5.0–50.0 vt% of cyclohexane was mixed with 95.0–50.0 vt% of n-octadecane as the oil-phase during the emulsion process in the in situ polymerization of melamine-formaldehyde. By heat-treating the microcapsules in an oven at 100°C, the cyclohexane was removed and expansion space was formed inside the microcapsules. The microcapsules were characterized by using FTIR, SEM, DSC, TGA, and gas chromatography. When the microcapsules are heattreated at temperatures higher than 180°C, Tm, △Hm, Tc, and △Hc of the microcapsules decrease. The attenuation of enthalpy of the microcapsules containing expansion space is obviously lower than that of the control sample, however. The permeability of the microcapsule shell decreases with the increase of cyclohexane content. There is a maximum between the thermal stabilities of the microcapsules and the cyclohexane contents. The microcapsules synthesized with 30.0-40.0vt% of cyclohexane have the highest thermal stabilities, with 230°C and 289°C in air and nitrogen atmosphere, respectively. The thermal stable temperatures are approximately 67°C and 102°C higher than that of the control sample, respectively. The expansion space inside the microcapsules allows the n-octadecane to expand in the temperature rising process and exert lower pressure to the shell, therefore keeping the shell intact and increasing the thermal stabilities of the microcapsules.

Microencapsulated n-alkanes (n-octadecane, n-nonadecane, and n-eicosane) were synthesized by in situ polymerization using urea-melamine-formaldehyde polymer as shells. Microcapsules 5.0 and 10.0 wt% of 1-tetradecanol, paraffin, and 1-octadecanol were used as nucleating agents. The fabrication was characterized using Fourier transform infrared, light microscopy, and scanning electron microscopy. The crystallization and prevention of supercooling of the microcapsules are studied using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. The crystal system of the microencapsulated n-alkane is the same as that of the bulk. The enthalpies of the microcapsules containing 70wt% n-alkanes are approximately 160J/g. The melting temperature of the n-alkanes in the microcapsule is the same as that in the bulk. There are multiple peaks on the DSC cooling curves that are attributed to liquid–rotator, rotator–crystal, and liquid–crystal transitions. The DSC cooling behavior of microencapsulated n-octadecane is affected by the average diameters. The measured maximum degree of supercooling of the microencapsulated n-octadecane is approximately 26.0◦C at a heating and cooling rate of 10.0◦C/min. The degree of supercooling of microencapsulated n-octadecane is decreased by adding 10.0 wt% of 1-octadecanol as a nucleating agent.

Microencapsulated phase change materials (MicroPCMs) used as thermal insulating coating and fabrics are usually required to have a prominent thermal stability and a lower permeability.MicroPCMs with a prominent thermal stability and a lower permeability were fabricated by feeding an appropriate content of cyclohexane into n-octadecane followed by heat-treatment at a suitable condition. Microcapsules containing 18-19% reserved expandable space are synthesized at 30-40wt.% cyclohexane in the oil phase, which have a highest thermal resistant temperature -270 ◦C, and a lower permeability, less than 1.2%. The weight loss of microcapsules is mainly attributed to the leakage of n-octadecane from some broken capsules, so improving their uniformity can efficiently enhance their thermal stability and lower the permeability.

以正二十烷、 聚乙烯和乙丙橡胶等为原料经熔融挤出，制成正二十烷含量 10%~65%的共混切粒。以正十八烷微胶囊和聚乙烯为原料经熔融挤出， 制成微胶囊含量 10%~60%的共混切粒。采用差示扫描量热仪和熔融指数仪测试了多种组成切粒的相变性能和流动性能。切粒的热焓随相变材料含量的增高而增大，含65正二十烷的切粒的热焓为160 J/g左右，含有6 0 wt微胶囊的切粒的热焓为70 J /g左右。切粒的熔融指数随相变材料或相变材料微胶囊添加量的增高呈现指数增大或反S曲线的形式。

Microcapsules and nanocapsules containing n-octadecane with melamine-formaldehyde shell were fabricated by in situ polymerization. The effects of stirring rate, contents of emulsifier and contents of cyclohexane on diameters, morphology, phase change properties and thermal stabilities of the capsules were studied by using FT-IR, SEM, DSC and TG. The diameters of the microcapsules decreased with the increase of stirring rate, emulsifier content and cyclohexane content. The relationship between stirring rate and number-average diameters or weight-average diameters of the microcapsules is an exponent. The relationship between emulsifier content and number-average diameters or weight-average diameters of the microcapsules is an exponent, too. The diameters had less effects on the melting behaviour of microcapsules, however, they had significant effects on the crystallization behaviour. As the diameters of the microcapsules decreased, two crystallization peaks were observed from the DSC cooling curves. The ratio of the integrated area of the peak in the lower temperature increased with the decrease in diameters of microcapsules. The thermal stability of micro/nanocapsule rises with the increase of stirring rates and TA content. The cyclohexane content has no significantly effect on thermal stability of the nanocapsule.