Probing the\nInterfacial Interaction Mechanisms of\nNitrogen with Dodecane/Toluene: Implications for Foam Flooding

Interfacial interactions between deformable bubbles and\noil drops\nhave attracted much attention in foam flooding. However, interactions\ninvolving nitrogen bubbles have not been reported. In this work, the\ninteraction forces between nitrogen and dodecane/toluene in aqueous\nsolutions were quantified using the atomic force microscopy bubble\nprobe technique. The effects of the solution pH, ionic type, and solution\nconcentration on the interactions were analyzed. The van der Waals\n(vdW), electric double layer (EDL), and hydrophobic (HB) interactions\nwere involved in the low-concentration solutions. The EDL repulsion\nin NaCl increased with solution pH, while in CaCl<sub>2</sub> and\nMgCl<sub>2</sub>, the EDL repulsion in general decreased and then\nincreased with pH, attributed to the adsorption of OH<sup>–</sup> and divalent cations and their hydration products. The adsorption\nof divalent cations at the toluene/water interface was pronounced\nby cation−π interactions. At pH 10, precipitated divalent\ncation hydroxides at the bubble/water and oil/water interfaces adsorbed\nmore cations, causing the increase of the surface potential. At high\nsalinity, the EDL interaction was suppressed and the vdW repulsion\nbecame predominant. The vdW force of nitrogen with toluene was stronger\nthan that with dodecane. Under all of the solution conditions, the\nattractive interaction could not overcome the total repulsive interaction\nat the minimum separation, and thus no bubble attachment was observed,\nwhich implied that a stable bubble/liquid/oil film was essential for\nmaintaining foam stability. This work provides useful insights into\nthe interfacial interaction mechanisms in nitrogen foam flooding.\nThe findings can be readily extended to other engineering systems\nsuch as oil flotation and bubble–oil–water emulsions.