Effect of Shear History on Rheology of Time-Dependent Colloidal Silica Gels

Abstract

This paper presents a rheological study describing the effects of shear on the flow curves of colloidal gels prepared with different concentrations of fumed silica (4%, 5%, 6%, and 7%) and a hydrophobic solvent (Hydrocarbon fuel, JP-8). Viscosity measurements as a function of time were carried out at different shear rates (10, 50, 100, 500, and 1000 s −1 ), and based on this data, a new structural kinetics model was used to describe the system. Previous work has based the analysis of time dependent fluids on the viscosity of the intact material, i.e., before it is sheared, which is a condition very difficult to achieve when weak gels are tested. The simple action of loading the gel in the rheometer affects its structure and rheology, and the reproducibility of the measurements is thus seriously compromised. Changes in viscosity and viscoelastic properties of the sheared material are indicative of microstructural changes in the gel that need to be accounted for. Therefore, a more realistic method is presented in this work. In addition, microscopical images (Cryo-SEM) were obtained to show how the structure of the gel is affected upon application of shear.

Sensory, Tribological, and Rheological Profiling of “Clean Label” Starch–Lipid Complexes as Fat Replacers

“…Thixotropic suspensions exhibit time‐dependent behavior and given time, sheared systems will regain their original structure . During the process of shearing, there is a decrease in viscosity with time until a balance is reached between structural breakdown and re‐formation for thixotropic suspensions …”

Rheological Properties of Organic Kerosene Gel Fuel

“…If the gel has not been subjected to shear effect, , whereas after the gel is sheared for a sufficiently long time (at a certain shear rate) that the viscosity no longer changes, the structure parameter at this point is the equilibrium structure parameter, . In this sense, the physical value of should be bounded between 0 and 1 [ 32 , 39 ].…”

“…The specific expressions of the structural parameters can be obtained from the so-called thixotropic loop test, typically a series of up and down shear rate ramps, given that the gel fuel has “memory” of the shear history. Santos [ 32 ] incorporated structural parameters into the HBE model, and applications on silica gel show that the time-dependent behavior of the viscous force was well predicted.…”

Understanding the Behaviour of Real Metaborates in Solution

“…Furthermore, if the pathway is not fully reversible, more permanent changes in structure, such as disentanglement of polymers, may occur. [31][32][33][34] The 5 w/w% solution showed that the viscosity reduction was reversible, albeit that the shear thinning proceeded by shear thickening followed different pathways. This implies a more complex microstructure rearrangement than just simple dispersion and agglomeration of spherical particles.…”