Influence of the nature of non-polar phase on the mechanical stability of adsorption layers of hydrocarbon and fluorocarbon surfactants at the interface between their aqueous solutions and non-polar media

A variety of experimental approaches has been used for companson of the stabilizing effect with respect to droplets coalescence caused by the interfacial adsorption layers (IAL) of a number of hydrocarbon and fluorocarbon surfactants at the boundary between their aqueous solutions and various non-polar hydrocarbon and fluorocarbon liquids: (I) compression of two individual droplets in surfactant solution up to their coalescence and consequent tension and rupture of a newly formed drop; (II) evaluation of the free energy of interaction between non-polar surfaces by measuring the contact rupture force for smooth spherical particles; (III) rheological study of IAL by torque pendulum method; (IV) SEM observation of the IAL morphology; (V) study of the stability with respect to the Ostwald ripening. These observations reveal the predominant role of the lyophilic structure-mechanical barrier formed by the IAL as a factor of strong stabilization with respect to coalescence and particular dependence of the mechanical strength of such layer on the nature of the non-polar liquid and on the interaction between this liquid phase and hydrophobic parts of the surfactant molecules. (C) 2001 Elsevier Science B.V. All rights reserved.