Polar nano-rods under shear: from equilibrium to chaos.
The orientational dynamics of rod-like particles with permanent (electric or magnetic) dipole moments in a plane Couette shear flow is investigated using mesoscopic relaxation equations combined with a generalized Landau free energy. The free energy contribution due to the coupling between average alignment and dipole orientation is derived on a microscopic basis. Numerical results of the resulting eight-dimensional dynamical system are presented for the case of longitudinal dipoles and thermodynamic conditions where the equilibrium state is a (polar or non-polar) nematic. Solution diagrams reveal presence of a large variety of periodic, transient chaotic, and chaotic dynamic states of the average alignment and dipole moment, respectively, appearing as a function of Deborah number and tumbling parameter. Compared to rods without dipoles we observe a significant preference of out-of-plane kayaking-tumbling states and, generally, a higher sensitivity to the initial conditions including bistability. We also demonstrate that the average (electric) dipole moment characterizing most of the observed states yields electrodynamic (magnetic) fields of measurable strength.
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Institut für Theoretische Physik, Sekr. PN 7-1, Technische Universität Berlin, Hardenbergstrasse 36, D-10623, Berlin, Germany.
Heidenreich
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Hess
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Klapp
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D003198:Computer Simulation; D004574:Electromagnetic Fields; D008956:Models, Chemical; D008958:Models, Molecular; D043942:Nanotubes / Q000737:chemistry* / Q000528:radiation effects* / Q000648:ultrastructure; D017711:Nonlinear Dynamics; D011829:Radiation Dosage; D033081:Shear Strength; D055672:Static Electricity