CN114797699B - Method for eliminating supercooling degree of paraffin phase-change microcapsule and loss-free phase-change enthalpy, prepared phase-change microcapsule and application thereof - Google Patents
Method for eliminating supercooling degree of paraffin phase-change microcapsule and loss-free phase-change enthalpy, prepared phase-change microcapsule and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of functional material preparation, and discloses a method for eliminating supercooling degree of paraffin phase-change microcapsules and having no loss of phase-change enthalpy, prepared phase-change microcapsules and application thereof. After the concentration of the specified modified nano particles is uniformly mixed with the paraffin phase change material, the phase change microcapsule which has uniform shell thickness and particle diameter and controllable quantity of nucleating agents in the capsule is obtained by adopting micro-fluidic double emulsification and ultraviolet light curing, and the nano particles have good dispersion stability and thermal cycle stability in the capsule under the action of a silane coupling agent. Meanwhile, as the titanium dioxide has strong surface activity and eliminates the agglomeration problem of the titanium dioxide in the organic solvent after modification, the nucleation area is greatly increased. The uniform distribution and the maximum utilization of the nano particles are realized by utilizing the microfluidic technology, so that the supercooling degree of the paraffin phase-change capsule is eliminated and no phase-change enthalpy loss exists at the same time under the condition of adding a very small amount of nano particles.
Description
Technical Field
The invention belongs to the technical field of functional material preparation, and particularly relates to a method for eliminating supercooling degree of paraffin phase-change microcapsules and having no loss of phase-change enthalpy, a prepared phase-change microcapsule and application thereof.
Background
The energy-saving effect and zero carbon emission of the phase-change energy storage material are widely paid attention to, and the phase-change energy storage material takes up a significant position in the future new energy development strategy. The phase change material has the characteristic of absorbing and releasing a large amount of latent heat in the liquid-solid phase conversion process, is a good heat storage material, and has the advantages of higher heat energy storage density, constant-temperature heat storage and release, less energy loss and the like compared with the common sensible heat storage method. Meanwhile, the latent heat energy storage technology based on the phase change energy storage material can solve the problem of time and space mismatch of low-grade heat energy, and has wide application prospects in the fields of solar water heating systems, heat preservation fabrics, energy-saving buildings, air conditioning systems, industrial waste heat recovery, heat control of electronic modules and the like. Paraffin is one of the most widely used organic phase change materials, and has stable chemical property, good economy, high enthalpy value and wide application temperature range. However, paraffin is unfavorable for application due to the problems of low heat conductivity, unshaped melting, combustibility, corrosion and the like in the use process. The microcapsule technology encapsulates paraffin into a solid phase shell to prepare paraffin phase change microcapsules (microppcs), so that leakage can be effectively prevented, the paraffin phase change microcapsules are isolated from a heat transfer medium to ensure safety and reliability, and meanwhile, the heat conduction area of the paraffin phase change microcapsules is increased, so that the effect of enhancing heat exchange can be achieved.
However, paraffin wax exhibits a significant supercooling phenomenon after microencapsulation, which is not present in paraffin wax in a large volume. Supercooling of the energy storage material can significantly reduce the efficiency of the thermal storage system, adding additional energy consumption. In recent years, in order to solve the supercooling problem of paraffin phase-change microcapsules, researchers have tried to add nanoparticles into microcapsule cores, which have a small particle size, a large specific surface area and extremely strong surface activity, and provide more nucleation sites for the matrix, thereby promoting heterogeneous nucleation thereof. For supercooling problems, adding suitable nanoparticles is the most convenient and efficient method. After the nanoparticles are added, each nucleation peak appears in the DSC curve of the phase-change microcapsule, and deformation or displacement occurs due to the change of conditions, so that the supercooling degree is reduced. Meanwhile, the heat conductivity of the composite phase change material is generally improved along with the addition of the nano particles, the heat diffusion coefficient is also increased, the specific heat is reduced, and the temperature distribution in the melting process of the composite phase change energy storage material is uniform.
The concentration of the nano particles required to be added for eliminating the supercooling degree of the paraffin phase-change microcapsule in the current literature is often different from a few percent to a dozen percent, so that the specific gravity of the phase-change material in the microcapsule is reduced, and the enthalpy value of the phase-change material is reduced. The main reason is that the dispersion of the nucleating agent in the microcapsule is poor, the nano particles are easy to agglomerate together because of the extremely strong activity of the surface, a plurality of agglomerates with larger connecting interfaces are formed, most of the surfaces are hydrophilic and oleophobic, and the nucleating agent is difficult to uniformly disperse in an organic medium, so that the effect of promoting the nucleation is greatly limited. The silane coupling agent can change the surface of the nano particles from hydrophilicity to lipophilicity, and improve the dispersion stability of the nano particles in organic matters. Meanwhile, the aggregation among particles is hindered by the action of chemical bonds, so that the nucleation area is increased. The existing majority of microcapsule preparation methods cannot accurately control the size of the capsules, the thickness of the shell layers and the quantity of nucleating agents in each microcapsule, so that the nano particles in each capsule are too much or too little to be utilized to the greatest extent. Microfluidic technology, in turn, can shear multiple, immiscible fluids to form single or multiple template droplets, which provides excellent templates for the synthesis of nano-microcapsules of uniform size, shape and functionality.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the primary aim of the invention is to provide a paraffin phase-change microcapsule which eliminates the supercooling degree and has no loss of phase-change enthalpy.
The invention further aims to provide a method for eliminating the supercooling degree and the phase-change enthalpy loss of the paraffin phase-change microcapsule, which can prepare the paraffin phase-change microcapsule without the supercooling degree and the phase-change enthalpy loss.
Still another object of the present invention is to provide an application of the paraffin phase-change microcapsule.
The aim of the invention is achieved by the following technical scheme:
the paraffin phase-change microcapsule with supercooling degree eliminated and no loss of phase-change enthalpy comprises a doped nanoparticle capsule core and a shell, wherein the mass percentage of the capsule core to the shell is (5% -95%): (5% -95%), the mass percentage concentration of the nano particles in the capsule core is 0.01% -0.1%; the grain diameter of the microcapsule is precisely regulated and controlled between 50 and 1500 mu m and the thickness of the shell layer of the shell is precisely regulated and controlled between 20 and 500 mu m by utilizing a microfluidic technology.
The capsule core is composed of an organic phase change material and nano particles, wherein the organic phase change material is at least one of a linear alkane compound and a linear alkane halide, and the nano particles are modified nano particles.
The shell is made of the following raw materials: 97% by mass of 1, 6-hexanediol diacrylate (HDDA), 2% by mass of photoinitiator 2-hydroxy-2-methylpropionacetone and 1% by mass of surfactant span80.
The organic phase-change material is more than one of tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane and composite paraffin phase-change material; the modified nano-particles are titanium dioxide nano-particles modified by a silane coupling agent; the silane coupling agent is one of n-octyl trimethoxy silane, n-dodecyl trimethoxy silane, hexadecyl trimethoxy silane and octadecyl trimethyl silane.
The method for eliminating supercooling degree and phase change enthalpy loss of the paraffin phase change microcapsule can be used for preparing the paraffin phase change microcapsule; the method comprises the following operation steps:
(1) Adding polyvinyl alcohol (PVA) into deionized water, and stirring at 70 ℃ to obtain a water phase fluid with the mass fraction of 2%; mixing 1, 6 hexanediol diacrylate (HDDA) with the mass fraction of 97%, 2-hydroxy-2-methyl propiophenone as a photoinitiator with the mass fraction of 2% and span80 as a surfactant with the mass fraction of 1%, and uniformly stirring at normal temperature to obtain a mesophase fluid; adding 0.01-0.1% of modified titanium dioxide nano particles into the organic phase change material, and taking the modified titanium dioxide nano particles as oil phase fluid after ultrasonic treatment for 30min under the condition that the melting point temperature of the organic phase change material is reached;
(2) Preparing microcapsules by using a microfluidic chip, wherein the specific operation steps are as follows: pushing aqueous phase fluid, intermediate phase fluid and oil phase fluid into a Teflon guide pipe from an injection pump of a microfluidic chip respectively, and introducing the aqueous phase fluid and the intermediate phase fluid into the microfluidic chip from a small-tip glass capillary, wherein the oil phase fluid is introduced into the microfluidic chip from a first closed liquid storage tank, and the aqueous phase fluid is introduced into the microfluidic chip from a second closed liquid storage tank; the oil phase fluid flows out of the small tip glass capillary, is cut by the intermediate phase fluid to form jet flow, is sheared by the aqueous phase fluid to form uniform and controllable liquid drops, the liquid drops are irradiated by an ultraviolet lamp as energy sources to be initiated when passing through the small glass capillary, 1, 6 hexanediol diacrylate is subjected to crosslinking reaction and polymerization to form a shell, and the organic phase change material containing nano particles is completely wrapped in the shell as a core material to obtain the phase change microcapsule;
(3) By changing the mass percentage concentration of the modified titanium dioxide nano particles in the oil phase fluid in the step (1), the accurate regulation and control of the supercooling degree are realized, the supercooling degree of the paraffin phase change capsule is regulated and controlled to be eliminated, and meanwhile, no phase change enthalpy loss exists.
The modified titanium dioxide nano-particles in the step (1) are prepared according to the following steps: tiCl is added to the mixture 4 Adding into absolute ethyl alcohol to generate transparent yellow slurry, adding absolute benzyl alcohol, and stirring in 90 ℃ oil bath until the slurry is slightly opaque; then precipitating in anhydrous diethyl ether, centrifuging, separating from solvent, washing with anhydrous ethanol, and directly collecting TiO which has not agglomerated 2 Dispersing the precipitate in a mixed solution of absolute ethyl alcohol and deionized water, crushing by using a cell crusher, adding a silane coupling agent, then continuing ice bath crushing, stirring in an oil bath at 70 ℃, separating the obtained suspension from a solvent by centrifugation, washing the precipitate with absolute ethyl alcohol to remove the residual coupling agent, and freeze-drying to form modified titanium dioxide nano particles.
The microfluidic chip in the step (2) is a double-emulsified glass capillary microfluidic chip in Chinese patent application number 201811008829.0.
The paraffin phase-change microcapsule which eliminates supercooling degree and has no loss of phase-change enthalpy is applied to the field of phase-change energy storage.
The relation between the flow rate of the injection pump and the particle size of the liquid drops of the microfluidic chip is as follows: increasing the flow rate of the aqueous phase fluid can enhance the cutting force of the aqueous phase and reduce the outer diameter of the capsule; increasing the flow rate of the oil phase fluid can increase the flow rate of the core material within the same time and increase the inner diameter of the capsule; increasing the flow rate of the mesophase fluid can increase the outer diameter and decrease the inner diameter simultaneously, so as to achieve the effect of increasing the wall thickness.
Compared with the prior art, the invention has the following advantages and effects:
(1) The invention breaks through the means that the quantity of the nucleating agent in the microcapsule cannot be controlled in the traditional capsule preparation means, realizes uniform control of the quantity of the nano particles in each capsule by means of the three-phase coaxial flow type microfluidic chip, and realizes the maximum utilization of the nano particles on the premise of eliminating supercooling degree.
(2) The invention breaks through the problems of agglomeration and uneven dispersion of the traditional phase change microcapsule by using a solid nucleating agent, prepares the titanium dioxide nano particles with small particle agglomeration and less agglomeration by a non-hydration method, and timely uses a silane coupling agent to carry out surface modification on the nano particles which do not start to agglomerate, thereby obtaining the modified titanium dioxide nano particles which can be uniformly dispersed in an organic phase change material and have less agglomeration.
(3) The invention breaks through the condition that the traditional method for adjusting the supercooling degree of the microcapsule by using the nano particles has obviously reduced phase transition enthalpy, and the concentration of the nano particles added in the phase transition microcapsule prepared by the method can be realized to eliminate the supercooling degree when the concentration of the nano particles is only between 0.01% and 0.1%, and the phase transition enthalpy is almost unchanged.
Drawings
FIG. 1 is a graph showing the change of the transmitted light intensity value of octadecane suspension after nano-particles are added with time;
FIG. 2 is a bar graph of particle size distribution of a suspension of octadecane after addition of nanoparticles;
FIG. 3 is a scanning electron microscope image of a phase change microcapsule;
FIG. 4 is a differential scanning calorimetric spectrum of microcapsules with or without nanoparticles added at 150 μm and 300 μm inner diameters.
Detailed Description
The present invention will be described in further detail with reference to examples, but embodiments of the present invention are not limited thereto.
Example 1:
nanoparticle preparation: 10ml of TiCl are introduced 4 Slowly addAdded to a 500ml round bottom flask containing 50ml absolute ethanol, resulting in a clear yellow slurry; 200ml of absolute benzyl alcohol is added, and then the mixture is stirred in an oil bath at 80 ℃ for 10 hours until the slurry is slightly opaque; then precipitating in 800ml of anhydrous diethyl ether, and precipitating TiO 2 Separating the precipitate from the solvent by centrifugation (10000 rpm,10 min), and washing with anhydrous ethanol for 3 times; directly mixing TiO which is not agglomerated 2 The precipitate is directly added into 390mL of mixed solution of absolute ethyl alcohol and 10mL of distilled water, crushed for 30min by using a cell crusher, added with 3.6g of octadecyltrimethoxysilane, and then continuously crushed by an ice bath for 60min (output power 600W, working time 2s and pause time 2 s), and then stirred in an oil bath at 60 ℃ for 3h while reflux is maintained; finally, separating the suspension from the solvent by centrifugation (10000 rpm,10 min), washing the precipitate with absolute ethanol for 3 times, and freeze-drying to obtain modified TiO 2 Nanoparticle powder.
Nanoparticle performance characterization: by modifying the above-prepared modified TiO 2 XRD testing of the nanoparticles and comparison with standard patterns gave: the prepared nano particles are anatase type TiO 2 Modified TiO 2 The nano particles are ground until the powder is added into octadecane, and the mass fractions are all 0.5 percent. After 30min of ultrasound with a cytobreaker, a suspension of octadecane containing nanoparticles was obtained. The stability analyzer is used for monitoring and analyzing the curves of the transmitted light intensity value and the back scattering light intensity value of the suspension, and the curve in fig. 1 shows that no sedimentation of nano particles occurs within 48 hours, and the change of the transmitted light intensity value is not more than 5%, which indicates that the modified TiO 2 The nano particles can be well dispersed in octadecane and have high stability. The particle size of the particles in the suspension was measured by a particle size analyzer, and the result showed that the nanoparticle size in the suspension was in the range of 25nm to 125nm and the average particle size was 60nm as shown in fig. 2. Indicating that the nano particles have no obvious agglomeration phenomenon in the suspension.
Preparing microcapsule raw materials: 5g of polyvinyl alcohol (PVA) was added to 250mL of deionized water, and stirring was continued at 70℃and 1000r/min for 40min to obtain an aqueous PVA solution as an aqueous phase fluid. 1, 6 hexanediol diacrylate (HDDA) weighing 14.55g and adding 0.15g of the surfaceAn active agent (span 80) and 0.3g of photoinitiator (2 hydroxy 2 methyl propiophenone) were placed on a magnetic stirrer and stirred at 25℃for 20min at 1000r/min as mesophase fluid. Weighing three groups of octadecane phase change materials with the mass of 10g, and respectively adding 0g, 0.007g and 0.01g of modified TiO 2 The nano particles are dispersed for 30min under the condition of 50 ℃ in an ultrasonic way and used as oil phase fluid.
The double-emulsified glass capillary microfluidic chip in the Chinese patent application No. 201811008829.0 is used as a microfluidic chip to prepare a microcapsule: pushing aqueous phase fluid, intermediate phase fluid and oil phase fluid into a Teflon guide pipe from an injection pump of a microfluidic chip respectively, and introducing the aqueous phase fluid and the intermediate phase fluid into the microfluidic chip from a small-tip glass capillary, wherein the oil phase fluid is introduced into the microfluidic chip from a first closed liquid storage tank, and the aqueous phase fluid is introduced into the microfluidic chip from a second closed liquid storage tank; the flow rate of the three-phase fluid was regulated by a syringe pump and the internal reaction of the microchip was visually observed using an optical microscope and a computer, in which microscope we can see: the oil phase fluid flows out of the small tip glass capillary, is cut by the intermediate phase fluid to form jet flow, is sheared by the aqueous phase fluid to form uniform and controllable liquid drops, the liquid drops are irradiated by an ultraviolet lamp as energy sources to trigger when passing through the small glass capillary, 1, 6-hexanediol diacrylate undergoes crosslinking reaction to polymerize into a shell, and the organic phase change material containing the nucleating agent is completely wrapped in the shell as a core material to obtain the phase change microcapsule. Changing the flow rate of the water phase to 700 mu L/min, the flow rate of the intermediate phase to 15 mu L/min, adjusting the flow rate of the oil phase to 5 mu L/min, adding 9ml of water phase solution into a 10ml collecting bottle for collection after the flow rate is stable, and obtaining the microcapsule with the inner diameter of 150 mu m and the shell thickness of 75 mu m after 5 minutes. And then, maintaining the three-phase flow rate unchanged, replacing the octadecane oil phase containing different nanoparticle concentrations, ensuring that the old oil phase is completely drained and then is collected by using a new collecting bottle, and finally obtaining two groups of octadecane phase-change microcapsules with the inner diameter of 100 mu m/250 mu m and the outer diameter of 0% and 0.1% of nanoparticle concentration after repeating. After the collection, continuously adjusting the flow rate of the water phase to 550 mu L/min, adjusting the flow rate of the intermediate phase to 20 mu L/min, adjusting the flow rate of the oil phase to 10 mu L/min, obtaining microcapsules with the inner diameter of 300 mu m and the shell thickness of 75 mu m, and obtaining two groups of octadecane phase-change microcapsules with the inner diameter of 300 mu m/450 mu m and the nano particle concentration of 0% and 0.07% respectively after changing different oil phases. And finally, washing the obtained product with deionized water for 45 times, filtering, and drying for 24 hours at 40 ℃ by using a vacuum drying oven to obtain the phase-change microcapsule.
The optical microscope photograph of the prepared phase-change microcapsule is shown in fig. 3. The capsule has regular morphology, the polydispersity index PDI is less than 3%, the particle size meets the high monodisperse standard, the particle size of the phase change microcapsule is considered to be uniform, and the thickness of the shell layer is controlled to be about 75 mu m, so that the influence of supercooling degree caused by the particle size and the thickness of the shell layer is eliminated.
The differential scanning calorimetric curves of the prepared phase-change microcapsules with the inner diameters of 150 μm and 300 μm are shown in fig. 4, and after nanoparticles are added, a new solidification phase-change peak appears in the high-temperature direction, and when the concentration of the nanoparticles reaches 0.1%, the supercooling degree is reduced to 0. It can also be seen from the differential scanning calorimetric curve of the phase-change microcapsules with an inner diameter of 300 μm that the supercooling degree has been reduced to 0 when the nanoparticle concentration reaches 0.07%. And it can also be seen from the melting curve that there is little change in enthalpy after the addition of nanoparticles, so it can be considered that it does eliminate supercooling and no loss of phase transition enthalpy.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (6)
1. The paraffin phase-change microcapsule is characterized by comprising a doped nanoparticle capsule core and a shell, wherein the mass percentage ratio of the capsule core to the shell is (5% -95%): (5% -95%), the mass percentage concentration of the nano particles in the capsule core is 0.01% -0.1%; the grain diameter of the microcapsule is precisely regulated and controlled between 50 and 1500 mu m and the thickness of the shell layer of the shell is precisely regulated and controlled between 20 and 500 mu m by utilizing a microfluidic technology;
the capsule core consists of an organic phase change material and nano particles, wherein the organic phase change material is at least one of a linear alkane compound and a linear alkane halide, and the nano particles are titanium dioxide nano particles modified by a silane coupling agent.
2. A paraffin phase-change microcapsule with no loss of supercooling degree and phase-change enthalpy according to claim 1, characterized in that: the shell is made of the following raw materials: 97% by mass of 1, 6-hexanediol diacrylate, 2% by mass of photoinitiator 2-hydroxy-2-methyl propiophenone and 1% by mass of surfactant span80.
3. A paraffin phase-change microcapsule with no loss of supercooling degree and phase-change enthalpy according to claim 1, characterized in that: the organic phase-change material is more than one of tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane and composite paraffin phase-change material; the silane coupling agent is one of n-octyl trimethoxy silane, n-dodecyl trimethoxy silane, hexadecyl trimethoxy silane and octadecyl trimethyl silane.
4. A method for eliminating supercooling degree and phase change enthalpy loss of paraffin phase change microcapsules is characterized by comprising the following steps: the paraffin phase-change microcapsule according to any one of claims 1-3 is prepared by the method; the method comprises the following operation steps:
(1) Adding polyvinyl alcohol into deionized water, and stirring at 70 ℃ to obtain a water phase fluid with the mass fraction of 2%; mixing 97% by mass of 1, 6-hexanediol diacrylate, 2% by mass of photoinitiator 2-hydroxy-2-methyl propiophenone and 1% by mass of surfactant span80, and uniformly stirring at normal temperature to obtain a mesophase fluid; adding 0.01-0.1% of modified titanium dioxide nano particles into the organic phase change material, and taking the modified titanium dioxide nano particles as oil phase fluid after ultrasonic treatment for 30min under the condition that the melting point temperature of the organic phase change material is reached;
(2) Preparing microcapsules by using a microfluidic chip, wherein the specific operation steps are as follows: pushing aqueous phase fluid, intermediate phase fluid and oil phase fluid into a Teflon guide pipe from an injection pump of a microfluidic chip respectively, and introducing the aqueous phase fluid and the intermediate phase fluid into the microfluidic chip from a small-tip glass capillary, wherein the oil phase fluid is introduced into the microfluidic chip from a first closed liquid storage tank, and the aqueous phase fluid is introduced into the microfluidic chip from a second closed liquid storage tank; the oil phase fluid flows out of the small tip glass capillary, is cut by the intermediate phase fluid to form jet flow, is sheared by the aqueous phase fluid to form uniform and controllable liquid drops, the liquid drops are irradiated by an ultraviolet lamp as energy sources to trigger when passing through the small glass capillary, the 1, 6-hexanediol diacrylate undergoes crosslinking reaction to polymerize into a shell, and the organic phase change material containing nano particles is completely wrapped in the shell as a core material to obtain the phase change microcapsule;
(3) By changing the mass percentage concentration of the modified titanium dioxide nano particles in the oil phase fluid in the step (1), the accurate regulation and control of the supercooling degree are realized, the supercooling degree of the paraffin phase change capsule is regulated and controlled to be eliminated, and meanwhile, no phase change enthalpy loss exists.
5. The method according to claim 4, wherein: the modified titanium dioxide nano-particles in the step (1) are prepared according to the following steps: tiCl is added to the mixture 4 Adding into absolute ethyl alcohol to generate transparent yellow slurry, adding absolute benzyl alcohol, and stirring in 90 ℃ oil bath until the slurry is slightly opaque; then precipitating in anhydrous diethyl ether, centrifuging, separating from solvent, washing with anhydrous ethanol, and directly collecting TiO which has not agglomerated 2 Dispersing the precipitate in a mixed solution of absolute ethyl alcohol and deionized water, crushing by using a cell crusher, adding a silane coupling agent, then continuing ice bath crushing, stirring in an oil bath at 70 ℃, separating the obtained suspension from a solvent by centrifugation, washing the precipitate with absolute ethyl alcohol to remove the residual coupling agent, and freeze-drying to form modified titanium dioxide nano particles.
6. Use of paraffin phase-change microcapsules with no loss of supercooling degree and phase-change enthalpy according to any of claims 1 to 3 in the field of phase-change energy storage.
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| CN113648943B (en) * | 2021-08-31 | 2023-07-25 | 广东工业大学 | Method for reducing supercooling degree of alkane phase-change microcapsule by using different shell materials, microcapsule prepared by method and application of microcapsule |
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| CN113549429A (en) * | 2021-08-19 | 2021-10-26 | 广东工业大学 | Phase change microcapsule with controllable supercooling degree and preparation method and application thereof |
| CN114288955A (en) * | 2021-12-31 | 2022-04-08 | 广东工业大学 | Method for reducing supercooling degree of alkane phase change microcapsule by mixing multiple particle sizes, prepared phase change microcapsule and application |
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