Dresden 2014 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 10: Wetting, Micro and Nanofluidics

CPP 10.1: Vortrag

Montag, 31. März 2014, 15:00–15:15, ZEU 114

Capillary focusing: New Breakup Regimes in Step-Emulsification — •Michael Hein¹, Shahriar Afkhami², Lou Kondic², and Ralf Seemann¹ — ¹Experimental Physics, Saarland University — ²Department of Mathematical Sciences, New Jersey Institute of Technology

Droplet based microfluidics has become very popular, both in research and application. But despite of a large number of studies on the droplet breakup, the physics behind this mechanism is only poorly understood. We present experimental research on the formation of droplets in a particular step-geometry by the breakup of a liquid filament. This non-equilibrium process arises from the interplay between flow properties and interfacial instabilities when the filament is suddenly released from a quasi 2d confinement at a topographic step. In particular we investigate the transition between two breakup mechanisms: the 'step-regime' where small droplets are generated just at the step and the 'jet-regime', where larger droplets are formed at some distance after the step. We provide experimental evidence that the breakup mechanism can be controlled by tuning the Capillary number and the channel geometry, which is supported by numerical simulations using the volume-of-fluid method. Interestingly, we observe new breakup mechanisms appearing during the transition from the 'step-' to the 'jet-regime' for large aspect ratios of the liquid filament.