Ultralow Interfacial Tensions of Polymer/Polymer Interfaces with Diblock Copolymer Surfactants

Abstract

The interfacial tension γ between polyisoprene (PI) and polydimethylsiloxane (PDMS) homopolymers mixed with poly(isoprene-b-dimethylsiloxane) (IDMS) diblock copolymers has been measured with a spinning drop tensiometer. Measurements have been conducted for mixtures containing each of 12 copolymers, in which the PDMS volume fraction fDMS varies from 0.49 to 0.73, and for mixtures containing a symmetric copolymer and PI homopolymers of varying molecular weight. The measured interfacial tension is found to be independent of copolymer concentration above an apparent critical concentration of order 0.1 wt % copolymer. Mixtures with a nearly symmetric copolymer are found to exhibit ultralow interfacial tensions, up to 3 orders of magnitude less than that of the bare PI/PDMS interface. Results are compared to the predictions of a numerical self-consistent field theory for the interfacial tension of an interface between a PDMS phase containing swollen spherical micelles and a phase of nearly pure PI. Agreement be...