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

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~William Bonificio

Original entry: William Bonificio, AP 225, Fall 2009


O. Gang, M. Fukuto, P. Huber and P. Pershan, Wetting of hydrocarbon liquid surfaces by fluorocarbon vapor: A microscopic study, Colloids & Surfaces A 206, 293-297 (2002)

Soft matter keywords

Wetting; Surface; Fluorocarbon; Hydrocarbon; Alkane; X-ray reflectivity; Surface freezing; thin film;


The wetting behavior of a liquid fluorocarbon on a liquid hydrocarbon was examined. At temperatures just above the freezing point of a liquid hydrocarbon there is an effect that occurs called surface freezing, where the surface of the hydrocarbon forms a periodic structure. The researchers discovered that when the hydrocarbon is coated even by the thinnest of fluorocarbon films, this surface freezing effect dissappears. Furthermore, the team researched the wetting effect of this system and discovered that, as expected, complete wetting occurred according to the law d~<math>\Delta T^{-1/3} </math>.

Soft matter discussion

Figure 1. (a) XR data for the dry (black circles) and wet (red and blue circles) obtained on the nanopatterned surface. (b) Corresponding electron density profiles for the dry (black) and wet surfaces in the filling (red) and growing regimes (blue).

Hydrocarbons with long carbon chains are known to have a surface freezing, or SF, effect at temperatures just above the bulk freezing point. The SF occurs when the chains are oriented normal to the surface, resulting in a hexagonal close packed structure with <math>a_{0}</math>~1000<math>\AA</math>.

The researchers aimed to first wet a substrate with the hydrocarbon, and then wet that hydrocarbon with a fluorocarbon. The experimental set up used a chamber that houses the substrate to be wetted, and a reservoir of a wetting liquid. Then by manipulating the activity of the liquid (by way of the vapor pressure using changes in temperature) the substrate is slowly wet by a thin film.