Light Scattering Techniques for the Determination of Mass Diffusivities in Molecular and Particulate Systems

Description

The aim of this thesis is to further develop and evaluate light scattering techniques, namely the dynamic light scattering (DLS), the shadowgraph method, and the differential dynamic microscopy (DDM), for the accurate determination of mass diffusivities in molecular and particulate systems. All of the aforementioned techniques are based on the temporal analysis of fluctuations in the intensity of scattered light. Their experimental realizations, however, differ significantly. While DLS typically detects scattered light in the far-field, the shadowgraph method and DDM analyze the scattered light in the near-field. Moreover, the shadowgraph method relies on the formation of non-equilibrium fluctuations in fluid density in the presence of macroscopic temperature and concentration gradients, whereas DLS and DDM can be applied to systems that are in thermodynamic equilibrium. In this work, DLS and the shadowgraph method were applied to determine the Fick diffusion coefficient in molecular systems. DLS and DDM methods were applied to determine the particle diffusivity in particulate systems. Based on the findings, the distinctions between these light scattering techniques in terms of experimental complexity, data analysis, applicability to various systems, and attainable uncertainty are identified. Guidelines regarding their applicability for the accurate determination of mass diffusivity are presented.