Comparison of the Ca2+/COO- Complexation Induced Controllable Aggregation of P(VCL-co-NaA) Spherical Microgels and Linear Chains

The Ca 2+ /COO - complexation induced aggregation of poly( N -vinylcaprolactam- co -sodium acrylate) (P(VCL- co -NaA)) spherical microgels as well as linear chains under different conditions, such as the Ca 2+ concentration, the COO - content, and the aggregation temperature, was studied by a combination of static and dynamic laser light scattering. Using thermally sensitive P(VCL- co -NaA) enabled us to vary the chain conformation and the sticking efficiency of two collided spherical microgels or linear chains by temperature, so that the aggregation was controllable and reversible. The time evolution of both the weight-average molar mass ( M w ) and the average hydrodynamic radius (〈 R h 〉) of the aggregates was simultaneously recorded. It showed that for the microgel aggregates M w could be scaled to 〈 R h 〉 as M w ∝ 〈 R h 〉 d f and the average scattering intensity I ( q ) varied with the scattered vector q as I ( q ) ∝ q - d q with d f and d q in the range 1.6−1.9, indicating a diffusion-limited process, while for the chain aggregates, both d q and d f decreased from ∼2.5 to ∼1.6 as the aggregation temperature increased from 32.5 to 50 °C, revealing, for the first time, that the structure of the resultant aggregates depends on the initial chain conformation. For both spherical microgels and linear chains, the aggregation rate and the aggregate size increased with the Ca 2+ concentration, but the structures of the resultant aggregates remained.