Influence of the molecular ordering on the wetting of SiO2/air interfaces by alkanes

Alkanes from 16 to 50 C atoms show three wetting topologies at SiO2/air interfaces. Below the bulk freezing temperature T-b, small crystallites (frozen droplets which can be annealed into mesas of uniform height) are observed. A monolayer of homeotropically oriented molecules covers the air/substrate interface in between. At T-b, the crystallites melt into droplets. The ordered monolayer remains up to T-S(SV) = T-b + 3 degrees C, probably due to fluctuation-stabilized ''surface freezing.'' Above T-S(SV), a liquid alkane film wets the surface. The decoupling of T-b and T-S(SV), and the difference between the ordered and liquid surface energies, causes the droplet-to-him transition.