Shape dependent heat transfer and nonlinear optical limiting characteristics of water stable ZnO nanofluid

Abstract

In this study, we experimentally investigated the shape dependent thermal and nonlinear optical properties of water stable ZnO nanostructures. It is important to note that morphology plays a significant role in determining thermo-optic properties of ZnO. The thermal conductivity of colloidal ZnO was measured using a dual beam collinear thermal lens technique. The result shows a 23% enhancement in thermal conductivity of ZnO nanofluid compared to that of base fluid water. The nanofluid with nonspherical ZnOnanoparticles exhibit greater thermal diffusivity than a fluid with spherical nanoparticles. This enhancement in thermal conductivity was explained using the Hamilton – Crosser model based on the formation of nanolayer and interfacial thermal resistance. The third-order nonlinear optical susceptibility and optical limiting properties were investigated using a single beam Z scan technique. All samples showed two photon absorption and a negative nonlinear refractive index which varied with the nanoparticle morphology. Higher dimensional structures showed better optical nonlinearity due to their large surface area, photon scattering and exciton oscillator strength. The Z scan results reveal an increment of three orders of magnitude in third-order susceptibility for the nanoparticles compared to that of bulk ZnO. The nanofluid also exhibits a good optical limiting behaviour. The findings suggest that ZnO nanostructures can be considered as promising candidates for future optoelectronic devices.