Layer-by-Layer Assembled Film of Asphaltenes/Polyacrylamide and Its Stability of Water-in-Oil Emulsions: A Combined Experimental and Simulation Study

Emulsions with interface-active components at the water/oil (w/o) interface are of fundamental and practical interest in many fields. Here we investigate the interfacial films of asphaltenes and asphaltenes/polyacrylamide (PAM) at the w/o interface of water-in-crude oil emulsions. With the combination of the dissipative particle dynamics simulation and experimental observation, the molecular interactions of asphaltenes and asphaltenes/PAM at the w/o interface are extensively analyzed. We show that the rigid mechanical film of asphaltenes originates from a rigid structure of polycyclic aromatic hydrocarbons (PAHs) and the pi-pi bonding interactions between the PAHs of asphaltenes, and at a higher concentration of asphaltenes, the nanoaggregates of asphaltenes, acting as a space fortress at the w/o interface, make the drop-drop coalescence more difficult. In addition, a layer-by-layer assembled architecture film of asphaltenes/polyacrylamide formed at the w/o interface is identified, and we observe that the inner layer is composed of PAM with a network structure and the outer layer is composed of rigid asphaltenes. While the rigidity and stability of this film are attributed to the viscoelasticity and rheology of PAM and the synergy effect between asphaltenes and PAM, its presence greatly enhances the stability of water-in-oil emulsions. We further conclude that PAM with higher concentrations and molecular weights can generate a more ordered network structure, leading to a more stable asphaltenes/PAM film at the w/o interface. This combined study provides helpful insight into the demulsification of water-in-oil emulsion.