Temperature and molecular structure-dependent self-assembly of PS-b-PEO at the liquid/liquid interface

Abstract

It is of great importance to explore the self-assembly behavior of amphiphilic block copolymers at the liquid/liquid interface for the construction of hierarchical nanostructures and evaluation of emulsifiers. In this work, the adsorption and self-assembly of PS-b-PEO, a typical amphiphilic and temperature-sensitive block copolymer with abundant coordination sites were investigated by using a liquid/liquid interfacial assembly method in which pure water covered a chloroform solution of PS-b-PEO to form a planar liquid/liquid interface first, and then the aqueous solution of copper acetate was added dropwise into the water. It was found that spontaneous interfacial emulsification occurred when Cu2+ aqueous solution was added into the water at 28 °C. The PS-b-PEOs with shorter PEO chains self-assembled into hollow spheres, hierarchical hollow spheres, and hollow spheres with layered walls, depending on the relative length of the PEO blocks; while the PS-b-PEO with a longer PEO chain formed Janus sheets. While, PS-b-PEOs self-assembled into Janus sheets with monolayer or stepped multilayer structures at 18 and 8 °C through interfacial adsorption and assembly, regulated by the molecular structures. In addition, the concentrations of PS-b-PEO and Cu2+ ions also affect the self-assembly behavior and the aggregate morphologies.