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 Tb, 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 Tb, the crystallites melt into droplets. The ordered monolayer remains up to TSVS~Tb+3 °C, probably due to fluctuation-stabilized ``surface freezing.'' Above TSVS, a liquid alkane film wets the surface. The decoupling of Tb and TSVS, and the difference between the ordered and liquid surface energies, causes the droplet-to-film transition.