%0 Book Section %1 statphys23_0432 %A Chakrabarti, D. %A Wales, D.J. %A Bagchi, B. %B Abstract Book of the XXIII IUPAP International Conference on Statistical Physics %C Genova, Italy %D 2007 %E Pietronero, Luciano %E Loreto, Vittorio %E Zapperi, Stefano %K crystals energy inherent landscapes liquid statphys23 structures thermotropic topic-7 %T Energy landscapes of thermotropic liquid crystals %U http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=432 %X The anisotropy in molecular shape plays a crucial role in the rich phase behaviour that thermotropic liquid crystals exhibit upon temperature variation. Calamitic liquid crystals consist of rod-like molecules while discotic liquid crystals comprise disc-like molecules. Upon cooling from the high-temperature isotropic phase, the mesophases that appear in these systems differ in order and symmetry, the simplest of the ordered phases for both the systems being the nematic, which has long-range orientational order but no translational order. The smectic phase, which is characterised by the appearance of long-range translational order in layers in addition to further increase in orientational order, is typically observed for calamitic liquid crystals. In the case of discotic liquid crystals, the columnar phase results from stacking of mesogens on top of each other, giving rise to a columnar structure. Here we explore the energy landscapes of model calamitic and discotic systems by determining the underlying potential energy minima (inherent strictures) as the systems settle into the increasingly ordered mesophases upon cooling. For both calamitic and discotic systems, the depth of the potential energy minima explored on average is found to grow through the nematic phase as the temperature drops along an isochor. In contrast, the average inherent structure energy is relatively insensitive to temperature in the high-temperature isotropic phase and the low-temperature smectic/columnar phase. The onset of the growth of orientational order in the parent phase is found to induce translational order, resulting in smectic-like layers in the inherent structures of the calamitic system if the parent nematic phase is sandwiched between the isotropic phase and the smectic phase D. Chakrabarti and B. Bagchi, Proc. Natl. Acad. Sci. USA 103, 7217 (2006). For the discotic system, the inherent structures are found to sustain short columns even when the parent phase is nematic. For both the systems, the Arrhenius temperature dependence of the orientational correlation time is found to break down near the isotropic-nematic (I-N) transition at a temperature below which the systems explore increasingly deeper potential energy minima. This work reveals a remarkable similarity in the exploration of the potential energy landscapes of thermotropic liquid crystals and those of supercooled liquids S. Sastry, P. G. Debenedetti, and F. H. Stillinger, Nature 393, 554 (1998), even though the latter have avoided a phase transition. In addition, this study provides insight into the interplay between orientational and translational order in the mesophases of thermotropic liquid crystals, which seems to have far-reaching implications.

@incollection{statphys23_0432, abstract = {The anisotropy in molecular shape plays a crucial role in the rich phase behaviour that thermotropic liquid crystals exhibit upon temperature variation. Calamitic liquid crystals consist of rod-like molecules while discotic liquid crystals comprise disc-like molecules. Upon cooling from the high-temperature isotropic phase, the mesophases that appear in these systems differ in order and symmetry, the simplest of the ordered phases for both the systems being the nematic, which has long-range orientational order but no translational order. The smectic phase, which is characterised by the appearance of long-range translational order in layers in addition to further increase in orientational order, is typically observed for calamitic liquid crystals. In the case of discotic liquid crystals, the columnar phase results from stacking of mesogens on top of each other, giving rise to a columnar structure. Here we explore the energy landscapes of model calamitic and discotic systems by determining the underlying potential energy minima (inherent strictures) as the systems settle into the increasingly ordered mesophases upon cooling. For both calamitic and discotic systems, the depth of the potential energy minima explored on average is found to grow through the nematic phase as the temperature drops along an isochor. In contrast, the average inherent structure energy is relatively insensitive to temperature in the high-temperature isotropic phase and the low-temperature smectic/columnar phase. The onset of the growth of orientational order in the parent phase is found to induce translational order, resulting in smectic-like layers in the inherent structures of the calamitic system if the parent nematic phase is sandwiched between the isotropic phase and the smectic phase [D. Chakrabarti and B. Bagchi, Proc. Natl. Acad. Sci. USA {\bf 103}, 7217 (2006)]. For the discotic system, the inherent structures are found to sustain short columns even when the parent phase is nematic. For both the systems, the Arrhenius temperature dependence of the orientational correlation time is found to break down near the isotropic-nematic (I-N) transition at a temperature below which the systems explore increasingly deeper potential energy minima. This work reveals a remarkable similarity in the exploration of the potential energy landscapes of thermotropic liquid crystals and those of supercooled liquids [S. Sastry, P. G. Debenedetti, and F. H. Stillinger, Nature {\bf 393}, 554 (1998)], even though the latter have avoided a phase transition. In addition, this study provides insight into the interplay between orientational and translational order in the mesophases of thermotropic liquid crystals, which seems to have far-reaching implications.}, added-at = {2007-06-20T10:16:09.000+0200}, address = {Genova, Italy}, author = {Chakrabarti, D. and Wales, D.J. and Bagchi, B.}, biburl = {https://www.bibsonomy.org/bibtex/2ba7a558c53b07f85aaca83a1978ab0be/statphys23}, booktitle = {Abstract Book of the XXIII IUPAP International Conference on Statistical Physics}, editor = {Pietronero, Luciano and Loreto, Vittorio and Zapperi, Stefano}, interhash = {da0a9e6bdc4b4bc2573b9daab3b14ccb}, intrahash = {ba7a558c53b07f85aaca83a1978ab0be}, keywords = {crystals energy inherent landscapes liquid statphys23 structures thermotropic topic-7}, month = {9-13 July}, timestamp = {2007-06-20T10:16:20.000+0200}, title = {Energy landscapes of thermotropic liquid crystals}, url = {http://st23.statphys23.org/webservices/abstract/preview_pop.php?ID_PAPER=432}, year = 2007 }