Chapter 9: Temperature Dependence of the Enthalpy of Alkanes and Related Phase Change Materials (PCMs)

High-resolution enthalpy data are a useful tool in the study of phase transitions. Alkanes of intermediate chain length show a complex melting behaviour, with phases with rotational degrees of freedom appearing between the crystalline and liquid phases. The results presented here show that for tricosane (C23), tetracosane (C24) and pentacosane (C25), the transitions between these rotator phases are first order. Recently, the attention on phase change materials (PCMs) in energy-saving applications has strongly increased. PCMs are used to store energy, and the selection is largely based on the phase transition properties (notably the transition temperature and transition heat) of these materials. These properties are naturally quantified by the enthalpy, as illustrated for a selection of potential PCMs, mostly mixtures of alkanes.