Biomedical Engineering Reference
In-Depth Information
Table 11.1 (cont.)
Nanofluid
Preparation method
Octahedral Cu
2
O nanoparticles in
water or water/EG mixtures
CePO
4
nanofibers in water, ethanol,
EG, and their mixtures
Hollow Cu or CuS nanoparticles in
water, ethanol, EG, and their
mixtures
Hollow and wrinkled Cu
2
O
nanoparticles in EG or EG/water
mixtures
Cu
2
O(core)/CuS(shell) nanoparticles in
water
Au-water
Pulsed laser ablation in liquids
technique (Kim et al., 2009)
Au (PVP)-water
Chemical reaction method (Mishra
et al., 2009)
Ag-diethylene glycol
Sputtering on running liquid technique
(Tamjid and Guenther, 2010)
11.2.2 Two-step process
The two-step method is extensively used in the synthesis of nanofluids
primarily due to the easy availability of several types of nanopowders and
the inherent versatility associated with this approach. In this method,
nanoparticles are first synthesized by mechanical alloying, chemical
reaction, vapor condensation, or decomposition of organic complex and
are then dispersed in the base fluid with mechanical agitation (stirring)
applying ultrasonic vibration (Hwang et al., 2008; Li et al., 2008) or any
such suitable dispersing technique. Generally, ultrasonic equipment is used
to intensively disperse the particles and reduce the agglomeration of
particles. The stability factor of the nanofluids is taken care of by using
surfactants. The main advantage of this two-step synthesis method is that it
produces nanoparticles under clean conditions, without undesirable surface
coatings and other contaminants (Lee et al., 1999). The major problem is
that agglomeration of nanoparticles may still occur. When finely divided
solid nanostructures are immersed in liquids, they often do not form a stable
dispersion. Many of the particles acquire surface charge and tend to
physically aggregate together in clusters. Though these particles can be
easily re-dispersed in liquids by mechanical vibration/agitation, they soon
cluster together again to form large aggregates that settle down quickly from
the suspension. This can be taken care of by adding dispersants during
preparation, which form a coating layer around the nanoparticles that is
