Interfacial Dilational Rheology of Molecular Films in DC Electric Fields

Area of Science:

• Interfacial science
• Rheology
• Materials science

Background:

• Asphaltenes are complex molecules found in crude oil.
• Understanding their interfacial behavior is crucial for oil recovery and processing.
• Electric fields can influence molecular film properties.

Purpose of the Study:

• To develop and apply a novel technique for measuring interfacial dilational rheology.
• To investigate the effect of direct-current (dc) electric fields on asphaltene films at a water-oil interface.
• To analyze how bulk concentration and electric field strength influence film elasticity.

Main Methods:

• Adsorption of a polar asphaltene subfraction at a water-oil interface.
• Application of a dc electric field to the system.
• Sinusoidal oscillation of a water drop to induce area changes.
• Measurement of dynamic interfacial tension (IFT) using axisymmetric drop shape analysis (ADSA).
• Calculation of interfacial dilational moduli using IFT response and phase difference.

Main Results:

• Asphaltene films exhibited increased elasticity with higher bulk concentrations and electric field strengths.
• The observed elastic behavior was not strictly monotonous.
• The interplay between concentration and electric field strength governed the rheological response.
• The Lucassen-van den Tempel (LVDT) model was used to interpret the results.

Conclusions:

• The study presents a viable method for characterizing interfacial rheology under electric fields.
• Asphaltene film elasticity is tunable via electric fields and concentration.
• Complex interactions dictate the rheological response of asphaltene films.