Viscosimetric and Neutron Scattering Study of Asphaltene Aggregates in Mixed Toluene/Heptane Solvents

A series of viscosimetric and small-angle neutron scattering experiments on asphaltenes diluted in mixed toluene/heptane solvents has been conducted, with the purpose of characterizing the size, molecular weight, and internal structure of asphaltene aggregates as a function of solvent conditions. Wi...

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Bibliographic Details
Published in:	Langmuir Vol. 14; no. 5; pp. 1013 - 1020
Main Authors:	Fenistein, Denis, Barré, Loïc, Broseta, Daniel, Espinat, Didier, Livet, Armand, Roux, Jean-Noël, Scarsella, Marco
Format:	Journal Article
Language:	English
Published:	Washington, DC American Chemical Society 03-03-1998
Subjects:	Applied sciences Condensed Matter Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics Crude oil, natural gas and petroleum products Energy Exact sciences and technology Fuels Physics Soft Condensed Matter Asphaltene Viscosity Small angle neutron scattering Hydrocarbon Molecular size Viscosimetry Measurement method Experimental study Colloid Molecular weight neutron scattering flocculation asphaltene colloid aggregation viscosimetry
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Summary:	A series of viscosimetric and small-angle neutron scattering experiments on asphaltenes diluted in mixed toluene/heptane solvents has been conducted, with the purpose of characterizing the size, molecular weight, and internal structure of asphaltene aggregates as a function of solvent conditions. With increasing flocculant (i.e., heptane) content in the solvent, the intrinsic viscosities of asphaltene aggregates first decreased, went through a minimum for heptane fractions ≈ 10−20%, and then increased at the approach of flocculation. These variations paralleled those of the volume of aggregate occupied per unit mass of asphaltene, a behavior reminiscent of the Flory−Fox relationship for polymers in a solvent. This volume, proportional to the cubed radius of gyration of the aggregates divided by their molecular weight, was determined from the neutron scattering data. For increasing heptane fractions in the solvent, the molecular weight of the aggregates increased with their radius of gyration according to a power law, the exponent being in the range of 2. This exponent also characterized the self-similar internal structure of the asphaltene aggregates. With due care to the possible systematic effects of the strong polydispersity of these aggregates, these results are discussed in light of recent models of colloidal aggregation.
Bibliography:	ark:/67375/TPS-TGH1WLKS-H istex:681B8201D0EFE0B3E6AC79C613426E47CBED64AC
ISSN:	0743-7463 1520-5827
DOI:	10.1021/la9709148