Light-scattering form factors of asymmetric particle dimers from heteroaggregation experiments

Abstract

Measurements of form factors of asymmetric particle dimers composed of oppositely charged polystyrene latex particles are presented. These measurements are based on time-resolved static and dynamic light scattering on dilute aggregating aqueous suspensions. The experimental form factors are compared with independent calculations based on the superposition T-matrix method and Rayleigh-Debye-Gans (RDG) approximation. While the RDG approximation is found to be reliable only up to particle diameters of about 250 nm, the superposition T-matrix method is very accurate for all types of dimers investigated. The present results show clearly the appropriateness of the superposition T-matrix method to estimate the optical properties of colloidal particles in the micrometer range reliably.

Progress in coagulation rate measurements of colloidal dispersions

“…16 The instrument resolution function is also generally ignored. 8,14,17 Therefore, by using the RGD theory, the scattered intensity of aggregates can be expressed as:…”

“…where V i is the volume of aggregate of i primary particles, and P i (q) is the so-called form factor, 14,17,18 which is equal to I i (q)/I i (0). By using RGD approximation, the form factor of the i-fold aggregate has the form:…”

“…Galletto et al 17 have compared the experimental form factors with calculations derived respectively by the T-matrix method and RDG approximation. Their measurements of form factors based on the SSDLS method were performed on dilute aggregating aqueous suspensions comprising asymmetric particle doublets composed of oppositely charged polystyrene latex particles.…”

A study on independently using static and dynamic light scattering methods to determine the coagulation rate

“…21,22 There have been some special efforts made in dealing with the optical factor of large particles, including the discrete dipole approximation (DDA) 23 modal analysis (MA). 24 Particularly, to bypass the difficulty in calculating the optical factor, the simultaneous static and dynamic light scattering (SSDLS) method was proposed and has successfully demonstrated its capability of determining the coagulation rates for large particles.…”

“…[25][26][27] The suitability of the T-matrix method was confirmed by comparing the experimentally obtained optical factors with that derived by the T-matrix method. 21 In turbidity measurement, we have effectively used T-matrix method in evaluating the extinction cross section of doublets to determine the coagulation rates of large sized particle dispersions. 14,15 It is supposed that if the T-matrix method is employed to achieve I 2 (q)/2I 1 (q), either SLS or DLS method should be able to be used alone in determining the coagulation rates, instead of combining both of them.…”