(450a) Mapping Evanescent Wave Scattering Form 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. We are currently working to develop the conceptual framework, experimental tools, and scattering model to extend TIRM to geometrically anisotropic particles. As part of this development, the morphology of light scattered by a micrometer scale polystyrene spheroid from an evanescent wave was measured while the particle was fixed at different heights and orientations. Experimental results showed the scattered morphology depended on orientation and aspect ratio of the particle. A complementary light scattering model based on the T-Matrix method was also developed to simulate 2D images of the scattered during an experiment. We expect to utilize these data as a map for "Scattering Morphology Resolved TIRM” (SMR - TIRM) to calculate the position and orientation of anisotropic colloids near a boundary to obtain the particle’s potential energy landscape.