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.

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 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.

Effect of graphene and its derivatives on thermo-mechanical properties of phase change materials and its applications:a comprehensive review

Phase change materials(PCMs)play a leading role in overcoming the growing need of advanced thermal management for the storage and release of thermal energy which is to be used for different solar applications.However,the effectiveness of PCMs is greatly affected by their poor thermal conductivity.Therefore,in the present review the progress made in deploying the graphene(Gr)in PCMs in the last decade for providing the solution to the aforementioned inadequacy is presented and discussed in detail.Gr and its derivatives((Gr oxide(GO),Gr aerogel(GA)and Gr nanoplatelets(GNPs))based PCMs can improve the thermal conductivity and shape stability,which may be attributed to the extra ordinary thermo-physical properties of Gr.Moreover,it is expected from this review that the advantages and disadvantages of using Gr nanoparticles provide a deep insight and help the researchers in finding out the exact basic properties and finally the applications of Gr can be enhanced.In this work,Gr and its derivatives based PCMs was characterized by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction spectroscopy(XRD),and scanning electron microscopy(SEM)by which crystal structure was known,phase was identified along with the knowledge of surface structure respectively.The increase in the mass fraction(%)of the filler(Gr and its derivatives)led to even better thermo-physical properties and thermal stability.The thermal characterization was also done by differential scanning calorimetry(DSC),thermo gravimetric analysis(TGA)and thermal conductivity tests.The enthalpy of freezing and melting showed that Gr and its derivatives based PCMs had a very high energy storage capability as reflected in its various applications.

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.

基于PCM的轻质智能调温墙体材料设计

基于相变材料(Phase Change Material,简称PCM)的轻质智能调温墙体,通过将PCM覆盖在墙壁内部,具有储存热量和环保等优点的相变材料可以实现室内温度自动调节。提出了一种基于PCM的轻质智能调温墙体设计方案,结合加气混凝土的生产工艺流程,探索采用后浸渍法和直接加入法,结果表明本材料可以有效地减小室内温度波动和能耗,实现初步的自动温控效果,为建筑节能提供了一种新的解决方案。

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。

相变微胶囊的制备及其在热储能中的应用进展

相变材料因高能量存储密度、高潜热和良好的热稳定性被广泛应用于潜热储能,但是泄漏、热导率低等问题限制了相变材料在热储能中的应用。微囊化能够防止相变材料的泄漏,降低与外界环境的反应并提高热导率,因此相变微胶囊是提高相变材料导热性和解决泄漏等问题的有效方法。介绍了相变微胶囊常见的制备方法及其在建筑材料、太阳能储能及热管理系统中的应用,并展望了该材料未来的发展趋势。

相变材料微胶囊的研究进展

为进一步提高能源利用率,满足当今社会对可持续能源的迫切需求,首先,列举了相变材料微胶囊的芯材和壁材的分类及其选择原则;其次,分析总结了相变材料微胶囊不同制备技术的国内外最新研究进展,重点对比归纳了物理法、化学法以及物理化学法等制备技术的原理、特点及其适用范围;然后,综述了相变材料微胶囊在纺织、医疗、建筑、能源等领域的应用进展并分析总结国内外最新相关研究;最后,针对相变材料微胶囊在生产制备和实际应用中的关键问题,提出其潜在解决方案和优先发展方向,以推进相变材料微胶囊不断向绿色化、多功能化方向深入发展。

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.

正十八烷@三聚氰胺-脲醛树脂微胶囊相变材料的制备与表征

以三聚氰胺-脲醛树脂(MUF)作为囊壁,以正十八烷为芯材,通过原位聚合法制备了正十八烷@三聚氰胺-脲醛树脂微胶囊相变材料,研究了乳化剂Span80、Tween80、十二烷基硫酸钠对微胶囊相变材料形貌、结构和热性能的影响。结果表明,乳化剂类型和乳化剂添加量对微胶囊相变材料的形貌会造成显著影响,使用非离子乳化剂和阴离子乳化剂复配时,微胶囊相变材料的团聚现象得到改善,粒径分布均匀,储热能力提高。制备的微胶囊相变材料潜热存储效率达到54%时,微胶囊相变材料的熔融焓和结晶焓分别为134.2J/g和109J/g。

Electroless plating of copper layer on surfaces of urea-formaldehyde microcapsule particles containing paraffin for low infrared emissivity

A copper coating was deposited by electroless plating on the surfaces of urea-formaldehyde microcap- sules containing paraffin （UFP） particles. This composite microcapsule structure had low infrared OR） emissivity and maintained a constant temperature, and could be used in IR stealth applications. The eiectroless copper layer formation and its micro-appearance, and the effect of the copper layer on the IR emissivity and thermal properties of the composite microcapsules were investigated. The IR emissivity of the composite microcapsules at wavelengths of 1-14 μm gradually decreased with increasing copper mass on the surface. After formation of an integrated copper layer, the rate of IR emissivity decrease was lower. This is because the copper coating improves the surface conductivity of the UFP; a high conductivity results in high reflectivity, which leads to a decrease in IR emissivity. The lowest IR emissivity achieved was 0.68. The phase-change enthalpy of the composite microcapsules decreased with increasing amount of copper coated on the surface because of the high density of copper. When the mass increase of the UFP after electroless copper plating was about 300%, the composite microcapsules had low IR emissivity （about 0.8） and a high phase-change enthalpy （80J/g）.

相变微胶囊材料导热增强研究进展

相变微胶囊是将相变材料包封在壳材中,有效解决了相变材料的泄漏等问题,是一种性能良好的相变储能材料,在热能储存领域具有广泛的应用。但壳材的存在削弱了内部相变材料与外部环境间的热传导,降低了相变微胶囊的热导率,制约了其实际应用范围。因此,对相变微胶囊进行改性是增强导热的有效途径。该文介绍了相变微胶囊的组成与结构,并从声子-声子与电子-声子相互作用的角度概述微观尺度下的导热机理;从芯材和壳材两方面对相变微胶囊导热增强改性进行了阐述,通过定量数据和导热机理对改性相变微胶囊的导热增强效果进行了分析;概括了改性相变微胶囊在纺织调温、浆料和建筑领域中的应用;最后,对相变微胶囊导热性能增强的研究前景和挑战以及实际应用方向进行了展望。

相变微胶囊的制备、性能评价及相变沥青的性能分析

为探究微胶囊对沥青性能的影响,通过正交试验,探明合成脲醛(三聚氰胺-尿素-甲醛)树脂壳材和正十四烷芯材对相变微胶囊性能的影响,解析其最佳制备工艺;采用差示扫描量热仪(DSC)、动态剪切流变试验仪(DSR)等实验手段,研究相变微胶囊改性沥青(相变沥青)的功能性。结果表明,微胶囊最佳制备工艺为乳化剂浓度7%,乳化转速2000 r/min,芯材与壁材质量比1∶1,油水体积比1∶7,合成时间90 min,合成温度80℃,此条件下制备的微胶囊潜热为117 J/g;微胶囊壳材密封性较好,能够在沥青中稳定存在,满足沥青施工温度区间要求;相变沥青放热区间为-7.1~-17.9℃,吸热区间为2.3~13.5℃,当微胶囊掺量为7%时,相变沥青相变焓为5.258 J/g;相变微胶囊能够有效延缓沥青硬化过程,且在常温条件下保持稳定,具有应用潜力。

一种微胶囊型石腊相变装饰材料制备及性能研究

为调节室内温度、节约能源,试验以异丁烯酸甲酯(MMA)和异丁烯酸乙酯(MSDS)为主要原料,以石蜡作为芯材,制备了一种微胶囊型石蜡相变材料,并研究其最佳参数。试验结果表明,苯乙烯-马来酸酐共聚物钠盐(NaSMA)优于聚乙烯醇(PVA),以NaSMA为分散剂所制备的微胶囊材料芯材含量高达61.76%,是以PVA时的8倍以上;最佳NaSMA分散剂含量为11%,引发剂过氧化二月桂酰(LPO)的最佳掺量为2%,此时,微胶囊团聚较少,球形表面无凹陷,成型较好;最佳芯材比为2∶1,此时,相变潜热达到84.1 J/g,实际芯材含量高达82.05%;在最佳参数下,试验制备的微胶囊型石蜡相变材料具备良好的保温储热性能。