Civil Engineering Reference
In-Depth Information
where
,
p
and
R
represent viscosity, pressure, and tube radius,
respectively.
There are two primary reasons a continuum theory of a molecular scale
slip is investigated. On the one hand, it helps to understand the behaviour
of a fl ow in a nanoscale tube. On the other hand, the slip length theory can
serve as a reference to explain large water fl ow enhancements, compared
with no-slip Hagen-Poiseuille formalism, observed by several experimental
studies (Majumder
et al.
, 2005a; Holt
et al.
, 2006; Whitby
et al.
, 2008) using
CNT membranes.
Although the ultrafast water transport in the CNT could be explained by
the slip length model to some extent, results of MD simulations, especially
on the water confi guration, are investigated as an effective way to under-
stand many fundamental nanofl uidic characteristics. In fact, lots of physical
properties of water depend on the coherence and the number of hydrogen
bonds. The hydrogen bond is useful in explaining water confi guration or
properties inside CNT, since water has a dipole and an electrostatic interac-
tion via hydrogen bonding.
The effect of CNTs on bacteria and viruses has not received particular
attention, probably due to the diffi culty of dispersing CNTs in water. Sur-
factants or polymers such as polyvinylpyrolidone (PVP) or Triton-X are
generally used to facilitate the dispersion. The few studies available credited
SWNTs with antimicrobial activity towards Gram-positive and Gram-
negative bacteria, and the damage infl icted was attributed to either a physi-
cal interaction or oxidative stress that compromise cell membrane integrity
(Narayan
et al.
, 2005; Kang
et al.
, 2008). However, the degre of aggregation
and the bioavailability of the nanotube will have to be considered to exploit
the antimicrobial properties effectively.
It is noteworthy here that CNTs are the only nanostructured material
bestowed with so many unusual (however essentially interesting) attributes
which can serve as a wonderful global water fi lter. The critical factor is
to put the CNTs in a membranous structure to exploit all their potential
benefi ts, which are discussed in Section 16.7.
μ
16.4.5 Other nanomaterials (nanoclays, micelles,
magnetic nanoparticles)
Clays are alumino silicates with a planar silicate structure. There are three
main categories of clay: kaolinite, montmorillonite-smectite and illite,
amongst which the fi rst two are the most widely studied (Pradeep and
Anshup, 2009b). Usually the structure contains silicate sheets (Si
2
O
5
)
bonded to aluminium oxide/hydroxide layers (Al
2
(OH)
4
) called gibbsite
layers. The primary structural unit of this group is a layer composed of one
octahedral sheet with one tetrahedral sheet (kaolinite is 1 : 1 clay mineral).
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