Dynamics of polyelectrolyte adsorption and colloidal flocculation studied using model colloids

提出了一种利用微流体和光镊研究水溶性聚合物在单粒子上吸附动力学的新方法。研究了聚乙烯氧化物（PEO）和带电聚丙烯酰胺基聚合物在二氧化硅颗粒上的层厚吸附动力学。研究了不同分子量PEO水溶液中二氧化硅颗粒间的远程相互作用力。考察了pH值、流速、盐浓度和粒径等不同参数的影响。PEO在二氧化硅颗粒上的吸附高度依赖于溶液pH， pH的作用也受流速的影响。观察到厚度与pH无关，而在高流速和高pH下观察到厚度减小。这是由于除了流体力的影响外，二氧化硅表面与聚合物之间的亲和力降低。研究了电荷密度和盐浓度的影响。所有的聚电解质都表现出对盐浓度的依赖性。吸引相互作用控制着阳离子聚电解质的吸附过程。同时，由于所吸附的聚电解质的环状构象和尾部构象不同，层厚取决于电荷密度和盐浓度。这为理解聚合物吸附动力学提供了一个新的视角，通过直接评估单颗粒观点上的层厚度，这是无法进行批量测量的。

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.