Water-in-crude oil emulsions from the Norwegian continental shelf 5. A comparative monolayer study of model polymers

Abstract

In an attempt to simulate the behaviour of emulsion-stabilizing fractions from North Sea crude oils, the pressure-area (π- A) isotherms and relaxation behaviour at constant pressure of monomolecular films at the air/aqueous solution interface of a copolymer of styrene and allyl alcohol (PSAA, mean molecular weight 1500 g mol −1) as well as mixtures of this polymer with 4-hexadecylaniline (HDA) or cicosylamine (EA) have been investigated. The polymer forms highly compressible films that are not affected by changes in the subphase pH or ionic strength and relax on the surface in a way which is consistent with rcconformation of the polymer without dissolution in the subphase. Both HDA and EA form mixed films with PSAA. These films expand at low pH due to electrostatic repulsion between ionized groups. The surface pressure of mixed PSAA/HDA films is additive at low pressures (< 12 mN m −1) at pH values for which ionization of the HDA is negligible. Addition of 1-butanol and benzyl alcohol to the subphase indicates that these compounds penetrate into the PSSA film. The mixtures of PSAA with HDA or EA essentially reproduce the π- A isotherms and relaxation properties of the films formed by interfacially active fractions of authentic crude oils (investigated earlier). The main differences are a lower maximum compressibility and a higher surface activity. Thus, although the crude oil fractions are complex mixtures of polyaromatic and aliphatic hydrocarbons, their monolayer properties appear to be well modelled by a relatively low molecular weight aromatic, weakly polar, water-insoluble hydrocarbon polymer to which has been added insoluble long-chain amines which are protonized at low pH.