EFFECTS OF SHEER FLOW ON LONG-RANGED CORRELATIONS, ON SPINODAL DECOMPOSITION KINETICS AND ON THE LOCATION OF THE CRITICAL-POINT AND CLOUD POINT

This contribution is about three related subjects: (i) The effect of s hear flow on long ranged critical correlations. An expression for the shear rate dependent structure factor is duscussed, together with the resulting anomalous behaviour of the turbidity. The predicted scaling behaviour of the turbidity, comprising both the effect of temperature and shear rate, is in good agreement with experiments on binary fluids . (ii) The effect of shear flow on initial spinodal decomposition kine tics. An explicit expression for the time and shear rate dependent eff ective diffusion coefficient is discussed, which shows all the typical characteristics of anisotropic light scattering patterns that are obs erved experimentally for binary fluids. (iii) The effect of shear how on the location of the spinodal, cq., the critical point, and the clou d point curve. it is shown that the critical point is shifted linearly with the Peclet number for not too large Peclet numbers, whereas the cloud point is singularly displaced into the unstable region on applic ation of a shear flow. It is argued that light scattering is useless t o determine the location of the critical point of a sheared system. Th is is in agreement with an experiment on a two polymer-solvent mixture .