Shear thickening in a solution undergoing inverse melting

Rheological measurements on a solution undergoing inverse melting are presented as a function of temperature and concentration. Under shear, this solution exhibits the phenomenon of shear thickening; i.e. an increase in apparent viscosity with increasing shear rate (gamma) over dot. In particular, a shear-thickening transition happens at a critical shear rate (gamma) over dot(c), which increases with increasing concentration. It defines two different regimes: at low shear rates (gamma) over dot < (gamma) over dot(c), the fluid shows Newtonian behaviour, while at shear rates (gamma) over dot > (gamma) over dot(c), a transition from the Newtonian to the shear-thickening regime is observed. This behaviour is interpreted on the basis of a relaxation process activated by the shear and characterised by a relaxation time tau = 1/(gamma) over dot(c). In the thickening region, the viscosity data are well fitted with a power-law model eta((gamma) over dot)) = A (gamma) over dot(n-1), with n = 1.8. The temperature and concentration behaviour of the zero shear viscosity, the power-law exponent and the critical shear rate are discussed.