Interfacial tension minima in oil–water–surfactant systems. Effects of cosurfactant in systems containing sodium dodecyl sulphate
- 1 January 1987
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 83 (8) , 2347-2357
- https://doi.org/10.1039/f19878302347
Abstract
In systems consisting of a non-polar oil in contact with aqueous NaCl, addition of an ionic surfactant reduces the oil–water interfacial tension until the aggregation point (c.m.c.) is reached and thereafter the tension remains constant (at γc) with increasing surfactant concentration. The value of γc depends on the salt concentration, ms, and the concentration, mco, of co-surfactant, e.g. an n-alkanol, if present. For the twin-tailed anionic surfactant AOT, addition of NaCl can produce ultra-low oil–water tensions and γc can be made to pass through a minimum. For the single-chain surfactant sodium dodecyl sulphate (SDS), however, salt alone cannot produce a minimum in γc, nor is γc very low. Addition of cosurfactant (octanol) to systems containing SDS above its c.m.c. can, however, result in very low values of γc and also a minimum as mco is varied. These effects are discussed quantitatively in terms of the composition of interfacial monolayers.Keywords
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