ARRA: Dynamics of Capillary Threads and High-Viscosity Droplets in Mircofluidic Systems

0932925 Cubaud This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This study describes an integrated suite of activities for the precise manipulation of high-viscosity fluids in a sheath of immiscible less viscous fluids at the small-scale. Microfluidics is a fast developing field, yet investigations of multi-fluids flows with large viscosity contrasts have remained limited. Numerous industrial and biological fluids such as heavy oils and solvents, however, exhibit widely varying viscosities. Their manipulation at the small-scale would provide new capabilities for lab-on-chip devices. Transparent high-pressure microdevices will display the mechanisms associated with the lubrication of high-viscosity materials in small fluidic passages. Two investigations are planned. The first pursues the dynamics of viscous core-annular flows in diverging-converging microfluidic chambers. Buckling instabilities of slender viscous structures in diverging microchannels will be exploited to control the threads morphology and induce breakup. The stability of thin intercalating films between threads and microchannel walls will be investigated for formation of ripples and forced wetting phenomena. The second investigation studies high-viscosity droplets in chambers and physicochemical stratifications. The hydrodynamic coupling and coalescence between high-viscosity droplets will be examined in extensional geometries. The PI will investigate the possibility to enhance micromixing by inducing coalescence between low- and high-viscosity droplets. Finally, physicochemical stratifications injected in cross-flow will engineer viscous droplets. This system will provide a simple model of multi-step flow reactors. This research program will characterize novel fluid behaviors in a relatively unexplored region of microscale multi-fluid flows. In particular, the alteration of convective time-scales using extensional microgeometries permits the manipulation of complex phenomena such as buckling, wetting, coalescence, breakup, and relaxation of highly-viscosity microstructures. Simple flow geometries will elucidate the interrelation between these phenomena. This study will integrate a systematic experimental approach with numerical simulations and theoretical predictions to aid development of next-generation microfluidic devices. This work combines research and training of a large spectrum of students, including underrepresented, high school, undergraduate, and graduate students. A central objective of the educational activities is to attract and nurture students in the science and engineering fields. An important aspect of this project is to devise methods to control novel continuous emulsification processes between highly viscous oils and solvents, such as ethanol. Thus, the technical expertise that will be developed can potentially provide disruptive advances for making more efficient engines, enhancing oil recovery, and developing continuous multi-step flow reactors for bio-fuel production.