Interfacial Shear Rheology of the Waxy Oil-Water Interfacial Layer Construction by Span80/60/65: Influence of Hydrophobic Chain Structure

The waxy oil-water interface has become a topic issue in the field of a two-phase oil-water pipe flow. Although some progress has been achieved in the understanding of interfacial rheological properties of the water-in-oil emulsion (W/O), the effect of surfactants (the main constituents of petroleum crude oil) still remains unclear. To test whether the structure of hydrophobic chains of surfactants influences the waxy oil-water interface, we monitored interfacial rheological parameters under different nonionic surfactants (Span80/60/65) using a DWR interfacial shear rheometer. Among these surfactants, the oil-water interface of Span65 characterized by multi-hydrophobic chains had the largest interfacial viscosity and critical storage modulus. A weak strain overshoot interface of Span65 suggested that sorbitan tristearate molecules provided a dominant contribution to the interfacial rheological properties of the waxy oil-water interface with much fewer effects of the interaction between wax molecules and surfactants. However, Span60/80 with a single hydrophobic chain was coupled to wax molecules and reshaped the waxy oil-water interface structure, which replaced the original wax crystal position (the interfacial viscosity and critical storage modulus decrease) and yielded an interfacial structure (the critical strain increase). The wax-surfactant interactions of Span60/80 with different hydrophobic chain saturation were discussed. These interfacial properties are of practical importance for the technological operations in oil production.