N-octadecane Core Research Articles

Phase Change Nanocapsules Enabling Dual-Mode Thermal Management for Fast-Charging Lithium-Ion Batteries.

The fast-charging performance of conventional lithium-ion batteries (LIBs) is determined by the working temperature. LIBs may fail to work under harsh conditions, especially in the low-temperature range of the local environment or in the high-temperature circumstances resulting from the release of substantial Joule heating in the short term. Constructing a thermal engineering framework for thermal regulation and maintaining the battery running at an appropriate temperature range are feasible strategies for developing temperature-tolerant, fast-charging LIBs. In this work, we prepare phase change nanocapsules as a thermal regulating layer on the cell surface. The polyurea shells of the nanocapsules are decorated with polyaniline, where the molecular vibration of polyaniline is enhanced under solar irradiation, enabling light-to-heat conversion that achieves an effective temperature increment at low temperatures. Based on the large latent heat storage capability of the n-octadecane core in the nanocapsules, the thermal regulating layer is sufficient to modulate strong heat release when operating LIBs at a high current rate, which efficiently prevents strong side reactions at high temperatures or even the occurrence of thermal runaway. This work highlights the promise of optimizing the operating temperature with a thermal regulator to ensure the safety and performance stability of fast-charging LIBs.

Enhancing solar photothermal conversion and energy storage with titanium carbide (Ti3C2) MXene nanosheets in phase-change microcapsules

We propose to enhance photothermal conversion via doping titanium carbide (Ti3C2) MXene nanosheets on the surfaces of phase-change microcapsules consisted of the n-Octadecane core and styrene divinylbenzene copolymer shell. Detected by scanning electron microscopy, the microcapsules showed a usually circular form with an appropriate dispersion. The thermal properties of the microcapsules were characterized using the differential scanning calorimetry and thermal conductivity instruments, realizing an excellent phase-change enthalpy of around 140 J/g, high encapsulation ratio of over 64 %, good heat transfer of 0.294 ± 0.003 W/(m·K), and great thermal reliability. More importantly, the microcapsules doped with Ti3C2 MXene nanosheets reach a solar-to-heat conversion efficiency of 85 ± 7 %, a substantial enhancement by 240 % in comparison with non-doping sample. The Ti3C2 MXene-doped microcapsules with excellent heat storage and solar-to-heat conversion capabilities offer great potential for high-efficiency solar energy utilization and can be applied to thermal energy storage systems and direct absorption solar collectors.

Construction of phase change n-Octadecane microencapsulated in carbon nanotubes-modified polymer for thermal management applications of finned heat sinks

The low thermal conductivity of organic shell-based phase change microcapsules severely limits their practical applications in thermal management of high-power-density electronic components. A novel microencapsulated phase change material (MPCM) was synthesized via suspension polymerization with n-Octadecane core shelled by aminated multiwalled carbon nanotubes-doped styrene–divinylbenzene copolymer (SDB/MWCNT-NH2). The chemical structure and micromorphology of the new microcapsules (MPCM/CNT) with various amounts of doped aminated multiwalled carbon nanotubes (MWCNT-NH2) were identified by the Fourier transform infrared spectroscopy and scanning electron microscopy. The thermal properties of various MPCM/CNT samples were analyzed based on the measurements of thermogravimetric analyzer, differential scanning calorimeter and thermal conductivity meter. The results indicated that the microcapsules with MWCNT-NH2 had good thermal stability, heat storage capacity and heat transfer properties. The thermal performance of the microcapsule samples in the low and medium temperature finned heat sink (FHS) was investigated and their thermal performance with that of bare FHS at four constant thermal loads of 5 W, 7 W, 10 W and 15 W was compared. The thermal performance was evaluated based on the time to setpoint temperature, heat dissipated and heat dissipation factors. Compared with the bare FHS, the FHS with the MPCM/CNT-2.5 sample (i.e., 2.5 wt% MWCNT-NH2) exhibited 17.70% longer operation time, 33.01% more heat dissipated, and 16.53% higher heat dissipation factor during heating at 10 W. This study aims to apply the phase change microcapsules modified with high thermal conductivity MWCNT-NH2 in medium and low temperature heat sinks to optimize the thermal management of high power density electronic components and improve the heat dissipation performance of heat sinks. The microcapsules with MWCNT-NH2 showed great potential for applications in thermal management of electronic components.

One step synthesis of novel CuS-ZnS/SiO2@n-octadecane nanocapsules with full spectral absorption range and high photothermal conversion efficiency

In this manuscript, CuS-ZnS/SiO2@n-octadecane nanocapsules were prepared by a simple one-step Cu2+ and Zn2+ co-deposition method. The results of XRD, SEM, TEM, FTIR and XPS show that nanocapsules composed of CuS-ZnS/SiO2 shell and n-octadecane core material were successfully prepared, and the particles deposited was proved to be composite structure of CuS-ZnS. The solution concentration, reaction temperature and pH value have significant effects on the morphology of the nanocapsules prepared. The appropriate conditions are 0.02 mol/L CuSO4, 0.02 mol/L Zn(CH3COO)2, 60 °C, and no additional pH adjustment. Under the optimum conditions, the melting enthalpy reached 45.11 J/g, and after 100 times of cold and hot cycles, the melting enthalpy of the sample only decreased by 3.2%, showing good thermal stability. The CuS-ZnS composite structure makes CuS-ZnS/SiO2 nanocapsules exhibit a wider spectrum absorption performance. The absorption effect of CuS-ZnS/SiO2 nanocapsules to ultraviolet light is significant, compared to the slight reducing of the visible light, while the absorption of near-infrared light is strong. The photothermal conversion efficiency of the samples is significantly improved from 9.7% to 86.6%. Hence, the prepared nanocapsules achieve full spectral absorption, which has a broad application prospect in solar thermal utilization.

Microencapsulated phase change n-Octadecane with high heat storage for application in building energy conservation

A novel type of microencapsulated phase change materials (microPCMs) with n-Octadecane core shelled by styrene–divinylbenzene copolymer were synthesized by the suspension polymerization. The morphologies and chemical compositions of the microPCMs with four different shell-to-core ratios were analyzed via the scanning electron microscopy and Fourier transform infrared spectroscopy. Based on the measurements from the thermogravimetric analyzers and differential scanning calorimetry, the thermal characteristics of the different microPCMs were analyzed. The results show that the sample microPCMs with 2:1 shell-to-core ratio (microPCM3) has good thermal stability and high heat storage capability, with melting enthalpy and encapsulation efficiency measured at 111.5 ± 0.7 J/g and 51.4 ± 0.7 %, respectively, which are the highest among all the prepared samples. The initial weight loss temperature of the microPCM3 increases to 160.5 ℃ compared to 115.5 ℃ for the pure n-Octadecane. Furthermore, we prepared four different building boards with different microPCM3 contents (0, 10, 20, or 30 wt%) in cement matrix. Compared to the conventional building material, the board with 30 wt% microPCM3 can store 67.82% more heat energy in the typical temperature range of 10–50 °C. We investigated the passive cooling and heating effects of the boards under extreme temperature conditions (10–70 °C), as well as their thermal regulation performance under multiple consecutive thermal cycling experiments. Compared with the cement board without addition of microPCM3, the board with 30 wt% microPCM3 has reduced temperature fluctuation by 59.0% with maximum temperature fluctuation only 23.5 °C. It has shown excellent thermal regulation and thermal insulation properties and is of great application potential in energy-saving buildings.

Novel metal-organic framework (MOF) based phase change material composite and its impact on building energy consumption

Space cooling (including dehumidification) is the fastest-growing use of energy in buildings. Materials that have high thermal and moisture buffer capacities can passively mitigate indoor temperature and humidity fluctuations, thus reducing the demand for air conditioning and improving building energy efficiency. Here, we report a novel metal–organic framework (MOF) based microencapsulated phase change material (MPCM) composite. The new MOF-MPCM is a dual-function material that can simultaneously absorb/release heat and moisture from surrounding air and passively regulate the indoor hygrothermal environment. MIL-160(Al), a novel green and biomass-derived MOF material with excellent sorption performance and large-scale production potential, was prepared for moisture buffering. MPCM containing an n-octadecane core and polymethylmetracrylate shells were synthesized for temperature control. Physicochemical and hygrothermal properties of MOF-MPCM composite were characterized by SEM, XRD, DVS, DSC, and TGA techniques, etc. A HAM-Enthalpy model was developed to study the impact of MOF-MPCM on the indoor hygrothermal environment and building energy performance in different climates. Seven cities around the world (i.e., Singapore, Hong Kong, Phoenix, Denver, Barcelona, London, and Beijing) were selected as the representative climate locations. The simulation indicates that MOF-MPCM can effectively mitigate indoor temperature and moisture variations and cut down the energy consumption of air conditioning systems, especially in hot-dry, temperate, and continental climates with large diurnal air temperature and humidity variations. The maximum energy-saving potential could reach 35.2% in Phoenix. The study provides guidance for the further improvement and application of dual-function MOF-MPCM composite in different climates.

Preparation and characterization of ZnO/SiO2@n-octadecane nanocapsule for ultraviolet absorbing and photothermal conversion energy storage

In this work, PCM nanocapsules composed of ZnO/SiO2 shell and n-octadecane core were successfully synthesized by emulsion polymerization and hydrothermal method. The crystallinity of ZnO was enhanced on the SiO2 shell by MPTS modification. The granule-like ZnO were distributed on the SiO2 shell. The encapsulation rate of n-octadecane in nanocapsules was about 45.2 % with enthalpy of 95.0 J/g melting at room temperature 28.3 °C. Furthermore, due to the presence of ZnO, the synthesized PCM nanocapsules had excellent UV absorption properties for whole wavelengths, and the absorbed UV light can be converted into heat energy for storage, and the photothermal conversion efficiency had reached 25.0 %. Hence, the prepared ZnO/SiO2@n-octadecane nanocapsules had broad application prospects due to its thermal energy storage, UV protection and photothermal conversion performance.

Effect of the PSSMA Content on the Heat Transfer Performances of Polyurea Nano-Encapsulated Phase Change Materials

Polyurea nano-encapsulated phase change materials (PUA-NEPCMs) were prepared from an n-octadecane core and through the formation of amide bonds by the reaction of toluene 2,4-diisocyanate and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSSMA), followed by the subsequent formation of a PUA shell using a miniemulsion system. The effects of the synthetic conditions on the thermal properties and encapsulat ion effect of the NEPCMs were systematically investigated. Differential scanning calorimetry (DSC) revealed that the melting enthalpy and encapsulation efficiency of the PUA-NEPCMs prepared under optimal conditions reached 123.00 J/g and 54.27%, respectively. Although previous results suggested that the introduction of PSSMA results in a reduced heat transfer performance for NEPCMs, DSC analysis of the prepared PUA-NEPCMs showed that increasing PSSMA contents enhanced the heat transfer performance due to a decrease in the degree of supercooling. Our results could therefore lead to further enhancements in the heat transfer performance of PUA-NEPCMs, in addition to expanding their field of application.

Poly(styrene-co-divinylbenzene-co-acrylamide)/n-octadecane microencapsulated phase change materials for thermal energy storage

The way of application is an important issue in thermal energy storage (TES) materials. Phase change materials are encapsulated to prevent leakage and to get application advantage. At the last decade, microencapsulated phase change materials (MEPCMs) are produced with functional outer surfaces. In this work preparation, characterization, and thermophysical property determination of microencapsulated n-octadecane in poly(styrene-co-divinylbenzene-co-acrylamide) shell was studied. N-octadecane core P(St-co-DVB-co-AAm) shell microcapsules were prepared with 0.5, 1, and 2% AAm contend to make the outer surface functional. Divinylbenzene was used as the cross-linker to produce stability and unimodal microcapsule size distribution. Microcapsules were synthesized by miniemulsion polymerization method, and characterized using fourier transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), particle sizer distribution (PSD) instrument, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) techniques. The average melting and freezing onset temperatures of the MEPCMs were found slightly lower than the phase transition temperatures of n-octadecane core material as the enthalpy values were affected from the amide pendant group contend. Besides, produced microcapsules were found stable up to 148 °C.

Development of thermo-regulating fabrics using PCM microcapsules with poly(methyl methacrylate-co-2-hydroxy ethyl methacrylate) shell and n-alkane core

PurposeThe purpose of this paper is to prepare microencapsulated phase change materials (PCMs) and apply them to cotton and wool fabrics for developing thermo-regulating fabrics.Design/methodology/approachMicroencapsulated n-hexadecane and n-octadecane with poly(methylmethacrylate-co-2-hydroxy ethyl methacrylate) shell was prepared. Microcapsules were fabricated using oil-in-water emulsion polymerization method. Their chemical structure, microstructure, thermal energy storage properties and thermal stability were analyzed by Fourier-transform infrared spectroscopy, polarized light microscope, differential scanning calorimeter and thermogravimetric analyzer, respectively. The mean particle size was tested by a particle sized instrument. The microcapsules were applied to the wool and cotton fabrics using pad-dry-cure method. The thermo-regulating property of the fabrics was evaluated using the T-History test. The distribution and durability of the microcapsules on the fabrics was investigated with scanning electron microscopy.FindingsSpherical microcapsules with p(MMA-co-HEMA) shell and n-alkane core have been produced successfully. n-hexadecane in microcapsule solidifies at 14.8−15.6°C with the latent heat of 65.6−129.8 J/g and melts at 16.7−16.9°C with the latent heat of 67.6−136.9 J/g. Microencapsulated n-octadecane solidifies at 25.8−26.3°C with the latent heat of 74.1−106.2 J/g and melts at 26.8−27.4°C with the latent heat of 80.3−113.4 J/g. The microcapsules have enough thermal stability to the temperature of 150°C that was applied during the fixation of microcapsules on the fabric. The thermo-regulating effect of the microcapsule-incorporated fabrics has been proved by the T-history test.Originality/valuePCM microcapsules with p(MMA-co-HEMA) shell and n-hexadecane and n-octadecane core have been produced and their usage to produce thermo-regulating textiles have been proved. To determine the thermo-regulating property of the fabrics treated with these new PCM microcapsules, a T-History system has been designed.

Fabrication and characterization of poly(melamine-formaldehyde)/silicon carbide hybrid microencapsulated phase change materials with enhanced thermal conductivity and light-heat performance

A new type of microcapsule based on n-octadecane core and poly(melamine-formaldehyde)/silicon carbide (PMF/SiC) shell was designed for near-infrared light harvesting, light-heat conversion, thermal energy storage and heat-transfer enhancement. A series of hybrid microcapsules were successfully synthesized through in situ polymerization in an oil-in-water emulsion stabilized by sodium salt of styrene-maleic anhydride copolymer and SiC synergistically. The scanning electron microscopic investigation revealed that the microcapsules presented regular spherical morphology. The chemical compositions and crystalline structures of the resultant microcapsules were characterized by energy-dispersive X-ray, Fourier transform infrared spectroscopy and X-ray powder diffraction, confirming that SiC nanoparticles have been embedded in the PMF shell. Thermogravimetric analysis and a temperature-regulated test indicated that the prepared microcapsules possessed high thermal stability and good thermoregulating ability. Differential scanning calorimetry examination showed that the resulting hybrid microcapsules can maintain high effective core content and high encapsulation efficiency, and the supercooling crystallization was obviously suppressed after the incorporation of nano-SiC. Compared with PMF microcapsules, thermal transfer properties of the PMF/SiC microcapsules were significantly improved, and the thermal conductivity increased by 60.34% after the addition of 7% nano-SiC. Furthermore, the synthesized hybrid microcapsules effectively absorbed near-infrared light and demonstrated good photothermal conversion performance under light radiation.

Dual-Functional Phase Change Nanocapsules Based on n-Octadecane Core and Polypyrrole Shell

Phase change method is one of the efficient approach in resolving energy problem for solar energy storage. However, phase change materials seriously affect the heat storage system with low heat releasing and absorbing rate for poor thermal conductivity performance, which result in an inefficient thermal energy storage technology and uncertain economic perspective. In this paper, we prepared dual-functional phase change nanocapsules based on n-octadecane core and polypyrrole shell. Polypyrrole was employed to enhance the electric conductivity and thermal conductivity. The nanocapsules was characterized using Fourier transformed infrared spectrophotometer (FTIR), field emission scanning electron microscope (FESEM), differential scanning calorimeter (DSC), thermal gravimetric analyzer (TGA) and infrared thermal imaging. The results shows a good thermal behavior and high latent heat of 81.99J/g. The dual-fuctional phase change nanocapsules can be expected with a prospect of future profits in energy storage technology.

Enhancement in thermal property of phase change microcapsules with modified silicon nitride for solar energy

Thermal behavior is one of the most important properties for phase change microcapsules in solar energy storage. Here, a new type of phase change microcapsules was synthesized based on n-octadecane core and polymethylmethacrylate shell supplemented with modified silicon nitride powders, aiming to achieve improvement of thermal property in the phase change materials. SEM micrographs showed that the as-prepared microcapsules have a regular spherical shape with a well-defined core-shell structure. FTIR curves and EDS spectrogram demonstrated that silicon nitride can be well cross-linked with microcapsules after surface modification. In addition, TGA, forward looking infra-red system and DSC (before and after 500 heating and cooling cycles) analyses were performed to investigate the thermal property of the as-prepared microcapsules. The results indicated that the microcapsules have high thermal storage capability, enhanced thermal reliability and stability, and increased thermal conductivity. Especially, the thermal conductivity of microcapsules is enhanced by 56.8% compared with that of the microcapsules without the addition of silicon nitride.

Self-assembly fabrication of microencapsulated n-octadecane with natural silk fibroin shell for thermal-regulating textiles

Novel microencapsulated n-octadecane with natural silk fibroin (SF) shell was prepared using a self-assembly method in oil-in-water (o/w) emulsion. The microstructures and chemical compositions of the resultant microcapsules were investigated by scanning electronic microscope (SEM) and Fourier transformation infrared spectroscope (FT-IR). SEM images demonstrated that the microcapsules presented spherical shape with a median size of 4–5 µm. FT-IR results confirmed that SF shell was successfully fabricated upon n-octadecane core. According to the DSC and TGA examinations, the resultant microcapsules exhibited good phase-change performance, high thermal-storage capability and high thermal reliability. The microencapsulated n-octadecane with SF shell synthesized in the present study would be a potential candidate for the application of thermal-regulating textiles or fibers and biological medical materials, etc.

Silver incorporated microencapsulation of n-hexadecane and n-octadecane appropriate for dynamic thermal management in textiles

This study concerns with interfacial in-situ encapsulation of n-hexadecane and n-octadecane cores in poly(urea-formaldehyde) shells to fabricate microcapsules, capable of absorbing and releasing high amounts of heat consistently. The microcapsules were designed to show improved thermal properties with drastically reduced particle sizes and included silver nanoparticles (Ag NPs). Using high stirring rates in preparation and polymerization processes resulted in particle sizes ranging in between 163 and 496nm on average. The encapsulation method was also improved by adding freshly produced silver nanoparticles (Ag NPs) into the in-situ polymerization processes, via the Tollen’s reaction, to investigate their contribution to the thermal properties of some types of microcapsules. Phase change enthalpies of the microcapsules produced with n-hexadecane core were obtained as 137Jg−1 at 22–26°C and the microcapsules produced with n-octadecane core were obtained as 168Jg−1 at 33–35°C even after hundred cycles. Thermal conductivities of the microcapsules including Ag NPs were considerably higher than those of the microcapsules, not treated with silver nanoparticles. Thus, the microcapsules produced in this study were found fairly appropriate for a wide range of industrial applications specifically in the thermally enhanced clothing fabrics, technical textiles such as medical and automobile textiles, and building materials. The encapsulation process has also the potential of large scale production in the manufacture of microcapsules.

Polymethyl methacrylate based phase change microencapsulation for solar energy storage with silicon nitride

Silicon nitride was applied to enhance the thermal performance and mechanical properties of phase change microencapsulation (PCM) based on polymethyl methacrylate (PMMA) shell and n-octadecane core. ‘A molecular bridge’ was constructed to modify the surface of silicon nitride and to eliminate boundary layer between inorganic silicon nitride particle and organic PMMA shell. Thus, an innovative modified silicon nitride phase change microencapsulation (MPCM) with which silicon nitride uniformly disperses in PMMA as shell and n-octadecane as core was successfully prepared. The microencapsulation was characterized using Fourier transformed infrared spectrophotometer (FTIR), field emission scanning electron microscope (FESEM), differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). A micro/nano-hardness tester was also employed, in order to investigate mechanical performance of shell. The result shows that the MPCM containing 66.4% n-octadecane has 121.11J/g latent heats of melting and 122.01J/g latent heats of crystallization with the modified silicon nitride percentage up to 10wt.%. The modified silicon nitride could not only enhance thermal performance, but also improve mechanical strength up to 16.24mN which is 4times higher than that of PCM. Additionally, wrinkles on the surface of MPCM improved special surface area as well as adaptation of volume changes during phase change process. The prepared MPCM is expected to exhibit better performance in solar energy storage technology.

Microencapsulation of n-octadecane phase change material with calcium carbonate shell for enhancement of thermal conductivity and serving durability: Synthesis, microstructure, and performance evaluation

A sort of new phase change material (PCM) microcapsules based on n-octadecane core and calcium carbonate (CaCO3) shell was synthesized through a self-assembly method to enhance the thermal conductivity and serving durability. Fourier transform infrared spectra confirmed that the CaCO3 wall material was successfully fabricated upon the n-octadecane core. Scanning electric micrographs demonstrated that the n-octadecane microcapsules presented a perfect spherical morphology and a well-defined core-shell microstructure. Wide-angle X-ray scattering patterns indicated that the CaCO3 shell was formed in the crystalline phase of vaterite while the n-octadecane core inside microcapsules still preserved good crystallinity. The microencapsulated n-octadecane also exhibited good phase-change performance and achieved a high thermal storage capability, and however, their encapsulation ratio and encapsulation efficiency were determined by the core/shell mass ratio. Thermogravimetric analysis showed that the microencapsulation of n-octadecane improved the thermal stability by upgrading the evaporating temperature of n-octadecane inside the CaCO3 shell. The thermal conductivity of n-octadecane microcapsules was significantly improved due to the fabrication of highly thermally conductive CaCO3 shell, and the anti-osmosis property and serving durability were also enhanced under the protection of compact CaCO3 shell. Owing to the easy availability and low cost of calcium carbonate, this synthetic technique indicates a high feasibility and a good prospect in industrial manufacture for the microencapsulated PCMs with inorganic shells.

Fabrication of microencapsulated phase change materials based on n-octadecane core and silica shell through interfacial polycondensation

In order to enhance the thermal transfer and phase change properties of microencapsulated phase change materials (micro-PCMs), a new micro-PCM based on n-octadecane core and silica shell was synthesized through interfacial polycondensation in different conditions. Fourier transform infrared spectra confirm the successful encapsulation of n-octadecane with inorganic silica. The silica microcapsules show a pronounced dependence of morphology and microstructure on the acidity of reaction solution in terms of the scanning electric microscopy observation, although all of them exhibit a well-defined core–shell structure. It is found that the microcapsules formed at pH 2.89 achieve a compact silica shell with fairly smooth surface as well as a large mean particle size of about 17.0 μm. Wide-angle X-ray scattering patterns indicate that the crystalline nature of the microencapsulated n-octadecane is maintained despite the confinement of silica shell. Thermogravimetric analysis shows that the silica microcapsules perform a typical two-step degradation process and present a good thermal stability. Differential scanning calorimetry investigation indicates that the silica-microencapsulated n-octadecane can achieve good phase change properties and high encapsulation efficiency by controlling the acidity of the reaction solution as well as the loading content of core material in synthesis. The thermal conductivity of the silica microcapsules is also significantly improved due to the presence of high thermal conductive silica shell. Encapsulation of n-octadecane with the silica shell material through interfacial polycondensation can be a perspective way to prepare the micro-PCMs with enhanced thermal transfer and phase change properties for potential applications to thermal-regulating textiles and fibers.

Silica encapsulation of n-octadecane via sol–gel process: A novel microencapsulated phase-change material with enhanced thermal conductivity and performance

A novel microencapsulated phase-change material (PCM) based on an n-octadecane core and an inorganic silica shell was designed to enhance thermal conductivity and phase-change performance. These silica microcapsules were synthesized by using TEOS as an inorganic source through a sol–gel process. Fourier transform infrared spectra confirm that the silica shell material was successfully fabricated onto the surface of the n-octadecane core. Scanning electronic microscopy images suggest that the silica microcapsules exhibit a spherical morphology with a well-defined core–shell microstructure. Furthermore, the silica microcapsules synthesized at pH 2.45 display a smooth and compact surface. These microcapsules also present a large particle size range of 7–16 μm. Wide-angle X-ray scattering patterns indicate that the n-octadecane inside the silica microcapsules still retains a good crystallinity. Thermogravimetric analysis shows that these silica microcapsules are degraded in two distinct steps, and have good thermal stability. The silica-microencapsulated n-octadecane can achieve good phase-change performance, high encapsulation efficiency, and good antiosmosis property by controlling the loading of core material and acidity of the reaction solution during the sol–gel process. The thermal conductivity of the microencapsulated n-octadecane is also significantly enhanced due to the presence of the high thermal conductive silica shell.

Fabrication and performances of microencapsulated phase change materials based on n-octadecane core and resorcinol-modified melamine–formaldehyde shell

A series of microencapsulated phase change materials (micro-PCMs) based on n-octadecane core and resorcinol-modified melamine–formaldehyde shell were synthesized by in situ polymerization method using different emulsifiers. The Fourier transform infrared spectra confirmed that the resorcinol-modified melamine–formaldehyde shell was successfully fabricated on the surface of the core material; however, the morphology investigation suggested that the sodium salt of styrene-maleic anhydride copolymer as an anionic emulsifier is optimal for the fabrication of the microcapsules in this study. And the microcapsules fabricated with a core/shell weight ratio of 75/25 have a compact surface of the shell and a mean particle size of below 20 μm with the centralized size distribution. The sample under this condition has much better phase change properties and a higher efficiency of encapsulation (about 92%) than the others through the evaluation of the differential scanning calorimetry, while it also exhibits an excellent stability from the anti-osmosis measurement. In addition, the confinement effect of n-octadecane inside the microcapsules also results in a significant decrease in both the melting and crystallization temperatures of the micro-PCMs.