Contact angles decrease with the increase in time, nanoparticle concentration and salinity (from Nwidee et al., 2017). a: Receding and advancing water contact angles (versus toluene) as a function of nanoparticle concentration (60 min exposure time). b: Receding and advancing water contact angles (versus toluene) as a function of time (7 wt% NaCl brine; 0.05 wt% nanoparticle concentration). c: Receding and advancing water contact angles (versus toluene) as a function of NaCl concentration (0.05 wt% nanoparticle concentration; 60 min exposure time).