ISSN:
1435-1528
Keywords:
Key words Suspension
;
Brownian motion
;
hydrodynamic interaction
;
shear-thinning
;
shear thickening
;
dynamic clustering
;
BKZ
;
constitutive equation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract Time-dependent nonlinear flow behavior was investigated for a model hard-sphere suspension, a 50wt% suspension of spherical silica particles (radius=40nm; effective volume fraction=0.53) in a 2.27/1(wt/wt) ethylene glycol/glycerol mixture. The suspension had two stress components, the Brownian stress σ B and the hydrodynamic stress σ H . After start-up of flow at various shear rates , the viscosity growth function was measured with time t until it reached the steady state. The viscosity decay function was measured after cessation of flow from the steady as well as transient states. At low ˙γ where the steady state viscosity ) exhibited the shear-thinning, the and data were quantitatively described with a BKZ constitutive equation utilizing data for nonlinear relaxation moduli . This result enabled us to attribute the thinning behavior to the decrease of the Brownian contribution (considered in the BKZ equation through damping of ). On the other hand, at high ˙γ where exhibited the thickening, the BKZ prediction largely deviated from the and data, the latter obtained after cessation of steady flow. This result suggested that the thickening was due to an enhancement of the hydrodynamic contribution (not considered in the BKZ equation). However, when the flow was stopped at the transient state and only a small strain (〈〉;0.2) was applied, was hardly enhanced and the data agreed with the BKZ prediction. Correspondingly, the onset of thickening of was characterized with a ˙γ-insensitive strain (≅0.2). On the basis of these results, the enhancement of (thickening mechanism) was related to dynamic clustering of the particles that took place only when the strain applied through the fast flow was larger than a characteristic strain necessary for close approach/collision of the particles.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s003970050067
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