Aggregation kinetics in two dimensions: Real experiments and computer simulations

The aggregation of silanized glass spheres (75 +/- 5 mum diam) was studied experimentally at liquid-air (water-air, aqueous surfactant solution-air, a nd aqueous glycerol solution-air) interfaces from a kinetic point of view. The number the size, and the polydispersity of clusters was Investigated as a function of time. Particles having water contact angles of approximate t o 30 degrees (lower hydrophobic sample) and approximate to 82 degrees (high er hydrophobic sample) were prepared and used in the aggregation experiment s. In the early stage of aggregation the kinetics was found to be-of the se cond order. The-experiments revealed that the increasing particle hydrophob icity increased the rate constants in every case, which could be attributed to the increasing particle-particle attractions and the decreasing hydrody namic resistance of particles (clusters) to motion. Moreover, the lower hyd rophobicity of particles manifested itself in a more important polydispersi ty of clusters and an unexpected cross-over during the growth. The cluster- cluster aggregation was succeeded by a particle- (large) cluster aggregatio n after the first (initial) part of the growth. An off-lattice computer sim ulation of cluster-cluster aggregation, based on molecular dynamics, was al so developed for the better understanding of the interfacial aggregation. T he simulations supported well the conclusions derived from the real experim ents, and gave an indispensable possibility for the study of the effect of single parameters on the complex phenomenon. (C) 2001 American Institute of Physics.