Comparison of aggregation of rodlike and spherical particles: A fractal analysis

Different structure-analyzing methods were applied to experimental and computer generated two-dimensional clusters. The real structures formed at water-air interfaces from polydisperse, cylindrical-shape carbon (thickness: 35 μm; average length: 140 μm) and close to monodisperse, spherical-shape glass (75 μm diam) microparticles. The clusters were characterized by the fractal dimension (D_f) and the surface coverage (q) values in the case of individual clusters. For a series of different sized aggregates, the fractal dimension (D_f) was also evaluated from the ln q versus ln R_g functions where R_g is the radius of gyration. The fractal dimensions for individual clusters determined by box counting, sand box, and by correlation function methods, were compared with each other and with those obtained for the series of clusters. Using the above methods, the aggregation of cylindrical carbon and spherical glass particles was studied from a structural point of view. The surface of glass beads was rendered hydrophobic chemically. Changing the extent of silylation, lower and higher hydrophobic samples were obtained (Θ/water/=68° and 89°, respectively). Conforming the earlier results, the ln q versus ln R_g functions revealed a crossover during the growth in every investigated case, which was an indication of cluster reorganization after the primary growth. At the first (quasi-non-equilibrium) stage of aggregation, the fractal dimensions obtained for the carbon particles (D_f= 1.44±0.07), for the lower (D_f= 1.53±0.05), and for the higher hydrophobic (D_f= 1.43±0.05) glass particles, indicated the universality of the growth.