Coagulation of Colloidal Particles

研究了纳米级胶体颗粒的凝聚;检查了其稳定性是否与所谓的DLVO理论一致，并且可以通过修改的Smoluchowski理论来评估速率。采用直径为5 nm至200 nm的二氧化硅颗粒、聚苯乙烯胶乳颗粒和氧化锆颗粒。通过停流法混合胶体溶液和电解质溶液（或聚合物溶液），然后通过低角光散射装置测量凝固速率的变化。研究了电解质、颗粒和聚合物对混凝速率的影响。结果表明：1）粒径小于100 nm的胶体颗粒的快速凝聚速率常数随粒径的减小而减小; 2）粒径小于100 nm的胶体颗粒的快速凝聚速率常数随阳离子水化焓的增大而减小，随阴离子水化焓的减小而减小;在过高的电解质浓度下，快速絮凝速率随电解质浓度的增加而降低; 4）由超细颗粒形成的絮体很难被外力反絮凝;这些结果表明，粒径小于100 nm的颗粒的稳定性不符合DLVO理论，并且不能用Smoluchowski理论预测混凝速率。随着聚合物尺寸的增加而增加，所述聚合物尺寸由粒径归一化。

The coagulation of colloidal particles of nm order in size was investigated; it was examined whether the stability is consistent with the so-called DLVO theory and the rate can be evaluated by the modified Smoluchowski theory. Silica particles, poly-styrene latex particles and zirconia particles of 5 nm to 200 nm in diameter were employed. A colloidal solution and an electrolyte solution (or polymer solution) were mixed by a stopped flow method, and then the change of coagulation rate was measured by a low angle light scattering apparatus. The dependences of the coagulation rate on electrolytes, particles and polymers were investigated. Following results were obtained.1) The rapid coagulation rate constant for colloidal particles smaller than about 100 nm in diameter decreases with decreasing particle size.2) The rapid coagulation rate constant for colloidal particles smaller than about 100 nm in diameter decreases with increasing hydration enthalpy of cations and de-creasing enthalpy of anions.3) The rapid coagulation rate at the excessively high electrolyte concentration de-creases with the increasing concentration.4) Flocs formed with ultrafine particles were hardly deflocculated by external forces.5) These results imply that the stability of particles smaller than about 100 nm in diameter is not consistent with the DLVO theory and the coagulation rate can not be predicted by the Smoluchowski theory.6) The flocculation rate of particles with polymers adsorbed on the surface in-creases with the increase of the polymer size normalized by the particle diameter.