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Issue 42, 2016
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Microscopic mechanism of thermomolecular orientation and polarization

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Recent molecular dynamics simulations show that thermal gradients can induce electric fields in water that are comparable in magnitude to electric fields seen in ionic thin films and biomembranes. This surprising non-equilibrium phenomenon of thermomolecular orientation is also observed more generally in simulations of polar and non-polar size-asymmetric dumbbell fluids. However, a microscopic theory linking thermomolecular orientation and polarization to molecular properties is yet unknown. Here, we formulate an analytically solvable microscopic model of size-asymmetric dumbbell molecules in a temperature gradient using a mean-field, local equilibrium approach. Our theory reveals the relationship between the extent of thermomolecular orientation and polarization, and molecular volume, size anisotropy and dipole moment. Predictions of the theory agree quantitatively with molecular dynamics simulations. Crucially, our framework shows how thermomolecular orientation can be controlled and maximized by tuning microscopic molecular properties.

Graphical abstract: Microscopic mechanism of thermomolecular orientation and polarization

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The article was received on 21 Aug 2016, accepted on 04 Oct 2016 and first published on 05 Oct 2016

Article type: Communication
DOI: 10.1039/C6SM01927G
Soft Matter, 2016,12, 8661-8665

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    Microscopic mechanism of thermomolecular orientation and polarization

    A. A. Lee, Soft Matter, 2016, 12, 8661
    DOI: 10.1039/C6SM01927G

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