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Molecular Interactions in Chiral Nematic Liquid Crystals and Enantiotopic Discrimination through the NMR Spectra of Prochiral Molecules I: Rigid Solutes

October 13th, 2016 Comments off

Anant Kumar, Alexandros G. Vanakaras and Demetri J. Photinos, J. Phys. Chem. B, Article ASAP DOI: 10.1021/acs.jpcb.6b07404

ABSTRACT: We have developed a molecular theory for enantiotopic discrimination in prochiral solutes dissolved in chiral nematic solvents by means of NMR spectroscopy. The leading rank tensor contributions to the proposed potential of mean torque include symmetric as well as antisymmetric terms with respect to spatial inversion; these lead to consistent determination of all prochiral solute symmetries for which enantiotopes are distinguishable by NMR and also to excellent quantitative agreement when tested against the available experimental data for the rigid solutes acenaphthene and norbornene as well as for the moderately flexible ethanol molecule.

Categories: 2016, A. G. Vanakaras, D.J. Photinos, Paper Tags:

On the structure of the Nx phase of symmetric dimers: inferences from NMR

December 19th, 2014 Comments off
Anke Hoffmann,   Alexandros G. Vanakaras,   Alexandra Kohlemeir,   Georg H. Mehl and   Demetri J. Photinos
Soft Matter, 11, 850-855, 2015. DOI: 10.1039/C4SM02480J (download:
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Abstract: NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, NX, experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies.
Categories: 2014, A. G. Vanakaras, D.J. Photinos, Paper Tags:

On the structure of the Nx phase of symmetric dimers

December 4th, 2014 Comments off

Anke Hoffmann, Alexandros G. Vanakaras, Alexandra Kohlmeier, Georg H. Mehl, Demetri J. Photinos, arXiv:1401.5445 [cond-Mat]. (2014). http://arxiv.org/abs/1401.5445.

Abstract: NMR measurements on a selectively deuteriated liquid crystal dimer CB-C9-CB exhibiting two nematic phases show that the molecules in the lower temperature nematic phase, Nx, experience a chiral environment and are ordered about a unique direction. The results are contrasted with previous reports that proposed a twist-bend spatial variation of the director. A structural model is proposed wherein the molecules show organization into highly correlated assemblies of opposite chirality.

Categories: 2014, A. G. Vanakaras, D.J. Photinos Tags:

Light scattering by a metallic nanoparticle coated with a nematic liquid crystal

November 25th, 2012 Comments off

V. Yannopapas, N. Fyttas, V. Kyrimi, E. Kallos, A.G. Vanakaras, D.J. Photinos, PSSA, DOI: 10.1002/pssa.201228489.

We study the optical properties of gold nanoparticles (NPs) coated with a nematic liquid crystal (NLC) whose director field is distributed around the NP according to the anchoring conditions at the surface of the NP. The distribution of the NLC is obtained by minimization of the corresponding Frank free-energy functional whilst the optical response is calculated by the discrete-dipole approximation (DDA). We find, in particular, that the anisotropy of the NLC coating does not affect much the (isotropic) optical response of the NP. However, for strong anchoring of the NLC molecules on the surface of NP, the inhomogeneity of the coating which is manifested by a ring-type singularity (disclination or Saturn ring), produces an enhancement of the extinction cross spectrum over the entire visible spectrum.