(550i) Simultaneous Characterization of Thermophoresis and Fluid Properties Using Multiple Particle Tracking Microrheology

Thermophoresis is the phenomenon that results in particle migration in a fluid driven by a temperature gradient. Existing literature has conflicting experimental results and descriptions of the fundamental mechanism of thermophoresis. However, potential applications utilizing thermophoresis are increasing, especially for biomolecular separations. The work presented here develops a process measure thermophoresis of dispersed fluorescent tracer particles and simultaneously measure the local rheological properties of the continuous phase using multiple particle tracking microrheology (MPT). MPT measures the Brownian motion of the embedded probe particles using their mean squared displacement to determine the rheological properties of the fluid. We characterize the particle motion induced by a unidirectional thermal gradient and, at the same time, measure the Brownian fluctuations perpendicular to the thermophoretic motion to measure rheology. In a Newtonian fluid, this technique validates the local temperature profile that drives the thermophoretic motion as correlated by the known temperature dependent viscosity. Measurements of thermophoretic motion are hindered by Rayleigh-Benard recirculation, thus these experiments are being designed for parallel observation in microgravity on the International Space Station. These techniques will be extended to thermophoretic motion of particles in non-Newtonian fluids such as polymer solutions and gels. A better understanding of the relationship between thermophoresis and material properties will allow for optimization of microfluidic device designed for effective and efficient bioseparations for enrichment methods for virus detection.