Research on microcapsules of phase change materials

Microcapsule technology is a kind of technology wrapping the solid or liquid into minute-sized particles within the field of micrometer or millimeter with film forming materials. This thesis introduces microcapsule technology of phase change materials and its main functions and the structural composition, preparation methods and characterization technology of microcapsule of phase change materials. The microcapsule of phase change materials is small in size and its temperature remains unchanged during the process of heat absorption and heat release. It is of great value in research and application prospect due to these characteristics.

Phase change microcapsules in thermal Energy applications:A critical review

Phase change microcapsules can carry large amounts of heat and be dispersed into other mediums either as a solid composite or as slurry fluids without changes to their appearance or fluidity. These two standout features make phase change microcapsules ideal for use in thermal energy applications to enhance the efficiency of energy utilisation. This review paper includes methods used for the encapsulation of phase change materials, especially the method suitable for large scale productions, the trends of phase change microcapsule development and their use in thermal energy applications in static and dynamic conditions. The effect of phase change microcapsules on convective heat transfer through addition to thermal fluids as slurries is critically reviewed. The review highlighted that so far the phase change microcapsules used mainly have polymeric shells, which has very low thermal conductivities. Their enhancement in convective heat transfer was demonstrated in locations where the phase change material experiences phase change. The phase change results in the slurries having higher apparent local specific heat capacities and thus higher local heat transfer coefficients. Out of the phase change region, no enhancement is observed from the solid microcapsule particles due to the low specific heat capacity and thermal conductivity of the phase change microcapsules compared to that of water, which is normally used as slurry media in the test. To further the research in this area, phase change microcapsules with higher specific heat capacity, higher thermal conductivity and better shape stability need to be applied.

Preparation of Phase Change Microcapsule and Its Plication in Textiles

Phase change microcapsules(PCMs)are prepared with n-hexadecane and n-octadecane as core material,and melamine-formaldehyde resin is used as shell material by in-situ polymerization.Differential scanning calorimetry(DSC)was used to analyze the phase change properties.Thermal conductivity and maximum heat flux of cotton fabric finished with PCMs before and after being washed were also measured.It has been found that melting and crystal enthalpy of the PCMs decrease with decreasing the core/shell ratio,while qmax of fabric treated with PCMs decreases and the thermal conductivity increases.Study shows that fabric finished by the PCMs has good temperature conditioning function.

Preparation and Performance of n-Dodecane Microencapsulated Phase Change Cold Storage Materials

Cold chain transportation is currently a hot research topic.Since the traditional refrigeration methods lead to the consumption of large amounts of energy,the search for new energy storage materials is a major trend.In the present contribution,n-dodecane/PMMA microencapsulated phase change materials were prepared by suspension polymerization for ice-temperature cold chain transportation and their preparation parameters were explored using the encapsulation ratio as optimization indicator.The results show that the n-dodecane-containing microcapsules have a maximum encapsulation ratio of 93.2%when using a core-to-wall ratio of 3:1,5%of emulsifier,30%of crosslinker,and 2000 rpm of emulsification speed.The phase transition temperature and enthalpy are-2℃and 195.9 kJ/kg,respectively.The microcapsules prepared with the optimized process parameters have good microscopic morphology,high energy storage efficiency,uniform particle size and good thermal stability,making them ideal materials for cold chain transportation.

Preparation and performance of novel magnetic phase-change-microcapsule-supported Bi_(2)WO_(6)catalyst

The design and synthesis of novel photocatalyst with self-temperature control function is an important topic in the field of advanced environmental functional materials.In this work,submicron-sized magnetic phase change microcapsules composed of paraffin core and Fe_(3)O_(4)-loaded silica shell are prepared,on which the Bi_(2)WO_(6)crystals is grown in situ through hydrothermal reaction to obtain novel magnetic phase-change-microcapsule-supported Bi_(2)WO_(6)catalyst(MP@FS/BWO).The MP@FS/BWO has a paraffin encapsulation ratio of 57.1%,and the phase change enthalpy of 105.1 J/g in a temperature range of 50–60℃,which endows the MP@FS/BWO with a certain self-temperature regulation ability.MP@FS/BWO shows excellent catalytic performance in the decomposition of rhodamine B under the simulated sunlight irradiation.After the light source is turned off,it still has good catalytic ability by maintaining high temperature due to its temperature control function based on the phase transition process.The MP@FS/BWO can be easily recycled by magnetic separation and shows good structural stability and reusability.This work provides a new idea for the development of long-effect and energy-saving outdoor photocatalysts.

Photothermal phase change material microcapsules via cellulose nanocrystal and graphene oxide co-stabilized Pickering emulsion for solar and thermal energy storage

Phase change materials(PCMs)have attracted significant attention in thermal management due to their ability to store and release large amounts of heat during phase transitions.However,their widespread application is restricted by leakage issues.Encapsulating PCMs within polymeric microcapsules is a promising strategy to prevent leakage and increase heat transfer area with matrices.Moreover,photothermal PCM microcapsules are particularly desirable for solar energy storage.Herein,we fabricated photothermal PCM microcapsules with melamine-formaldehyde resin(MF)as shell using cellulose nanocrystal(CNC)and graphene oxide(GO)co-stabilized Pickering emulsion droplets as templates.CNC displays outstanding Pickering emulsifying ability and can facilitate the fixation of GO at the oil-water interface,resulting in a stable CNC/GO co-stabilized PCM Pickering emulsion.A polydopamine(PDA)layer was coated in-situ on the emulsion droplets via oxidization self-polymerization of dopamine.Meanwhile,GO was reduced to reduced GO(rGO)due to the reducing ability of PDA.The outmost MF shell of the PCM microcapsules was formed in-situ through the polymerization and crosslinking of MF prepolymer.The resulted PCM@CNC/rGO/PDA/MF microcapsules exhibit uniform sizes in the micrometer range,excellent leakage-proof performance,high phase change enthalpy(175.4 J g^(−1))and PCM encapsulation content(84.2%).Moreover,the presence of rGO and PDA endows PCM@CNC/rGO/PDA/MF microcapsules with outstanding photothermal conversion performance.The temperature of PCM@CNC/rGO/PDA/MF microcapsule slurries(15wt.%)can reach 73°C after light irradiation at 1 W cm^(−2).Therefore,photothermal PCM@CNC/rGO/PDA/MF microcapsules are promising for solar energy harvesting,thermal energy storage,and release in various applications,such as energy-efficient buildings and smart textiles.

Preparation and characterization of hexadecane microcapsule with polyurea-melamine formaldehyde resin shell materials

This paper gives a brief report of the preparation of hexadecane microcapsule with polyurea-melamine formaldehyde resin shell materials(HMPM).The sealing performance and thermal stability of HMPM was enhanced much more effectively than that of microcapsule with polyurea shell material(HPM).The results of microscopical imaging analysis system,DSC,TG,and laser particle analyzer were briefly introduced.

Preparation and Characterization of Poly(melamine-urea-formaldehyde) Tetradecanol Microcapsules Coated with Silver Particles

A novel type of microencapsulated phase change materials(microPCMs)based on 1-tetradecanol(TD)core and silver-coated poly(melamine-urea-formaldehyde)(MUF)shell was successfully synthesized by in situ polymerization method followed by silver reduction.Fourier-transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),scanning electron microscopy with energy dispersive X-ray spectrometry(SEM/EDS),thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC)were used to characterize the chemical structure,morphology and thermal properties of the as-prepared silver-coated microPCMs.FTIR analysis confirmed the successful encapsulation of TD with MUF wall materials.The SEM and EDS results indicated that the prepared silver-coated MUF microPCMs exhibited uniform spherical shape with a perfect silver outer layer.From XRD analysis,the Ag metal dispersed on the surface of microcapsules presented the form of elementary substance.The deposition weight of silver particles on the microcapsule surface increased with increasing the amount of silver nitrate,as indicated by EDS tests.The DSC results indicated that the melting temperature and the melting latent heat of microPCMs modified with 0.7g of silver nitrate in 150mL aqueous solution were 39.2°C and 126.6J·g^-1,respectively.Supercooling of the microPCMs coated with silver particles was effectively suppressed,compared with that of microPCMs without Ag.Thus,the encapsulation of TD with silver-coated MUF shell developed by this work can be an effective method to prepare the microPCMs with enhanced thermal transfer performance and phase change properties.

Preparation of Microcapsules Containing Erythritol with Interfacial Polycondensation Reaction by Using the (W/O) Emulsion

It was tried to microencapsulate erythritol as a phase change material with the interfacial polycondensation reaction method by using the (W/O) emulsion and to characterize the microcapsules prepared. In the experiment, toluene diisocyanate, diphenyl methane diisocyanate and hexamethylenediisocyanate were used to form the polyurethane shell and the effects of them on the heat storage density and the microencapsulation efficiency were investigated. Furthermore, the effect of supercooling prevention agent on the phase change behavior of erythritol was investigated. The microcapsules prepared with toluendiisocyanate monomer showed the highest heat storage density and the higher microencapsulation efficiency. Considerable supercooling phenomenon in the microcapsule was observed and prevented to a certain degree by addition of potassium dihydrogen phosphate and calcium sulfate as the supercooling prevention agent.

The Application of Microcapsule in the Infrared Stealth Camouflage

Infrared radiation is one of the main exposure symptoms of military targets. Infrared radiation differences between targets and backgrounds should be eliminated to the greatest extent to fight against all kinds of infrared reconnaissance. In addition to the employment of the camouflage paint with low emissivity, reducing the surface temperature of targets is an urgent and difficult challenge. PCM (phase-change material) can be used to effectively solve this problem. The application of microcapsule in the infrared stealth materials greatly promotes the development of infrared stealth technology.

Preparation and characterization of silica microcapsules containing butyl-stearate via sol-gel method

For thermal energy storage application in energy-saving building materials,silica microcapsules containing phase change material were prepared using sol-gel method in O/W emulsion system. In the system droplets in microns are formed by emulsifying an organic phase consisting of butyl-stearate as core material. The silica shell was formed via hydrolysis and condensation from tetraethyl silicate with acetate as catalyst. The SEM photographs show the particles possess spherical morphology and core-shell structure. The as-prepared silica microcapsules mainly consist of microsphere in the diameter of 3-7 μm and the median diameter of these microcapsules equals to 5.2 μm. The differential scanning calorimetry(DSC) curves indicate that the latent heat and the melting point of microcapsules are 86 J/g and 22.6 ℃,respectively. The results of DSC and TG further testify the microcapsules with core-shell structure.

Synthesis of N-Alkane Mixture Microcapsule and Its Application in Low-Temperature Protective Fabric

We investigated synthesis and characterization of melamine-urea-formaldehyde（MUF） microcapsules containing n-alkane mixture as phase change core material for thermal energy storage and low-temperature protection. The phase change microcapsules（microPCMs） were prepared by an in situ polymerization using sodium dodecyl sulfate（SDS） and polyvinyl alcohol（PVA） as emulsifiers. Surface morphology, particle size, chemical structure, and thermal properties of microPCMs were, respectively, characterized by using scanning electron microscopy（SEM）, field emission scanning electron microscopy（FESEM）, Fourier transform infrared spectroscopy（FT-IR）, differential scanning calorimetry（DSC）, and thermal gravimetric analysis（TGA）. Low-temperature resistance performances were measured at-15,-30,-45, and-60 ℃ after microPCMs were coated on a cotton fabric by foaming technology. The results showed that spherical microPCMs had 4.4 μm diameter and 100 nm wall thickness. The melting and freezing temperatures and the latent heats of the microPCMs were determined as 28.9 and 29.6 ℃ as well as 110.0 and 115.7 J/g, respectively. Encapsulation of n-alkane mixture achieved 84.9 %. TGA analysis indicated that the microPCMs had good chemical stability below 250 ℃. The results showed that the microencapsulated n-alkane mixture had good energy storage potential. After the addition of 10 % microPCMs, low-temperature resistance duration was prolonged by 126.9%, 145.5%, 128.6%, and 87.5% in environment of-15,-30,-45 and-60 ℃, respectively as compared to pure fabric. Based on the results, phase change microcapsule plays an effective role in lowtemperature protection field for the human body.

Study on the Heat Conduction of Phase-Change Material Microcapsules

The 3ω approach was used to measure the effective thermal conductivity of phase-change material microcapsules (PCMMs) based on urea formaldehyde and sliced paraffin. The effective thermal conductivities of PCMMs with different densities were measured within the phase-change temperature range. The relationships between effective thermal conductivity, density and temperature were analysed. The effective thermal conductivity reached peak values within the phase-change temperature range and the temperature peak value was consistent with the peak value of the phase-change temperature. The effective thermal conductivity increased with increasing density due to the decreased porosity of samples and their increased solid-phase conduction.

Preparation and characterization of magnetic phase-change microcapsules

Magnetic microcapsules containing paraffin cores within urea-formaldehyde shells were fabricated utilizing in situ polymerization, with iron nano-particles as magnetic particles. The thermal properties, surface morphologies, magnetic properties and iron nano-particles content of the magnetic phasechange microcapsules were investigated by scanning electronic microscopy (SEM), differential scan- ning calorimetry (DSC), vibrating sample magnetometry (VSM) and inductively coupled plasma quantometry (ICP). The influence of iron nano-particles on morphologies was also considered. The results indicate that the melting point of magnetic phase-change microcapsules is almost identical to that of paraffin. The magnetism parameters such as specific saturation magnetization and residual magnetization of magnetic phase-change microcapsules increase with the increase of iron nano-particles content.

Enhanced photothermal conversion and thermal conductivity of phase change n-octadecane microcapsules shelled with nano-SiC doped crosslinked polystyrene

Microcapsules incorporating phase change material n-octadecane(ODE)shelled with crosslinked polystyrene(CLPS)were prepared via the suspension polymerization.SiC nanoparticles(nano-SiC)were employed to modify the shell to improve the heat transfer and photothermal conversion of the microcapsules.The scanning electron microscopic analysis revealed the microcapsules of a general spherical shape.The surface components and chemical composition of the microcapsule samples were evaluated by the energy-dispersive X-ray and Fourier transform infrared spectroscopy,confirming that the nano-SiC have been embedded in the CLPS shell.Results show that the microcapsule sample with 1.25 wt.%nano-SiC(denoted as MPCM3)exhibits the best heat property among the four kinds of samples prepared with various nano-SiC dosages,and all the nano-SiC doped samples have improved thermal conductivity and photothermal conversion as compared to the microcapsule sample without doping(denoted as MPCM1).Compared to the MPCM1,the thermal conductivity of the MPCM3 is increased by 65.3%,reaching 0.124±0.005 W·m^(−1)·K^(−1).The MPCM3 has excellent thermal stability as well.Differential scan-ning calorimetry examination shows that the MPCM3 has higher melting and crystallization enthalpies than the MPCM1,achieving 106.8±0.3 J·g^(−1) and 104.9±0.2 J·g^(−1),respectively.In the photothermal conversion experi-ments,the MPCM3 exhibited great photothermal conversion capability,with a 54.91%photothermal conversion efficiency,which is 145.68%higher than that of the MPCM1.

Experimental design of paraffin/methylated melamine-formaldehyde microencapsulated composite phase change material and the application in battery thermal management system

In order to maintain the optimal operating temperature of the battery surface and meet the demand for thermal storage technology,battery thermal management system based on phase change materials has attracted increasing interest.In this work,a kind of core-shell structured microcapsule was synthesized by an in-situ polymerization,where paraffin was used as the core,while methanol was applied to mod-ify the melamine-formaldehyde shell to reduce toxicity and improve thermal stability.Moreover,three different types of heat conductive fillers with the same content of 10 wt.%,i.e.,nano-Al_(2)O_(3),nano-ZnO and carbon nanotubes were added,generating composites.The microcapsules were uniform,and were not affected by the thermal fillers,which were evenly dispersed around.The composite sample with carbon nanotubes(10 wt.%)showed the highest thermal conductivity of 0.50 W/(m K)and latent heat of 139.64 J/g.Furthermore,according to the leakage testing and battery charge/discharge experiments,compared with Al_(2)O_(3)and ZnO,the addition of carbon nanotubes remarkably enhances the heat storage ability as latent heat from 126.98 J/g for the prepared sample with Al_(2)O_(3)and 125.86 J/g for the one with ZnO,then to 139.64 J/g,as well as dissipation performance as a cooling effect by decreasing the sur-face temperature of battery from 2%to 12%of microcapsule,composite sample with carbon nanotubes presents a broad application prospect in battery thermal management system and energy storage field.

碳纳米管和纳米铜导热粒子的热调节性能研究

采用原位聚合法制备了以石蜡(PA)为芯材、三聚氰胺-甲醛-树脂为壁材、碳纳米管(CNT)及纳米铜(CNP)为导热粒子的改性相变微胶囊。结果表明:随着CNT和CNP添加量的增加,CNT改性相变微胶囊(MPCM/CNTs)的导热系数从0.25W/(m·K)增大到0.38W/(m·K),最大增加率为52%;CNP改性相变微胶囊(MPCM/CNPs)导热系数从0.25W/(m·K)增大到0.47W/(m·K),最大增加率为88%。

基于纳米TiO 2对十四烷-正辛酸二元相变微胶囊的改性制备及性能表征

通过溶剂挥发法制备以十四烷-正辛酸二元相变材料为芯材,纳米TiO 2改性壁材聚砜的相变微胶囊。探究不同添加量的纳米TiO 2对微胶囊性能的影响,使用FT-IR、DSC、电子显微镜对相变微胶囊的化学结构、表面形态、相变特性及包裹率进行检测。分析发现,当纳米TiO 2添加量为3%时,相变微胶囊的表面形态最佳,粒径最为平均,其熔化焓和结晶焓分别为88.91J/g和80.4J/g,且包覆率可达44.42%。

相变调温纤维的制备技术研究进展

介绍了相变材料的分类及各自的性能特点,综述了目前相变微胶囊及相变调温纤维的制备方法,并指出了不同制备方法存在的优缺点及应用范围。目前,适用于纺织领域的相变材料主要为有机相变材料石蜡;相变微胶囊的制备主要采用化学法,该方法在纺织领域应用较多,关键技术是乳化工艺;相变调温纤维的制备多采用复合纺丝法和后整理法,但存在相变微胶囊的制备工艺较复杂、加入相变材料损伤纤维机械性能、相变调温纤维经过纺纱及织造等流程后调温能力减弱等问题。指出相变微胶囊的制备技术、相变调温纤维的制备工艺、相变材料的保持率及温度调节能力的稳定性等是相变调温纤维未来发展的重点研究方向。

高储能性石蜡相变微胶囊的微流控制备与性能研究

高储能性相变微胶囊的可控制备对于相变潜热的高效利用具有重要意义。基于此,利用微流控技术,分别以石蜡和碳纳米管(CNT)复合海藻酸钠为芯材和壳材,通过乳化固化法制备得到了石蜡相变微胶囊,并研究了CNT含量对相变微胶囊性能的影响规律。结果表明:随着壳层中CNT含量的不断增加,微胶囊对石蜡的包封能力显著提高,当其含量为3%时,石蜡相变微胶囊的包封率接近96%,热焓值达206.8J/g。同时,石蜡相变微胶囊的光热转换能力也随CNT含量的增加而增强,并在光照11min后,其温度可达47℃。相关研究结果可为可控制备具有高储能性和光热转换性能的相变微胶囊提供科学指导。