Amphiphilic Janus SiO ₂ Nanoparticles with Different Alkyl Chains for Stable Pickering Emulsion and Enhanced Oil Recovery

Pickering emulsions stabilized by Janus particles have promising prospects in replacing traditional emulsion flooding. Janus SiO2 particles (JSN-Cn) with different hydrophobic chain (alkyl chain) lengths were prepared and compared in terms of their emulsion stability and enhanced oil recovery (EOR) potential. The emulsion stability of JSN-Cn showed the regularity of JSN-C18 > JSN-C16 > JSN-C14 > JSN-C12 > JSN-C10. The emulsification index (EI) of the emulsion stabilized by JSN-C18 was maintained above 70% under temperature (<90 °C) and pH (4–7) conditions. Salt was conducive to the stability of the emulsion at low concentrations (or valence state) and the strong aggregation of particles at high concentrations (or valence state) led to emulsion instability. The longer hydrophobic chain (JSN-C18) improved the perturbation capacity of particle adsorption at the interface from the perspective of dilational and shear rheology. Pickering emulsion ([JSN-C18] = 0.1 wt %) can alter the contact angle of oil droplets on underwater–oil-wetted rock surfaces from 55° to 107°, achieving wetting reversal. JSN-Cn increased the recovery by 8.62–10.82% compared to initial water flooding. The cumulative recovery increased continuously with the growth of the hydrophobic chain, which was attributed to the stability of the emulsion.