(198i) Mapping Evanescent Wave Scattering from Anisotropic Particles

Multiple experimental techniques have been developed over the past few decades to probe surface interactions in colloidal systems, which are typically a few ~kT in strength. Total Internal Reflection Microscopy (TIRM) is one such technique that measures the surface force experienced by a single spherical colloidal particle immersed in a liquid nearby, but not adhered to, a substrate. TIRM is suitable for measuring ~kT scale interactions because the technique utilizes a ‘thermal’ energy scale. Given that a broad range of colloidal particles in natural and synthetic systems are anisotropic, we are currently working to develop the conceptual framework and experimental tools to extend TIRM to anisotropic particles. Our hypothesis is that the morphology of scattered light from a particle will be a sensitive function of height and orientation. For this purpose, the scattering morphology of a spheroid at different heights and orientations is collected for sphere and ellipsoids in a map format as a standard reference for a "Scattering Morphology Resolved" - TIRM (SMR - TIRM) experiment. Results show a profound difference in the morphology of evanescent scattered light between spherical and ellipsoidal particles at various conditions. Mapping of this morphology with SMR-TIRM will be used to predict the height and orientation of the anisotropic particle at each frame, which provides an avenue to calculate the interaction energy for an anisotropic particle near a boundary.