Perikinetic Aggregation of Alkoxylated Silica Particles in Two Dimensions

Aggregation and cluster formation of a two-dimensional colloidal system consisting of 2-µm alkoxylated silica particles trapped at the air-toluene interface have been studied. This novel system allows particle interactions to be controlled by varying the length of the grafted alkyl chains; simple estimates suggest particle bond strengths of 15 and 30 kT for the octadecyl- and octyl-coated system, respectively. Video-enhanced microscopy and image analysis enabled a simultaneously study of kinetics and structure of the ensemble of clusters in situ. The octyl system displayed a DLCA-like structure, D(f) approximately 1.45, whereas the octadecyl system resulted in a more dense structure, D(f) approximately 1.55. The temporal evolution of the cluster-mass distribution displayed a transition point between regimes of slower and faster aggregation for both systems, which was interpreted as a transition from DLCA to convection-limited cluster aggregation (CLCA). Copyright 1999 Academic Press.