Biomedical Engineering Reference
In-Depth Information
Fig. 1.44
Signal switching in an SWNT. Trajectories of the average dipole angle
N
.t/ of the
water orientations in an SWNT for the charge signal switch from negative to positive (
top
)and
from positive to negative (
bottom
) for four typical cases with different initial states. The dipole
orientations in the SWNT fully respond in approximately 0.07 ns when the charge switches from
negative to positive and in 3.2 ns in the case of positive-to-negative transition (reprinted from [
132
].
Copyright 2010 Royal Society of Chemistry)
and its neighboring water molecules. As is shown in Fig.
1.45
, a typical process
displays the reorientation of water molecules in the nanochannel in response to
a
C
e
!
-
e
signal switch. In this process, the dipoles of water chain molecules
always flip over one by one, from the bottom to the top (see Fig.
1.43
). In order
to observe the motion of this flipping forefront point, we can trace the position of
the water molecule (along the nanochannel axial direction), whose dipole angle
falls into the ranges of [70
ı
, 110
ı
], while its two nearest neighbor molecules have
their dipole angles falling into [110
ı
,70
ı
]and[10
ı
,70
ı
], respectively. If there is no
such water molecule at any given moment, we take the position of the last-turning
molecule as the current forefront. We have also plotted the value of ' as a function
of the time. Clearly, the turning forefront is consistent with the value of '.
As we have seen above, charge polarity signal can transmit via the one-
dimensional water dipole chain confined within nanochannels with suitable radii.
More importantly, we have achieved signal multiplication at the nanoscale, making
use of the Y-shaped water chain confined in the Y-shaped nanochannels.
Recently, Y-shaped nanotubes have been successfully fabricated by several
different methods, including alumina templates [
113
], chemical vapor deposition
of products generated from a pyrolysis of metallocenes [
114
-
116
], nano-welding of
overlapping isolated nanotubes using high-intensity electron beams [
117
], and spon-
taneous growth of nanotube mats using Ti-doped Fe catalysts [
118
]. In Ref. [
42
],
we have constructed a computational model of Y-shaped CNT, called Y-SWNT,
