Polymer phase behavior, kinetic arrest and aging: a minimalist view

During processing of solutions or blends of functional polymers, for instance in organic and hybrid electronics, bioelectronics, light emitting devices and energy harvesting, phase transitions, such as (liquid-)crystallization and demixing, may give rise to a characteristic morphology of which the structural features determine the performance of the active element in the eventual device. Natural polymers, i.e. proteins, RNA and DNA, undergo similar phase transitions during compartmentalization of the cyto- or nucleoplasm. From a thermodynamic perspective, the driving forces for such transitions are given by the free energy of the system, which, in case of a passive process, decreases until a state of dynamic arrest is reached. Active systems comprise a source of energy that maintains the system out of equilibrium. I in this contribution, I will demonstrate how minimal thermodynamic models can (re)produce multi-component phase behavior. We extend classical mixing theory with contributions due to specific interactions, thermal transitions and compressibility. I will highlight examples from solution processing, thermal annealing and biopolymer phase separation to show that these coarse grained descriptions appear surprisingly versatile, not only in predicting the equilibrium behavior of complex mixtures, but also in estimating their rheological properties.