Anisotropic CuO nanostructures of different size and shape exhibit thermal conductivity superior than typical bulk powder

This work demonstrates the preparation of monoclinic crystalline CuO nanospheres (5–10 nm), nanorods (L × W = 100–140 nm × 30–40 nm) and nanowires (200–210 nm × 2–5 nm) for the study of thermal conductivities when dispersed in de-ionized water and ethylene glycol (0.005–0.1 vol%). It has been observed that CuO nanorods and nanowires having surface area 53 and 61 m2 g−1, respectively, always displayed higher thermal conductivity than CuO nanospheres possessing lower surface area (41 m2 g−1), which attributed to the differences in their per-particle surface area, percentage of surface exposed atoms, anisotropic lengthy shape, large phonon-mean-free paths. The experimental results revealed higher thermal conductivities than obtained from theoretical models due to particle shape effect as expected from Hamilton–Crosser equation. It has also been found that density is directly proportionally to thermal conductivity and increases with the increase in volume fraction. The decrease in aggregated particle size (130–104 nm) and an increase in zeta potential value (−32 to −37 mV) of CuO nanospheres causes more stability of CuO dispersion with 3–6 h of sonication.