Understanding the effect of different size silica nanoparticles and SDS surfactant mixtures on interfacial tension of n-hexane-water

The impact of different size modified silica nanoparticles (NPs) and sodium dodecyl sulfate (SDS) on the interfacial tension (IFT) of n-hexane-water was investigated. Temperature and atmospheric pressure were constant at 293.2 K and 81.5 kPa. The Results show that SDS with aqueous phase bulk concentrations of up to 3.50 . 10(-3) mol . dm(-3) and different NPs with mass fractions up to 1.00 . 10(-4) are adsorbed positively and cause IFT to decrease. Interestingly, IFT decreases more with the mixtures of SDS and NPs, compared with the case of only SDS. The results also show that the maximum IFT decrease is achieved with the smallest size NP, due to the dominant Brownian motion and the more chance of displacement at the interface. The experimental data of equilibrium IFT were nicely reproduced by the Szyszkowski equation. Accordingly, maximum interface excess decreases with the concentration and the size of NPs; however, adsorption equilibrium constant increases with these parameters. (C) 2016 Elsevier B.V. All rights reserved.