Synthesis and Characterization of Nanofluids …
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relationship for electrical conductivity and temperature of Al 2 O 3 and SiO 2 nanofluids prepared using mixture of propylene glycol and water as a basefluid. On the other
hand, electrical conductivity of water-based Al 2 O 3 nanofluids was found to remain
constant with respect to temperature by Minea and Luciu (2012). Dong et al. (2013)
showed that for aluminium nitride-transformer oil-based nanofluids, the electrical
conductivity shows a decreasing trend from 25 °C to 40 °C, but it became stable
after 40 °C. Higher temperature of nanofluids is found to promote aggregation and
thus formation of transport paths for conduction of electric charge leads to enhancement in electrical conductivity of the nanofluids (Bagheli et al. 2015). Naddaf and
Heris (2018) studied the electrical conductivity of MWCNT-based nanofluids using
diesel oil as a basefluid and oleic acid as a surfactant and recorded the electrical
conductivities as 0.18, 135.2, 299.9 and 444.9 μS/cm for MWCNT-based nanofluids
of concentrations 0.05, 0.1, 0.2 and 0.5 wt%, respectively, at a temperature of 20 °C.
4.3 Role of Zeta Potential
When nanoparticles are dispersed in the basefluid, there is a certain layer of the
basefluid surrounding it. The thin layer of the liquid formed on the particle in a
nanofluid is called as the Stern layer. There is also a layer known as diffuse layer that
comprises the loosely associated ions at the outer surface of the Stern layer. Both
of these layers are responsible for the formation of the electrical double layer. The
loosely associated ions in the diffuse layer shear with the ions in the bulk fluid when
the particle undergoes a motion, most commonly the Brownian motion. Zeta potential
is the electric potential at this shear surface. Schematic of zeta potential is shown in
Fig. 10. The zeta potential is known by measuring the velocity of the particle moving
towards the electrode in the presence of an electric field externally maintained across
the nanofluid sample. A value of zeta potential of ± 30 mV is considered as a value
exhibited by a stable nanofluid and that exhibiting a value above or below this value
is known as stable nanofluid or unstable nanofluid, respectively. Zeta potential is
measured by determining the electrophoretic mobility of the particles.
4.4 Relation of Stability and Electrical Conductivity
of Nanofluids
Stability is the degree of uniform dispersion of the nanoparticles in the basefluid and
also one of the factors considered in electrical conductivity of the nanofluids (Shoghl
et al. 2016). Nanofluids contain nanoparticles that are susceptible to surface charges.
These surface charges that have major role in electrical conductivity also have a
major role in the stability of the nanofluid (White et al. 2011). The surface charge on
a nanoparticle is due to the protonation and de-protonation of functional groups on its
27
relationship for electrical conductivity and temperature of Al 2 O 3 and SiO 2 nanofluids prepared using mixture of propylene glycol and water as a basefluid. On the other
hand, electrical conductivity of water-based Al 2 O 3 nanofluids was found to remain
constant with respect to temperature by Minea and Luciu (2012). Dong et al. (2013)
showed that for aluminium nitride-transformer oil-based nanofluids, the electrical
conductivity shows a decreasing trend from 25 °C to 40 °C, but it became stable
after 40 °C. Higher temperature of nanofluids is found to promote aggregation and
thus formation of transport paths for conduction of electric charge leads to enhancement in electrical conductivity of the nanofluids (Bagheli et al. 2015). Naddaf and
Heris (2018) studied the electrical conductivity of MWCNT-based nanofluids using
diesel oil as a basefluid and oleic acid as a surfactant and recorded the electrical
conductivities as 0.18, 135.2, 299.9 and 444.9 μS/cm for MWCNT-based nanofluids
of concentrations 0.05, 0.1, 0.2 and 0.5 wt%, respectively, at a temperature of 20 °C.
4.3 Role of Zeta Potential
When nanoparticles are dispersed in the basefluid, there is a certain layer of the
basefluid surrounding it. The thin layer of the liquid formed on the particle in a
nanofluid is called as the Stern layer. There is also a layer known as diffuse layer that
comprises the loosely associated ions at the outer surface of the Stern layer. Both
of these layers are responsible for the formation of the electrical double layer. The
loosely associated ions in the diffuse layer shear with the ions in the bulk fluid when
the particle undergoes a motion, most commonly the Brownian motion. Zeta potential
is the electric potential at this shear surface. Schematic of zeta potential is shown in
Fig. 10. The zeta potential is known by measuring the velocity of the particle moving
towards the electrode in the presence of an electric field externally maintained across
the nanofluid sample. A value of zeta potential of ± 30 mV is considered as a value
exhibited by a stable nanofluid and that exhibiting a value above or below this value
is known as stable nanofluid or unstable nanofluid, respectively. Zeta potential is
measured by determining the electrophoretic mobility of the particles.
4.4 Relation of Stability and Electrical Conductivity
of Nanofluids
Stability is the degree of uniform dispersion of the nanoparticles in the basefluid and
also one of the factors considered in electrical conductivity of the nanofluids (Shoghl
et al. 2016). Nanofluids contain nanoparticles that are susceptible to surface charges.
These surface charges that have major role in electrical conductivity also have a
major role in the stability of the nanofluid (White et al. 2011). The surface charge on
a nanoparticle is due to the protonation and de-protonation of functional groups on its