Graphene oxide (GO) has gathered widespread interest within the scientific community as a result of its unique properties. In the present work, the interfacial behavior of the GO nanosheet at the crude oil/water interface was explored to investigate its demulsification mechanism for crude oil/water emulsions. The interfacial rheology properties and the interfacial tension were systematically discussed. The results revealed that GO was able to decrease the interfacial tension of the emulsion to a large extent, implying that the GO nanosheet was interfacially active. Unexpectedly, the dilational modulus monotonically increased with increasing the GO dosage. In addition, the coalescence kinetics and the interfacial assembly behaviors of GO were investigated. It was observed that the oil droplet became wrinkled once contacting with the crude oil/water interface, and a thin film was finally left at the interface. Therefore, the GO nanosheet was thought to be able to diffuse to the oil/water interface and self-assembled to jam into a new solid thin "GO film", leading to the increase of the determined dilational modulus of the interface. The morphology of the film was revealed by a confocal fluorescence microscope, and a wrinkled and continuous morphology was observed, implying that the GO nanosheet aligned parallel to the oil/water interface. The findings in the present study are crucial for fully understanding the demulsification mechanism of GO and might provide a facile way to prepare largearea GO thin films.

No abstract

Chemical demulsification is widely used in the petroleum industry to remove water from crude oil all over the world. In this work, the relationship between the rheological properties of oil/water interfacial film and demulsification of crude oil emulsions was investigated. The results showed that the elastic modulus was the critical factor for the dehydration ratio, the emulsions showed high dehydration ratio when demulsifiers reduced the elastic modulus of oil–water film to a certain extent (below 5 mN/m). Correlations between dehydration ratio and equilibrium interfacial tension, dynamic interfacial tension, and loss modulus were also investigated. The results showed no correlation between the interfacial tension (IFT), the loss modulus, and the dehydration ratio. However, correlations were observed between dynamic IFT, loss modulus, and demulsification speed when the demulsifier could reduce the elastic modulus of the oil–water film to <5 mN/m. The loss modulus was directly proportional to the surface viscosity and could influence the demulsification speed, but it was not the critical factor. The dynamic interfacial tension was decisive factor to influence the demulsification speed. Dynamic Interfacial tension could be used to characterize the adsorption time (τ1) and the reorganization time (τ2) of demulsifier molecules at the interface, with the decrease of the τ (τ = τ1 + τ2), the demulsification speed increased. The rupture rate constant (k) of interfacial film increased with the decrease of τ, which accelerated the thinning and rupture of the film, thus increasing the demulsification speed.

No abstract

No abstract

No abstract

No abstract

In the present work, the effects of shear fields on the aggregation of asphaltene molecules in heptane were investigated by means of dissipative particle dynamics simulations. The geometries of asphaltene aggregates without shear fields were studied, and the simulation results provide an interpretation of the experimental results on the microscopic level. The effects of shear fields on asphaltene aggregates were also investigated by accessing the radial distribution functions, spatial orientation correlation functions, and the radii of gyrations. We show that the shear fields can destroy the conformational order of the aggregates by damaging the organized structure and isolating the asphaltenes. As the radius of gyration results show, the asphaltene molecules are elongated to be alike-polymers by shear fields. Moreover, the reason why the viscosity decreases under shear fields is that the shear fields lead to the increase of dimerization free energies.