MICRO AND NANOSCALE SYSTEMS - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 174

2.1 INTRODUCTION
Viscous forces in the fluid can lead to large dispersion flow along the axis of mo-
tion. They have a significant impact, both on the scale of individual molecules,
and the scale of microflows; near the borders of the liquid-solid (beyond a few
molecular layers), during the motion on a complex and heterogeneous borders.
Influence of the effect of boundary regions on the particles and fluxes have
been observed experimentally in the range of molecular thicknesses up to hun-
dreds of nanometers. If the surface has a super hydrophobic property, this range
can extend to the micron thickness. Molecular theory can predict the effect of
hydrophobic surfaces in the system only up to tens of nanometers.
Fluids, the flow of liquid or gas, have properties that vary continuously under
the action of external forces. In the presence of fluid shear forces are small in
magnitude, leads large changes in the relative position of the element of fluid. In
contrast, changes in the relative positions of atoms in solids remain small under
the action of any small external force. Termination of action of the external forces
on the fluid does not necessarily lead to the restoration of its initial form.

2.1.1 CAPILLARY EFFECTS
To observe the capillary effects, one must open the nanotube, that is, to remove
the upper part lids. Fortunately, this operation is quite simple.
The first study of capillary phenomena has shown that there is a relationship
between the magnitude of surface tension and the possibility of its being drawn
into the channel of the nanotube. It was found that the liquid penetrates into the
channel of the nanotube, if its surface tension is not higher than 200 mN/m. For
example, concentrated nitric acid with surface tension of 43 mN/m is used to
inject certain metals into the channel of a nanotube. Then annealing is conducted
at 4000°С for 4 h in an atmosphere of hydrogen, which leads to the recovery of
the metal.
Along with the metals, carbon nanotubes can be filled with gaseous substanc-
es, such as hydrogen in molecular form. This ability is of great practical impor-
tance and can be used as a clean fuel in internal combustion engines.

2.1.2 SPECIFIC ELECTRICAL RESISTANCE OF CARBON NANOTUBES

(R)
The resistivity of the nanotubes can be varied within wide limits to 0.8 ohm/cm.
The minimum value is lower than that of graphite. Most of the nanotubes have
metallic conductivity, and the smaller shows properties of a semiconductor with
a band gap of 0.1 to 0.3 eV.
The resistance of single-walled nanotube is independent of its length, because
of this it is convenient to use for the connection of logic elements in microelec-
tronic devices. The permissible current density in carbon nanotubes is much