Comparison of the Ca2+/COO- complexation induced controllable aggregation of P(VCL-co-NaA) spherical microgels and linear chains

The Ca2+/COO(-)complexation induced aggregation of poly(N-vinylcaprolactam- co-sodium acrylate) (P(VCL-co-NaA)) spherical microgels as well as linear c hains under different conditions, such as the Ca2+ concentration, the COO- content, and the aggregation temperature, was studied by a combination of s tatic and dynamic laser light scattering. Using thermally sensitive P(VCL-c o-NaA) enabled us to vary the chain conformation and the sticking efficienc y of two collided spherical microgels or linear chains by temperature, so t hat the aggregation was controllable and reversible. The time evolution of both the weight-average molar mass (M-w) and the average hydrodynamic radiu s <R-h> of the aggregates was simultaneously recorded. It showed that for t he microgel aggregates M-w could be scaled to <R-h> as M-w proportional to <R-h> (d f) and the average scattering intensity I(q) varied with the scatt ered vector q as I(q) proportional to q(-d q) with d(f) and d(q) in the ran ge 1.6-1.9, indicating a diffusion-limited process, while for the chain agg regates, both d(q) and d(f) decreased from similar to2.5 to similar to1.6 a s the aggregation temperature increased from 32.5 to 50 degreesC, revealing , for the first time, that the structure of the resultant aggregates depend s on the initial chain conformation. For both spherical microgels and linea r chains, the aggregation rate and the aggregate size increased with the Ca 2+ concentration, but the structures of the resultant aggregates remained.