Regensburg 2010 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: Interfaces and Thin Films I

CPP 17.5: Vortrag

Dienstag, 23. März 2010, 11:00–11:15, H39

Delayed Coalescence of Sessile Droplets with Different but Miscible Liquids — •Stefan Karpitschka and Hans Riegler — Max-Planck-Institut für Kolloid- und Grenzflächenforschung, 14476 Potsdam, Germany

Due to capillary forces two sessile droplets of miscible liquids will fuse when they get in contact with each other. Usually the droplet fusion proceeds very fast, delayed mostly by viscous forces. However, quite unexpected, it was observed recently [1] that the coalescence of sessile droplets of completely miscible liquids can be delayed up to minutes. After first contact, the droplets remain separated by a thin liquid neck and push each other across the substrate before they finally merge.

It is assumed [1] that the coalescence is delayed by a marangoni convection through the thin film connecting the drops. This suggests that the effect is quite common. Meanwhile it could also be modeled in the framework of phase field formalism and lubrication approximation [2]. The delayed coalescence may be relevant for technical applications, e.g. in the field of microfluidics.

We present new results from experiments addressing the influence of the liquid properties on the coalescence behavior. A sharp transition from fast to delayed coalescence is observed when the difference in surface tensions exceeds approximately 4 mN/m. Other parameters like absolute surface tensions, viscosities, and contact angles have been varied to generate a phase diagram of coalescence.

[1] H. Riegler et al., Langmuir 24, 6395-6398, 2008.

[2] R. Borica et al., Phys. Fluids, submitted.