Dynamics of polyelectrolyte adsorption and colloidal flocculation studied using model colloids

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A novel technique for investigating the adsorption kinetics of water-soluble polymer onto a single particle was developed using microfluidics and optical tweezers. The adsorption kinetics of polyethylene oxide (PEO) and charged polyacrylamide-based polymer onto a silica particle in terms of layer thickness were studied. The long-range interaction forces between silica particles in aqueous solutions with different molecular weights of PEO were studied. The effect of different parameters such as pH, flow rate, salt concentrations, and particle size were evaluated. The adsorption of PEO onto silica particles was found to be highly dependent on the solution pH. The effect of pH was also found to be influenced by the flow rate. The thickness was observed to be independent of pH, while it was observed to decrease at a high flow rate and high pH. This is attributed to the decrease in the affinity between the silica surface and the polymer, in addition to the influence of fluid force. The effect of charge density and salt concentrations was studied. All polyelectrolytes exhibited dependence on salt concentration. The attractive interactions control the adsorption process of cationic polyelectrolytes. Meanwhile, the layer thickness is dependent on the charge density and salt concentration, due to the differences in the loop and tail conformation of the adsorbed polyelectrolyte. This presents a novel perspective in understanding polymer adsorption kinetics by directly evaluating the layer thickness on a single particle viewpoint that is not accessible to bulk measurements.