Microgels Based on Amphiphilic Polymer Conetworks at a Liquid–Liquid Interface: Microphase Segregation in Swollen Particles

Amphiphilic microgels with a diblock copolymer-like network architecture (each subchain of the network is a diblock copolymer chain) were studied at the interface of two immiscible liquids (oil and water) using mesoscopic computer simulations. It was shown that adsorption of microgels to the interface causes not only deformation of the soft particles, which is primarily controlled by their cross-linking density and incompatibility of the liquids but also microphase separation inside them. One of the blocks is considered to be water-soluble and the other as soluble in oil only, i.e., both liquids are selective solvents for the copolymer. In contrast to dense block copolymer systems, where microphase separation is driven by the incompatibility of the blocks, the microphase separation within the microgel swollen at the interface is solely caused by the incompatibility of the different liquids. Water-soluble blocks uptake water from the water phase, and water-insoluble blocks uptake oil from the oil phase in a proportion, which is determined by a composition of the copolymer. Therefore, the location of the different blocks determines the location of the different liquids, whose incompatibility stabilizes nanodomains. Thus, the subchains remain swollen (each block is swollen in the corresponding liquid) and the incompatibility between blocks alone does not cause microphase separation. Under uniaxial compression of monolayers of such microgels, the morphology of the interfacial ensemble was found to vary from elongated lamellar domains oriented along the compression axis for highly cross-linked particles to onion-like structures for weakly cross-linked particles. Finally, using one-dimensional structure factor analysis and two-dimensional diffraction patterns, the evolution of nanoscale ordering in monolayers during compression was tracked, confirming the emergence of lamellar nanodomains.