Distinctive dielectric properties of nematic liquid crystal dimers

We provide an overview of the effect of the molecular structure on the dielectric properties of dimers exhibiting nematic and twist-bend nematic phases with special focus on how the conformational distribution changes are reflected by the dielectric behaviour. Nematic dimers show distinctive dielectric properties which differ from those of archetypical nematic liquid crystals, as for example, unusual temperature dependence of the static permittivity or dielectric spectra characterised by two low-frequency relaxation processes with correlated strengths. The interpretation of such characteristic behaviour requires that account is taken of the effect of molecular flexibility on the energetically favoured molecular shapes. The anisotropic nematic interactions greatly influence the conformational distribution. Dielectric behaviour can be used to track those conformational changes due to dependence of the averaged molecular dipole moment on the averaged molecular shape. Results for a number of dimers are compared and analysed on the basis of the influence of details of the molecular structure, using a recently developed theory for the dielectric properties of dimers.Postprint (author's final draft

The phase behavior of a binary mixture of rodlike and disclike mesogens: Monte Carlo simulation, theory, and experiment

Published versio

Accessible Light Bullets via synergetic nonlinearities

We introduce a new form of stable spatio-temporal self-trapped optical packets stemming from the interplay of local and nonlocal nonlinearities. Pulsed self-trapped light beams in media with both electronic and molecular nonlinear responses are addressed to prove that spatial and temporal effects can be decoupled, allowing for independent tuning. We numerically demonstrate that (3+1)D light bullets and anti-bullets, i. e. bright and dark temporal solitons embedded in stable (2+1)D nonlocal spatial solitons, can be generated in reorientational media under experimentally feasible conditions.Comment: 17 pages, 4 figures A scale error in the index perturbation vs average power dependence has been fixe

VOLUMETRIC STUDIES OF THE HOMOLOGOUS SERIES OF ALKYL-CYANO-BIPHENYL LIQUID CRYSTALS

Des mesures de densité en fonction de la température ont été rapportées pour les séries homologues de cristaux liquides d'alkyle-cyano-biphényle CnH2n+1ØØCN pour n = 5 à 9. Des lignes cubiques Bsp ont été trouvées en accord avec les résultats expérimentaux et leurs dérivées ont donné les coefficients d'expansion thermique. Des changements de volume transitionnels ont été déterminés par extrapolation de la densité des phases de chaque côté d'une transition, et les variations de volume de nématique à isotrope montrent un effet pair-impair marqué. Les densités de phases nématique et isotrope en équilibre ont été utilisées avec une théorie de van der Waals des cristaux liquides pour fournir une information sur les paramètres d'un potentiel de champ moyen, les paramètres d'ordre transitionnel et les rapports longueur sur largeur moléculaire.Measurements are reported of densities as a function of temperature for the homologous series of alkyl-cyano-biphenyl liquid crystals CnH2n+1.Ø.Ø.CN for n = 5 to 9. Cubic B-splines have been fitted to the experimental results and their derivatives have given the coefficients of thermal expansivity. Transitional volume changes have been determined by extrapolation of the densities of phases each side of a transition, and the nematic to isotropic volume changes show a marked odd-even effect. The densities of the nematic and isotropic phases in equilibrium have been used in conjunction with a van der Waals theory of liquid crystals to provide information on mean field potential parameters, transitional order parameters and molecular length to breadth ratios