Endowing catanionic surfactant vesicles with dual responsive abilities via a noncovalent strategy: introduction of a responser, sodium cholate

A noncovalent strategy is proposed for endowing responseless catanionic surfactant (a mixture of cationic and anionic surfactants) aggregates with responsive abilities by addition of a responser. In this strategy, the composition of catanionic surfactant can be carefully selected to render aggregates sensitive to added responsers, and the responsers can be chosen from plenty of commercialized candidates, which bear responsive groups and will be noncovalently incorporated into the aggregates. In this paper, we report an illustrative example for the strategy: dual-responsive vesicles are realized by simply adding a responser, SC (sodium cholate), to a stimuli-inert DEAB/SDS (dodecyl triethyl ammonium bromide/sodium dodecyl sulfate) vesicular aqueous solution at a low responser/surfactant molar ratio of 0.045. The resultant DEAB/SDS/SC aggregates undergo reversible transitions between vesicles and micelles in response to temperature or pH variations. Possible mechanisms for these responsive behaviors are speculated, where the temperature-responsive hydroxyl groups and pH-responsive carboxylate group of SC are thought to be crucial. This responsive ability-endowing noncovalent strategy shows potential as a general, versatile, and economical method for fabricating stimuli-responsive self-assemblies.