Temperature-Sensitive Flocculants Based on Poly(N-isopropylacrylamide-co-diallyldimethylammonium Chloride)

The flocculation of aqueous colloidal TiO2, average diameter 266 nm, with a cationic copolymer ofN-isopropylacrylamide and diallyldimethylammonium chloride (2.2 mol%) was faster over a broader range of copolymer concentrations at 42°C than at 23°C. At room temperature the copolymer formed a solution, whereas at 42°C the polymer was present as cationic colloidal particles with an average diameter of 87 nm. Both physical forms of the copolymer adsorbed/deposited onto TiO2at pH 7 due to favorable electrostatic interactions. Reversible temperature-sensitive flocculation was observed at intermediate copolymer concentrations. At room temperature the copolymer concentration was high enough to sterically stabilize the TiO2whereas flocculation occurred at 42°C when the copolymer was present as cationic colloidal particles.