Influence of additives and cation chain
length on the kinetic stability of supersaturated catanionic systems,
Nina Vlachy, Alexandro F. Arteaga, Angelika Klaus, Didier Touraud, Markus
Drechsler, and Werner Kunz,
Colloids and Surfaces, A: Physicochemical and Engineering Aspects
(2009) 338(1-3), 135-141.
Abstract
The stability of mixed surfactant solns. of sodium dodecylsulfate (SDS) with
cetyltrimethylammonium bromide (CTAB) and with dodecyltrimethylammonium bromide
(DTAB) was studied as a function of time. These specific mixts. are shown to
have a soly. temp. below that of pure surfactant solns. in the anionic-rich
region. The stability of such supersatd. solns. was studied with and without
different additives. Surfactant mixts. without additives are shown to
destabilize with time varying between 3 and 28 days, depending on the
surfactant ratio. Generally, the stability of soln. increases by increasing the
percentage of the anionic surfactant. The variation of the chain length of the
cationic surfactant produces a large effect on the stability of such mixed
surfactant systems. The presence of simple electrolytes decreases, while the
addn. of middle-chain alcs. increases its stability. Bluish solns.
corresponding to a vesicular region were obsd. at ratios close to equimolarity
in samples without salt, and in the anionic-rich region upon the addn. of
middle-chain alcs. Fluorescence and dynamic light scattering measurements
showed that the destabilization of the solns. is not due to the formation of
bigger aggregates, but rather due to a shift of the equil. between micelles and
monomers, leading to the liberation of monomers, which ppt. The lifetime of
vesicles and micelles can therefore be controlled by varying the compn. of the
surfactant solns. and by additives. Controlling the pptn. phenomena is of
importance for a large no. of industrial processes, such as oil/solute recovery
processes after extns. or chem. reactions. |
