Cooperative effects of polypropylene oxide spacers and alkyl chains on dynamic amphipathicity of extended surfactants

Abstract

Polypropylene oxide (PPO) spacers have long been inserted into conventional surfactants with branched alkyl chains to create branched extended surfactants (e-surfactants) and to further improve the solution and interfacial properties; nevertheless, limited information is available about the structure-activity relationships of branched e-surfactants. In this study, ten sulfate e-surfactants were designed and synthesized from three commercially available branched alcohols by propoxylation, sulfation and neutralization reactions. The cooperative effects of PPO spacers and branched chains on the solution and interfacial properties of the branched e-surfactants (b-CcPpS) were investigated to highlight correlations between the molecular structure and the amphipathicity of b-CcPpS. An intramolecular PPO spacer cooperates with variable branched chains to regulate the dynamic amphipathicity of b-CcPpS according to the environment, due to its biphasic affinity. The biphasic affinity is also responsible for promoting the coiling of the surface molecules into a rugby ball shape that is similar to the reported straight chain counterparts, and dominates the solution and interfacial properties of b-CcPpS. Furthermore, this study suggests the feasible design and synthesis of novel amphiphiles with a special surfactant shape by introducing a “simple” PPO spacer into the molecules.