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Microscopic structure and dynamics of a partial bilayer smectic liquid crystal.
Y Lansac1, M A Glaser, N A Clark
1Condensed Matter Laboratory, Department of Physics, and Ferroelectric Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|December 12, 2001
Summary
Atomistic simulations reveal that short-range antiparallel association of cyanobiphenyl molecules, driven by dipole-dipole interactions, is key to the unique Smectic-A(d) phase structure. This study validates molecular models for liquid crystals.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Chemistry
Background:
- Cyanobiphenyls (nCBs) are extensively studied liquid crystals known for unique properties like the partial bilayer smectic-A(d) phase.
- These properties are often attributed to short-range antiparallel molecular associations driven by cyano group dipole-dipole interactions.
Purpose of the Study:
- To investigate the microscopic structure and dynamics of the Smectic-A(d) phase of 4-octyl-4'-cyanobiphenyl (8CB).
- To test and refine existing models of microscopic ordering in cyanobiphenyls using large-scale atomistic simulations.
- To validate the molecular model by comparing simulation results with experimental data.
Main Methods:
- Large-scale atomistic simulations were employed to study the Smectic-A(d) phase of 8CB.
- Thermodynamic, structural, and dynamical properties were computed.
- Simulation results were rigorously compared with experimental measurements.
Main Results:
- The simulation achieved semiquantitative agreement with experimental data.
- Smectic layer spacing and mass density were accurately reproduced.
- Translational diffusion constants were found to be similar to experimental values, though alkyl chain orientational ordering was overestimated.
- Detailed insights into molecular conformation, layer structure, and intermolecular correlations were obtained.
Conclusions:
- Short-range antiparallel association of molecules, stemming from dipole-dipole interactions, is a dominant factor in shaping the molecular-scale structure of 8CB.
- Atomistic simulations provide a valuable tool for understanding the complex behavior of liquid crystalline phases.
- The study validates the molecular model for 8CB, highlighting its strengths and areas for refinement.