Thermal-lens probing of the enhanced thermal diffusivity of gold nanofluid-ethylene glycol mixture

The thermal diffusivity values of mixtures comprising ethylene glycol and an aqueous dispersion of gold nanoparticles (50/50 volume ratio) is measured using dual-beam thermal-lens technique, as a function of concentration of gold nanoparticles, and the results are compared with the corresponding thermal diffusivity values of gold nanofluids alone. The results show that, in addition to the well-known effect of nanoparticle concentration, the host fluid also play a crucial role in determining the effective thermal diffusivity value of the mixture. The UV-Vis spectroscopic studies of nanoparticles, prepared via citrate reduction method, exhibit the surface plasmon resonance band peaking around 520 nm and the transmission electron microscopic studies reveal that the particles are well dispersed and are having an average size of 15 nm. The transmission electron microscopy images of the gold nanoparticles in the mixture clearly indicate the formation of chain-like aggregates due to dipole-dipole interaction. Such a chain-like structure allows easy transport of thermal energy, which results in enhancement of thermal diffusivity values of the mixture as compared to the gold nanofluids alone.