| Description |
Atomistic molecular dynamic (MD) simulations of cyanobiphenyl liquid crystal both in the bulk and at interfaces have been conducted using the highly transferable, quantum chemistry-based force field from our group. The influence of induced polarization effects force field details on the predicted thermodynamic, dynamic, and structural properties of 4-cyano-4’-pentylbiphenyl (5CB) bulk systems have been systematically investigated in the 292-368 K temperature range. Variations in the magnitude of molecular dipole moment and the details of dihedral potential for biphenyl unit were investigated using both polarizable (POL) and nonpolarizable (NP) versions of the aforementioned force field. The predicted densities for the nematic and isotropic phases of bulk 5CB were found to be in excellent agreement with available experimental data. However the simulation predicted nematic-isotropic transition temperature (TNI) show an overestimation when the partial atomic charges were taken directly from high-level quantum chemistry calculations. Subsequent rescaling of partial charges significantly improved the prediction of TNI and other thermodynamic and dynamic properties. We also studied the interface anchoring effect and energetics of 5CB in contact with free surface, pure water, and aqueous solution of surfactant C10TAB in both nematic and isotropic phases via atomistic molecular dynamic simulation. The resulting anchoring behaviors of 5CB at different interfaces are in good agreement with experiment. For the free surface system, we demonstrated that a small change of the biphenyl torsional parameter of 5CB can lead to stronger positional ordering both at the interface and in the bulk. Overall the results show our force field is fully capable of capturing the crucial planar to homeotropic anchoring reorientation of 5CB in a complex four component environment. Initial data and comparison on structure, conformations, and dynamics of cyanobiphenyl-(CH2)7-cyanobiphenyl (CB7CB) in twist-bend nematic, regular nematic, and isotropic phases were provided. The simulation predicted order parameter, average bend angle β and the nanoscale angular modulation of β are in good agreements with experiments. |
