Dynamics in polymer blends and polymer-solvent blends close to the glass transition

Overview & Synopsis

In this work, we propose a model for describing the dynamics in polymer blends or polymer-solvent blends close to and below Tg. The model is solved on a 2D lattice corresponding to spatial scales from 10 nm up to a few micrometers and incorporate the heterogeneous nature of the dynamics at the scale of a dynamic heterogeneity (3-5 nm). In case of polymer blends, we apply this model to study phase separation close to and below Tg upon cooling, and rejuvenation in miscible range upon heating. In the course of phase separation, we observe slow structures forming in coexistence with faster ones. In the same time, the global dynamics of the system slows down and domains grow like the logarithm of the time. During rejuvenation, we observe that morphologies melt much faster the elapsed time required to build them during aging. In the case of polymer-solvent blends, the system is put in contact with a solvent reservoir and is at temperatures far below the pure polymer glass transition. We consider situations where the activity of the solvent reservoir is varied in order to describe either films drying or swelling. Our model allows for explaining case-II diffusion in the context of the plasticisation of a glassy polymer by penetrating solvent during swelling. Regarding the process of film drying, we show that films up to 1 micrometer thick can be completely dried. When drying a thicker film, we show that a glassy crust may appear on the free surface, as shown experimentally