MICRO AND NANOSCALE SYSTEMS - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 175

greater than in metallic wires of the same cross section and one hundred times
better achievement for superconductors.

2.1.3 EMISSION PROPERTIES OF CARBON NANOTUBES
The results of the study of emission properties of the material (where the nano-
tubes were oriented perpendicular to the substrate) have been very interesting for
practical use. An attained value of the emission current density is of the order of
0.5 mA/mm 2 . The value obtained is in good agreement with the Fowler-Nordheim
expression.

2.2 ELECTRO-KINETIC PROCESSES IN MICRO AND NANOSCALE
SYSTEMS
The most effective and common ways to control microflow substances are elec-
trokinetic and hydraulic. At the same time the most technologically advanced and
automated considered electrokinetic.
Charges transfer in mixtures occurs as a result of the directed motion of charge
carriers' ions. There are different mechanisms of such transfer, but usually are
convection, migration and diffusion .
Convection is called mass transfer the macroscopic flow. Migration is the
movement of charged particles by electrostatic fields. The velocity of the ions de-
pends on field strength. In microfluidics the electrokinetic process can be divided
into: electro-osmosis, electrophoresis, streaming potential and sedimentation po-
tential. These processes can be qualitatively described as follows:
a)

electro-osmosis ; the movement of the fluid volume in response to the ap-
plied electric field in the channel of the electrical double layers on its
wetted surfaces.

b)

Electrophoresis ; the forced motion of charged particles or molecules, in
mixture with the acting electric field.

c)

Streamy potential ; the electric potential, which is distributed through a
channel with charged walls, in the case when the fluid moves under the
action of pressure forces. Joule electric current associated with the effect
of charge transfer is flowing stream.

The potential of sedimentation ; an electric potential is created when
charged particles are in motion relative to a constant fluid.
In general, for the microchannel cross-section S amount of introduced probe
(when entering electrokinetic method) depends on the applied voltage U , time t
during which the received power, and mobility of the sample componentsm:

d)

m SUt

Q = . c

L

where c - probeconcentrationin the mixture; L -the channel length.