Viscoelastic properties of crude oil components at oil-water interfaces.: 1.: The effect of dilution

The dilational viscoelastic properties of diluted crude oil-water interfaces have been studied using the oscillation drop method. The study focuses on the effect of altering aromaticity of the solvent and the concentration of the crude oil on the viscoelastic response of the crude oil-water interface. Dynamic interfacial tension experiments (pendant drop), asphaltene aggregation state experiments (near-infrared spectroscopy) and emulsion stability experiments (bottle test) have complemented the studies of interfacial rheological parameters in order to understand the mechanisms of film formation and emulsion stabilization. The overall w/o-emulsion stability seemed to be determined by the aggregation state of asphaltenes in bulk and the reduced sedimentation rate of water droplets in concentrated systems. The storage E' and loss E" moduli of the crude oil/water systems were determined with dilation rheology. At a perturbation frequency omega = 0.1 Hz, the equilibrium storage and loss moduli passed through distinct maxima as a function of bulk concentration. The apparently low viscoelasticity of the interfaces in systems with high bulk concentration was probably caused by high diffusion flux of interfacially active components from bulk and was not entirely due to interactions within the adsorbed layers. Dilation experiments at other perturbation frequencies confirmed this phenomenon. Results have been discussed in connection with recent findings regarding the stabilization of water-in-oil emulsions.