Biomedical Engineering Reference
In-Depth Information
Fig. 1.3
(
a
,
b
) A snapshot of the simulation system. The single-walled carbon nanotube and the
graphite sheet are solvated in a box (3
4 nm) with water molecules. The gap between the
graphite plane and the nanotube is too small for a water molecule to penetrate. An external force,
marked by “F,” acts on an atom of the carbon nanotube and a deformation can be clearly seen
(reprinted from [
40
]. Copyright 2005 American Chemical Society). (
c
) ı is the displacement of the
atom directly acted by the external force from its initial equilibrium position
3
molecules using TIP3P water model. The SWNT can be controllably deformed by
an external force
F
applied to one carbon atom (namely, the forced atom) in the right
side of the CNT while the carbon atoms in the left half of the CNT were fixed [
40
].
In reality, the force can be the active force to control the flow or the perturbations
from the other parts in the biological systems.
An additional acceleration of 0.1 nm ps
2
along the
C
z
direction is added at each
atom to mimic an osmotic pressure difference of 133 MPa between two ends of the
SWNT [
23
,
40
]. The carbon atoms at the inlet, outlet, and where the external force
is exerted are fixed to prevent the SWNT from being swept away in the simulation.
The simulation is carried out at a constant pressure (1 bar) and temperature (300 K).
For each ı corresponding to an external force
F
, the time for the numerical
simulation is 232 ns. The last 216 ns of the simulation are collected for analysis.
Figure
1.4
displays the average number of water molecules inside the tube
N
,
together with the net water flux averaged each 18 ns, as a function of time for each
ı. For the unperturbed nanotube, the average number of water molecules inside the
tube is about 5. During the entire 216 ns simulation, 1955 and 726 water molecules
