Multiple scattering effects on intercept, size, polydispersity index, and intensity for parallel (VV) and perpendicular (VH) polarization detection in photon correlation spectroscopy

Ragy Ragheb,Ulf Nobbmann

doi:10.1038/s41598-020-78872-4

Abstract

Dynamic light scattering (DLS) is well established for rapid size, polydispersity, and size distribution determination of colloidal samples. While there are limitations in size range, resolution, and concentration, the technique has found ubiquitous applications from molecules to particles. With the ease of use of today’s commercial DLS instrumentation comes an inherent danger of misinterpretation or misapplication at the borderlines of suitability. In this paper, we show how comparison of different polarization components can help ascertain the presence of unwanted multiple scattering, which can lead to false conclusions about a sample’s mean size and polydispersity. We find that the contribution of multiple scattering events effectively reduces both the measured scattering intensity and the apparent size from the autocorrelation function. The intercept of the correlation function may serve as an indicator of relative strength of single to multiple scattering. Furthermore, the abundance of single scattering events at measurement positions close to the cell wall results in an apparent increase in uniformity yielding a lower polydispersity index which is more representative of the physical system.

Highlights

In dynamic light scattering (DLS), the scattered light from a dispersion containing diffusing particles is correlated with itself
The decay rate of each single-scattering exponential decay function leads to the corresponding translational diffusion coefficient, D, given by the thermal energy divided by the viscous drag of a particle
We observe a general decrease in the Derived Count Rate (DCR) for all three traces because multiple scattering events in a typical path increase as the measurements position goes further into the cuvette

Summary

Introduction

In dynamic light scattering (DLS), the scattered light from a dispersion containing diffusing particles is correlated with itself. Further observable effects of multiple scattering from higher particle concentrations include a decrease in the Y-intercept of the correlogram, a decrease in apparent average size, and an increase in polydispersity. Multiple scattering of stock commercial whole milk as an analyte with both high and low concentrations at different measurement positions affect the scattered light detected through a vertical and horizontal polarizer.

Results

Conclusion