Investigating the effects of pH, surfactant and ionic strength on the stability of alumina/water nanofluids using DLVO theory

Alumina nanofluids are one of the most useful nanofluids. In order to evaluate the colloidal behavior of nanoparticles in alumina/water nanofluid, the influence of effective factors such as pH, ionic strength and surfactants, was studied. Zeta potential, particle size and turbidity change of each nanofluid was investigated. According to the results for 0.05, 0.1 and 0.2 mass% nanofluid, point of zero charge was obtained at pH values of 9.5, 10.2 and 10.5, respectively. The highest nanofluid stability occurred at pH 4 and its lowest was at pH 10. The anionic surfactant had a greater effect on the stability in compared with cationic and nonionic surfactants. By increasing in ionic strength, zeta potential and as result nanofluid stability decreased and average particle size reduced. Sulfate salts had a more effect on reducing the nanofluid stability than chloride and carbonate salts. Experimental results of nanofluids stability, theoretically confirmed by plotting and analysis of DLVO theory curves.