Effect of ZrO2 nanoparticles on the interfacial behavior of surfactant solutions at air–water and n-heptane–water interfaces

We have studied air–water and oil–water interfacial tensions of systems containing both surfactants and ZrO2 nanoparticles. Anionic surfactant (sodium dodecyl sulfate, SDS), Cationic surfactant (Dodecyl trimethyl ammonium bromide, C12TAB), and nonionic surfactant (Lauryl alcohol 7 mole ethoxylate, LA7) effectively decrease n-heptane–water interfacial tension and air–water surface tension. At water–air interface, inclusion of negatively charged ZrO2 nanoparticles considerably alters the surface activity of SDS molecules and has negligible impact on the surface tension of CTAB and LA7 solutions. At n-heptane–water interface and below the critical micelle concentration (cmc) of the selected surfactants, addition of nanoparticles increases the surface activity of all selected surfactants and reduces the interfacial tension. At and above cmc, nanoparticles have no impact on the interfacial tension. The calculated adsorption energies show that nanoparticles are surface active at oil–water interface with negligible tendency toward adsorption at air–water interface. Inclusion of nanoparticles showed strongest impact on the interfacial behavior of LA7 solutions, resulting in almost constant interfacial tension value in all ranges of surfactant concentration. Dynamic light scattering technique, zeta potential measurement, and centrifugation of the nanofluids are performed to explain the interfacial behavior of nanoparticle-surfactant systems.