Wetting of hydrocarbon liquid surfaces by fluorocarbon vapor: a microscopic study

The wetting of the liquid fluorocarbon (perfluoromethylcyclohexane) on the liquid hydrocarbon (eicosane) surface was studied just above the eicosane melting point, where the eicosane exhibits surface freezing (SF) behavior. The thickness of the wetting layer was controlled by changing the fluorocarbon chemical potential relative to the reservoir through temperature differences ΔT. The evolution of the microscopic structure of the fluorocarbon layer along the normal-to-surface was measured in situ using X-ray reflectivity. Observed effects include suppression of the SF phase for the thinnest absorbed fluorocarbon layer (d∼7 Å) as well as complete wetting that following the d∼ΔT−1/3 law.