Discrete microfluidics: manipulation of gel emulsions in confined geometries

• Applicants: Martin Brinkmann, Ph.D.; Professor Dr. Ralf Seemann
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2008 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 67909302

• Final Report Year: 2014

Final Report Abstract

At volume conservation static packings of droplets in confining channel geometries are determined by minimizing their surface energy. In certain parameter ranges, i.e. for certain confinement ratios and volume fractions, the droplet packings can have a negative compressibility and are thus mechanically unstable. In this regime the coexistence of two packing geometries can be observed. The experimental observations in shallow quasi 2d channels agree quantitatively with the theoretical results obtained for a 2d system. Surprisingly, the same behavior could be found also for slowly moving droplet packings. A mechanically stable droplet packing remains intact when moving along a straight microfluidic channel. A mechanically homogeneous unstable droplet packing decays into segments of the two stable droplet packings when moving slowly along a microfluidic channel. For increasing flow velocity the segments of the stable droplet packing increase in length. For sufficiently large flow velocity the droplet packings show an irregular behavior that can possibly be explained by the transport limitation of the microfluidic channel for those droplets using the typical ‘traffic jam models’. The research on the dynamic aspects is still ongoing. Not only is the packing of droplets in linear micro-channels governed by the buildup of interfacial stresses, also the contact forces between colliding droplets need to be considered to understand the passive sorting behavior at a T-junction. The role of direct interactions between consecutive droplets could be demonstrated in numerical simulations of droplets flowing in flat micro-channels. Different dynamic sorting regimes could be identified in good agreement the results of microfluidic experiments.

Publications

• “Topological transition in a stack of water droplets” Proc. 2nd Europ. Conf. Microfluidics, December 8-10, 2010, µFLU10-221
  J.-B. Fleury, O. Claussen, S. Herminghaus, M. Brinkmann, R. Seemann
  
• “Mechanical stability of ordered droplet packings in microfluidic channels” Applied Physics Letters 99 (2011) 244104
  J.-B. Fleury, O. Claussen, S. Herminghaus, M. Brinkmann, R. Seemann
  
• “Microfluidic Method to specifically excite transversal phonon modes in one dimensional microfluidic crystal” Proc. 3rd Europ. Conf. Microfluidics, December 3-5, 2012, µFLU12-185
  J.-B. Fleury, U. D. Schiller, S. Thutupalli, G. Gompper, R. Seemann
  
• “Packings of monodisperse emulsions in flat microfluidic channels”, Phys. Rev. E 85 (2012) 061403
  O. Claussen, S. Herminghaus, and M. Brinkmann
  
• “Topological Transition in a Stack of Water Droplets” Special Issue IJMNTFTP Issue 1 Vol. 3 (2012)
  J.-B. Fleury, E. Surenjav, S. Herminghaus, M. Brinkmann, R. Seemann
  
• “Droplet sorting in a microfluidic loop”, J. Phys.: Condens. Matter 25 (2013) 285102
  E. Kadivar, S. Herminghaus, and M. Brinkmann
  
• „Why can artificial membranes be fabricated so rapidly in microfluidics?“ Chem. Commun. (2013)
  S. Thutupalli, J.-B. Fleury, A. Steinberger, S. Herminghaus, R Seemann
  
• “Mode Coupling of Phonons in a dense one-dimensional microfluidic crystal” New Journal of Physics (2014)
  J.-B. Fleury, U. D. Schiller, S. Thutupalli, G. Gompper, R. Seemann