for a variety of colloidal and aerocolloidal aggregates includ-Diffusion limited cluster aggregate (DLCA) morphology is studing soot. Until recently, however, the prefactor has been ied as a function of monomeric particle overlap for finite sized ignored. Its accepted importance has been increasing because clusters. The morphology is parameterized by both the fractal of its relation to cluster mass, transport, and light scattering dimension D and the prefactor k 0 . For clusters created on a threeproperties. Wu and Friedlander (8) reviewed a variety of dimensional cubic lattice we find D Γ
1.80 { 0.03 and k 0 Γ
1.30 simulation and real system data to find that k 0 was of order { 0.07 when the spherical monomers are in point contact. Both unity. Work from this laboratory has measured k 0 Γ
1.23 { these values increase as overlap increases. Also presented is an 0.07 (9) and 1.66 { 0.4 (6) for soot from two different analysis of the two-dimensional projection of these clusters in orflames and our DLCA simulations have found k 0 Γ
1.2 { der to facilitate electron micrograph images of real clusters. Quantitative relations between actual three-dimensional cluster parame-0.15 (10). In contrast, Samson et al. (4) found D Γ‘ 1.44 ters such as cluster radius of gyration, fractal dimension and numand k 0 Γ‘ 3.4 using stereo views of 3d aggregates. Using the ber of monomers per aggregate, and measurable two-dimensional data of Samson et al., Puri et al. (11) also found D Γ‘ 1.40 quantities such as longest lengths and projected area are given as and k 0 Γ‘ 3.5. Independently, Koylu et al. (12) found D Γ‘ a function of monomer overlap. Relationships between lengths can 1.64 and k 0 Γ‘ 2.4 using stereo views of 3d aggregates and be explained only by use of the proper density correlation function have supported this value of k 0 with subsequent studies (13and accounting for cluster anisotropy. Finally, we make an unsuc-15). Considering the role of D and k 0 in describing light cessful attempt to find the source of recent experimental discrepanscattering from fractal aggregates it is important to rectify cies in the prefactor k 0 in terms of a possible unknown degree of the discrepancies among the experimental values.
overlap. α§ 1997 Academic Press
With this motivation and given the simulation result of k 0 Γ
1.2 we ask, how could the morphology of soot differ from flame to flame and especially from ideal aggregates as some of the results above imply? Perhaps the answer to this