Abstract
Stable viscoelastic suspensions of bentonite clay particles in semi-dilute solutions of wormlike micelles of mixed zwitterionic (oleyl amidopropyl dimethyl carboxybetaine) and anionic (sodium dodecyl sulfate) surfactants were elaborated. They represent a novel type of soft nanocomposite with tunable viscoelastic matrix. Structural studies revealed that the clay is dispersed in a dense network of entangled wormlike micelles in the form of 100-nm tactoids. Rheological investigations demonstrated that clay particles can induce an increase of viscosity by up to one order of magnitude. The effect of the clay becomes more pronounced with increasing content of anionic surfactant in the mixture with zwitterionic surfactant, when the micelles become branched. This behavior was explained by the stabilization of micelle-nanoclay junction points due to the screening of the repulsion between positively charged fragments of zwitterionic head groups by added anionic surfactant. As a result of stabilization, the lifetime of surfactant-nanoclay junctions becomes much larger than the breaking time of micelles. The elaborated systems are of interest for many industrial applications.
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