(494a) Probing Viscosity of Complex Emulsions with Micro-Rheometry

Rapid in-situ characterization of emulsions is of direct relevance to the chemical processing industry. Conventional surface science and rheological tools require large sample volumes and possess well-known limitations. For instance, a pendant drop tensiometer is inaccurate for fluids with a low density and optical contrast and a rheometer is chiefly developed for probing viscosities at a macro scale. Microfluidics provide the opportunity to probe rheological and interfacial properties of emulsions at the single drop level.

Current microfluidic methods focus on using pressure driven flow through various geometries to investigate shear response of single phase fluids (Newtonian and non-Newtonian). We extend this approach to design lab on a chip devices for simultaneous measurement of viscosity and interfacial tension in two phase droplet flows. A PDMS based device is micro-fabricated and coupled to a pressure driven Labview controlled system to generate emulsions with high mono-dispersity. The dispersed phase droplets are systematically perturbed by tuning the flow field in the dispersed phase. High speed camera imaging is used to record the drop deformations. Drop shapes are compared to analytical models for drop shape relaxation (after an initial well-defined deformation) and viscosity and interfacial tension are obtained by direct comparison of experiments with theory.