Strain-thickening and shear-thickening phenomena in suspensions: Comparison of steady and dynamic properties
- North Carolina State Univ., Raleigh, NC (United States)
Concentrated suspensions of non-interacting particles are known to exhibit shear-thickening under steady shear. Recent studies have found that these systems also exhibit an analogous behavior under dynamic oscillatory shear, termed {open_quotes}strain-thickening{close_quotes}. The latter phenomenon deals with the abrupt increase in complex viscosity, {eta}{sup *} when the strain-amplitude and frequency of the oscillations both exceed critical values. Our studies on fumed silica suspensions in polar glycols indicate a strong link between the two phenomena. We have found a close correspondence between the steady viscosity plotted as a function of shear-rate, and the complex viscosity plotted as a function of the maximum dynamic shear-rate. Both phenomena can be explained by a `clustering` mechanism, consistent with Stokesian dynamics simulations of such systems. According to this mechanism, the increase in viscosity ({eta} or {eta}{sup *}) is due to the formation of hydrodynamic clusters, generated when hydrodynamic forces overcome the repulsive interactions between the particles. Suspensions of non-interacting particles often exhibit shear-thickening, i.e., their viscosity increases over a range of steady shear-rates. At the onset of shear-thickening, the hydrodynamic forces on the suspended particles become predominant. The nature of the microstructural changes induced by these hydrodynamic forces is still a matter of conjecture. According to the `clustering` theory, the particles are temporarily forced into larger clusters, thereby accounting for the increase in viscosity. The same suspensions which show shear-thickening under steady flow also show an analogous behavior under oscillatory shear, termed strain-thickening. The latter phenomenon refers to the abrupt increase in the complex viscosity, {eta}{sup *} observed at large strain-amplitudes and oscillation frequencies. The present study is concerned with the rheological behavior of fumed silica suspensions.
- OSTI ID:
- 602827
- Report Number(s):
- CONF-961108--
- Country of Publication:
- United States
- Language:
- English
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