The thermal properties of n-hexadecane (HD) encapsulated in crosslinked capsule particles containing a water and/or air domain were studied from the viewpoint of heat-storage applications. The capsule particles were prepared by the microsuspension polymerization of divinylbenzene at 70 degrees C with the self-assembling of phase-separated polymer method that we developed. In the differential scanning calorimetric thermograms, pure HD had a single solidification temperature (T-s) peak at 15 degrees C, whereas the encapsulated HD containing a water domain had two peaks at 6 and 1 degrees C. That is, the encapsulated HD containing the water domain required a longer time and lower temperature to complete the solidification than pure HD, which was negative for heat-storage applications. However, once the particles were dried and the water domain was replaced with air, the problem with the partially lowered T, improved. The air domain was also found in the encapsulated HD core after solidification because of the shrinkage of HD. The presence of the air domain did not affect the thermal stability of the encapsulated HD. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3257-3266, 2009