4 years ago

Dilatational Rheological Properties of Asphaltenes in Oil–Water Interfaces: Langmuir Isotherm and Influence of Time, Concentration, and Heptol Ratios

Dilatational Rheological Properties of Asphaltenes in Oil–Water Interfaces: Langmuir Isotherm and Influence of Time, Concentration, and Heptol Ratios
Claudio Dariva, Cesar C. Santana, Gustavo R. Borges, Alexandre F. Santos, Elton Franceschi, Walisson J. S. Morais
The dilatational rheological interfacial properties are important in colloidal systems due to the possibility of studying changes in the interfacial tension because of interface relaxation and diffusion. Information on these properties enables analyses on the interfacial activity and mechanical behavior of surfactants in the interfaces for different colloidal systems such as petroleum emulsions. The determination of elastic modulus is crucial for characterizing the interfacial behavior of films containing asphaltenes at interfaces. In this study, the pendant drop tensiometry technique was used to describe the rheological interfacial properties of asphaltenes extracted from two Brazilian oils at toluene/water and heptol (heptane + toluene)/water interfaces under varying proportions of organic solvents (1:1 and 1.5:1) and asphaltene concentrations. The applicability of adsorption isotherm models for involving Gibbs theory and Langmuir equation was investigated for the systems studied. For systems containing a good solvent (toluene), the attraction between the solvent and asphaltene molecules was stronger due to their high solubility, thereby reducing the interfacial activity of asphaltene molecules. For systems containing poor solvents (heptol 1:1 and 1.5:1), the interaction between the asphaltene and solvent molecules was weak, resulting in an increase in the interfacial activity of asphaltenes. Maximum surface concentrations in excess (Γ) of 1.69 × 10–5 mol/m2 and 2.77 × 10–6 mol/m2 were obtained for petroleums A and B, respectively, resulting in cross-sectional areas of 9.8 and 59.9 Å2, respectively. The dilatational rheological interfacial properties of the systems studied, surface pressure, and elastic modulus depend exclusively on the interfacial coverage. These results are useful to understand how asphaltene adsorption processes occur at fluid/fluid interfaces at the microscopic level.

Publisher URL: http://dx.doi.org/10.1021/acs.energyfuels.7b01633

DOI: 10.1021/acs.energyfuels.7b01633

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