Kinetics of the aggregation of polyethylene oxide at temperatures above the polyethylene oxide–water cloud point temperature

The kinetics of the aggregation of high molecular weight polyethylene oxide (PEO) at temperatures above the PEO–water cloud point temperature (CPT) was studied by monitoring the particle size profile with time using photometric dispersion analysis and light diffraction. Upon PEO–water phase separation, hydrophobic inter/intra molecular PEO–PEO interactions cause the random PEO coils to collapse to a compact configuration and aggregate with each other. The rate of aggregation was found to increase with increasing temperature deviation from the CPT, PEO concentration and molecular weight. Higher temperature and lower shear gave rise to larger equilibrium PEO aggregates. These aggregates can reach a size of 600 μm in diameter. Aggregation was also found to proceed until the aggregation rate is balanced out by the breakup rate. It was observed that the aggregation process could be reversed repeatedly by shifting across the phase boundary. It is suggested that the main mechanism for the breakup of the aggregates is surface erosion, which is caused by the shearing action of the water surrounding the aggregates.