Self-association of 1,10-decanedicarboxylates in aqueous solution

Abstract

Two separate transition concentrations are observed in surface tension and pH data for aqueous solutions of 1,10-decanedicarboxylic acid neutralized with either triethanolamine or sodium hydroxide. This is taken as an indication of the occurrence of a two-stage micellization process. The first transition is believed to be caused by dimer formation, while the second irregularity in surface tension and pH vs concentration curves probably corresponds to the formation of loosely associated micelles. Aggregational transitions are less distinct in conductivity—concentration data, indicating rather weak monomer interactions. With sodium counterions, surface tension data and pH data indicate the possible existence of a third aggregational transition. Substantial differences in cross-sectional areas at the air—water interface for the difunctional surfactant were observed for different cations and ionic strengths but corresponding values for CMCs are not much affected. It is concluded that the disodium α,ω-dodecanedioate assumes a folded conformation at the air—water interface. Data for the corresponding triethanolamine salt imply a similar but more tightly folded conformation for the surfactant hydrocarbon chains, and conductivity data suggest that diamine salt micelles of the dicarboxylic acid are sparesly ionized.