Subcooling in PCM emulsions – Part 2: Interpretation in terms of nucleation theory

A systematic study of the melting, nucleation and solidification behavior of different paraffin–water emulsions, presented in part 1 of this publication, has shown that paraffins in emulsified form as finely dispersed droplets behave significantly different than in the bulk. Especially, strong subcooling for droplet sizes below 20 μm was observed. In this second part, an interpretation of the experimental data based on theory of subcooling and nucleation in emulsions is presented and discussed. It is shown that many different effects can play a role in the nucleation of PCM emulsions. Both deactivation and creation of nucleation sites have to be expected when dividing a PCM volume into small droplets. The nucleation rate in small droplets could be dominated by homogeneous nucleation, which again depends on the droplet volume. It is shown clearly that the surfactant used to stabilize the emulsion has a strong impact on the nucleation of the sample, too. Finally, it is lined out that not only the nucleation, but also the melting and the solidification temperature are affected by the emulsification of the PCM.