Article,
Monolayer Frustration Contributions to Surface and Interfacial Tensions: Explanation of Surfactant Superspreading
Langmuir, 16 (6): 2595--2603 (Mar 1, 2000)
DOI: 10.1021/la991215t
Abstract
A simple model for calculation of the spreading coefficient of an aqueous surfactant solution on an apolar solid is proposed. The spreading coefficient is predicted to have two components: (i) the van der Waals component, which is similar to the spreading coefficient of the alkane, making up the surfactant tail; (ii) the monolayer frustration component, dependent on the bending moduli and the spontaneous curvature of the surfactant. The frustration term is minimized at a negative spontaneous curvature, above the surfactant cloud point. The maximum of the spreading coefficient as the function of spontaneous curvature H0 does not coincide with the minimum of the surface tension. The latter is predicted to occur approximately 2 times higher in absolute value negative H0. For a solution to spread, the van der Waals component of the spreading coefficient must be positive and larger than the monolayer frustration term. The spreading is facilitated by surfactants having very short and branched alkyl tails.
