Rheological behavior and stability of concentrated silica suspensions

Abstract

In the present article, the rheological behavior and phase stability of concentrated silica suspensions were investigated experimentally by examining the effects of particle size and temperature. The silica particles were stabilized by adsorption of a silane coupling agent, ␥-methacryloxypropyl triethoxy silane ͑MPTES͒. The MPTES-coated silica particles behaved like hard spheres and exhibited the dispersion stability in tetrahydrofurfuryl alcohol which was used as a refractive-index matching solvent. For a monodisperse suspension, the limiting viscosities at high shear rates were correlated satisfactorily with the Krieger-Dougherty equation until the particle volume fraction reached 0.45 above which the limiting high-shear-rate viscosities did not exist. The highly concentrated monodisperse suspensions above ϭ 0.50 displayed the rapidly shear thinning viscosity at low shear rates and underwent the shear thickening at high shear rates. Specifically, the onset of shear thickening shifted to a higher shear rate either as temperature rose or as the suspension became stable. The dichroism from light passed in the flow-gradient direction probed the most effectively the order-disorder transition such as disappearance of hexagonally ordered layered structure and formation of particle clustering, which caused shear thickening at high shear rates. The abrupt change in dichroism caused by the breakdown of hexagonally layered structure occurred almost 1 decade before the onset of shear thickening. Finally, the bimodal suspensions prepared here possessed the reduced shear viscosity and stress in comparison with the monodisperse suspensions of identical volume fraction. The degree of the viscosity reduction became conspicuous for concentrated suspensions usually above ϭ 0.40.

Influence of surfactants on shear-thickening behavior in concentrated polymer dispersions

“…For each sample, with increasing of shear rate, viscosity firstly decreased and then surged when critical shear rate was reached. The shear thinning at lower shear rate arises from transformation from three-dimensional ordered structure to a twodimensionally layered structure that permits continuous deformation (Lee et al 1999). As shown in Fig.…”

“…The rheological properties of STF are influenced by various factors, such as the characteristics of dispersed particles (including the maximum packing fraction, type, shape, size, polydispersion, and interparticle action) and the solvents (Yu et al 2012;Maranzano and Wagner 2001;Maranzano and Wagner 2002;Lee et al 1999;Brown et al 2010;Chang et al 2011;Shenoy and Wagner 2005;Jiang et al 2010). Besides these parameters of the system itself, additives also exhibited great effect on ST behavior.…”

Shear thickening in polymer stabilized colloidal suspensions

“…We want to mention another rheological investigation, carried out by Lee et al (1999) on sterically stabilized silica particles in THFFA, in which they studied the onset of shear thickening as a function of the temperature. They suggested that the onset of shear thickening must be associated with an activation process, since the critical shear rate and the corresponding viscosity are straight lines in an Arrhenius plot.…”

Stabilizing Colloidal Particles against Salting-out by Shortening Surface Grafts

“…Some examples are the glass transition or the crystal nucleation of hard spheres. For instance, poly(methylmethacrylate) and silica particles in organic solvents have been used to study glass formation and other aspects related to phase behavior of hard spheres and attractive spheres [1,2,3,4]. Polystyrene and fluorinated sphere systems have been employed to understand the effect of long-range repulsion on static and dynamic [5,6] properties, and also crystal formation [7].…”