Biomedical Engineering Reference
In-Depth Information
Fig. 1.6
Water distributions
along
z
axis together with the
positions of carbon atoms
(the
open circles
and the
filled
circles
). The
arrow
,marked
by
P
, is the position of
forced-atom. (
a
) ı D
0.0, 1.4,
1.8
˚
A(
b
) ı D
2.0, 2.4, 2.5 A
radius of a water atom. Only when ı>ı
C
2.0 A, the net flux and the occupancy
N
decrease as ı further increases. When ı
D
2.6 A, the water flux through the tube
becomes a negligible value. In the total 216 ns simulation, no water molecules enter
the tube from one end or leave from the other, indicating that at ı
D
2.6 A, the
nanotube is functionally closed. It shows that a CNT can be completely closed from
an open state by moving the forced-atom by only 0.6 A. Here, the CNT shows
excellent gating behavior corresponding to external mechanical signals. On one
hand, the water flux and occupancy of the CNT are extremely irrespective of external
signals (ı<2.0 A), for example, deformations due to noise. On the other hand, the
water flux and occupancy of the nanotube are sensitive to further deformations. An
additional increase of 0.6
˚
Aforı leads to an abrupt transition from an open state
(flux same as an unperturbed nanotube) to a closed state (no flux).
In order to further study the physics for such gating behavior, we show the
water distribution inside the CNT for different ı in Fig.
1.6
. As is well known, the
density of water is constant along a macroscopic channel with a uniform radius.
However, for a CNT with 8.1 A in diameter and 13.4 A in length, the water
density distribution appears in wavelike pattern. Furthermore, the gating of the water
transportation through the CNT is found related to the wavelike pattern of water
density distribution.
