Surfactant-Mediated Interfacial Flows at the Microscale

Uniform submicron emulsions have unique properties including enhanced stability, improved optical properties, and the ability to permeate the skin barrier, promoting effective release of active pharmaceuticals in the body. Generating these materials is challenging, since conventional approaches involve high shear mixing that allow for little-to-no control of size distribution.  We use a fluid dynamical phenomenon called “tipstreaming” to produce uniform submicron droplets robustly and continuously in a microfluidic flow-focusing device. We have developed scaling criteria describing the operating conditions for tipstreaming by using experimental observations and considering the competing timescales for convection and adsorption.

Droplet-based processing strategies are also promising for lab-on-a-chip devices due to their precise volumes, protection of encapsulated materials, and ability to be easily manipulated. To use droplets effectively, there is a need for simple design rules that can enable development; however, nontrivial geometries and flow fields in microfluidic devices hinder the quantitative analysis of droplet behaviors. We have used experiments and dimensional analysis to establish scaling arguments elucidating which of the many geometric and flow parameters are important in drop formation, tipstreaming, coalescence, splitting, and packing of concentrated emulsions. The resulting semi-empirical relationships provide useful design rules for the implementation of droplet-based microfluidic devices. Our current interests focus on using transport within microscale droplets to control separation and crystallization processes.

Funding: NSF CBET 1033814, NSF CBET 0934456, NSF CBET 0735359, ACS PRF-G

Current Students: Chris Nelson, Todd Moyle, Sharon Vuong, Anthony Kotula

Former Students: Wingki Lee, Gordon Christopher, Hans Mayer, Maria Poon, Nadia Noharrudin, Aaron Greiner

Collaborators: Lynn Walker

Related Publications

T.M. Moyle, L.M. Walker, and S.L. Anna, “Predicting conditions for microscale surfactant-mediated tipstreaming,” submitted.

A.P. Kotula and S.L. Anna, “Probing timescales for probing particle adsorption using slug bubbles in rectangular microchannels,” submitted.

S.M. Vuong and S.L. Anna, “Tuning Bubbly Structures in Microchannels,” Biomicrofluidics, Special Issue on Multiphase Microfluidics, Guest Ed. Saif Khan, 6 (2012) 022004.

W. Lee, L.M. Walker, and S.L. Anna, “Competition between Viscoelasticity and Surfactant Dynamics in Flow Focusing Microfluidics,” Macromolecular Materials and Engineering, Special Issue on Rheology, Mixing, and Flow of Polymeric Materials, 296 (2011) 203-213.

G.F. Christopher and S.L. Anna, “Passive breakup of viscoelastic droplets and filament self-thinning at a microfluidic T-junction,” Journal of Rheology 53 (2009) 663-683.

W. Lee, L.M. Walker and S.L. Anna, “Role of geometry and fluid properties in droplet and thread formation processes in planar flow focusing,” Physics of Fluids 21 (2009) 032103.

G.F. Christopher, J. Bergstein, N.B. End, C. Nguyen, and S.L. Anna, “Coalescence and Splitting of Droplets at Microfluidic Junctions,” Lab on a Chip 9 (2009) 1102-1109.

G.F. Christopher, N.N. Noharuddin, J.A. Taylor and S.L. Anna, “Experimental observations of the squeezing-to-dripping transition in microfluidic T-junctions,” Physical Review E, 78 (2008) 036317.

W. Lee, L.M. Walker and S.L. Anna, “Impact of Viscosity Ratio on the Dynamics of Droplet Breakup in a Microfluidic Flow Focusing Device,” The XVth International Congress on Rheology, Monterey, CA, USA, August 2008.

G.F. Christopher and S.L. Anna, “Microfluidic methods for generating continuous droplet streams,” Journal of Physics D – Applied Physics, 40 (2007) R319-R336.

S.L. Anna and H.C. Mayer, “Microscale Tipstreaming in a Microfluidic Flow Focusing Device,” Physics of Fluids, 18 (2006) 121512.

G.F. Christopher, N. Noharuddin and S.L. Anna, “Droplet Breakup in Shear and Elongation Dominated Flows in Microfluidic Devices,” Proceedings of the IMECE2005, 2005 ASME International Mechanical Engineering Congress, November 5-11, 2004, Orlando, FL, IMECE2005-80625.

D.R. Link, S.L. Anna, H.A. Stone, and D.A. Weitz, “Geometrically-Mediated Breakup of Drops in Microfluidic Devices,” Physical Review Letters, 92 (2004) 054503.

S.L. Anna, N. Bontoux, and H.A. Stone, “Formation of dispersions using ‘flow-focusing’ in microchannels,” Applied Physics Letters, 82 (2003) 364-366.

H.A. Stone, S.L. Anna, N. Bontoux, D.R. Link, D.A. Weitz, I. Gitlin, P. Garstecki, W. DiLuzio, G.M. Whitesides, and E. Kumacheva, “Method and Apparatus for Fluid Dispersion,” U.S. Patent Application 60/392,195 & 60/424,042 and Intl. Patent Application PCT/US03/20542, June 3, 2003.