Experimental and theoretical analysis of NiO nanofluids in presence of surfactants

This study presents a combined experimental and theoretical analysis of the stability of NiO nanofluid systems based on a base fluid composed of the eutectic mixture of diphenyl oxide and biphenyl in presence of surfactants. The base fluid is used as a heat transfer fluid in concentrated solar energy and the surfactants were used to analyse the stability of the nanofluids: Benzalkonium Chloride (BAC) and 1-Octadecanethiol (ODT). The stability was analysed experimentally by using UV-vis spectroscopy, particle size and ζ potential measurements. The experimental results indicate that the presence of BAC as surfactant enhance the stability of the nanofluids. Molecular dynamic calculations were performed for three systems (75% BAC, 75% ODT and 75% BAC-75% ODT) to understand the behaviour of both surfactants in the stability of the nanofluid. The analysis of the radial distribution functions (RDFs) and spatial distribution functions (SDFs) revealed a competition of ODT with both base fluid and NiO nanoparticles that explains why the BAC surfactant favoured the formation of stable NiO nanofluid over that with ODT.