(328e) Characterizing Steady-State Size and Structure of Aggregates Outside the Limits of the Rayleigh-Debye-Gans Theory with Small-Angle Static Light Scattering and Image Analysis

Ehrl, L. - Presenter, ETH Zurich
Morbidelli, M. - Presenter, Institute of Chemical and Bioengineering, ETH Zurich

The steady-state size and structure of aggregates outside the limits of the Rayleigh-Debye-Gans theory produced under turbulent conditions in stirred tank (using polystyrene latexes with primary particle sizes equal to 810nm, 420nm, and 120nm) was studied experimentally for various values of the volume average shear rate and solid volume fraction. The steady-state aggregate structure was characterized by image analysis of two-dimensional pictures of the aggregates obtained by confocal microscopy and compared to the value of the scaling exponent evaluated from light scattering data. The mass fractal dimension showed to be invariant to primary particle size and applied shear rate with a value equal to 2.64±0.18 for all primary particle sizes investigated. The cluster mass distributions were characterized by two characteristic moment ratios, i.e., the root-mean-square radius of gyration and the zero angle intensity, obtained from small-angle static light scattering. The root-mean-square radius of gyration for all studied conditions follows a power-law scaling with the volume average shear rate with an exponent equal to -1/2, which is in agreement with data published in the literature. Relating the two measured moments of the cluster mass distribution with the independently measured aggregates structure can be used to evaluate the effect of multiple scattering within the aggregates.