Ca2+-induced complexation between thermally sensitive spherical poly(N-vinyl-caprolactam-co-sodium acrylate) microgels and linear gelatin chains in water

The temperature dependence of the complexation between thermally sensitive spherical poly(N-vinylcaprolactam-co-sodium acrylate) microgels and linear gelatin chains without and with the addition of Ca2+ was studied by a combi nation of static and dynamic laser light scattering over a wide range of th e gelatin/microgel ratios ([G]/[M]) in terms of the complex's average hydro dynamic radius (<R-h>), weight average molar mass (M-w), average aggregatio n number (N-agg), and average chain density (<p >). Without Ca2+, the compl exation is weak and each complex, on an average, contains not more than two microgels. In the presence of Ca2+, the complexation occurred at similar t o 32 degreesC is much stronger and the onset of complexation is independent of [G]/[M], but both N-agg and <p > decrease as [G]/[M] increases because the adsorption of too many hydrophilic gelatin chains on the microgels hind ers the complexation and reduces the shrinking of the complexes. The comple xation is essentially reversible but there exists a slight hysteresis on co oling. On the basis of this study, a gel composite made of microgel and gel atin was prepared and its biomedical applications have been considered. (C) 2001 Published by Elsevier Science Ltd.