Interaction of a cationic amphiphile with monomeric and polymeric electrolytes: From morphological transition to associative phase separation.

Abstract

The discrete effects of a series of structurally divergent monomeric viz. Sodium Chloride (NaCl), Tetra-butyl Ammonium Chloride (TBAC) and Sodium Benzoate (NaBz) and polymeric viz. Sodium Polystyrene Sulfonate (NaPSS) electrolytes towards the morphological and/or aggregation properties of Octadecyl-trimethyl Ammonium Bromide (OTAB) micelles have been quantified spectroscopically by means of the modulations of the absorption and emission spectral properties of an extrinsic anthracene-based probe 9-methyl anthroate (9-MA) within the concerned media. Further corroboration of the spectroscopic results was acquired from the non-invasive dynamic light scattering technique. The qualitatively similar mode of action of all the monomeric salts has been explained on the basis of the archetypal Israelachvili model whereas the corresponding extent of the morphological transition of the micelles, which is found to follow the order NaBz > NaCl > TBAC, has been explained invoking the co-sphere overlap model. Conversely, to explain the aggregation behaviour of the micelles in the presence of the polymeric electrolyte, a two-step model has been formulated. According to this model, at the low concentration regime, the polymeric salt is found to only neutralize the surface charge of the micelles inducing micellar growth; whereas further increment in the concentration of the polymer assists the hydrophobic association between the micelles leading to the formation of larger aggregates, eventually causing a phase separation.