On the Origins of Morphological Complexity in Block Copolymer Surfactants

TLDR

Amphiphilic compounds such as lipids and surfactants are fundamental building blocks of soft matter. We describe experiments with poly(1,2‑butadiene‑b‑ethylene oxide) (PB‑PEO) diblock copolymers that form Y‑junctions and three‑dimensional networks in water at intermediate PEO weight fractions associated with vesicle and wormlike micelle morphologies. Fragmentation of the PB‑PEO networks yields a nonergodic array of complex reticulated particles imaged by cryogenic TEM, and self‑assembly occurs only above a critical molecular weight, allowing these copolymers to mimic low‑molecular‑weight three‑component microemulsions without a separate hydrophobe.

Abstract

Amphiphilic compounds such as lipids and surfactants are fundamental building blocks of soft matter. We describe experiments with poly(1,2-butadiene-b-ethylene oxide) (PB-PEO) diblock copolymers, which form Y-junctions and three-dimensional networks in water at weight fractions of PEOintermediate to those associated with vesicle and wormlike micelle morphologies. Fragmentation of the network produces a nonergodic array of complex reticulated particles that have been imaged by cryogenic transmission electron microscopy. Data obtained with two sets of PB-PEOcompounds indicate that this type of self-assembly appears above a critical molecular weight. These block copolymers represent versatile amphiphiles, mimicking certain low molecular weight three-component (surfactant/water/oil) microemulsions, without addition of a separate hydrophobe.