Configurable Self-Assembly of Block Copolymers at the Liquid-Liquid Interface

Self-assembly of charged block copolymers has a range of potential applications such as fabrication of reconfigurable patterns in liquid-liquid systems, thin-film nanopatterning, bottom-up nanofabrication, demulsifying and antifoaming in extraction methods, drug delivery, protein encapsulation, among many others. Here we investigate the configurations of amphiphilic block copolymers at the water-chloroform interface using molecular dynamics simulations. The copolymers are constituted by one hydrophilic block and one hydrophobic block. A fraction of monomers (f_q) in the hydrophilic block bear a positive elementary charge which is balanced by free counterions. Our model represents the block copolymer poly(styrene)-poly(2-vinylpyridine) (PS-b-P2VP) with a degree of quaternization (f_q). A variety of structures going from circular domains to elongated stripes is observed by varying the polymer charge fraction and the hydrophilic/hydrophobic ratio. The adsorption and the structural changes are driven by a combination of effects such as the dielectric mismatch at the liquid-liquid interface, ionic correlations, hydrophilic-hydrophobic forces, and solvation effects.