All Structures Great and Small: Nanoscale Modulations in Nematic Liquid Crystals.

The nature of the nanoscale structural organization in modulated nematic phases formed by molecules having a nonlinear molecular architecture is a central issue in contemporary liquid crystal research. Nevertheless, the elucidation of the molecular organization is incomplete and poorly understood. One attempt to explain nanoscale phenomena merely "shrinks down" established macroscopic continuum elasticity modeling.

Polar Molecular Ordering in the N Phase of Bimesogens and Enantiotopic Discrimination in the NMR Spectra of Rigid Prochiral Solutes.

The potential of mean torque governing the orientational ordering of prochiral solutes in the two nematic phases (N and N) formed by certain classes of symmetric achiral bimesogens is formulated and used for the analysis of existing NMR measurements on solutes of various symmetries dissolved in the two phases. Three distinct attributes of the solvent phase, namely polarity of the orientational ordering, chirality of the constituent molecules, and spatial modulation of the local director, are identified as underlying three possible mechanisms for the generation of chiral asymmetry in the low temperature nematic phase (N). The role and quantitative contribution of each mechanism to enantiotopic discrimination in the N phase are presented and compared with the case of the conventional chiral nematic phase (N*).

Direct Measurement of the Angular Pair Correlation Coefficients in Molecular Liquids Using NMR. Benchmarking Force Fields for Atomistic Simulations.

High-field deuterium NMR spectroscopy is used to characterize a number of molecular liquids and their mixtures in order to probe the directional part of the intermolecular interactions through the orientational ordering induced in the isotropic liquid phase by the spectrometer magnetic field. The systems studied include benzene, chloroform, hexafluorobenzene, and thiophene at various concentrations and in mixtures. Dilution with the magnetically isotropic tetramethylsilane provides quantification of ordering at "infinite magnetic dilution", that is, in the absence of magnetic intermolecular correlations, and thereby allows identification of the contribution of these correlations to the orientational ordering in neat phases and at various degrees of magnetic dilution.

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

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.

A molecular theory of nematic-nematic phase transitions in mesogenic dimers.

We study theoretically the molecular origins of the fascinating, and still debated, nematic-nematic phase transition exhibited by symmetric, statistically achiral, mesogenic dimers. A simple molecular model that mimics the key features and symmetry (C2V) of this class of mesogens is presented. In the mean-field approximation, the model yields up to three positionally disordered phases, one isotropic and two nematic.