title: Fluid-dynamical model for antisurfactants.
abstract: We construct a fluid-dynamical model for the flow of a solution with a free surface at which surface tension acts. This model can describe both classical surfactants, which decrease the surface tension of the solution relative to that of the pure solvent, and antisurfactants (such as many salts when added to water, and small amounts of water when added to alcohol) which increase it. We demonstrate the utility of the model by considering the linear stability of an infinitely deep layer of initially quiescent fluid. In particular, we predict the occurrence of an instability driven by surface-tension gradients, which occurs for antisurfactant, but not for surfactant, solutions.
authors.affiliation: Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, Scotland, United Kingdom.
authors.forename: Justin J A
authors.initials: JJ
authors.lastname: Conn
authors.affiliation: Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, Scotland, United Kingdom.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Duffy
authors.affiliation: Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, Scotland, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Pritchard
authors.affiliation: Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, Scotland, United Kingdom.
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Wilson
authors.affiliation: Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, United Kingdom.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Halling
authors.affiliation: School of Engineering, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JL, Scotland, United Kingdom.
authors.forename: Khellil
authors.initials: K
authors.lastname: Sefiane