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CPP: Chemische Physik und Polymerphysik

CPP 24: POSTER Microfluidics

CPP 24.5: Poster

Donnerstag, 30. März 2006, 17:00–19:00, P2

Wetting random assemblies of cylindrical rods — •Martin Brinkmann — Max-Planck-Institut for Dynamics and Self-Organization, Bunsenstr.10, D-37073 Goettingen, Germany

The mechanical properties of loose random assemblies of rigid rods undergo a significant change when a liquid phase is dispersed in between the bodies. In experiments a strong tendency to form bundles of rods is obseverd. The anisotropic capillary interaction between cylindrical rods can be obtained from numerical minimizations of the interfacial energy and, for elongated liquid states, computed in an analytical model. As the relative tilt angle α of the cylinders tends to zero the liquid spreads between the two clyinders. If the surfaces are in contact the wetted length L and the capillary torque T diverge as L∝α^−ξ and T∝α^−(ξ+1), respectively, for hydrophilic contact angles θ<π/2. As predicted from the analytical model and confirmed by numerical minimizations one has ξ=1 if the Laplace pressure of the bridge is prescirbed while ξ=3/4 if the volume of the liquid of bridge is fixed. In the latter case, one finds a discontinuous transition between droplets localized at the contact point for α≈ 1 and elongated liquid filaments for small tilt angles α≪ 1. The capillary force F between the cylinders is studied for a variety of fixed tilt angles including the particular cases α=π/2 and α≪ 1 .