Direct observation of a diblock copolymer-induced microemulsion at a polymer/polymer interface

We have studied the segregation of a block copolymer of poly(d₈-styrene-b-2-vinylpyridine) (dPS-PVP) at the interface between polystyrene and a random copolymer of poly(styreneran-4-hydroxystyrene) (PS-r-PPHS). Forward recoil spectrometry (FRES) was used to measure the equilibrium excess (z^*) of the dPS-PVP chains at the interface as a function of its volume fraction in the bulk PS phase (?_∞). It was found that there is a sharp increase in z^* at a critical value of ?_∞. This upturn indicates the formation of a microemulsion of PS and the random copolymer PS-r-PPHS due to a vanishing of the interfacial tension caused by the strong adsorption of the block copolymer. Cross-sectional transmission electron microscopy (TEM) of the interface shows that this microemulsion starts to form at the interface by forming a deeply corrugated structure where the “wavelength” of the corrugations is of the order of 50 nm. © 1995 John Wiley & Sons, Inc.