Characterization of surface tension and contact angle of nanofluids

Abstract

This paper investigates the effects of nanoparticles on surface tension and equilibrium contact angle of TiO₂ - DI water nanofluids. Experimental measurements of surface tension by using the pendant droplet method show that the surface tension of the TiO₂ - DI water nanofluids depends weakly on nanoparticle concentration; however, at higher nanoparticle concentrations the surface tension is lower. Various mechanisms are reported to explain this behavior. Experimental measurements of contact angles of the TiO₂ - DI water nanofluids droplets on borosilicate glass slides exhibit strong nanoparticle dependence, and the general trend is increment of the contact angles with nanoparticle concentration. The effect from the so-called disjoining pressure due to the presence of nanoparticles within the thin nanofluid film wedge at the vicinity of the three-phase contact line is examined. However, the phenomenon is attributed to the pinning of contact line and local changes in solid-liquid interfacial tension due to the depositing of nanoparticles on adsorption sites on solid surface.