Mission immiscible: overcoming the miscibility limit of semiconducting:ferroelectric polymer blends via vitrification

Blending offers a versatile processing platform to combine multiple properties in a given material system that may not be realized in one single component, or to induce co-operatively entirely new features. Polymers can, however, be challenging to blend due to their low tendency to mix, especially when processed from the melt. Here, we demonstrate that essentially the entire spectrum of phase morphologies, from basically fully intermixed to strongly phase-separated, can be induced reliably in blends produced from the archetypal polymer semiconductor, poly(3-hexyl thiophene), P3HT, and poly(vinylidene fluoride), PVDF, a polymer that can exhibit ferroelectric polymorphs, despite the intrinsically limited miscibility featured by P3HT and PVDF. We achieve this by manipulating chain entanglements in solution, which in turn dictates the molecular mobility of the two components (i.e., mass transport during solidification), and in extreme cases leads to pronounced vitrification in the solid state. Since partly- to well-intermixed systems can be produced when processed from a good solvent for both components, we conclude that entanglements form between P3HT and PVDF molecules, provided their molecular weight and concentration is sufficiently high. Hence, specific phase morphologies can be targeted towards broad materials discovery via the establishment of reliable interrelationships between structure, phase morphology, and properties.