Shape Dependent Thermal Conductivity of TiO2-Deionized Water and Ethylene Glycol Dispersion.

This paper presents the importance of different shapes and crystal phases of TiO2 nanostructures such as TiO2 P-25 (70:30 anatase and rutile), as-prepared nanorods (pure anatase) and sodium titanate nanotubes (orthorhombic Na2Ti2O5 x H2O crystal) on the thermal conductivity of de-ionized water and ethylene glycol. It revealed that TiO2 nanorods (L x W = 81-134 nm x 8-13 nm and surface area = 79 m2 g(-1)) showed always higher thermal conductivity than porous nanotubes (L x W = 85-115 nm x 9-12 nm and surface area = 176 m2 g(-1)) and commercial TiO2 P-25 (30-55 nm surface area = 56 m2 g(-1)), which was explained by their differences in crystallinity, crystal phases, compactness, surface exposed atoms, surface area and much greater mean free path of longitudinal phonon vibrations along its lateral dimensions. The subsequent effect of sonication time from 5-10 h results into the breakdown of TiO2 nanorods cluster (42 to 28 nm) with the instantaneous increase in negative zeta potential values from -31 to -45 mV, respectively, seems to be an additional cause for enhancement in its thermal conductivity.