Systematic Trends in the Melting Temperature and Composition of Eutectic Binary Mixtures with One Component from a Homologous Series

Materials that store a significant amount of heat in a narrow temperature range by phase change solid–liquid or solid–solid are called Phase Change Materials (PCMs). Many PCMs are members of homologous groups of materials with similar composition and properties. Often, similarities are due to a common molecular composition with a repeating unit, e.g., for n-alkanes H-(CH2)n-H. An n related trend is typical in the melting temperature. Based on observations on solvents, the question arises whether such a trend also exists in eutectic binary mixtures with one component fixed while the other, from a homologous series, is varied. For verification, data from the literature were collected, specifically experimental data, each set having at least three variations from a single source. Eight data sets were collected, covering eutectic binary mixtures of n-alkanes, n-alkanols, and n-alkanoic acids. With one exception, all data sets show a systematic trend in the melting temperature and the composition. It is shown that the trends can be understood from thermodynamic theories of mixtures (Schröder–van Laar equation) combined with typical trends within homologous series. The findings offer new options in PCM development as well as the selection of PCMs for specific application temperatures.