Synthesis of smart dual-responsive microgels: correlation between applied surfactants and obtained particle morphology†
Thermo- and pH-responsive copolymer microgels were obtained by surfactant-assisted precipitation polymerization of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc). The surfactants used were sodium dodecylsulfate (SDS), dodecyltrimethylammonium bromide (DTAB) and the nonionic n-octyl-β-D-glucopyranoside (C8G1). We investigate the influence of the surfactants on the acrylic acid incorporation rate, the particle size, particle morphology, and the swelling behaviour at pH 4 and pH 7, at which AAc is neutral or charged, respectively. It is shown that each surfactant has a specific influence, which is connected to its role in the polymerization mechanism and its charge. A combined FTIR and PCS study reveals that the particles undergo a temperature-induced change in microstructure, even if the particle hydrodynamic radius does not change significantly.