Kinetics and Mechanism of Poly(3-hexylthiophene) Crystallization in Solution under Shear Flow

The morphology of poly (3-hexylthiophene) (P3HT) in its liquid phase and its manipulation via flow-induced solution crystallization and its crystallization kinetics was studied to determine its mechanism. Shear flow-induced ordering of semiconducting P3HT, which generates more perfect crystal structures than quiescent methods, is elucidated using in situ rheo-SANS and rheo-SALS measurements, and an Avrami analysis is performed. Characteristic lengths of P3HT crystals were measured as a function of time, and 3-D networks of percolated P3HT fibril crystals were determined by measuring the apparent fractal, ∼2.6, by fitting the rheo-SANS data with a power law function. Additionally, UV-vis and DSC results revealed a process of P3HT crystal perfection determined by following the evolution of absorption peak characteristics of pi-pi stacking at 600 nm and the melting peaks as they shifted and narrowed with respect to increasing shear time. The Avrami exponent, m, reached a maximum value of 2 indicating homogeneous nucleation of P3HT macromolecules that allowed one-dimensional fibril crystal growth and was limited by contact time between the P3HT molecules rather than the diffusion of P3HT chains and this is attributed to the highly directional pi-pi stacking attractions of electron pi in the thiophene rings.