Influence of the Mixed Propoxy/Ethoxy Spacer Arrangement Order and of the Ionic Head Group Nature on the Adsorption and Aggregation of Extended Surfactants

Two families of extended surfactants were prepared with the same head groups (carboxylate, sulfate, disodium phosphate) and different intermediate spacer structures. In one there was an average of 7 propylene oxide groups on the side of the tail and an average of 7 ethylene oxide groups on the side of the head, to produce a sequence of two different polarity segments. In the other case the spacer contained the same average numbers of propylene and ethylene oxide groups but in some homogeneous arrangement. The intermediate spacer structure, without ionic head group and in the cases of the carboxylate and sulfate extended surfactants, had a packing density reduction which is associated to the homogeneously alkoxide arrangement in the spacer. Such an arrangement was found to produce about 20% more surface area at the interface, apparently because it results in some plumpness due to the spacer folding to remain close to the interface. Both the critical micelle concentration and occupied interfacial area of the extended surfactant increased with the ionization of the anionic group associated with the electrostatic repulsion effect.