Photopyroelectric Characterization of Magnetic Nanofluids. Influence of Type and Size of Nanoparticles on the Thermal Parameters

The influence of type and size of nanoparticles on the thermal parameters of some magnetic nanofluids is investigated. Two types of carrier liquids (transformer oil and polypropylene glycol) were combined with two types of iron based magnetic nanoparticles (\(\hbox {Fe}_{3}\hbox {O}_{4}\) and \(\hbox {MnFe}_{2}\hbox {O}_{4})\). Different sizes (10 nm–80 nm) and shapes (spherical, octahedral or cubic) of nanoparticles were obtained depending on the oleic acid/oleylamine molar ratio, which drastically influences the nanocrystals growth rate. This influence is due to the different binding ability of the two stabilizers onto crystal facets. The average size of nanoparticles was 10 nm, 35 nm and 50 nm for \(\hbox {Fe}_{3}\hbox {O}_{4}\) and 10 nm, 20 nm and 80 nm for \(\hbox {MnFe}_{2}\hbox {O}_{4}\) at a concentration of 50 mg\({\cdot }\)ml\(^{-1}\) in all cases. The results obtained by PPE technique indicate that, at this concentration, the presence of the nanoparticles reduces the value of the thermal parameters of pure carrier liquids and both thermal diffusivity and effusivity decrease with increasing nanoparticles size, independently on the carrier liquid. The influence of the nanoparticles size is more pronounced for the thermal effusivity (relative change 24 %) compared with thermal diffusivity (relative change 7 %).