Influence of water domain formed in hexadecane core inside cross-linked capsule particle on thermal properties for heat storage application

The influence of a water domain formed in n-hexadecane (HD) core in cross-linked polymer capsule particles on the thermal properties of encapsulated HD was studied from the view point of heat storage application. The capsule particles were prepared by micro-suspension polymerization of divinylbenzene at 70 °C utilizing the Self-assembling of Phase-Separated Polymer (SaPSeP) method that the authors proposed. The water domain was not observed for particles taken just after the polymerization and kept at 70 °C, but it was gradually formed with an increase of the size during cooling process from 70 °C to room temperature. In differential scanning calorimetric thermograms, pure HD had a single peak because of solidification (T _s) at 15 °C, and the encapsulated HD containing the water domain had two peaks of T _s1 and T _s2, at 6 and 1 °C, respectively. That is, the encapsulated HD containing the water domain required longer time and lower temperature to complete the solidification than the pure HD, which is negative for its application. However, the lower temperature-side peak at T _s2 gradually disappeared with an increase of capsule particle diameter, which seems to be based on the decrease of total interfacial area between the water domains and encapsulated HD in the capsule particles.