The rheological behavior of heavy oils is critical for oil exploitation in different stages, such as extraction, transportation, and refining; during this process, the oil undergoes temperature changes that directly affect the viscosity. For light oils, the viscosity decreases around 1 order of magnitude when the temperature increases 100 K, whereas for heavy oils, this change could be of more than 3 orders of magnitude for the same temperature increment. Furthermore, the heavy oils exhibit a viscoelastic behavior, usually characterized by a viscosity reduction with the increment in the shear rate, the presence of elasticity, and time-dependent rheological behavior. As the temperature increases, the oils acquire a Newtonian behavior. This change is illustrated with the rheological characterization of five heavy oils with an American Petroleum Institute (API) gravity around 12°, different compositions, and zero-shear viscosity that varies up to 2 orders of magnitude among oils. The measurements were carried out in a controlled stress rheometer using a 40 mm parallel plate geometry with a gap of 1 mm. The fluids were tested in rotational and oscillatory modes at temperatures from 5 to 100°C. In the oscillatory experiments, the loss and storage moduli, associated with viscosity and elasticity, respectively, are presented. Above a transition temperature, not only does the viscosity decrease but also the normal force and the elastic modulus tend to vanish, suggesting that the non-Newtonian behavior is also strongly related to the temperature. Furthermore, the departure from linearity of the logarithm of zero-shear viscosity versus the inverse of the temperature appears to correlate with the transition from non-Newtonian to Newtonian behavior.

A nylon 6 nanocomposite with copper nanoparticles processed by ultrasound-assisted extrusion was prepared at concentrations between 0.01 and 0.50 wt.%, and its thermal and mechanical properties were determined. The presence of the crystalline phase α (α1 and α2) in the polymer matrix was confirmed by X-ray diffraction, and the presence of the α2 phase showed a greater increase than the α1 phase as a function of the copper nanoparticle concentration. This process was attributed to secondary crystallization. Furthermore, it was determined that the chemical composition of the nanoparticles is a blend of metallic copper and cupric oxide. The formation of copper nanowires was observed by scanning electron microscopy, and the concentration of 0.10% exhibited the best dispersion in comparison with the other concentrations. The melting temperature of the nanocomposites underwent a slight decrease in comparison with the nylon 6, while thermal stability, crystallization temperature, and crystallinity were increased in relation to the pure polymer. This behavior is attributed to an efficient dispersion of the nanoparticles and to their functionality as crystal nucleation sites. For the 0.10% concentration nanocomposite, higher mechanical properties were obtained; tensile strength increased by 8.9%, and the tensile modulus increased by 25.4%; as a consequence, elongation at break was 62% less than that of the polymer matrix.

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