Premicelle Formation of Double-chain Surfactants and Bile Salts in the Neighborhood of the CMC Region: Application of a Differential Conductivity Technique to the Determination of Micellization Parameters

摘要

It has been demonstrated that differential conductivity, dκ/dC, is useful for experimentally extracting the contribution of micellar aggregates from the conductivity data of an ionic surfactant solution in which aggregates and monomers coexist. This extraction allows us to treat the micellization process using a simple two-state model (nS→M) instead of the general mass action model of micellization (nS+qG→M). As a result, the three parameters of micellization, i.e., aggregation number (n), micellization constant, and ionization degree (α) of micelles, for homologous double-chain surfactants and bile salt derivatives can be determined. It was found that when the side-chain was long enough, the double-chain surfactants examined formed highly ionized (α = 0.6-0.9) and small (ca. n = 20) aggregates, regarded as premicelles.