(142bg) Drop Circulation and Liquid-Liquid Extraction in Hele Shaw Flow

Understanding interfacial mass transport on a droplet scale is essential for modeling liquid-liquid extraction processes. A model system is investigated whereby neodymium is extracted from buffered aqueous droplets to a continuous phase of dodecane, tributyl phosphate and thenoyltrifluoroacetone. A thin flow-focusing channel is used to generate monodisperse aqueous phase droplets of varying size, with drop diameter to channel height ratios ranging from 0.5 to 2.  Liquid streamlines within the droplets are inferred by particle tracking, revealing a fountain flow recirculation pattern.  Larger droplets that are more confined in the channel move with a slower velocity relative to the continuous fluid and have a stronger recirculation pattern in the plane of the microfluidic chip.  Knowledge of the recirculation pattern is then applied to understand species mass transfer from the droplet fluid.  Quantitative mass transfer measurements are obtained using high speed imagery and spectrophotometry for various flow rates and droplet sizes.

This research is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.