Decreased thermal diffusivity in fluids containing InP nanocrystals

Colloidal suspensions of semiconductor InP nanocrystals were prepared using the reaction of indium myristate and tris(trimethylsilyl)phosphine in 1-octadecene at elevated temperatures. The semiconductor nanocrystals are highly crystalline, monodisperse and soluble in various organic solvents. Thermal properties of toluene containing 4.6 nm InP semiconductor with different percentage mass (6.0-16.0 %) were measured using the mode-mismatched dual-beam thermal lens technique. This was performed to determine the effect on nanofluids' thermal diffusivity caused by the presence and concentration of semiconductor nanocrystals. The characteristic time constant of the transient thermal lens was estimated by fitting the experimental data to the theoretical expression for transient thermal lens to determine the thermal diffusivity of the semiconductor nanofluids (toluene containing InP nanocrystals). The results obtained show that the nanofluids' thermal diffusivity depends strongly on the contents of the nanocrystals. The thermal diffusivity enhancement in nanofluids is negative when concentration of nanocrystals increases. Such behavior differs from other nanofluids, since they have shown positive thermal diffusivity enhancements. The minimum diffusivity was achieved on nanofluids with higher concentrations. A possible explanation for such low thermal diffusivity of the nanofluids with semiconductor nanocrystals is given. In order to characterize the InP nanocrystals, the following techniques were used: UV-Vis spectroscopy, transmission electron microscopy and high-resolution electron microscopy.