Adsorption and aggregation properties of homogeneous polyoxyethylene alkyl ether- and ester-type nonionic surfactants with multi-branched double chains

Homogeneous polyoxyethylene (EO) alkyl ether- and ester-type nonionic surfactants with multi-branched double chains were newly synthesized. Their adsorption and aggregation properties were investigated through cloud point, surface tension, and small-angle X-ray scattering measurements, and compared to those of homogeneous EO alkyl ether- and ester-type nonionic surfactants with symmetric and asymmetric linear double chains as well as a conventional surfactant with a linear single chain. The surface tension at the critical micelle concentration for the multi-branched double-chain type decreased considerably to 27.9–28.8 mN m−1 despite having a large hydrophilic group of EO12 when multi-branched methyl groups with low surface energy were used as the hydrophobic groups of the surfactants. In the temperature vs. concentration phase diagrams, the regions of lamellar liquid crystals were more extensive for the linear double-chain surfactants because of the small interfacial curvature induced by the steric hindrance of the multi-branched chains.