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Preparation and characterization of pH-responsive and thermoresponsive hybrid microgel particles with gold nanorods



We report on pH-responsive and thermoresponsive hybrid materials based on the assembly of gold nanorods, Au NRs, into multiresponsive, crosslinked copolymer microgel particles. These microgel particles were prepared by the surfactant-free emulsion polymerization of N-isopropylacrylamide and acrylic acid using N, N′-methylene bis-acrylamide as a crosslinker, which produces particles measuring approximately 160 nm that are interconnected to one other. Cetyltrimethyl ammonium bromide-stabilized Au NRs were also prepared independently using a seed-mediated growth method and then loaded into swollen, deprotonated, acrylic acid-containing microgel particles using the electrostatic interactions between the oppositely charged particles. Transmission electron micrographs of the as-prepared hybrid Au NR–microgel particles confirmed that the Au NRs were attached to the surface of the microgel particles. The size-dependent temperature-responsive characteristics of the hybrid microgel particles were studied by dynamic light scattering, and it was found that as the temperature increased across the phase transition temperature, the particle size decreased to 56% of the original volume. The thermoresponsive and pH-responsive optical properties of the hybrid microgel particles were also systematically investigated. The thermo- and pH-induced shrinkage of the microgel led to an increase in the UV–vis absorption intensity and caused a significant blue shift in the longitudinal surface plasmon bands of the Au NRs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013