Thermodynamic and aggregation properties of gemini surfactants with ethoxylated spacers in aqueous solution

Critical micelle concentration (cmc), degree of micelle ionization (alpha), headgroup area (a(0)), enthalpy ofmicellization (DeltaHdegrees(M)), and volume of micellization (DeltaVphi,(M)) properties are reported for a series of (oligooxa)-alkanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) gemini surfactants, 12-EOx-12 (x = 0-3), having several ethylene oxide moieties within the spacer group. The cmc and headgroup areas are observed to increase with an increase in the number of EO groups in the spacer, in contrast to the complex behavior of gemini surfactants (M-S-M) having a normal hydrocarbon chain. Also, the DeltaHdegrees(M) increases (becomes less exothermic) and DeltaV(M) decreases with an increase in the number of EO groups in the spacer. These observations are rationalized in terms of changes in the hydration and conformation of the spacer group at the micelle-bulk solution interface. Gibbs energies of micellization, DeltaGdegrees(M),, and entropies of micellization, DeltaSdegrees(M), are calculated from the DeltaHdegrees(M), cmc, and alpha values. The results indicate that the micellization process for these surfactants is entropy-driven.