Enhanced thermophysical properties via PAO superstructure
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Date
2017-01-11Author
Pournorouz, Zahra
Mostafavi, Amirhossein
Pinto, Aditya
Bokka, Apparao
Jeon, Junha
Shin, Donghyun
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For the last few years, molten salt nanomaterials have attracted many scientists for their enhanced specific heat by
doping a minute concentration of nanoparticles (up to 1% by weight). Likewise, enhancing the specific heat of
liquid media is important in many aspects of engineering such as engine oil, coolant, and lubricant. However, such
enhancement in specific heat was only observed for molten salts, yet other engineering fluids such as water, ethylene
glycol, and oil have shown a decrease of specific heat with doped nanoparticles. Recent studies have shown that the
observed specific heat enhancement resulted from unique nanostructures that were formed by molten salt molecules
when interacting with nanoparticles. Thus, such enhancement in specific heat is only possible for molten salts because
other fluids may not naturally form such nanostructures. In this study, we hypothesized such nanostructures can be
mimicked through in situ formation of fabricated nano-additives, which are putative nanoparticles coated with useful
organic materials (e.g., polar-group-ended organic molecules) leading to superstructures, and thus can be directly used
for other engineering fluids. We first applied this approach to polyalphaolefin (PAO). A differential scanning calorimeter
(DSC), a rheometer, and a customized setup were employed to characterize the heat capacity, viscosity, and thermal
conductivity of PAO and PAO with fabricated nano-additives. Results showed 44.5% enhanced heat capacity and 19.8
and 22.98% enhancement for thermal conductivity and viscosity, respectively, by an addition of only 2% of fabricated
nanostructures in comparison with pure PAO. Moreover, a partial melting of the polar-group-ended organic molecules
was observed in the first thermal cycle and the peak disappeared in the following cycles. This indicates that the in situ
formation of fabricated nano-additives spontaneously occurs in the thermal cycle to form nanostructures.
Figure of merit analyses have been performed for the PAO superstructure to evaluate its performance for
heat storage and transfer media.