Molecular Dynamics Simulation Study of the Influence of Chirality on the Stability of the Smectic Q Liquid Crystal Phase

• Published in: The journal of physical chemistry. B Vol. 112; no. 29; pp. 8452 - 8458
• Main Authors: Yoneya, Makoto, Yamamoto, Takahiro, Nishiyama, Isa, Yokoyama, Hiroshi
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.07.2008
• Subjects: B: Macromolecules, Soft Matter
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp712121v

The structure of smectic Q (SmQ) liquid crystal phase consisting of a dichiral molecule, called M7BBM7, was studied by submicrosecond molecular dynamics (MD) simulation. A detailed atomic model was used to study the stability of a model SmQ structure proposed by Levelut et al. ( Levelut A.-M. ; Hallouin E. ; Bennemenn ; Heppke G. ; Lotzsch D. J. Phys. II 1997, 7, 981 ) and its difference between (S,S)-, (S,R)-M7BBM7 and racemic mixture systems. Negative values of the fourth-rank orientational order parameter (⟨P 4⟩), which characterize the model SmQ structure, were stably kept up to a 100 ns MD run only in the (S,S)-M7BBM7 system and lost in the other systems. The results correspond well to the marked chiral sensitivity in real systems where only the (S,S)-M7BBM7 system (among the three above-mentioned systems) shows the SmQ phase. Our simulation results imply that the asymmetric intramolecular potentials and resultant chirality-dependent molecular conformations are primarily responsible for keeping the negative values of ⟨P 4⟩ and the model SmQ structure.