Eur. Phys. J. E 6, 315-323 (2001)

Adsorption from pure and mixed vapours of n-hexane and n-perfluorohexane

M.M. Kohonen and H.K. Christenson

Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra A.C.T. 0200, Australia

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(Received 30 July 2001)

Abstract
We have used a modified surface force apparatus (SFA) to study adsorption onto mica surfaces from near-saturated vapours of n-hexane and n-perfluorohexane, and mixtures thereof. For relative vapour pressures in the range 0.9-0.998 the films adsorbed from vapours of the pure liquids range in thickness from 1 to 4 nm, in crude agreement with the predictions of non-retarded van der Waals-Lifshitz theory. The observed deviations from theory show a qualitative difference between the two liquids, which may reflect differences in the significance of structural contributions to the disjoining pressure. Under the same experimental conditions, adsorption from vapours of (one-phase) liquid mixtures gives rise to films which are significantly thicker, over a broad range of intermediate compositions, than those adsorbed from the pure vapours, with a broad maximum in thickness observed near the critical composition of the bulk liquid mixture.

PACS
68.08.Bc - Wetting.
68.15.+e - Liquid thin films.
64.75.+g - Solubility, segregation, and mixing; phase separation.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001