Rheological properties of highly concentrated dense packed layer emulsions (w/o) stabilized by asphaltene

Abstract

Dense packed layers (DPLs) were sedimented and removed from various asphaltene stabilized w/o emulsion batches, and contained aqueous phase volume fractions (ϕ) between 0.701 and 0.808. These values are close to the theoretical value of hexagonally close-packed spheres (0.74). Rheological properties of the DPLs were investigated using a rheometer equipped with plate–plate and cone–plate geometries. Flow curves and oscillatory shear measurements were obtained at 20 °C. Shear thinning and yield stress behaviour is observed. The measurements confirm the existence of a DPL yield stress which increases with the aqueous phase volume fraction. Hysteretic flow curve data show agreement with the Herschel–Bulkley relation. Oscillatory shear measurements within the linear viscoelastic regime are confirmed by strain-invariant values of G′ (storage modulus) and G″ (loss modulus). Beyond the linear viscoelastic regime, non-linear relaxation processes are observed. The rheometric results indicate weak gel-like behaviour and a dispersed-fraction dependent gel strength. Correlated UV–vis spectroscopy and NMR measurements indicate asphaltene adsorption amounts (Γ) of 1.95 mg m−2 to 2.15 mg m−2 and average surfaces areas per asphaltene molecule (σ) were in the range of 64–69 Å2 in the DPL.