Factors affecting the swelling of poly(N-isopropylacrylamide) microgel particles: fundamental and commercial implications

A microgel particle is a cross-linked latex particle which is swollen by a good solvent. Particle swelling is intrinsically related to the nature of t he interaction between the polymer and continuous phase. Microgel particles based on PNP [PNP =poly(N-isopropylacrylamide)] are particularly interesti ng since the parent homopolymer undergoes a coil-to-globule transition in w ater when the temperature increases above 32 degrees C. In this work, PCS ( photon correlation spectroscopy) and SANS (small-angle neutron scattering) are employed in a complementary manner to study the environmentally induced de-swelling of PNP particles. Further, we show that particle de-swelling m ay be induced at room temperature by addition of alcohols or excluded free polymer (i.e. non-adsorbing free polymer) to the continuous phase. (The ext ents of particle de-swelling observed using these additives are similar to those achieved by heating the pure microgel particles in water above 32 deg rees C.) Particle de-swelling in the presence of added alcohol or free poly mer arises from "co-non-solvency" and osmotic de-swelling effects, respecti vely. Copolymerization of N-isopropylacrylamide (NP) with acrylic acid yields mic rogel particles whose diameters are sensitive to both pH and temperature. T hese particles adsorb Pb-II ions from solution in a reversible manner. The latter property has potential application in water purification. (C) 1999 E lsevier Science B.V. All rights reserved.