Pattern Evolution Induced by Periodic Temperature Modulation in a Binary Polymeric Mixture

Summary: The process of periodic phase separation is numerically studied based on Cahn‐Hilliard‐Cook theory for a binary polymer blend. The model system is quenched blow and above the critical point alternatively. And hierarchic morphologies consisting of large and small domains are observed. As the periodic phase separation proceeds, small domains are created and destroyed periodically, whereas large domains keep growing. Within the first half of each period, the behavior of small domains is similar to the two‐step phase separation. And the quench to one‐phase region during the second half period not only decreases the peak intensity of structure function for large domains, but also eliminates the high‐wave number peak corresponding to small domains. The average order parameter under oscillatory quenches exhibits a periodic behavior. The minimum of average order parameter in each period approaches to its equilibrium value monotonously and the maximum value increase in the early time regime and decrease in the late time regime. The magnitude of oscillation has considerable effects on the evolution of hierarchic structures. Small magnitude of oscillation hinders the formation of hierarchic morphologies. Moreover, large magnitude of oscillation slows down the coarsening of large domains in the early stage of periodic phase separation and accelerates the growth of large domains in the late time regime. In addition, no scaling invariance could be observed for the net growth of large domains.Snapshot picture of periodic phase separation with \bar \chi , Δ χ , and τ p .