Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: POSTERS Micro- and Nanofluidics

CPP 22.6: Poster

Wednesday, February 27, 2008, 16:00–18:30, Poster A

Separation of Model Emulsions on Chemically Patterned Surfaces: Confinement, Hysteresis & Droplet Coalescence — •Pagra Truman, Petra Uhlmann, and Manfred Stamm — Leibniz-Institut für Polymerforschung, Hohe Str. 6, 01069 Dresden, Germany

Chemically patterned surfaces can be used to drive liquid flow along surfaces in microfluidic systems. In this work we investigate the separation of model emulsions consisting of an aqueous and a non-polar component on step gradient surfaces with one hydrophilic and one hydrophobic side. The separation is driven by the strong affinity of the aqueous component to the hydrophilic side.

Analysing the separation process in detail we identify droplet coalescence as a key phenomena during separation. Thus droplet coalescence in the presence of hydrophobic and hydrophilic surfaces in confinement and on open systems is studied. Surprisingly we find that the impact of surface wettability on droplet coalescence in confinement is opposite to the case of an open system. Introducing a simple theoretical model taking into account surface energy hysteresis we are able to explain such behaviour.