Impact of Spatial Distribution of Charged Groups in Core Poly(N-isopropylacrylamide)-Based Microgels on the Resultant Composite Structures Prepared by Seeded Emulsion Polymerization of Styrene

A series of raspberry-shaped composite microgels were synthesized by seeded emulsion polymerization of styrene in the presence of hydrogel particles with different distributions of charged groups. Unlike microgels whose charged groups are localized in their center,29 polystyrene nanoparticles were formed inside the core microgels when the microgels whose charged groups were localized on their surface were used as cores for seeded emulsion polymerization. The effects of the surface charge densities of the core microgels and the concentration of styrene monomer during the polymerization on the resultant structures of composite microgels were investigated. The surface structures of obtained composite microgels were mainly evaluated by electron microscopy, and their stimuli responsiveness was evaluated by dynamic light scattering and laser Doppler velocimetry. The internal structures of the composite microgels were visualized from ultrathin cross sections observed by transmission electron microscopy (TEM). Cryo-TEM was used to clarify the microscopic structures of composite microgels when they were in hydrated states. Through a series of characterizations, we summarize the effects of structures of core microgels on the resultant composite structures.