Atomistic simulations of nematic phases formed by cyano-biphenyl dimers

Abstract

Molecular dynamics simulations of selected members of the cyano-biphenyl series of dimers (CBnCB) have been set up using atomistic detail interactions among intermolecular pairs of united atoms and allowing fully for the flexibility of the spacer chain. Detailed results are presented for the CB7CB dimers, showing an isotropic fluid phase and two nematic phases. The positional and orientational correlation functions extracted from the simulations are used to elucidate the structure of the low-temperature nematic phase. Polar molecular ordering is clearly identified along a direction undergoing helical twisting at right angles to the helical axis, with a constant pitch of about of 8nm. The local ordering of the various molecular segments is calculated and found to be in excellent agreement with experimental NMR measurements. Key findings of the simulation are shown to be correctly predicted by the theoretical model of the polar-twisted nematic (NPT) phase [A.G. Vanakaras, D.J. Photinos, Soft Matter. 12 (2016) 2208-2220]. The complete failure of the usual twist bend model (NTB) to account for these findings is demonstrated.

23 pages, 7 figures, 3 tables

References in corpus (5)

• Thermotropic Biaxial Nematics: Spontaneous or Field-Stabilized?
• Molecular organization in the twist-bend nematic phase by resonant X-ray scattering at the Se K-edge and by SAXS, WAXS and GIXRD
• Extending the Maier-Saupe theory to cybotactic nematics
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Cited by in corpus (4)

• The Twist Bend Nematic: A Case of Mistaken Identity
• Probing Molecular Ordering in the Nematic Phases of para-Linked Bimesogen Dimers through NMR Studies of Flexible Prochiral Solutes
• In silico study of liquid crystalline phases formed by bent-shaped molecules with excluded-volume type interactions
• Dipole-dipole correlations in the nematic phases of symmetric cyanobiphenyl dimers and their binary mixtures with 5CB