Aggregation/association And Fragmentation/dissolution Of Polymer In Solution

The aggregation and association behaviors in polymer solution or dispersion have attracted much attention. This is partially due to their practical importance in colloid science (stability), metallurgy (phase seperation), biology (growth of tumors), and also partially due to the shortage of our knowledge about these fascination phenomena.Basically, there exist two kinds of distinct regime; namely, diffusion limited cluster aggregation (DLCA) and reaction limited cluster aggregation (RLCA) in the aggregation process in dispersion.Using thermally-induced controllable association of narrowly distributed spherical poly(vinyl caprolactam-co-sodium acrylate) (PVCL-co-PSA) microgels in the presence of Ca⁺⁺ as a model system, we studied the reversible aggregation near the lower critical dispersion temperature (LCDT～35 °C). We found that when such an aggregation is a diffusion limited process, it is usually governed by a second-order aggregation and a first-order fragmentation kinetics. The aggregation and fragmentation rates strongly depend on the dispersion temperature. The final ratio of the two rates approaches one, indicating that there exists a dynamic equilibrium between the two opposite processes.The intermediate regime between DLCA and RLCA was also examined in the system. We found the increase of temperature, as well as the increase of ionic strength will quicken the aggregation, which will prefer the presence of DLCA.In the aggregation process of polymer chains, when the time scale for the chain impenetration is far shorter than that for the chain collision, the polymer chains will aggregate to form spherical clusters. If there is specific interchain or intrachain...