The impact of different size modified silica nanoparticles (NPs) and sodiumdodecyl 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 showthat the maximumIFT decrease is achievedwith the smallest size NP, due to the dominant Brownianmotion and themore chance of displacement at the interface. The experimental data of equilibriumIFT were nicely reproduced by the Szyszkowski equation. Accordingly, maximuminterface excess decreaseswith the concentration and the size of NPs; however, adsorption equilibrium constant increases with these parameters.
