Relaxation and growth of concentration fluctuations in binary fluids and polymer blends

Concentration dynamics in binary fluid mixtures and polymer blends is considered on the basis of the continuum field model, where we focus on effects of convective flow generated by the osmotic body force associated with the spatially inhomogeneous concentration. We discuss a subtle point in treating these hydrodynamic effects within a continuum model for incompressible fluid. We also briefly discuss two polymer effects. One is concerned with the natural short length cutoff for the continuum model for unentangled polymer blend, and another is the effects of stress induced by the concentration fluctuation in the blends of entangled polymers. Some representative numerical results on the early stage dynamics after sudden quench will be presented.