Shear Thickening of Concentrated Suspensions: Recent Developments and Relation to Other Phenomena

Shear thickening is the increase of the apparent viscosity as shear rate or shear stress increases. This phenomenon is pronounced in concentrated (dense) suspensions of both colloidal-scale and larger particles, with an abrupt form, known as discontinuous shear thickening, observed as the maximum flowable solid fraction is approached. An overview of observed shear thickening behavior is presented, with a discussion of present understanding of the relationship of suspension shear thickening to granular jamming. Mechanistic arguments for the extreme change in rheological properties are outlined, and recent evidence from experiment and simulation for the role of contact forces is presented. Interactions of particles by fluid mechanical lubrication, contact, and steric and electrostatic forces, together with extreme stresses that may lead to solid deformation, require consideration of surface interactions and their tribological consequences in describing shear thickening.