| Understanding of the near-surface behavior of colloidal particles is not only of fundamental interest in fluid mechanics and colloidal science, but also crucial for expanding the capabilities and applications of micro-scale fluidic devices. Many near-surface dynamic processes can be revealed and understood through accurate characterization of tracer particles using optical diagnostic techniques. One popular measurement method is evanescent wave illumination, which is capable of characterizing particle motion and position distribution within a few hundred nanometers of a surface.;In the first study, we present an experimental investigation of three-dimensional mobility of colloidal particles in the vicinity of a liquid-liquid interface through evanescent wave particle velocimetry. We demonstrate that particle mobility is hindered and anisotropic as a particle suspended in a less viscous liquid approaches the interface of two immiscible liquids. The measured hindered mobilities are in good agreement with reported hydrodynamic models.;The second part of this dissertation presents a probability model of tracer particles' intensities and positions in an evanescent field, through which the effects of particle size variation, particle-wall interactions and detection intensity threshold on the characterization of near-surface particles are studied. The implications for velocity measurements are also examined. Based on our theoretical model, Monte Carlo simulations of positions, sizes, and intensities of individual particles are developed. The inaccurate characterization of polydisperse particle ensemble, specifically the biased particle position distribution and particle depletion layer, is demonstrated using the simulated data. The findings lead to the development of a statistical analysis algorithm that incorporates particle size variation as a variable. Through both simulations and experiments, we demonstrate that this method provides more accurate information on the characterization of near-surface particles using evanescent wave illumination. |
