  A model of shear thickening in dense suspensions of Brownian soft sphere
colloidal particles is established. It suggests that shear thickening in soft
sphere suspensions can be interpreted as a shear induced phase transition.
Based on a Landau model of the coagulation transition of stabilized colloidal
particles, taking the coupling between order parameter fluctuations and the
local strain-field into account, the model suggests the occurrence of clusters
of coagulated particles (subcritical bubbles) by applying a continuous shear
perturbation.The critical shear stress of shear thickening in soft sphere
suspensions is derived while reversible shear thickening and irreversible shear
thickening have the same origin. The comparison of the theory with an
experimental investigation of electrically stabilized colloidal suspensions
confirms the presented approach.
