Title

Computational assessment of an effective-sphere model for characterizing colloidal fractal aggregates with holographic microscopy

Document Type

Article

Publication Date

10-1-2019

Abstract

© 2019 Elsevier Ltd We perform simulations to evaluate a recent experimental technique for using in-line holographic microscopy and an effective-sphere model to measure the population-averaged fractal dimension Df of an ensemble of colloidal fractal aggregates. In this technique, models based on Lorenz–Mie scattering by a uniform sphere are fit to digital holograms of a population of fractal aggregates to determine the effective refractive indices neff and effective radii aeff of the aggregates. A scaling relationship between neff and aeff based on the Maxwell Garnett effective-medium theory then determines Df. Here we use a multisphere superposition code to calculate the exact holograms produced by aggregates with tunable fractal dimensions Df. We show that neff and aeff become less sensitive to the aggregate orientation as Df increases. We also show that the Maxwell Garnett scaling relationship correctly determines Df to within 10.5% when multiple scattering is negligible and the population-averaged coefficient of determination ⟨R2⟩p > 0.6, indicating that the holograms are well-described by the effective-sphere model.

Publication Name

Journal of Quantitative Spectroscopy and Radiative Transfer

Volume Number

236

DOI

10.1016/j.jqsrt.2019.106591

Article

106591

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