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CPP: Chemische Physik und Polymerphysik
CPP 8: SYMPOSIUM Nonequilibrium Phenomena in Soft-Condensed Matter
CPP 8.6: Vortrag
Dienstag, 28. März 2006, 15:15–15:30, ZEU Lich
The depinning transition of a driven droplet on a heterogeneous substrate — •Uwe Thiele1 and Edgar Knobloch2 — 1Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, D-01187 Dresden, Germany — 2Department of Physics, University of California, Berkeley CA 94720, USA
On non-ideal real substrates used in experiments the onset of droplet motion under driving along the substrate is strongly influenced by chemical or physical defects. A finite driving force is necessary to overcome the pinning influence of the heterogeneities occurring on a micro- or mesoscale. This is thought to be responsible, for instance, for the observed hysteresis between advancing and receding contact angles.
In the present paper we aim at understanding not only the processes that lead to pinning, but also the bifurcation that leads to depinning and the subsequent behavior of a moving droplet. We study driven droplets on a heterogeneous inclined plate using a long-wave evolution equation for the film thickness profile in two cases: (a) a periodic sinusoidal modulation of the disjoining pressure, and (b) strongly localized hydrophilic or hydrophobic ’defects’. As a result the drop may be pinned at the rear by an enhanced wetting region, or at its front by a region of reduced wettability. The results are obtained by a combination of branch following methods, linear stability theory and direct numerical simulation of the model equation.