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 of N-isopropylacrylamide and diallyldimethylammonium chloride (2.2 mol%) was faster over a broader range of copolymer concentrations at 42 degrees C than at 23 degrees C, At room temperature the copolymer formed a solution, whereas at 42 degrees 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 TiO2 at 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 TiO2 whereas flocculation occurred at 42 degrees C when the copolymer was present as cationic colloidal particles. (C) 1996 Academic Press, Inc.