290
V. Raczy´ nska et al.
two benzene rings in 5CB structure lead to the formation of planar alignment of
anchored mesogene molecules.
17.2 Simulation Details
The model of 5CB mesogene, which has been proved to well describe the
isotropic−nematic phase transition temperatures and the appropriate values of the
order parameter assigned to these phases, has been adopted from the CHARMMtype united atom potential developed by Tiberio and co-workers [6].
Interactions between the mesogens have been described taking into account
electrostatics and van der Waals forces modeled with Lennard-Jones 12–6 potential
with Lorentz−Berthelot mixing rules and cutoff of 12 Å. Interactions between
graphene sheets and 5CB molecules have been described with a model that
accounts for van der Waals interactions modeled with Lennard-Jones 12–6 potential.
Periodic boundary conditions (PBC) were applied and long-range interactions were
calculated using particle mesh Ewald (PME) summation technique with grid spacing
of 1.5 Å. Equations of motion were integrated for 20 ns, using the BrungerBrooks-Karplus (BBK) scheme implemented in NAMD 2.9 [7] with the time
step of integration of 1 fs. The simulation was performed in NVT ensemble, for
temperature T = 270 K, controlled with Langevin thermostat (damping coefficient
γ = 5.0 ps − 1). Visualizations were prepared with the use of VMD software [8].
The simulated system was composed of 63 5CB molecules located between two
parallel graphene sheets (approx. 70 × 70 Å). The distance between the sheets
varied from 9 Å to 18 Å. The simulation cell was set to 70.7 × 72.4 × 90.0 Å.
The value of z-component of simulation cell was large enough to minimize the selfinteraction component of long-range electrostatic interaction between the primary
layer and its PBC image. The remaining x- and y-components were selected to
accommodate for the periodicity of the graphene sheets. Figure 17.1 shows the
snapshot of the instantaneous configuration of 5CB mesogene phase between the
graphene sheets at the lowest studied distance – 9 Å, forming single homogeneous
layer.
17.3 Results and Discussion
We have studied the properties of the phases of 5CB embedded between two parallel
graphene sheets. Geometrical constraints and anchoring effects moderate strongly
structure and inner dynamics of the mesogenes. The accessible volume per 5CB
molecule varies from 0.7 to 1.4 nm 3 for different distances between graphene planes
(9–18 Å). Taking into account only the geometrical constraints, one would expect
that dynamics of the system should significantly accelerate. Figure 17.2 shows
calculated values of the Lindemann index δ L defined as [9].
V. Raczy´ nska et al.
two benzene rings in 5CB structure lead to the formation of planar alignment of
anchored mesogene molecules.
17.2 Simulation Details
The model of 5CB mesogene, which has been proved to well describe the
isotropic−nematic phase transition temperatures and the appropriate values of the
order parameter assigned to these phases, has been adopted from the CHARMMtype united atom potential developed by Tiberio and co-workers [6].
Interactions between the mesogens have been described taking into account
electrostatics and van der Waals forces modeled with Lennard-Jones 12–6 potential
with Lorentz−Berthelot mixing rules and cutoff of 12 Å. Interactions between
graphene sheets and 5CB molecules have been described with a model that
accounts for van der Waals interactions modeled with Lennard-Jones 12–6 potential.
Periodic boundary conditions (PBC) were applied and long-range interactions were
calculated using particle mesh Ewald (PME) summation technique with grid spacing
of 1.5 Å. Equations of motion were integrated for 20 ns, using the BrungerBrooks-Karplus (BBK) scheme implemented in NAMD 2.9 [7] with the time
step of integration of 1 fs. The simulation was performed in NVT ensemble, for
temperature T = 270 K, controlled with Langevin thermostat (damping coefficient
γ = 5.0 ps − 1). Visualizations were prepared with the use of VMD software [8].
The simulated system was composed of 63 5CB molecules located between two
parallel graphene sheets (approx. 70 × 70 Å). The distance between the sheets
varied from 9 Å to 18 Å. The simulation cell was set to 70.7 × 72.4 × 90.0 Å.
The value of z-component of simulation cell was large enough to minimize the selfinteraction component of long-range electrostatic interaction between the primary
layer and its PBC image. The remaining x- and y-components were selected to
accommodate for the periodicity of the graphene sheets. Figure 17.1 shows the
snapshot of the instantaneous configuration of 5CB mesogene phase between the
graphene sheets at the lowest studied distance – 9 Å, forming single homogeneous
layer.
17.3 Results and Discussion
We have studied the properties of the phases of 5CB embedded between two parallel
graphene sheets. Geometrical constraints and anchoring effects moderate strongly
structure and inner dynamics of the mesogenes. The accessible volume per 5CB
molecule varies from 0.7 to 1.4 nm 3 for different distances between graphene planes
(9–18 Å). Taking into account only the geometrical constraints, one would expect
that dynamics of the system should significantly accelerate. Figure 17.2 shows
calculated values of the Lindemann index δ L defined as [9].