Electrical double layer interactions in a non-polar liquid measured with a modified surface force apparatus

Abstract

Surface force measurements have been made between mica surfaces immersed in a non-polar liquid, decane, in the presence of an amphiphilic electrolyte, sodium di-2-ethylhexyl sulphosuccinate (AOT), using a modified Surface Force Apparatus (SFA). The modifications, notably the employment of a pair of sensitive force measuring springs and the implementation of a magnetic drive mechanism, have appreciably improved the sensitivity of SFA, which enables the detection of a weak long-range repulsion in the non-polar system. The origin of the repulsion is ascribed to electrical double layer interactions, and it may be satisfactorily described by a counterion-only double layer theory. This comprises the first report of electrical double layer interactions in a non-polar liquid.

Acknowledgements We are indebted to many helpful discussions from Phil Attard. Image analysis software developed by Jason Connor has been used for data analyses. PALS and FTIR measurements were performed by Roland Keir and Kathryn Hanton. Financial support from the Australian Research Council is acknowledged.

Presented at XV European Colloid and Interface Society Conference