Sky-white Temperature/pH-sensitive Nanocomposite Microgels with Lower Size and Good Temperature-Sensitivity

Adopting inorganic nanoclay (lithium magnesium silicate hydrate, LMSH) as physical crosslinking agent, a kind of novel temperature/pH double-sensitive nanocomposite microgels based on N-isopropylacrylamide (NIPAM) and acrylic acid (AAc) were synthesized by using surfactant- free emulsion polymerization method. As a comparison, the traditional poly(NIPAM-co-AAc) microgel using N,N’-methylene-bis-acrylamide(MBA) as chemical crosslinker was prepared by same method. The chemical structure, shape, particle size and phase transition behavior of two kinds of microgels were confirmed by FTIR, XRD, SEM and DSC respectively. The results show that nanocomposite microgel was successful prepared under LMSH severing as physical crosslinker, and the prepared nanocomposite microgel dispersions present sky-blue state, different from oyster white of microgels crosslinked by MBA. The nanocomposite microgels crosslinked by LMSH present good spherical shape with hydrodynamic diameter less than 430 nm, which is much smaller than that of microgels crosslinked by MBA. In addition, the microgels crosslinked by LMSH show same good temperature-sensitivity. With increasing temperature from 20 to 50°, turbidity value increases, but lower than that of poly(NIPAM-co-AAc) microgel. Although a 7 mol.% ratio of AAc/NIPAM was used, the volume phase transition temperature of microgels still keeps at about 31° because of crosslinking structure of LMSH platelets.