Correlation among copolyether spacers, molecular geometry and interfacial properties of extended surfactants

Abstract

Extended surfactants (e-surfactants) generally occupy larger surface adsorption areas and display better properties than conventional surfactants, which is attributed to propoxy-containing polyether spacers coiled more and collapsed more on various interfaces but lack of firm evidences. In this work, the target products of sodium dodecyl poly(propoxy-ethoxy) sulfates are synthesized on the basis of designing copolyether spacers by both diblock and random copolymerization mechanisms. A unique insoluble monolayer experiment is proposed to estimate surface spreading areas of the copolyether intermediates. Moreover, the correlation between copolyether spacers and molecular geometry and interfacial properties of the e-surfactants is investigated. We find that surface spreading areas of the copolyether intermediates are much larger than that of the dodecanol precursor and slightly larger than and positively correlated with surface adsorption areas of the corresponding target e-surfactants, which provides a direct evidence for biphasic affinity of the copolyether spacers to drive the spacers three-dimensionally extended on various interfaces and make e-surfactants becoming rugby ball shapes. Furthermore, it is shown that the more random copolyether spacer, the larger molecular area on the surface the e-surfactant occupies, being responsible for many unique interfacial properties of e-surfactants.