KR20220055765A - Manufacturing method of organic-inorganic hybrid capusle type phase change materials with excellent thermal conductivity and shape stability - Google Patents

Abstract

The present invention relates to a method for manufacturing an organic-inorganic hybrid capsule-type phase change material (PCM) with excellent thermal conductivity and shape stability, and more particularly, to a method for manufacturing an organic-inorganic hybrid microcapsule and an organic-inorganic hybrid microcapsule manufactured thereby, in which the method includes: preparing a metal nanoparticle solution; preparing a capsule having a core-shell structure in which an inorganic shell surrounds a circumference of a phase change material (PCM); and loading metal nanoparticles in the capsule by adding the prepared metal nanoparticle solution to the prepared capsule. A phase change material in a form of the organic-inorganic hybrid microcapsule according to the present invention solves a problem of a conventional phase change material and has improved thermal conductivity and shape stability, so that the phase change material is used as a promising phase change material capable of storing and releasing energy in various fields.

Description

Manufacturing method of organic-inorganic hybrid capsule-type phase-change material with excellent thermal conductivity and shape stability

The present invention relates to a method of manufacturing an organic-inorganic hybrid capsule-type phase change material (PCM) having excellent thermal conductivity and shape stability.

The advanced industry is causing various unexpected environmental problems along with the economic development of modern society. The indiscriminate increase in consumption of oil and coal has caused global warming due to greenhouse gas emissions along with a shortage of energy resources. Accordingly, we are actively coping with non-renewable energy and environmental crises, such as increasing the use of clean energy worldwide and seeking national strategies to increase energy utilization efficiency.

Phase change materials (PCMs) are considered candidates for increasing energy efficiency from various angles because they can store and release a huge amount of latent heat energy by changing their state in an appropriate temperature range. Because of its high energy storage density, PCM is being used in various fields such as building air conditioners, electronic cooling, waste heat recovery, textiles, solar energy storage, and battery industries.

Recently, there has been a growing movement to apply PCM as a battery thermal management material. Lithium ion batteries (Li-ion batteries, LiB) are currently widely used as the most successful secondary batteries due to their advantages such as high energy density, low memory effect, and low energy loss rate. As the usage of mobile devices such as smartphones, tablets, and laptops increases, high-capacity and large-sized batteries are increasingly required. In particular, as automobiles and generators that used fossil fuels as power sources in the past are replaced by electric vehicles (EVs) and energy storage systems (ESS), the demand for lithium secondary batteries is increasing exponentially. am. As battery demand and capacity increase, interest in battery safety is also rapidly increasing. Batteries are very sensitive to even slight temperature changes and affect battery life and safety, so designing an effective battery thermal management system is very important. In particular, the increase in battery capacity due to the electrification of future electric vehicles is accompanied by enormous heat, and the development of cooling materials to effectively control this heat is expected to influence the future development of electric vehicles.

The PCM cooling method is a passive thermal management system, and is designed to absorb excessive heat generated by the battery by the PCM located close to the battery module. PCM can maintain the operating temperature of the battery while absorbing or dissipating heat from the battery by undergoing a phase transition over a relatively constant temperature range. Key parameters for selecting a suitable PCM include high thermal conductivity and high specific heat, a melting point in the desired operating range, little or no auxiliary coolant, and negligible changes in volume during solidification or melting. In addition, it must be stable, non-toxic, non-flammable, non-explosive, and can be purchased in bulk at low cost.

Among the various PCMs, paraffin is widely used in energy storage due to its excellent thermal properties such as large phase change enthalpy, low vapor pressure, and excellent chemical and magnetic nucleation properties. However, since the phase transition of paraffinic PCM is a solid-liquid-solid physical change, in practical applications, it is necessary to use a special latent heat device or a heat exchange surface, liquid leakage when a solid-to-liquid phase change occurs, low thermal conductivity and It has limitations such as overcooling. Accordingly, there is a need to develop a new type of PCM material in which these problems are improved.

Republic of Korea Patent Publication No. 10-2013-0143342 (published on December 31, 2013)

An object of the present invention is to provide a method for manufacturing a new type of phase change material having excellent thermal conductivity and shape stability in order to solve the above problems.

Another object of the present invention is to provide a phase change material prepared by the above manufacturing method.

In order to achieve the above object, the present invention comprises the steps of preparing a metal nanoparticle solution; manufacturing a capsule having a core-shell structure in which an inorganic shell surrounds a phase change material (PCM); and adding the prepared metal nanoparticle solution to the prepared capsule to load the metal nanoparticles into the capsule.

In addition, the present invention provides an organic-inorganic hybrid microcapsule manufactured according to the above manufacturing method, wherein the organic-inorganic hybrid microcapsule has a thermal conductivity of 1 to 2 W/mk.

According to the organic-inorganic hybrid microcapsule manufacturing method according to the present invention, by encapsulating the phase-change material with an inorganic shell, it is possible to solve the problem of dissolution of the phase-change material due to the existing organic shell encapsulation, and metal nanoparticles of a specific size are manufactured to the capsule. By loading into the , it is possible to improve the low thermal conductivity of the inorganic shell.

Accordingly, the microcapsules manufactured according to the above manufacturing method solve the problems of the existing phase-change materials and have improved thermal conductivity and shape stability, so that they can be used as promising phase-change materials that can store and release energy in various fields. can

1 schematically shows a microcapsule manufacturing process according to an embodiment of the present invention.
FIG. 2 is an X-ray diffraction analysis (XRD) result of the microcapsules prepared according to FIG. 1 .
3 is an infrared spectroscopy (FT-IR) analysis result of the microcapsule.
4 is a transmission electron microscope (TEM) image of the microcapsule.
5 is a scanning electron microscope (SEM) image and energy dispersive spectroscopy (EDS) spectrum of the microcapsule.
6 is a particle distribution diagram of the microcapsules.
7 is a thermogravimetric analysis (TGA) result of the microcapsule.
8 is a differential scanning calorimeter (DSC) analysis result of the microcapsule.
Fig. 9A shows the DSC curve over 50 times of the microcapsules, and Fig. 9B shows the FT-IR spectrum results before and after repeating 50 cycles of melting/cooling.
10 is a result of calculating the activation energy of the microcapsule.
11 is a graph for evaluating the thermal conductivity of the microcapsule.
12 is a result of evaluating the shape stability and thermal stability of the microcapsule according to the temperature rise.

Hereinafter, the present invention will be described in detail.

The present inventors prepare a phase change material of a ternary capsule type in the form of a phase change material (PCM) core/inorganic shell/metal nanoparticle, and confirm that there is no leakage of liquid during phase change and thermal conductivity is improved, so that the present invention is completed.

In the present specification, "Phase Change Materials (PCM)" accumulates heat or releases stored heat through a kind of physical change process that changes from one state to another, such as from solid to liquid, from liquid to solid, etc. It may be used interchangeably with terms such as "phase change material" and "phase change material".

As used herein, "PCM@inorganic" means a capsule having a PCM core-inorganic shell structure, and "PCM@inorganic@metallic nanoparticles" is a form in which metal nanoparticles are adhered to the outside of a capsule having a PCM core-inorganic shell structure. means

The present invention provides a method for manufacturing an organic-inorganic hybrid microcapsule having excellent thermal conductivity and shape stability.

The method of manufacturing the organic-inorganic hybrid microcapsules includes preparing a metal nanoparticle solution; manufacturing a capsule having a core-shell structure in which an inorganic shell surrounds a phase change material (PCM); and loading the metal nanoparticles into the capsule by adding the prepared metal nanoparticle solution to the prepared capsule.

In the manufacturing method according to the present invention, the step of preparing the metal nanoparticle solution may be performed by adding a dispersing agent to the metal precursor solution to react, and then adding a reducing agent to react.

The metal precursor solution is prepared by dissolving a metal precursor in a solvent, and the metal precursor is one selected from the group consisting of gold, silver, copper, tungsten, iron, nickel, cobalt, zinc, titanium, palladium, ruthenium and platinum. It may be a compound containing more than one metal, for example, HAuCl ₄ , AgNO ₃ , AgBF ₄ , AgClO ₄ , AgCl, CuO, Cu(NO ₃ ) ₂ , CuCl ₂ , NiCl ₂ , Ni(NO ₃ ) ₂ , NiSO ₄ , CoCl ₂ , Co(NO ₃ ) ₂ , RuCl ₃ , PtCl ₄ , PtCl ₂ It may be, but is not limited thereto.

The solvent may be selected from water, alcohol, polyol, and the like, but is not limited thereto.

The dispersant is gelatin, polyvinylpyrrolidone (PVP), surfactant (cationic, anionic and neutral), ethyl cellulose, dextrin, and sodium tripolyphosphate. It may be selected from the group consisting of polyphosphates, such as, and preferably, gelatin.

The reducing agent may be selected from the group consisting of hydrazine, sodium citrate, ascorbate, NH ₄ OH and LiAlH ₄ , and preferably hydrazine.

The dispersing agent and the reducing agent are not limited thereto, and may include both a dispersing agent and a reducing agent known in the art, and may be selectively used according to the type of the metal.

In the manufacturing method according to the present invention, the metal nanoparticles may have an average particle diameter of 10 to 100 nm, preferably 50 to 100 nm, more preferably 80 nm. According to an experimental example of the present invention, when the metal nanoparticles are manufactured to have a size within the above range, it can be confirmed that the thermal conductivity of the microcapsules loaded with the metal nanoparticles is the best.

The size of the metal nanoparticles may be controlled by the amount of the dispersant and the reducing agent. For example, when the amount of the dispersing agent is small and the amount of the reducing agent is large, the size of the metal nanoparticles increases. Conversely, when the amount of the dispersing agent is large and the reducing agent is small, the size of the metal nanoparticles becomes small.

Accordingly, in order to prepare metal nanoparticles having an average particle diameter in the above range, preferably, the dispersant is added in an amount of 0.1 to 1 part by volume, more preferably 0.75 part by volume, based on 100 parts by volume of the total metal precursor solution. may be, and the reducing agent may be added in an amount of 10 to 20 parts by volume, more preferably 15 parts by volume.

In the manufacturing method according to the present invention, the step of preparing a capsule having a core-shell structure in which an inorganic shell surrounds the phase change material (PCM) comprises mixing the phase change material and the inorganic compound in a mass ratio of 1: (1 to 2). mixing to prepare a mixture; preparing an emulsion by mixing the mixture with a solvent containing a surfactant; and dropping an acidic solution to the prepared emulsion and stirring.

The step of preparing the mixture comprises the phase change material and the inorganic compound in a mass ratio of 1: (1 to 2), preferably 1:1.5, at 40 to 60 °C, preferably at 50 °C for 30 minutes to 2 hours, Preferably, it can be carried out by mixing by stirring for 1 hour. When mixed in the mass ratio in the above range, the average thickness of the inorganic shell may be prepared to be 20 to 40 nm, and preferably to 20 to 30 nm, since it can be manufactured to the optimal thickness of the inorganic shell excellent in thermal conductivity, the above It would be preferable to mix by mass ratio.

The phase change material is n-eicosaen (n-eicosaen), n-heneicosane, n-docosane (n-docosane), n-tricho having a melting point in the temperature range of 35 to 51 ℃ It may be a paraffinic organic material selected from the group consisting of acids (n-tricosane) and n-tetracosane, but is not limited thereto.

The inorganic compound may be a silica precursor compound selected from tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), but is not limited thereto.

The preparing of the emulsion may be performed by mixing the prepared mixture of the phase change material and the inorganic compound in a solvent containing a surfactant.

The surfactant is a cationic surfactant selected from cetyl trimethylammonium bromide (CTAB), dodecyl trimethylammonium bromide (DTAB), or tetradecyl trimethylammonium bromide (TTAB) However, the present invention is not limited thereto.

The emulsion preparation may be carried out at a temperature slightly higher than the melting temperature of the phase change material, and may be carried out at 40 to 60 °C, preferably at 50 °C.

After that, the step of stirring while dropping the acid solution to the prepared emulsion is slowly dropping a 35 to 37% HCl solution into the prepared emulsion for 2 to 4 hours, preferably for 3 hours for 1 to 3 hours, preferably may be performed by further stirring for 2 hours, and thus, a capsule having a core-shell structure in which an inorganic shell surrounds the phase change material core may be formed.

In the manufacturing method according to the present invention, in the step of loading the metal nanoparticles, the prepared metal nanoparticle solution is added to the prepared capsule and stirred for 30 to 2 hours, preferably for 1 hour, and then 40 to 60 It can be carried out by aging at ℃, preferably at 50 ℃ for 20 to 30 hours, preferably for 24 hours, followed by filtration, washing and drying.

Accordingly, it is possible to obtain a microcapsule powder in a form in which the metal nanoparticles are adhered to the outside of the capsule having the core-shell structure.

In addition, the present invention provides an organic-inorganic hybrid microcapsule manufactured according to the manufacturing method of the organic-inorganic hybrid microcapsule.

The microcapsule has a thermal conductivity of 1 to 2 W/mk, preferably 1 to 1.5 W/mk, and a pure phase change material prior to the capsule form or a phase change material core to which metal nanoparticles are not bonded. It can have superior thermal conductivity of more than twice that.

Hereinafter, examples will be described in detail to help the understanding of the present invention. However, the following examples are merely illustrative of the content of the present invention, and the scope of the present invention is not limited to the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

<Example 1> Preparation of organic-inorganic hybrid microcapsules

1. PCM@SiO ₂ Preparation of microcapsules

In order to prepare the phase change material in the form of microcapsules, first, n-eicosane (Alfa aesar, Netherlands) and tetraethyl orthosilicate (TEOS, Junsei Chemical, Japan) were mixed in a mass ratio of 1:1. The mixture was stirred at 50° C. for 1 hour. At the same time, the cationic surfactant cetyl trimethylammonium bromide (CTAB, Junsei Chemical, Japan) (about 0.3 to 1 weight per weight of PCM) was added. The prepared two solutions were mixed and stirred to prepare a uniform emulsion. After that, the HCl (35-37%, Daejung Chemicals, Korea) solution was slowly dropped for 3 hours, and stirred for 2 hours more. After aging at 50° C. for 24 hours, the obtained powder was washed several times with deionized water and dried at room temperature for 24 hours. The above manufacturing process can be applied to all paraffinic PCM materials from n-eicosane to n-tetracosane.

At this time, the temperature to make the emulsion should be carried out at a temperature slightly higher than the melting temperature of PCM, and the concentration of the cationic surfactant CTAB as a dispersant was fixed to 1, and the concentrations of the PCM core and TEOS shell were different. By doing so, SiO ₂ capsule thickness can be adjusted.

For example, if the concentration of PCM and TEOS is 1:1 by mass ratio (or molar ratio), a shell of 20 nm is produced. was made, and the shell thickness tended to increase by 20 nm for every one-fold increase in concentration.

When the thickness of the shell becomes thick, the capsule is stable because PCM does not melt out, but the thermal conductivity is poor, so a fast latent heat response is impossible. Therefore, considering the thermal conductivity, the concentration of PCM and TEOS was 1:1.5 as the most optimal condition, and the shell thickness was 30 nm as thin and stable as possible.

2. Metal Nanoparticle Sol Manufacturing Process

2-1. Preparation of copper nanoparticles

A predetermined CuO powder (Alfa aesar, Netherlands) was dissolved in an aqueous ammonia solution, and gelatin (gelatin, Sigma-Aldrich, USA) was added as a dispersant and stirred for 2 hours. Separately, hydrazine (hydrazin, Deoksan, Korea) and gelatin were added to an aqueous ammonia solution and stirred for 2 hours. The two uniformly mixed solutions were mixed and stirred under N ₂ gas bubbling for 1 hour to finally prepare a Cu metal nanoparticle solution.

2-2. Preparation of silver nanoparticles

AgNO ₃ (Sigma-Aldrich, USA) and NH ₄ OH (28%, Daejeong Hwageum, Korea) were mixed in an appropriate molar ratio to prepare a solution. Polyvinylpyrrolidone (polyvinylpyrrolidone, PVP, Sigma-Aldrich, USA) was added to the solution as a dispersant and stirred for 10 minutes. Thereafter, NaBH ₄ (Daejeong Hwageum, Korea) was added as a reducing agent to prepare a silver nanoparticle solution.

Depending on the type of metal, the dispersing agent and the reducing agent may be used differently or the same may be used. As a reducing agent used to prepare metal nanoparticles, NH ₄ OH, (hydrazin), sodium citrate, ascorbate, LiAlH ₄ , etc. can be used, and the most optimal reducing agent is hydrazine, As a dispersant, PVP, gelatin, surfactant (cation, anion, neutral), ethyl cellulose, dextrin, polyphosphate, etc. can be used, and the most optimal dispersant is gelatin.

The size of the metal nanoparticles can be controlled from 10 nm to 100 nm in size, which can be controlled by the amount of the reducing agent and the amount of the dispersing agent. It was confirmed that the size with the best thermal conductivity was 50 ~ 100 nm, and the most optimal size was 80 nm. The concentration of the metal raw material solution used was 0.1M, the concentration of the reducing agent was 0.1M, and the concentration of the dispersant was 0.03M. Different volume ratios of the reducing agent and the dispersing agent were used for a constant volume of the metal raw material solution. Assuming that the volume of the metal raw material solution is 1, the volume of the reducing agent used is 10 to 20% (10, 12.5, 15.0, 17.5, and 20) of the volume of the metal raw material solution, and the volume of the dispersing agent is 0.1 compared to the volume of the metal raw material solution ~1.0% (0.1, 0.25, 0.5, 0.75 and 1.0). And when the metal nanoparticles had an optimal size of 80 nm, the volumes of the reducing agent and the dispersing agent were 15% and 0.75%, respectively, relative to the volume of the metal raw material solution.

3. PCM@SiO ₂ @Metal ternary microcapsule manufacturing

In the process of synthesizing the PCM@SiO ₂ microcapsules prepared according to Example 1 1, the metal nanoparticle solution prepared according to Example 1 2 was added before the aging step. After sufficient stirring for about 1 hour, it was filtered and washed. After drying at room temperature for 24 hours, PCM@SiO ₂ @Cu powder was finally obtained (FIG. 1).

<Experimental Example 1> Morphological characterization of microcapsules

1-1. X-ray diffraction (XRD) analysis

The crystal structure of the microcapsules prepared according to Example 1 was obtained by using CuKα radiation (30.0 kV, 30.0 mA) with nickel wavelength filtered in a 2θ angle of 20-90° at a rate of 5°/min using powder X-rays. determined by diffractometer (XRD, model MPD, PANalytical).

As a result of XRD analysis of the microcapsules prepared according to Example 1, as shown in FIG. 2, in the XRD pattern of a pure n-eicosane (PCM) sample, a rhombohedral-shaped cubic crystal structure A typical tetrahedral structure with

On the other hand, in the PCM@SiO ₂ sample, although the peak of n-eicosane corresponding to the core was weakly observed, the peak intensity was greatly reduced, and a broad peak was clearly observed around 2θ = 20° by SiO ₂ , the shell of the capsule. This implies an amorphous structure for the silica shell and demonstrates microencapsulation.

In the PCM@SiO ₂ @Cu sample, additional peaks corresponding to the (111) and (200) crystal planes of metallic Cu were clearly observed, and the peak for copper oxide was not confirmed. In the PCM@SiO ₂ @Ag sample using n-tetracosane, the results were also the same. This means that copper metal nanoparticles or silver nanoparticles loaded to improve thermal conductivity are stably loaded in the microcapsule.

1-2. Fourier transform infrared spectroscopy (FT-IR) analysis

The chemical structure and composition of the microcapsule samples prepared according to Example 1 above were characterized using a Fourier transform infrared (FT-IR) spectrometer (Nicolet iS10 spectrometer, Thermo Fisher Scientific Inc., USA). FT-IR spectra were recorded as the average of 32 scans in the 400 to 4000 cm ^-1 frequency range.

As a result of analyzing the FT-IR of the microcapsules prepared according to Example 1, as shown in FIG. 3, in the spectrum of the pure n ^- eicosane (PCM) sample, -CH ₃ and - A split peak due to the stretch of CH ₂ was observed. At 1470 and 710 cm ^-1 , sharp and strong peaks were observed due to the strain vibration of CH and the stretch of -CH ₂ . A strong peak was observed due to the stretch of -CH ₂ and the in-plane oscillation of -CH ₂ at 717 cm ^-1 .

On the other hand, in the microencapsulated PCM@SiO ₂ , and PCM@SiO ₂ @Cu or PCM@SiO ₂ @Ag samples, the peak intensity assigned to n-eicosane as a whole was greatly reduced, and characteristic peaks due to the silica shell were additionally observed. became The broad peak in the 1000-1200 cm ^-1 region originates from the vibration of O-Si-O, and is characterized by the carbonyl stretching vibration of =CO and -CO due to the physical interaction between n-eicosane and SiO ₂ negative peaks were observed. In addition, the broad band for the OH stretching vibration of 3570 cm ⁻¹ demonstrates the presence of abundant hydroxyl groups on the microencapsulated sample surface.

1-3. Transmission electron microscope (TEM) analysis

The morphology and microstructure of the microencapsulated sample prepared according to Example 1 were determined by a high-resolution transmission electron microscope (TEM, H-7600, Hitachi, Japan) operating at 120 kV.

As a result of analyzing the microcapsules prepared according to Example 1 by TEM, as shown in FIG. 4 , (a) PCM@SiO ₂ microcapsules exhibit a regular spherical shape having a size of about 400 nm. The n-eicosane core and the SiO ₂ shell can be clearly distinguished by the difference in brightness, showing a uniform and stable shell formation.

On the other hand, two samples of PCM@SiO ₂ @Cu (b) and (c) clearly showed that Cu nanoparticles of different sizes of 10 nm and 50 nm were stably loaded in the silica shell. In particular, the amount of Cu particles observed in the capsule was higher in the PCM@SiO ₂ @Cu (50 nm) sample, despite the addition of Cu nanoparticles in the same proportion.

The TEM image results of the PCM@SiO ₂ @Ag sample using n-tetracosane were similar. It is expected that there is a difference in the mutual bonding strength depending on the size of the Cu or Ag metal nanoparticles and is affected by the charge and thickness of the silica shell surface. In the end, although partially broken microcapsules and the shapes of Cu or Ag nanoparticles were also observed, the TEM results indicate that PCM@SiO ₂ @metal nanoparticle capsules were successfully formed.

1-4. Scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS) analysis

The overall shape of the microcapsules prepared according to Example 1 was determined by scanning electron microscopy (SEM, S-4100, Hitachi, Japan) at an acceleration voltage of 15 kV, and energy dispersive X-ray spectroscopy (EDS, EX-250) , Horiba, Japan) were used to confirm the elemental components.

As a result of analyzing the microcapsules prepared according to Example 1 by SEM-EDS, as shown in FIG. 5 , the PCM@SiO ₂ sample exhibited spherical particles having a relatively smooth surface. Microcapsules partially damaged by the sample preparation process and electron beam irradiation were observed, and due to this, a high percentage of carbon corresponding to the core was detected in the EDS result.

On the other hand, the SEM image of the PCM@SiO ₂ @Cu sample showed that metallic Cu nanoparticles were uniformly loaded on the outside of the capsule, and the EDS result also clearly showed the elemental composition of the PCM@SiO ₂ @Cu hybrid capsule.

1-5. Particle Distribution Analysis

For the particle size distribution diagram of the microcapsules prepared according to Example 1, an electrophoretic light scattering measurement device (ELS 8000, Otsuka Electronics, Japan) was used, and a laser light source of 670 nm, a module frequency of 250 Hz, and a scattering angle were used for reference. Measured in beam mode.

As a result of analyzing the particle distribution of the microcapsules prepared according to Example 1, as shown in FIG. 6, PCM@SiO ₂ , PCM@SiO ₂ @Cu (10nm), PCM@SiO ₂ @Cu distributed in an aqueous solution The average size of the (50 nm) particles was 428.7, 563.9, and 631.0 nm, respectively. The loading of metal nanoparticles increased the particle size of the capsules.

<Experimental Example 2> Thermal characteristics analysis of microcapsules

2-1. thermogravimetric analysis (TGA)

Thermal stability in latent heat storage applications is one of the important parameters for shape-stable phase-change materials. The thermal stability of the microcapsule sample prepared according to Example 1 was analyzed through thermogravimetric analysis (TGA, TGA-N1000, SCINCO, Daejeon, Korea), and the range of 25 ~ 600 °C with a heating rate of 10 °C min ^-1 was measured in

As a result of analyzing the TGA of the microcapsules prepared according to Example 1, as shown in FIG. 7, the pure n-eicosane starts to lose mass from about 170° C. It exhibits degradation behavior, which results from major degradation of linear alkane chains.

The PCM@SiO ₂ and PCM@SiO ₂ @Cu samples also showed a one-step mass loss of 70.1 and 65.3 wt%, and the thermal decomposition temperature was significantly increased by encapsulation. The introduction of the metal oxide can improve the morphological stability by inducing an improvement in thermal stability. In addition, it means that the silica shell and Cu metal nanoparticles can serve as a barrier to prevent thermal vaporization of n-eicosane and improve the thermal stability of the capsule at the same time.

In particular, the carbon mass loss in the TGA curve correlates with the actual mass of n-eicosane contained in the microencapsulated sample. All samples can be expected to be utilized as thermally stable phase change materials containing 65% or more of n-eicosane.

2-2. Different scanning calorimetry (DSC) analysis

The characteristics of the phase change behavior, storage and release of latent heat of the microcapsules prepared according to Example 1 were analyzed using a differential scanning calorimeter (DSC, Q200, TA Instruments, USA) at Yeungnam University Natural Products Medical Material Core Research Support Center (CRCNM) in Korea. ) was investigated. The DSC measurement was performed in the range of 10-50° C. at a scanning speed of 5° C. min ⁻¹ under a nitrogen stream, and the amount of each sample was about 6-7 mg.

As a result of DSC analysis showing the phase change behavior and heat storage and release performance of the microcapsules prepared according to Example 1, as shown in FIG. A melting peak was shown.

The bimodal crystallization behavior of n-eicosane refers to exothermic peaks corresponding to the transition from the homogeneously nucleated liquid state to the rotating phase (T _r ) and the heterogeneous nucleated rotating phase to the crystalline phase (T _c ). This is a characteristic seen in paraffin wax.

In addition, the single endothermic peak that appears during the melting process means that n-eicosane is a stable phase change material, and n-eicosane-based encapsulated material can be used as a latent heat storage material with excellent heat resistance and crystallinity.

Meanwhile, the calculation results of the phase change parameters and phase change characteristics related to the DSC curve are summarized in Table 1 below.

The crystallization temperature (T _c ) of all microencapsulated samples was moved to a high temperature, which is due to the improvement of crystallinity due to the formation of heterogeneous nuclei. In particular, it is believed that the crystallization temperature increased as the molecular motion of n-eicosane was restricted by the inorganic silica shell and Cu metal nanoparticles. In particular, as two distinct bimodal crystallization peaks observed in n-eicosane were encapsulated, the boundary was integrated as a whole. It is expected that the rotational phase is stabilized as the crystallization time is prolonged and the crystallite size is increased by encapsulation.

Moreover, crystallization enthalpy (ΔH _c ) and melting enthalpy (ΔH _m ) of PCM materials are important parameters directly related to latent heat storage and release, implying heat storage capacity. n-eicosane has high melting enthalpy and crystallization enthalpy values of 250.41 and 244.15 J/g, respectively, indicating excellent storage and release ability of energy generated during phase transition.

On the other hand, the absolute phase change enthalpy of the microencapsulated samples decreased. This is a natural result of the loading of inorganic silica shells and Cu metal nanoparticles that cannot absorb latent heat. Surprisingly, the enthalpy of phase change of the PCM@SiO ₂ @Cu sample loaded with Cu metal nanoparticles was slightly increased compared to the encapsulated PCM@SiO ₂ . This means fast heat transfer due to the improvement of thermal conductivity by Cu metal nanoparticles, and indicates that the storage and release rate of latent heat of the PCM material can be improved.

The increase in thermal conductivity and heat transfer ability by the silica inorganic shell and metal particles are related to the overcooling of the material. Since overcooling is an obstacle to heat transfer due to the difference between the melting temperature and the crystallization temperature, overcooling must be effectively suppressed for an excellent phase transition material. In this regard, the microencapsulated material improves heat transfer by reducing the heteronucleation barrier of n-eicosane inside the capsule and suppresses overcooling, suggesting that it is a potential latent heat storage and release material.

Additionally, encapsulation efficiency (E _en ), energy storage efficiency (E _es ), and heat storage capacity (C _es ) were calculated as another phase change performance index in Table 1 above. The encapsulation efficiency is a value determined by the latent heat of release of the core PCM material, and all showed an efficiency of 60% or more. This is almost the same value as the mass loss in the aforementioned TGA curve, and it is considered that it can effectively store or release latent heat because it contains more than 60% n-eicosane.

The working efficiency of PCM materials is closely related to energy storage efficiency and heat storage capacity. Energy storage efficiency was almost similar to encapsulation efficiency according to the content of n-eicossane, and in particular, all of the heat storage capacity showed high efficiency of 99% or more. It is encapsulated in an appropriate size and shape, and it is expected that the energy storage and release of the material can be stably without deformation even at the phase transition temperature or higher.

2-3. Multi-cycle analysis

As a result of performing multi-cycle DSC scan to investigate the reliability of the phase change behavior and thermal properties of the microcapsules prepared according to Example 1, as shown in FIG. Accordingly, T _r changed significantly, which is considered to be the result of a decrease in the crystallinity of n-eicosane as the melt-cooling process was repeated.

Table 2 below summarizes the thermal properties accordingly.

On the other hand, in the microencapsulated PCM@SiO ₂ @Cu sample, the values of T _r , T _c and T _m did not change even when the number of cycles was increased, and all cycle curves were almost identical to the initial curves. This shows that the microencapsulated samples have excellent phase change stability and structural and thermal stability. In particular, despite the multi-cycle phase transition, the melting and cooling enthalpy values also remained the same, which means a long life cycle due to the morphological stability and excellent thermal reliability of microcapsules.

As a result of FT-IR analysis before and after repeating 50 cycles of melting/cooling of the sample, as shown in FIG. 9B, n-eicosnae undergoes crystal phase transformation by repeated melt-cooling process, and new hydrocarbon-related peaks are observed. became Additional -CH stretch at 2800 cm ^-1 , and peaks assigned to -C≡C- were observed near 2000 cm ^-1 , indicating that structural deformation due to crystal shrinkage according to the solid-liquid phase transition of n-eicosane was observed. It is expected.

On the other hand, the microencapsulated PCM@SiO ₂ @Cu sample was almost identical to the FT-IR pattern before the reaction even after 50 cycles of repetition. These results mean that the microencapsulated sample can maintain a stable microstructure without damaging the capsule shape even after repeated melt-cooling cycles. Therefore, it proves that the encapsulation was successful as a phase change material with excellent reliability for phase change reversibility and thermal stability.

2-4. Activation Energy Analysis

As a result of calculating the Ozawa equation based on the DSC curve to calculate the activation energy for the phase change and thermal decomposition of the microcapsules prepared according to Example 1, as shown in FIG. 10, pure n-eicosane is a melting process The difference between T _m and melting enthalpy area was large according to the DSC scan rate.

On the other hand, the microencapsulated PCM@SiO ₂ @Cu (50 nm) sample had a relatively small change range, and the trend of the melting enthalpy peak was the same. This is related to the stability of the phase change behavior and thermal properties of the two samples mentioned above. The absence of change in enthalpy of melting despite different scan rates means that the encapsulated sample can stably store and release energy, and its crystallinity is high.

The activation energy according to the phase change characteristics is affected by both crystal nucleation and growth crystals. The slope value obtained by the corresponding plot of ln(ψ/Tm ₂ ) versus 1/Tm is the activation energy for melting, and the values of n-eicosane and PCM@SiO ₂ @Cu (50 nm) are 148.40 and 245.07, respectively. kJ/mol. It can be seen that n-eicosane melts faster and the crystal shrinkage-expansion process occurs well due to the heterogeneous nucleation effect.

On the other hand, it is believed that microencapsulated PCM@SiO ₂ @Cu (50 nm) has improved crystallinity by encapsulation of inorganic substances and increased activation energy for melting by protecting n-eicosane. In conclusion, the high melt activation energy of PCM@SiO ₂ @Cu (50 nm) indicates that the morphology and thermal properties can be stably maintained even during phase transition in latent heat storage applications.

2-5. Thermal Conductivity Assessment

Thermal conductivity is a measure of efficient heat transfer. The thermal conductivity of the microcapsules prepared according to Example 1 was measured at room temperature (25° C.) using a thermal conductivity analyzer (C-Therm Technologies Ltd., TCi Thermal Conductivity Analyzer, New Brunswick, Canada).

As a result of evaluating the actual thermal conductivity of the microcapsules prepared according to Example 1, as shown in FIG. 11, the thermal conductivity of pure n-eicosnae was measured as 0.4716 W/mK at room temperature, and PCM@SiO ₂ was 0.4924 There was a slight increase in thermal conductivity with encapsulation in W/mK. In particular, the thermal conductivity (1.3926 W/mK) of the PCM@SiO ₂ @Cu (50 nm) sample was improved compared to the thermal conductivity (1.1469 W/mK) of the PCM@SiO ₂ @Cu (10 nm) sample.

This means that, as observed in the TEM image, a larger amount of Cu metal nanoparticles were loaded into the capsule, and the larger the size of the metal nanoparticles, the better the thermal conductivity. The effective thermal conductivity of the nanofluid can be improved as the size of the particles dispersed below the critical particle increases. In order to rapidly transfer the released energy and increase the storage efficiency, it must have high thermal conductivity, which in turn suggests that microencapsulated PCM@SiO ₂ @Cu (50 nm) samples can perform effective thermal management through latent heat storage and release. do.

2-6. Evaluation of thermal stability and shape stability according to temperature rise

For the practical application of the phase change material in the industrial field, there should be no leakage of the liquid during the phase change, and in the end, the shape stability characteristic is very important. The thermal stability and shape stability of the microencapsulated materials according to the temperature increase in the 25-50 °C temperature range were compared. As a result of observing the phase transition of the material in real time using a melting point measuring device, as shown in FIG. 12 , pure n-eicosane, which was in a solid state at room temperature (25° C.), was in a liquid state at a melting temperature of 37° C. or higher. Complete melting was observed.

On the other hand, the microencapsulated PCM@SiO ₂ and PCM@SiO ₂ @Cu (10nm, 50nm) samples did not leak liquid n-eicosane even above the melting temperature, and the initial state was maintained the same. This suggests that all samples were successfully encapsulated and are promising phase-change materials that can store and release energy in a shape-stable manner.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. Do. That is, the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (13)

preparing a metal nanoparticle solution;
manufacturing a capsule having a core-shell structure in which an inorganic shell surrounds a phase change material (PCM); and
A method of manufacturing an organic-inorganic hybrid microcapsule comprising; adding the prepared metal nanoparticle solution to the prepared capsule and loading the metal nanoparticles into the capsule. The method of claim 1,
The step of preparing the metal nanoparticle solution,
It is carried out by adding a dispersing agent to the metal precursor solution and reacting, and then adding a reducing agent to react,
With respect to 100 parts by volume of the total metal precursor solution,
The method for producing an organic-inorganic hybrid microcapsule, characterized in that the dispersant is added in an amount of 0.1 to 1 part by volume, and the reducing agent is added in an amount of 10 to 20 parts by volume. 3. The method of claim 2,
The metal precursor is
Gold, silver, copper, tungsten, iron, nickel, cobalt, zinc, titanium, palladium, ruthenium and a method of manufacturing an organic-inorganic hybrid microcapsule, characterized in that the compound containing one or more metals selected from the group consisting of platinum . 3. The method of claim 2,
The dispersant is
Organic-inorganic, characterized in that selected from the group consisting of gelatin, polyvinylpyrrolidone (PVP), surfactant, ethyl cellulose, dextrin and polyphosphates (polyphosphate) Method for manufacturing hybrid microcapsules. 3. The method of claim 2,
The reducing agent,
Hydrazine (hydrazin), sodium citrate (trisodium citrate), ascorbic acid (ascorbate), NH ₄ OH and LiAlH ₄ A method of manufacturing an organic-inorganic hybrid microcapsule, characterized in that selected from the group consisting of. 3. The method of claim 2,
The metal nanoparticles,
A method of manufacturing an organic-inorganic hybrid microcapsule, characterized in that the average particle diameter is prepared in a range of 10 to 100 nm. The method of claim 1,
The phase change material is
n-eicosaen, n-heneicosane, n-docosane, n-tricosane and n-tetracosane A method for producing an organic-inorganic hybrid microcapsule, characterized in that it is a paraffin-based organic material selected from the group consisting of The method of claim 1,
The step of preparing the capsule,
preparing a mixture by mixing the phase change material and the inorganic compound in a mass ratio of 1: (1 to 2);
preparing an emulsion by mixing the mixture with a solvent containing a surfactant; and
A method of producing an organic-inorganic hybrid microcapsule comprising a; the step of stirring while dropping an acidic solution to the prepared emulsion. 9. The method of claim 8,
The inorganic compound is
A method of manufacturing an organic-inorganic hybrid microcapsule, characterized in that the silica precursor compound is selected from tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS). 9. The method of claim 8,
The surfactant is
A cationic surfactant selected from cetyl trimethylammonium bromide (CTAB), dodecyl trimethylammonium bromide (DTAB), or tetradecyl trimethylammonium bromide (TTAB), characterized in that , Method for manufacturing organic-inorganic hybrid microcapsules. The method of claim 1,
The inorganic shell,
A method of manufacturing an organic-inorganic hybrid microcapsule, characterized in that the average thickness is manufactured to 20 to 40 nm. The method of claim 1,
The step of loading the metal nanoparticles,
Organic-inorganic hybrid microcapsules, characterized in that the prepared metal nanoparticle solution is added to the prepared capsule and stirred, then aged at 40 to 60° C. for 20 to 30 hours, followed by filtration, washing and drying. manufacturing method. 13. An organic-inorganic hybrid microcapsule prepared according to any one of claims 1 to 12, wherein the organic-inorganic hybrid microcapsule has a thermal conductivity of 1 to 2 W/mk.

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