Responsive properties of crystalline colloidal arrays formed by core-shell microspheres with pH and temperature sensitivities

Abstract

Polymeric microspheres responsive to pH and temperature changes have been prepared by a two-step surfactant-free emulsion polymerization with a polystyrene core and a hydrogel shell. The double sensitivity is achieved by the copolymerization in the shell layer of acrylic acid and N-isopropylacrylamide, which are pH- and thermo-responsive, respectively. Above a certain critical concentration, these microspheres are able to self-assemble into crystalline colloidal arrays, causing intense visible light diffraction. The behavior of these structures has been studied and correlated to the properties of the microspheres. The packing of these microspheres results in stimuli-sensitive colloidal crystals, with a behavior directly linked to the interactions between the particles and the surrounding media.