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D Caprion

Publications and source records attributed to D Caprion.

6 recordsLinked to original sources
PubMed2004

Surface ordering of diskotic liquid crystals.

We present Monte Carlo simulations of diskotic molecules using the Gay-Berne potential in a slab geometry. The disk-wall interaction is described by two different functions according to whether or not the equilibrium distance is dependent on the relative orientation of the disk to the wall. Furthermore, by changing the parameters of these potentials, we model either homeotropic (face-on) or planar (edge-on) anchoring of the disks. We have found that the isotropic-nematic transition does not change in comparison with the bulk situation. The temperature of the nematic-columnar transition, on the contrary, is found to increase for homeotropic anchoring, and decrease for planar anchoring, independently of the details of the potential. We explain the decrease of the transition temperature in the planar anchoring situation as the result of an induced frustration, due to the competition between the two orientations induced independently by the upper and lower walls.

Journal Article↗
PubMed2003

Influence of shape and energy anisotropies on the phase diagram of discotic molecules.

We present Monte Carlo simulations of discotic molecules using the Gay-Berne potential with shape (kappa) and energy (kappa(')) anisotropies. Following the previous work of Bates and Luckhurst [J. Chem. Phys. 104, 6696 (1996)] at kappa=0.345, kappa(')=0.2 when we determine the sequence of different phases at the same reduced pressure P(*)=50, we find an additional phase at low temperatures corresponding to an orthorhombic crystalline phase and we characterize it. Keeping the shape anisotropy fixed at kappa=0.2, we determine the evolution of the phase diagram with varying energy anisotropy. At high kappa('), low anisotropy, the system is not able to build columns while at low kappa('), the system exhibits both orthorhombic crystal as well as hexagonal liquid crystal phases over a wide range of pressures and temperatures. The domain of stability of the nematic phase is found to systematically shift towards higher pressures as kappa(') decreases.

Journal Article↗
PubMed2000

Dynamic heterogeneity of relaxations in glasses and liquids

We report an investigation of the heterogeneity in supercooled liquids and glasses using the non-Gaussianity parameter. We simulate selenium and a binary Lennard-Jones system by molecular dynamics. In the non-Gaussianity three time domains can be distinguished: an increase on the ps scale due to the vibrational (ballistic) motion of the atoms, followed by a growth, due to local relaxations ( beta relaxation) at not too high temperatures, and finally a slow drop at long times. The non-Gaussianity follows in the intermediate time domain a sqrt[t] law. This is explained by collective hopping and dynamic heterogeneity. We support this finding by a model calculation.

Journal Article↗