An activation energy approach for viscous flow: A complementary tool for the study of microstructural evolutions in sheared suspensions

Time-Dependent Viscous Flow Behavior of a Hydrophobic Fumed Silica Suspension

The viscous flow behavior of a 12.5 vol% hydrophobic fumed silica (Aerosil® R816) suspension in polypropylene glycol of low molecular weight (PPG400) was studied in a stress-controlled rheometer. The steady flow curve showed shear thickening between two shear thinning regions. Time-dependent viscosity response provoked by step changes in shear stresses corresponding to the shear-thickening region apparently agrees with thixotropic behavior just after the very initial stages are surpassed. Almost instantaneous jamming can justify misinterpretation of the results.

Temperature-Induced Aggregation in Portlandite Suspensions

Temperature is well known to affect the aggregation behavior of colloidal suspensions. This paper elucidates the temperature dependence of the rheology of portlandite (calcium hydroxide: Ca(OH)₂) suspensions that feature a high ionic strength and a pH close to the particle's isoelectric point. In contrast to the viscosity of the suspending medium (saturated solution of Ca(OH)₂ in water), the viscosity of Ca(OH)₂ suspensions is found to increase with elevating temperature. This behavior is shown to arise from the temperature-induced aggregation of polydisperse Ca(OH)₂ particulates because of the diminution of electrostatic repulsive forces with increasing temperature. The temperature dependence of the suspension viscosity is further shown to diminish with increasing particle volume fraction as a result of volumetric crowding and the formation of denser fractal structures in the suspension. Significantly, the temperature-dependent rheological response of suspensions is shown to be strongly affected by the suspending medium's properties, including ionic strength and ion valence, which affect aggregation kinetics. These outcomes provide new insights into aggregation processes that affect the temperature-dependent rheology of portlandite-based and similar suspensions that feature strong charge screening behavior.

Activation energy for the viscoelastic flow: Analysis of the microstructure-at-rest of (water- and milk-based) fruit beverages

Fresh fruit beverages are a tasty way to follow the recommendations of World Health Organization. A study on the rheological behaviour of water-based and milk-based fruit beverages with emphasis on the temperature effect was made. The power law model adjusted data of apparent viscosity. The flow index of each beverage was practically constant with temperature variation. Then, one could discuss the variation with temperature of the consistency index. This parameter decreased around 40% in both cases in the temperature interval 5-30 °C. The stability of beverages against the sedimentation of the fruit pulp was clearly affected by the increase of temperature. Viscoelastic moduli were obtained in the linear region. Temperature dependency of both moduli was described in the interval 5-30 °C. The activation energy for linear viscoelastic flow was slightly higher than the activation energy for viscous flow. This result was interpreted as an indication of the strength of the microstructure-at-rest.

Research on Polymer Viscous Flow Activation Energy and Non-Newtonian Index Model Based on Feature Size

The viscous flow activation energy and non-Newtonian index properties of polymer based on feature size were studied through a series of experiments on the rheological properties of amorphous polymer polymethyl methacrylate (PMMA), semi-crystalline polymer polypropylene (PP), and crystalline polymer high-density polyethylene (HDPE) using capillary die with hole diameters of φ0.3 mm, φ0.5 mm, φ1.0 mm, and φ2.0 mm. The results show that the viscous flow activation energy of PMMA decreases with the feature size under microscopic scale. And the viscous flow activation energy of PP and HDPE increases with hole diameters of the die. Under macroscopic scale, the difference in viscous flow activation energy of all polymer materials is significantly reduced with hole diameters of the die. For the non-Newtonian index of the three polymer materials, it decreases with the feature size under the microscopic scale while it increases or does not change with the feature size under the macroscopic scale. At the same time, for different high polymer materials, the viscous flow activation energy model (SVAE model) and non-Newtonian index model (SNNE model) based on feature size were established. Finally, the accuracy and effectiveness of the SVAE model and the SNNE model are verified by comparing with the traditional model and reference data. The viscous flow activation energy and non-Newtonian index values of the polymer material can be calculated conveniently and accurately.