Frequency domain photon migration measurements of dense monodisperse charged lattices and analysis using solutions of Ornstein Zernike equations

Abstract

Isotropic scattering coefficient measurements were made of monodisperse polystyrene lattices of two different diameters of 144nm and 223nm and at volume fractions ranging from 0.15 to 0.22, using frequency domain photon migration measurements at wavelengths of 660, 685, 785 and 828nm. The isotropic scattering coefficient measurements were shown to be sensitive to the changing ionic strength (0.5–4mM, NaCl equiv.) of the dispersions exhibiting hindered scattering owing to structure at the lowest ionic strength values. Monte Carlo simulations and numerical solution of the Ornstein Zernike equations were used to compute isotropic scattering coefficients for comparison to measured values. The interaction potential was modeled as a hard sphere Yukawa potential and the Hypernetted Chain closure was used to solve the OZ equation. Effective particle charges were found after renormalization of the bare particle charge and used to predict the isotropic scattering coefficient. The model data were found to follow similar trends as experimental measurements. The refractive index of the particles has found to be an important factor for predicting experimental isotropic scattering coefficient values.