THE EFFECT OF OVERLAP BETWEEN MONOMERS ON THE DETERMINATION OF FRACTAL CLUSTER MORPHOLOGY

Diffusion limited cluster aggregate (DLCA) morphology is studied as a function of monomeric particle overlap for finite sized clusters. The morphology is parameterized by both the fractal dimension D and the pr efactor k(0). For clusters created on a three-dimensional cubic lattic e we find D = 1.80 +/- 0.03 and k(0) = 1.30 +/- 0.07 when the spherica l monomers are in point contact. Both these values increase as overlap increases. Also presented is an analysis of the two-dimensional proje ction of these clusters in order to facilitate electron micrograph ima ges of real clusters. Quantitative relations between actual three-dime nsional cluster parameters such as cluster radius of gyration, fractal dimension and number of monomers per aggregate, and measurable two-di mensional quantities such as longest lengths and projected area are gi ven as a function of monomer overlap. Relationships between lengths ca n be explained only by use of the proper density correlation function and accounting for cluster anisotropy. Finally, we make an unsuccessfu l attempt to find the source of recent experimental discrepancies in t he prefactor k(0) in terms of a possible unknown degree of overlap. (C ) 1997 Academic Press.