Molecular dynamics simulations of model asphaltene films to investigate the compositional dependence of the dilational properties

• Multiple independent MD simulations ensure robust sampling of asphaltene film equilibrium properties. • Interfacially active asphaltene efficiently forms robust films with smaller amount than less active ones. • Asphaltene orientation shifts from perpendicular to disordered arrangement with increasing concentration. • Dilational modulus of mixed films is governed by the more surface-active components. Asphaltenes, high-molecular-weight crude oil components, pose challenges in petroleum production and transportation by precipitating and aggregating at oil–water interfaces, forming stable emulsions that hinder separation. The stability of the asphaltene emulsion is linked to the viscoelastic properties of the asphaltene film, which are highly dependent on the film composition. The influence of the additives is often discussed in relation to the asphaltene-to-additives ratio. However, the influence is still inconclusive because of the lack of investigations into the interfacial affinity of the original asphaltene and additives. This study performed molecular dynamics simulations for model asphaltene films where compounds have different interfacial affinities: N -(1-hexylheptyl)- N ′-(5-carboxylicpentyl)perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe), its methylated analogue (C5PeM), and stearate. Multiple independent simulations were performed to overcome the poor sampling of the film properties by a single simulation. The asphaltene molecular orientations within the films show a concentration-dependent shift from the perpendicular-to-interface polyaromatic plane orientation at low concentrations ( c I n t f = 0.33 μmol/m 2 ) to a more disordered arrangement as the asphaltene concentration increases. The transition agrees well with the evolution of the dilational modulus. Crucially, the dilational modulus of mixed films is significantly influenced, and governed by, more interfacially active components like C5Pe and stearate. Microscopic analysis reveals that the dilational modulus is overridden by the accumulation of the interfacially active components, and asphaltene desorption is not necessary for this effect. This study provides the relationship between microscopic behaviors and properties (interfacial tension and dilational modulus), advancing our understanding of the stability of crude oil emulsions. These findings offer a critical basis for optimizing the selection and dosage of demulsifiers in crude oil production, thereby enhancing the efficiency of oil–water separation processes.