Biomedical Engineering Reference
In-Depth Information
A
Fig. 1.19
The water probability density distributions along the nanotube axis for ı D
2.1
(reprinted from [
129
]. Copyright 2008 American Physical Society)
where x
0
is the initial position of the vibrating carbon atom,
A
is the amplitude, !
is angular frequency, and is the initial phase. The frequency is defined as
2
.It
is found that the vibrating frequency,
f
, plays a role in water transportation through
(6,6) CNT.
From the simulation result shown in Fig.
1.20
, we can find that the water flow, net
flux, and <
N
> almost keep the value of the unperturbed system when the frequency
f<f
c
1; 333 GHz. The corresponding period time is 0.75 ps and the velocity of
the moving-atom under this frequency (
f
c
) is about 200 m/s, about half the average
thermal velocity of water molecules (nearly 400 m/s) at room temperature. In real
systems, it is impossible for a carbon atom in CNT to vibrate at such a high velocity
andinsuchalargeamplitude(2 A). Thus, the permeation property of the water
molecules confined in the nanochannel can be effectively shielded from strong
noise.
From Fig.
1.21
, we can find that the water density distribution maintains the
similar wavelike pattern for f<f
c
1; 333, which leads to the invariability of the
total number of water molecules inside the nanotube. The single-filed water chain
connected with hydrogen bonds can accommodate the fluctuation of the CNT due to
external force. For f>f
c
, the wavelike pattern of density distribution is destroyed.
