Interfacial dilational rheology properties of films formed at the oil/water interface by reaction between tetrameric acid and calcium ion

This article aims to determine the applicability of interfacial dilational rheology to study the formation of viscoelastic film at the oil/water interface by reaction between tetrameric acids ARN and calcium ions, and to determine the influence of asphaltenes and naphthenic acids (NA) on this film. It was first found that the formation of viscoelastic film by reaction between ARN and calcium ions is easily observed by dilational rheology: Significantly high values of E′ (130?mN/m) were measured for this system at low ARN concentration (10?µM). These values are at least 5 to 10 times higher than values obtained for ARN without Ca²⁺ or other crude oil components such as asphaltenes and naphthenic acids.

The influence of asphaltenes and NA on the viscoelastic film formation has been studied. When asphaltenes or NA are present, the interfacial viscoelastic film is weakened: There is a gradual decrease of E′ and E″ when the asphaltenes or NA concentration increases. These two components can therefore inhibit the ARN/Ca²⁺ film formation. This decrease is similar to the one previously observed by shear rheology. Several explanations are proposed.