Phase transition of n-alkane layers adsorbed on mica

Thin (thickness h approximately 3 nm) films of n-octadecane and n-hexadecane adsorbed on mica surfaces from vapor close to their bulk melting points (T(m)) have been studied in a surface force apparatus. Using data on the growth rate of capillary condensates between the mica surfaces in contact and measurements of h, we have identified a transition in the structure of the adsorbed films a few degrees above T(m). As T decreases the alkane layers appear to undergo a transition to a more ordered structure, akin to the postulated "surface freezing" of long-chain liquid n-alkanes.