Structure and dynamic properties of colloidal asphaltene aggregates.

Area of Science:

• Colloid and Surface Science
• Materials Science
• Petroleum Chemistry

Background:

• Asphaltene literature presents conflicting particle size data from dynamic vs. static scattering measurements.
• Discrepancies exist between small (1-3 nm) dynamic sizes and larger (7 nm) static radii of gyration.

Purpose of the Study:

• To reconcile conflicting asphaltene size data using complementary scattering techniques.
• To investigate asphaltene polydispersity and aggregation mechanisms in toluene solutions.
• To characterize the structure and fractal nature of asphaltene aggregates.

Main Methods:

• Utilized a custom dynamic light scattering (DLS) setup for dark/fluorescent solutions.
• Employed small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS).
• Prepared asphaltene solutions via centrifugation to analyze polydispersity.

Main Results:

• Asphaltene solutions consist of Brownian colloidal aggregates with hydrodynamic radii of 5-10 nm.
• Radii of gyration were comparable, ranging from 3.7 to 7.7 nm.
• A small fraction of larger aggregates (~40 nm) was found in the centrifugation pellet, exhibiting fractal character over a decade length scale.

Conclusions:

• Dynamic light scattering and small-angle scattering techniques are complementary for asphaltene characterization.
• Asphaltene nanoaggregates (3 nm) aggregate to form fractal clusters.
• Findings confirm and elaborate on previously proposed asphaltene aggregation mechanisms.