ETH Polymer Physics seminar


2007-02-14
10:15 at HCI J 574

Boundary conditions for fluid flow: Apparent slip associated with the molecular alignment

Sebastian Heidenreich

Institute of Theoretical Physics, Technical University Berlin, Germany

In nano- and microfluidics the length scales of devices are comparable to the molecular lengths and fluid-wall interactions become significant for the flow behavior. In continuum mechanical descriptions fluid-wall interactions can be taken into account by special boundary conditions. Here the relaxation equation [1], an amended Landau-de Gennes potential [2] is used to model the spatially inhomogeneous orientational dynamics of the fluid and the momentum balance equation to couple the velocity on the orientational dynamics. In order to model fluid-wall interactions we use conditions on the alignment tensor as well as conditions on the alignment flux tensor (consequences of irreversible thermodynamics [3]). We show analytically that for stationary flows in the isotropic phase for special geometries (plane Couette, plane Poiseuille, cylindrical Couette and a flow down an inclined plane) boundary conditions on the alignment flux tensor lead to an apparent velocity slip and to a decrease of the effective viscosity. Furthermore the interplay between the flow velocity and the orientational dynamics in the non-Newtonian flow regime and in the nematic phase is considered. Preliminary results are presented. [1] S. Hess, Z. Naturforsch. 30a, 728, 1224 (1975) [2] S. Heidenreich, P.Ilg and S. Hess, Phys. Rev. E 73, 061710 (2006) [3] L. Waldmann, Z. f. Naturf. 22a, 1269 (1967); L. Waldmann and H. Vestner, Physica 99A, 1 (1979); S. Hess and H. M. Koo, J. Non-Equilibrium Thermodyn. 14, 159 (1989); H. Vestner, Z. f. Naturforsch. 28a, 869, (1973).


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