Nonlinear rheological behavior of a concentrated spherical silica suspension |
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Authors: | Prof Hiroshi Watanabe Ming-Long Yao Atsuko Yamagishi Kunihiro Osaki Toshiyuki Shitata Hirokazu Niwa Yotaro Morishima |
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Institution: | (1) Institute for Chemical Research Kyoto University, 611 Uji, Kyoto, Japan;(2) Rheometric Scientific, FE. 2-19-6 Yanagibashi Taito-ku, 111 Tokyo, Japan;(3) Department of Macromolecular Science, Osaka University, 560 Toyonaka, Osaka, Japan |
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Abstract: | Linear and nonlinear viscoelastic properties were examined for a 50 wt% suspension of spherical silica particles (with radius of 40 nm) in a viscous medium, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture. The effective volume fraction of the particles evaluated from zero-shear viscosities of the suspension and medium was 0.53. At a quiescent state the particles had a liquid-like, isotropic spatial distribution in the medium. Dynamic moduli G* obtained for small oscillatory strain (in the linear viscoelastic regime) exhibited a relaxation process that reflected the equilibrium Brownian motion of those particles. In the stress relaxation experiments, the linear relaxation modulus G(t) was obtained for small step strain ( 0.2) while the nonlinear relaxation modulus G(t, ) characterizing strong stress damping behavior was obtained for large (>0.2). G(t, ) obeyed the time-strain separability at long time scales, and the damping function h( ) (–G(t, )/G(t)) was determined. Steady flow measurements revealed shear-thinning of the steady state viscosity ( ) for small shear rates (< –1; = linear viscoelastic relaxation time) and shear-thickening for larger (> –1). Corresponding changes were observed also for the viscosity growth and decay functions on start up and cessation of flow, + (t, ) and – (t, ). In the shear-thinning regime, the and dependence of +(t, ) and –(t, ) as well as the dependence of ( ) were well described by a BKZ-type constitutive equation using the G(t) and h( ) data. On the other hand, this equation completely failed in describing the behavior in the shear-thickening regime. These applicabilities of the BKZ equation were utilized to discuss the shearthinning and shear-thickening mechanisms in relation to shear effects on the structure (spatial distribution) and motion of the suspended particles.Dedicated to the memory of Prof. Dale S. Parson |
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Keywords: | Suspension Brownian motion hydrodynamic interaction stress relaxation damping function shear-thinning shear-thickening BKZ constitutive equation |
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