Energetic and entropic contributions to the work of adhesion in two-component, three-phase solid–liquid–vapour systems

For one-component liquid–vapour (lv) systems Lyklema (1999) [1] has shown that the excess entropy is a rather constant quantity whereas the excess energy varies over several orders of magnitude. In this work we use literature data from two-component, three-phase solid–liquid–vapour (slv) systems to show for the first time that in these systems the majority of excess entropies of adhesion fall in a narrow range between 0.1 and 0.2 mJ/m2 K and show no direct relation to excess energies of adhesion. From this it is concluded that excess energy and excess entropy of adhesion are, at least in two-component, three-phase slv systems, not coupled. This finding agrees with the corresponding states principle suggested for lv systems by Lyklema [1]. Definitive conclusions are hampered by the lack of a data set with a broader range of excess energies. ric mean approaches relating contact angles to interface tensions are critically examined within the framework of Lyklemaʹs [1] analysis and the insights obtained from the temperature dependence of contact angles. It turns out that none of the approaches considered can take proper account for the temperature dependence of interface tensions, which is first of all due to the neglect of entropic contributions to surface/interface tensions. At 25 °C entropic contributions make up 30–50% of the total Helmholtz free energy of adhesion.