Multifunctional nanofluids: Synthesis, aggregation and thermal conductivity

We synthesize multifunctional nanofluids by incorporating fluorescent dyes into magnetite nanoparticles. The synthesis is car- ried out in two different routes, in which nanoparticles with two sizes are coated by two different kinds of stabilizers. The structures of coating layers of the as-synthesized nanoparticles are characterized by the analysis of Fourier transform infrared spectra. Magnetic- interaction-induced aggregation still exits and is traced by the DLS. Thermal conductivities of the synthesized nanofluids are measured under day-light, in the dark and under the UV irradiation. The fluid thermal conductivity varies in a wave-like shape as a function of par- ticle concentration due to the existence of aggregation. Furthermore, the measured thermal conductivity under UV light is higher than those with the other conditions. The collapse of aggregates under UV irradiation due to the unidirectional non-radiative energy transfer increases the number of single magnetite particles and is thus assumed to be responsible for the increase of fluid thermal conductivity.