Experimental investigation for stability and surface properties of TiO2 and Al2O3 water-based nanofluids

Nanofluids have gained recent attention because of their potential applications in diverse engineering fields like enhancing thermal transport, particle deposition, coating, surface patterning, etc. Stability of nanofluid is vital for their use in these industrial applications, although the pertinent database in the literature is often inadequate. Herein, we investigate the effect of surfactant concentration and particle solid volume fraction (φ) on stability of Ti- and Al-oxide nanoparticle suspensions that are stabilized with different surfactants. While TiO2-AA, TiO2-CTAB nanofluids are found to have appreciable stability, SDBS-stabilized Al2O3 nanofluid shows otherwise. TEM images provide the morphological characteristics of freshly prepared nanofluids, whereas the data of DLS and ZP are used to describe the nanofluid particle size distribution and stability, respectively. SANS data confirm the formation of the different sized particles for all the nanofluids. Surface tension (ST) and contact angle (CA) of the prepared nanofluids have also been reported. Results show that the sessile droplet CA of a surfacted-water solutions decreases as more and more nanoparticles are added in the suspension. ST measurements corroborate with the CA measurements, where the nanofluid ST is found to decrease with increase in solid volume fraction (φ) and temperature. Time-lapse images indicate that the settling behaviour of Al2O3-water nanofluids changes with φ and surfactant ratios, but the TiO2-water nanofluids show consistent stability for all φ and surfactant ratios. The reported trend of variation of the mean deposition fraction per unit time with φ for different surfactant ratios helps in making better choice of surfactant ratio for individual φ.