Assessing the Interfacial Activity of Insoluble Asphaltene Layers: Interfacial Rheology versus Interfacial Tension

Area of Science:

• Colloid and Surface Science
• Materials Science
• Petroleum Chemistry

Background:

• Asphaltenes, polar components of crude oil, are surface-active and adsorb at oil/water interfaces.
• Dense asphaltene packing at interfaces can lead to solid-like mechanical properties, influencing emulsion stability.
• The precise mechanisms of asphaltene action in emulsion stabilization remain incompletely understood.

Purpose of the Study:

• To investigate the rheological properties of insoluble asphaltene Langmuir monolayers.
• To differentiate the mechanical contributions from thermodynamic aspects of interfacial activity.
• To understand the factors governing the mechanical response of dense asphaltene systems.

Main Methods:

• Measurement of compression isotherms for spread asphaltene Langmuir monolayers.
• Determination of both shear and dilatational rheological properties at the interface.
• Deconvolution of surface tension changes from mechanical contributions using precise interfacial kinematics.

Main Results:

• Asphaltene nanoaggregates show limited efficiency in lowering interfacial tension but provide significant mechanical stresses.
• Physical aging effects, observed in adsorbed layers, are absent in spread asphaltene monolayers.
• Compressional and rheological data align with the soft glassy rheology model, indicating dense packing, with potential multilayer formation at higher coverages.

Conclusions:

• Asphaltenes primarily contribute to emulsion stability through interfacial mechanical properties rather than interfacial tension reduction.
• The behavior of spread asphaltene layers differs from adsorbed layers, particularly regarding physical aging.
• The soft glassy rheology model effectively describes the mechanical response of dense asphaltene systems, with implications for water-in-crude oil emulsion stability.