Co-adsorption behavior of asphaltenes and carboxylic acids with different alkyl chain lengths and its effects on the stability of water/model oil emulsion

•Co-adsorption behavior of asphaltenes and organic acids at interface is studied.•Dispersive state of asphaltenes is improved by the alkyl carboxylic acids.•Different chain-length acids interact with asphaltenes by consistent mechanism.•The addition of carboxylic acids causes a more compressible but weaker interface.•Hexadecanoic acid exhibits strongest interactions with asphaltenes among the acids. Asphaltenes and organic acids are commonly-seen crude oil components possessing interfacial affinity. In this work, the co-adsorption behavior of asphaltenes and carboxylic acids and its effects on the emulsion stability are explored. Above all, the acids are found to deteriorate the stability of the original asphaltene-stabilized emulsion. Subsequently, the investigation of the co-adsorption behavior probes a competitive adsorption between the asphaltenes and acids. The interactions between the both components perform further contributions to the formation of the interfacial layer by affecting the dispersive state of asphaltenes. The decreasing dilational modulus of the interface and the decreasing crumpling ratio of the oil droplet with the addition of the acids both indicate a more compressible but weaker asphaltene-containing interfacial layer with the participation of the acids. The interactive mechanism is correlated with the dispersive state of the asphaltenes influenced by the acids, which is characterized by the conductivity and asphaltene precipitation experiments. The acids are verified to modify the dispersive state by combining with the asphaltenes and forming composite-like units, giving a better oil compatibility to the asphaltenes. With the changes in the alkyl chain length of the carboxylic acids, the oil compatibility of the acids changes correspondingly, thus influencing the combining tendency and the oil compatibility of the composite-like units. The hexadecanoic acid exhibits the strongest interactions with the asphaltenes among the acids.