Micellization and Adsorption of Heterogemini Surfactants Containing a Hydroxyl Headgroup in Aqueous Solution

The micellization of a homologous series of heterogemini surfactants, C_mOhpNC_n (m, n = 10, 8; 12, 8; 14, 8; 16, 8; and 10, 14), in aqueous solution and their adsorption at the air/water interface have been investigated by surface tension, conductivity, and fluorescence techniques. The surface tension curves of C₁₆OhpNC₈ and C₁₀OhpNC₁₄ showed two break points, corresponding to the critical concentration of the premicellar aggregation and the general micellization, respectively. The results of conductivity and fluorescence spectra using pyrene as probe confirmed the premicellization behavior in the two cases. This indicated that these surfactants have strong aggregation ability in the solution. The micelle formed nearby the cmc displayed only a small aggregation number but a large ionization degree. The C₂₀ that characters the efficiency in surface tension reduction was quite small in comparison with those of conventional surfactant and even smaller than those of symmetric gemini surfactants such as 12-s-12 homologous. The special molecular packing of C_mOhpNC_n in aqueous solution was closely related to the intermolecular hydrogen bonding and a weak electrostatic repulsion.