dispersant solution with molten gallium, shearing at a preset rotating speed, and performing ultrasonic crushing after shearing to obtain a gallium microsphere suspension;

mixing the suspension and a silicon dioxide precursor, uniformly stirring, adjusting the pH value, and reacting to obtain a product solution;

and filtering the product solution to obtain a solid precipitate, washing, and freeze-drying to obtain the phase-change microcapsule.

Preferably, the surfactant is selected from any one of sodium dodecyl sulfate, cetyl trimethyl ammonium bromide and sodium dodecyl benzene sulfonate.

Preferably, the mass fraction of the surfactant in the dispersant solution is 1-15%.

Preferably, the volume ratio of the deionized water to the ethanol in the mixed solution of the deionized water and the ethanol is (1-2): 1.

Preferably, the shearing rotating speed is 2500-15000 rpm, the shearing time is 1-10 min, and the ultrasonic crushing time is 3-10 min.

In order to ensure the thermal property and the coating effect of the microcapsule, the mass ratio of the silicon dioxide precursor to the gallium is (0.5-3): 1.

In order to ensure that the silicon dioxide precursor is subjected to hydrolytic polycondensation reaction, ammonia water or hydrochloric acid is added to coat the silicon dioxide precursor on the outer layer of the gallium to adjust the pH value, wherein the pH value of the mixed solution is adjusted to 2-3 after the hydrochloric acid is added, or the pH value of the mixed solution is adjusted to 9-10 after the ammonia water is added.

The phase change microcapsule prepared by the preparation method of the phase change microcapsule is applied to reducing the hydration heat release rate and heat release amount of cement.

The technical mechanism is as follows:

the principle of dispersing gallium by adopting the synergistic effect of high-speed stirring and strong ultrasound is as follows: the relatively high surface tension, low melting point, high toughness, etc., of gallium metal make it difficult to disperse by conventional means. The metal atoms are bonded through a firm metal bond, and large external energy needs to be injected to convert macroscopic liquid metal into microspheres. In the shearing process of the high-speed homogenizer, gallium moves in a rotor gap at a high speed and is broken into small liquid drops under the comprehensive actions of centrifugal force, pressure, collision and the like. The formation process of the gallium microspheres is often accompanied with the fusion and the splitting of gallium, and the cavitation effect generated when the ultrasonic wave is transmitted in the liquid can generate enough energy to further act on the surfaces of gallium liquid drops, so that the more stable gallium microspheres are prepared. The high-speed stirring and the strong ultrasound synergistic effect ensure the stability of the gallium microspheres while ensuring the high-efficiency dispersion.

The principle of coating the surface of the gallium microsphere with the silicon dioxide is as follows: gallium dispersed into microspheres can prevent droplets from colliding with each other by the action of an electric double layer under the action of a surfactant. The cetyl trimethyl ammonium bromide active agent is taken as an example to illustrate: under the action of hexadecyl trimethyl ammonium bromide, the surface of the gallium microsphere particles is subjected to electrostatic activation; uniformly distributing the silicon dioxide precursor in a mixed solution after stirring, hydrolyzing the mixed solution under the catalysis of ammonia water to form a monomer, and further performing polycondensation reaction on the generated monomer to form a silicon dioxide cluster with electronegativity; due to the electrostatic interaction between the silicon dioxide cluster generated by hydrolysis and the hydrophilic section of the surfactant, the silicon dioxide cluster is adsorbed on the surface of the gallium microsphere, and a silicon dioxide shell layer is gradually formed on the surface of the gallium microsphere along with the continuous progress of the polycondensation reaction, so that the silicon dioxide-coated gallium phase-change microcapsule is finally formed.

Has the beneficial effects that: the invention overcomes the inherent defects of the traditional phase-change material, the adopted core material gallium has high energy storage density and good thermal conductivity and mechanical strength, the coated inorganic shell layer silicon dioxide can be well compatible with the building material, and is not easy to break when being mixed with cement to prepare the phase-change temperature-control cement-based heat storage material, thereby not only effectively preventing the phase-change material from leaking in a liquid state, but also reducing the strength difference between the phase-change material and the base material. When the temperature in the matrix is raised to the phase transition temperature of gallium by the heat released by cement hydration, the gallium is converted from a solid state to a liquid state and absorbs a large amount of heat to keep the temperature stable, and meanwhile, the gallium-gallium composite material has good thermal conductivity, reduces the temperature difference between the interior and the surface of the matrix and reduces the formation of temperature cracks.

Drawings

FIG. 1 is a scanning electron microscope and EDS photograph of phase change microcapsules prepared according to example 5 of the present invention, wherein (a) - (b) are electron micrographs, and (c) - (e) are EDS photographs, Ga is the main component of elemental gallium metal, Si and O are derived from a silica shell layer coated on particles;

FIG. 2 is a graph of the comparative hydration heat release rate for the silica-coated gallium phase change microcapsules prepared in example 5;

FIG. 3 is a graph of the comparative hydration cumulative exotherm for the silica-coated gallium phase change microcapsules produced in example 5.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Example 1

Weighing 1g of sodium dodecyl sulfate, dissolving in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating in a water bath at 35 ℃, and magnetically stirring at the rotating speed of 500rpm for 30min to obtain a dispersing agent solution. 10g of metallic gallium was weighed into a beaker and the gallium was heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, maintaining the rotating speed of 5000rpm for shearing for 5min, and transferring to an ultrasonic cell crusher for ultrasonic treatment for 3min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 10g of methyltriethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding hydrochloric acid to adjust the pH value to 2-3, and continuing stirring and reacting for 6 h. And after the reaction is finished, filtering the product solution, fully washing the product solution by using ethanol and deionized water, collecting solid precipitates, placing the solid precipitates in a culture dish, and freeze-drying the solid precipitates to obtain the silicon dioxide coated gallium phase change microcapsule.

The phase change microcapsules prepared in example 1 were subjected to scanning electron microscopy and EDS tests, and the results are shown in fig. 1, in which it can be seen that Ga is a main component of elemental gallium metal, and Si and O are derived from the silica shell layer coated on the particles.

Example 2

Accurately weighing 1g of sodium dodecyl sulfate, dissolving the sodium dodecyl sulfate in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating the mixture in a water bath at 35 ℃, and magnetically stirring the mixture for 30min at the rotating speed of 500rpm to obtain a dispersing agent solution. 10g of metallic gallium was weighed into a beaker and the gallium was heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, maintaining the rotating speed of 5000rpm for shearing for 5min, and transferring to an ultrasonic cell crusher for ultrasonic treatment for 8min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 12g of methyltriethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding hydrochloric acid to adjust the pH value to 2-3, and continuing stirring and reacting for 6 h. And after the reaction is finished, filtering the product solution, fully washing the product solution by using ethanol and deionized water, collecting solid precipitates, placing the solid precipitates in a culture dish, and freeze-drying the solid precipitates to obtain the silicon dioxide coated gallium phase change microcapsule.

Example 3

Accurately weighing 1.2g of hexadecyl trimethyl ammonium bromide, dissolving in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating in a water bath at 35 ℃, and magnetically stirring at the rotating speed of 500rpm for 30min to obtain a dispersing agent solution. 10g of metallic gallium was weighed into a beaker and the gallium was heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, shearing for 5min at the rotation speed of 8000rpm, and transferring to an ultrasonic cell crusher for ultrasonic treatment for 3min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 10g of tetraethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding ammonia water to adjust the pH value to 9-10, and continuing stirring and reacting for 16 h. And after the reaction is finished, filtering the product solution, fully washing the product solution by using ethanol and deionized water, collecting solid precipitates, placing the solid precipitates in a culture dish, and freeze-drying the solid precipitates to obtain the silicon dioxide coated gallium phase change microcapsule.

Example 4

Accurately weighing 1.2g of hexadecyl trimethyl ammonium bromide, dissolving in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating in a water bath at 35 ℃, and magnetically stirring at the rotating speed of 500rpm for 30min to obtain a dispersing agent solution. 10g of metallic gallium was weighed into a beaker and the gallium was heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, maintaining the rotating speed of 12000rpm for shearing for 5min, and transferring to an ultrasonic cell crusher for ultrasonic treatment for 8min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 10g of tetraethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding ammonia water to adjust the pH value to 9-10, and continuing stirring and reacting for 16 h. And after the reaction is finished, filtering the product solution, fully washing the product solution by using ethanol and deionized water, collecting solid precipitates, placing the solid precipitates in a culture dish, and freeze-drying the solid precipitates to obtain the silicon dioxide coated gallium phase change microcapsule.

Example 5

Accurately weighing 1.2g of hexadecyl trimethyl ammonium bromide, dissolving in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating in a water bath at 35 ℃, and magnetically stirring at the rotating speed of 500rpm for 30min to obtain a dispersing agent solution. 10g of metallic gallium was weighed into a beaker and the gallium was heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, shearing for 5min at the rotation speed of 8000rpm, and transferring to an ultrasonic cell crusher for ultrasonic 5min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 6g of tetraethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding ammonia water to adjust the pH value to 9-10, and continuing stirring and reacting for 16 h. And after the reaction is finished, filtering the product solution, fully washing the product solution by using ethanol and deionized water, collecting solid precipitates, placing the solid precipitates in a culture dish, and freeze-drying the solid precipitates to obtain the silicon dioxide coated gallium phase change microcapsule.

When the doping amount of the phase-change microcapsule with gallium coated by silicon dioxide prepared in the example 5 is 7.5% of the mass of cement, a hydration heat test is carried out, and an obtained hydration heat release rate curve is shown in figure 2, wherein the peak value of the maximum hydration heat release rate is reduced by 15.7% compared with that of standard cement paste; the hydration cumulative exotherm is shown in fig. 3, and is reduced by 16.3% compared with the reference cement paste.

Example 6

Accurately weighing 1.2g of hexadecyl trimethyl ammonium bromide, dissolving in a mixed solution of 45mL of deionized water and 30mL of absolute ethyl alcohol, heating in a water bath at 35 ℃, and magnetically stirring at the rotating speed of 500rpm for 30min to obtain a dispersing agent solution. 10g of metallic gallium was weighed in a beaker and heated to a molten state at a temperature above the melting point of gallium. And pouring the prepared dispersant solution into a beaker containing molten gallium, shearing for 5min at the rotation speed of 8000rpm, and transferring to an ultrasonic cell crusher for ultrasonic 5min after shearing to obtain a stable gallium microsphere suspension. Transferring the suspension into a three-neck round-bottom flask provided with a polytetrafluoroethylene stirring rod, adding 20g of tetraethoxysilane, stirring and reacting for 30min at a set rotating speed of 500rpm, then adding ammonia water to adjust the pH value to 9-10, and continuing stirring and reacting for 16 h. And after the reaction is finished, filtering the product solution, fully washing with ethanol and deionized water, collecting solid precipitate, placing the solid precipitate in a culture dish, and freeze-drying to obtain the silicon dioxide coated gallium phase-change microcapsule.

The phase-change microcapsules coated with gallium prepared in examples 1 to 6 were added to cement to perform a hydration heat test of the cement, and the phase-change microcapsules equally replace the gelled material. The cement paste without the phase change microcapsules was used as a comparative example, and the test results are shown in table 1:

TABLE 1

Numbering	Mixing amount/%	Hydration cumulative exotherm decrease/%
			Example 1	7.5	14.2
Example 2	7.5	10.4
			Example 3	7.5	12.9
Example 4	7.5	11.8
			Example 5	7.5	16.3
Example 6	7.5	8.3
			Comparative example 1	0	0

From the test results in table 1, compared with comparative example 1 without any treatment, the cement slurry added with the phase change microcapsules coated with silicon dioxide prepared in examples 1-6 of the present invention has the hydration accumulated calorific value reduction range of more than 10.4%, the maximum reduction range of example 5, and the hydration accumulated calorific value reduction of 16.3% in examples 1-5, except for example 6, on the premise of not delaying cement hydration, which illustrates the effectiveness of the phase change microcapsules coated with silicon dioxide in controlling hydration exotherm of cement. The test results in table 1 also indicate that the shearing rotation speed and the ultrasonic time in the gallium dispersion treatment process should be moderate, the minimum particle size of the prepared phase-change microcapsule can reach dozens of nanometers if the shearing rotation speed is too high and the ultrasonic time is too long, and the size effect of the nanoparticles is not beneficial to the regulation and control of the phase-change microcapsule on the hydration heat release rate. It is noted that a higher mass ratio of the precursor to gallium also has an adverse effect, because the phase-change microcapsule has a higher content of the silica shell, which leads to a decrease in the heat storage capacity of the phase-change microcapsule.

Claims

1. A phase change microcapsule comprising a core material and a shell, wherein the shell surrounds the core material, the shell is formed of silica, and the core material is formed of gallium.

2. The method for preparing phase-change microcapsules according to claim 1, comprising the steps of:

heating a proper amount of gallium to a molten state;

3. The method for preparing phase-change microcapsules according to claim 2, wherein the surfactant is selected from any one of sodium dodecyl sulfate, cetyltrimethylammonium bromide and sodium dodecylbenzenesulfonate.

4. The method for preparing the phase-change microcapsule according to claim 2, wherein the mass fraction of the surfactant in the dispersant solution is 1-15%.

5. The preparation method of the phase-change microcapsule according to claim 2, wherein the volume ratio of the deionized water to the ethanol in the mixed solution of the deionized water and the ethanol is (1-2): 1.

6. The preparation method of the phase-change microcapsule according to claim 2, wherein the shearing rotation speed is 2500-15000 rpm, the shearing time is 1-10 min, and the ultrasonic pulverization time is 3-10 min.

7. The preparation method of the phase-change microcapsule according to claim 2, wherein the mass ratio of the silicon dioxide precursor to gallium is (0.5-3): 1.

8. The method for preparing phase-change microcapsules according to claim 2, wherein the pH value is adjusted by adding ammonia water or hydrochloric acid, wherein the pH value of the mixed solution is adjusted to 2-3 after adding hydrochloric acid, or the pH value of the mixed solution is adjusted to 9-10 after adding ammonia water.

9. Use of a phase change capsule according to claim 1 or prepared by a process for the preparation of a phase change microcapsule according to any one of claims 2 to 8 for reducing the rate and amount of heat released during hydration of cement.