Simulation studies of dipole correlation in the isotropic liquid phase |
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Authors: | Melanie J Cook Mark R Wilson |
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Institution: | Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK |
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Abstract: | The Kirkwood correlation factor g1 determines the preference for local parallel or antiparallel dipole association in the isotropic phase. Calamitic mesogens with longitudinal dipole moments and Kirkwood factors greater than 1 have an enhanced effective dipole moment along the molecular long axis. This leads to higher values of Δ? in the nematic phase. This paper describes state-of-the-art molecular dynamics simulations of two calamitic mesogens 4-(trans-4-n-pentylcyclohexyl)benzonitrile (PCH5) and 4-(trans-4-n-pentylcyclohexyl)chlorobenzene (PCH5-Cl) in the isotropic liquid phase using an all-atom force field and taking long range electrostatics into account using an Ewald summation. Using this methodology, PCH5 is seen to prefer antiparallel dipole alignment with a negative g1 and PCH5-Cl is seen to prefer parallel dipole alignment with a positive g1; this is in accordance with experimental dielectric measurements. Analysis of the molecular dynamics trajectories allows an assessment of why these molecules behave differently. |
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