Effect of Electrolyte on the Interfacial Dilational Properties of Sodium 4,5-Diheptyl-2-propylbenzene Sulfonate at the Oil–Water Interface

Abstract

The dilational viscoelastic properties of 4,5-diheptyl-2-propylbenzene sulfonate (377) in the presence or absence of electrolyte were investigated by means of two methods: the interfacial tension response to sinusoidal area variations and the relaxation of an applied stress. The higher dilational modulus of 377 than ordinary surfactant indicates that the strength against perturbation of interfacial layer of the former is greater. This may due to the two long and flexible branched alkyl chains, which are easily cross-linked and entangled. Moreover, the results reveal that the added electrolyte results in screening of electrostatic interactions between the ionized groups, which decreased the interfacial dilational modulus.

Keywords:

• 4,5-Diheptyl-2-propylbenzene sulfonate
• dilational modulus
• dilational phase angle
• electrolyte
• interface
• relaxation process