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Advanced Self-Healing Asphalt Reinforced by Graphene Structures: An Atomistic Insight
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Behavior of asphaltene model compounds at w/o interfaces.

Erland L Nordgård1, Geir Sørland, Johan Sjöblom

  • 1Ugelstad Laboratory, Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. erlandn@chemeng.ntnu.no

Langmuir : the ACS Journal of Surfaces and Colloids
|October 27, 2009
PubMed
Summary

Acidic asphaltene subfractions stabilize water-in-oil emulsions. This study used polyaromatic surfactants as model compounds, employing pulse-field gradient NMR to analyze droplet sizes and interfacial behavior, revealing insights into emulsion stability mechanisms.

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Area of Science:

  • Petroleum Chemistry
  • Colloid and Surface Science
  • Emulsion Science

Background:

  • Asphaltenes in heavy crude oil stabilize water-in-oil emulsions.
  • The precise composition and stabilizing mechanism of asphaltene subfractions remain unclear.
  • Understanding interfacial concentrations and compositions is key to emulsion stability.

Purpose of the Study:

  • To use polyaromatic surfactants with acidic moieties as model compounds for asphaltene surface-active subfractions.
  • To investigate droplet sizes and emulsion stability using a modified pulse-field gradient (PFG) NMR method.
  • To compare PFG NMR with traditional microscopy droplet counting and analyze adsorption behavior.

Main Methods:

  • Modified pulse-field gradient (PFG) NMR for droplet size and stability analysis.
  • Microscopy droplet counting for comparative analysis.
  • UV depletion for studying model compound adsorption onto silica.
  • Liquid-liquid Langmuir trough for investigating interfacial film behavior.

Main Results:

  • Droplet size and stability were dependent on surfactant concentration and water content, linked to interfacial area and available surfactant.
  • Minor structural variations in model compounds significantly affected their adsorption affinity to polar silica surfaces.
  • NMR-derived surface-to-volume ratios correlated with cross-sectional areas from adsorption studies for one model compound.
  • Interfacial film formation was confirmed using a Langmuir trough.

Conclusions:

  • Acidic or strong hydrogen-bonding fractions of asphaltenes promote stable water-in-oil emulsions.
  • Model compounds provide a pathway to study emulsion behavior and demulsifier efficiency based on actual interfacial concentrations.
  • The study suggests a tilted geometry for the aromatic core of asphaltenes at the interface, consistent with real samples.