Book contents
- Frontmatter
- Contents
- Preface
- General list of symbols
- Useful physical constants and values
- 1 Introduction to colloid science and rheology
- 2 Hydrodynamic effects
- 3 Brownian hard spheres
- 4 Stable systems
- 5 Non-spherical particles
- 6 Colloidal attractions and flocculated dispersions
- 7 Thixotropy
- 8 Shear thickening
- 9 Rheometry of suspensions
- 10 Suspensions in viscoelastic media
- 11 Advanced topics
- Index
- References
8 - Shear thickening
Published online by Cambridge University Press: 05 December 2011
- Frontmatter
- Contents
- Preface
- General list of symbols
- Useful physical constants and values
- 1 Introduction to colloid science and rheology
- 2 Hydrodynamic effects
- 3 Brownian hard spheres
- 4 Stable systems
- 5 Non-spherical particles
- 6 Colloidal attractions and flocculated dispersions
- 7 Thixotropy
- 8 Shear thickening
- 9 Rheometry of suspensions
- 10 Suspensions in viscoelastic media
- 11 Advanced topics
- Index
- References
Summary
Introduction
A commonplace example of the phenomenon of shear thickening in suspensions is cornstarch. Mixed in water under the right conditions, it exhibits a well-known behavior: although it can flow under gravity and be stirred, when it is stirred fast or kneaded, it appears to nearly solidify and strongly resists stirring [1]. Upon a reduction in the stirring speed or applied stress, the material returns to its fluid-like state. Such aqueous dispersions of starch are commonly found in classroom demonstrations, as this remarkable rheological behavior continues to inspire very young students as well as accomplished scientists to inquire more deeply into the nature of multiphase flows.
In a seminal review of shear thickening in suspensions [2], Howard Barnes writes:
We shall find that so many kinds of suspensions show shear thickening that one is soon forced to the conclusion that given the right circumstances, all suspensions of solid particles will show the phenomenon. It is important to note also that in suspensions, the shear thickening is almost immediately reversible, that is to say as soon as the shear rate is decreased, the viscosity (however high it might be) immediately decreases.
Indeed, as discussed in Chapter 3, shear thickening is predicted and observed for dilute dispersions of hard spheres. Figure 3.1 demonstrates that shear thickening can lead to a viscosity higher than the zero shear viscosity, so that very high stresses are encountered in the high shear rate flow of colloidal dispersions. This can be a challenge to the processing of suspensions, limiting pumping, coating, and spraying operations as well.
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- Information
- Colloidal Suspension Rheology , pp. 252 - 290Publisher: Cambridge University PressPrint publication year: 2011