SHEAR-INDUCED DISPLACEMENT OF THE SPINODAL OF BROWNIAN SYSTEMS

The displacement of the gas-liquid spinodal of colloids on applying a shear flow is analyzed on the basis of the Smoluchowski equation. Rela tively simple arguments predict that the off-critical part of the spin odal is displaced linearly with the shear rate gamma, while the shift of the critical temperature is similar to gamma(1/gamma) with gamma th e critical exponent for the reciprocal equilibrium compressibility. Th is differs considerably from what is known for molecular systems. It i s also argued that the cloud-point curve under shear no longer coincid es with the spinodal, and is displaced far into the unstable region of the phase diagram. A sharp increase of forward scattered intensity in a sheared system does not probe the location of the spinodal.