Nucleation Control of Poly(3-Hexylthiophene) through Crystallization Parameters and Self-Seeding
The aim of this proposal is to control the number density and geometry of nucleation of a conjugated polymer by tuning the stability of selected crystalline aggregates and by using self-seeding as a step towards achieving optimal control of semicrystalline morphology. Regulating the crystallization and morphology of conjugated polymers is key to optimizing properties of single component materials and of their blends. While crystallization of classical polymers like polyethylene is well established, several aspects of conjugated polymer crystallization remain obscure. Some differences are expected due to backbone rigidity, low contour lengths, pi-pi interactions and lateral alkyl chains of conjugated polymers. We expect that some control techniques developed for classical polymers will be applicable to conjugated polymers, but they require a thorough understanding of their crystallization mechanism.
Here, we will investigate the basic mechanism of crystallization of a benchmark conjugated polymer Poly(3-hexylthiophene) and explore how processing can be used to tailor its semicrystalline morphology and properties. Blends of P3HT with Phenyl-C61-butyric acid methyl ester (PCBM) have recently been found to exhibit ferroelectric properties. The final morphology and properties of these blends are thought to be partly regulated by the P3HT crystallization process, so it is crucial to thoroughly understand and control its crystallization mechanism. This project will first seek to find well-defined crystallization parameters to obtain populations of P3HT crystallites with different stabilities. Then, self-seeding protocols will be applied to obtain control of nuclei density and to evaluate stability differences. Second, we will investigate the effect of imposing a flow field on crystalline stability and on subsequent self-seeding behavior. In this case, the focus will be on control of location and geometry of nucleation. This Seed Project is relevant to the IRG2 research focused on the development of organic photovoltaic devices that employ conjugated P3HT semiconducting polymers. Initial results will help define a research direction leading towards rational design of materials and processes to achieve optimal control over morphology and properties.