The influence of sodium dodecyl sulfate (SDS) and SiO2 nanoparticles (NPs), individually and simultaneously, on the interfacial tension of n-hexane – water system was studied. Results showed that SDS with concentration range within (0 - 5.00•10−4) mol•dm−3 and NPs in the mass fraction range of (0 to 1.00•10−4) are adsorbed positively; and cause interfacial tension to decrease. Interestingly, with the presence of both SDS and NPs, interfacial tension is reduced more than with SDS only, because the repulsive interactions between SDS molecules are intensified in the presence of negatively charged NPs. The experimental data were nicely reproduced by the Szyszkowski equation. Accordingly, obtained SDS maximum saturated interface excess is reduced with increasing NPs mass fraction. However, adsorption equilibrium constant increased in the presence of NPs.
