Dynamic interfacial tension measurement of heavy crude oil-alkaline systems - The role of the counterion in the aqueous phase

The dynamic behaviour of the interfacial tension at the oil-water interface gamma((t)) for oleic acid and a 90% v/v Cerro Ne,oro-xylene solution had b een studied under alkaline conditions. For the system oleic acid in paraffi n, aqueous sodium carbonate with or without added sodium chloride, the usua l gamma((t)) behaviour was observed, i.e, gamma drops to low or ultralow va lues at short times, remains low during a short period, and then rises to h igh( > 1 N m(-1)) values. However, when alkyl amines (ethyl, diethyl and tr iethyl amine) were used as alkalis in the aqueous phase, gamma((t)) first d ropped to a relatively high value (1.5<gamma<3 N m(-1)) and then remained a lmost constant afterwards. The presence of sodium chloride in the aqueous p hase was required to observed the aforementioned usual gamma((t)) behaviour . From these results it is clear that the presence of sodium ions is esenti al for both reducing (to very low values) and increasing gamma((t)). It is suggested that ultralow transient (values and the formation of spontaneous emulsion are due to a phase inversion (from w/o to o/w) going through a mic roemulsion intermediate. (C) 1999 Elsevier Science Ltd. All rights reserved .