Regensburg 2002 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 17: Kritische Ph
änomene und Phasenumwandlungen II

DY 17.4: Vortrag

Montag, 11. März 2002, 17:00–17:15, H3

Spontaneous orientational order in confined thin dipolar liquid films — •Sabine Klapp and Martin Schoen — Stranski-Laboratorium für Physikalische und Theoretische Chemie, Sekretariat TC 7, Technische Universität Berlin, Strasse des 17. Juni 124, 10623 Berlin, Germany

Monte-Carlo simulation results are reported for systems of strongly interacting dipolar soft spheres confined between structureless planar walls with separation L_z. The simulations are performed in the (N,L_z,P_∥,T) ensemble, P_∥ being the pressure parallel to the walls. All calculations are started from orientationally disordered states. Choosing T and P_∥ such that the corresponding bulk system is a polarized nematic fluid, the microscopic structure of confined films with various thicknesses is investigated. At the highest L_z considered (L_z=14σ), spontaneous polarization does occur, and the orientational order parameters and thermodynamic quantities are close to the bulk values. The global director points parallel to the walls, as understandable from the properties of the dipolar interaction. With decreasing L_z, the system undergoes significant changes not only in the translational structure (layering), but also orientationally. In particular, the global polarization and (to a smaller extent) the nematic order parameter exhibit pronounced oscillations as functions of L_z, indicating that orientational and spatial order are strongly coupled. The thinnest films (L_z=1.6−1.8σ) investigated are essentially unpolarized, whereas the nematic order parameter is still quite large.