8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P9.54Tue 611:23-14:00Molecular alignment under thermal gradients: anon-equilibrium molecular dynamics studyFrank Römer 1 and Fernando Bresme 11 Department of Chemistry, Imperial College London, South Kensington Campus,SW7 2AZ, London, United KingdomA fundamental understanding of heat transport is needed to design high performance coolant.Thermal gradients are responsible for a number of interesting coupling effects, such as thermoelectricityor mass separation in electrolyte solutions and binary mixtures. A full microscopicexplanation of this phenomenon (Ludwig-Soret effect) is nonetheless still outstanding. Veryrecently we have uncovered novel physical effects by showing that temperature gradients caninduce molecular orientation or alignment in anisotropic molecules. This alignment, in the caseof polar fluids, results in strong ‘thermo-polarization’ effects, and sizable electrostatic fields [1].Computer simulations offer the opportunity to study such processes at a molecular level and enablethe computation of properties that are experimentally hard to obtain or not directly accessible.Non-equilibrium molecular dynamics (NEMD) simulations [2], where an energy or mass flux isapplied to the system, provides a route to determine transport properties directly. In this work weuse boundary driven NEMD to investigate the heat transport mechanism and molecular alignmentof diatomic molecules in thermal gradients. Thermal gradients induce alignment in non-polarfluids, showing that the concept of thermo-molecular orientation is general and dependent onmolecular anisotropy. The magnitude of the gradients needed to induce the effect is currentlyachievable, e.g., heating of metallic nanoparticles with light. This opens exciting possibilities tomanipulate molecular fluids. Moreover we find that the heat transport is anisotropic with regardsto the relative size of the molecular sites, with the larger sites transporting more heat. We havedeveloped a phenomenological model that quantitatively explains this trend in terms of the surfacearea accessible to each site.[1] F. Bresme, A. Lervik, B. Dick, S. Kjelstrup, Phys. Rev. Let. 101, 020602 (2008).[2] F. Bresme, J. Chem. Phys. 115, 7564 (2001).54