Wetting transitions at fluid–solid interfaces

Liquid films on solid substrates can exhibit three types of wetting behaviour, as shown by the values of their contact angles, corresponding to complete wetting, partial wetting or non-wetting. Closely related to this is the fact that adsorption isotherms for gases on solid surfaces fall into three classes, depending on the variation of the adsorbate coverage near saturation. Phase transitions between these different wetting classes can occur on varying the temperature or the composition of the materials present. A statistical mechanical theory of such transitions, based on concepts introduced by van der Waals, is surveyed and compared with available experimental evidence.