Xenon NMR of liquid crystals confined to cylindrical nanocavities: a simulation study

0443867 - ÚOCHB 2016 RIV GB eng J - Článek v odborném periodiku
Karjalainen, J. - Vaara, J. - Straka, Michal - Lantto, P.
Xenon NMR of liquid crystals confined to cylindrical nanocavities: a simulation study.
Physical Chemistry Chemical Physics. Roč. 17, č. 11 (2015), s. 7158-7171. ISSN 1463-9076. E-ISSN 1463-9084
Grant CEP: GA ČR(CZ) GA14-03564S
Institucionální podpora: RVO:61388963
Klíčová slova: 129Xe NMR * liquid crystals * cylindrical cavities * phase transitions * Monte-Carlo simulations
Kód oboru RIV: CF - Fyzikální chemie a teoretická chemie
Impakt faktor: 4.449, rok: 2015

In this work, the NMR shielding of atomic Xe-129 dissolved in a uniaxial thermotropic LC confined to nanosized cylindrical cavities is computed from coarse-grained (CG) isobaric Monte Carlo (MC) simulations with a quantum-chemically (QC) pre-parameterised pairwise-additive model for the Xe nuclear shielding tensor. We report the results for the Xe-129 nuclear shielding and its connection to the structure and order of the LC appropriate to two different cavity sizes, as well as a comparison to the results of bulk (non-confined) simulations. We find that the confinement changes the LC phase structure dramatically and gives rise to the coexistence of varying degrees of LC order, which is reflected in the Xe shielding. Furthermore, we qualitatively reproduce the behaviour of the mean Xe-129 chemical shift with respect to temperature for atomic Xe dissolved in LC confined to controlled-pore glass materials. In the small-radius cavity the nematic - paranematic phase transition is revealed only by the anisotropic component of the Xe-129 nuclear shielding. In the larger cavity, the nematic - paranematic - isotropic transition is clearly seen in the Xe shielding. The simulated Xe-129 NMR shielding is insensitive to the smectic-A - nematic transition, since in the smectic-A phase, the Xe atoms largely occupy the imperfect layer structure near the cavity walls. The direct contribution of the cavity wall to Xe-129 nuclear shielding is dependent on the cavity size but independent of temperature. Our results show that the combination of CG simulations and a QC pre-parameterised Xe-129 NMR shielding allows efficient studies of the phase behaviour and structure of complex systems containing thousands of molecules, and brings us closer to the simulation of NMR experiments.
Trvalý link: http://hdl.handle.net/11104/0246564