Binary liquid mixtures. The relation between surface tension and surface composition as studied by MIES (metastable induced electron spectroscopy).

Langmuir

Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, University Leipzig, Linnéstrasse 2, D-04103 Leipzig.

Published: February 2006

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For a binary liquid mixture, we define the surface fraction of a component as the fraction of the surface which is covered by this species. The perfectly surface-sensitive electron spectroscopy MIES (metastable induced electron spectroscopy) allows to derive this quantity in a very direct manner from experiment with no model assumption needed. We find for several binary mixtures that the surface tension depends linearly on the surface fraction with striking accuracy. Even more surprising is the fact that for a system which deviates from this simple linear behavior the surface tension turns out to be a piecewise linear function of the surface fraction. Tentatively, we introduce as possible explanation the concept of phase separation within the surface layer. Further, we show that the surface molar fraction, i.e., the molar fraction within the top surface layer, deviates significantly from a linear or a piecewise linear relation to the surface tension.

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http://dx.doi.org/10.1021/la052444kDOI Listing

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