Synthesis of Al2O3–SiO2/water hybrid nanofluids and effects of surfactant toward dispersion and stability

In this work, a series of Al2O3–SiO2/water hybrid nanofluid with different volume fractions and surfactant types were prepared. The Al2O3 and SiO2 were synthesized using the sol-gel method, and ultrasonic vibration was used to disperse the powders into the DI water to form nanofluids. The effects of anionic (SDS), cationic (CTAB) and nonionic (PVP) surfactants toward the stability, electrical conductivity, and viscosity of the nanofluid were then investigated. Zeta potential analysis, spectral analysis method, sedimentation method, and centrifugation method were used to compare the stability of the nanofluids. The obtained results indicated that the surfactant played an important role in dispersing the nanoparticles (NPs) and forming stable nanofluids. Nanofluids with low concentration of Al2O3 showed good dispersion in water, but it tended to aggregate when the amount used was higher. The viscosity of nanofluids increased slightly when the surfactant was added due to the increase of solid-phase concentration in the nanofluids. SDS positively affected the dispersion and stability of the nanofluids, and the best ratio of Al2O3:SiO2 was at 30:70. The electrical conductivity increased with temperature, and nanofluid containing CTAB and SDS had a higher increment in conductivity.