Calorimetric Evidence for the Structure of Films adsorbed at the Solid/Liquid Interface: the Heats of Wetting of ‘Graphon’ by some n-Alkanes

Abstract

EARLY work showed that the heat of wetting of graphitized carbon (for example ‘Graphon’) by non-polar liquids was largely independent of the precise nature of the liquid. In particular, in the alkane series, the number (n) of carbon atoms in the chain was said to have little effect on the heat of wetting of unit area of solid1–3. Robert4 suggested that alkane molecules were adsorbed parallel to the surface, that a methyl group and a —(CH2)2— unit occupied roughly equal areas (14 A2) and that a methyl group and a single methylene group were each adsorbed with an energy, relative to the liquid, of about 1,500 calories mole−1. On this basis the heat of wetting per unit area should rise slowly to a limiting value (dotted curve Fig. 1a). More recently, Robert5 measured the heat of wetting of several carbons by alkanes at 20° C: for some carbons (‘Vulcan 3’, ‘Spheron’) the heats of wetting varied only slightly with n, while for others (‘Graphon’, Acheson graphite) they increased rapidly. Robert offered no explanation of this behaviour, and it is inconsistent with his earlier proposal.