Journal of the American Chemical Society, Vol.133, No.19, 7244-7247, 2011
Solvent Evaporation Induced Liquid Crystalline Phase in Poly(3-hexylthiophene)
We report on the evolution of the chain orientation of a representative pi-conjugated polymer, poly(3-hexylthiophene) (P3HT), during the solution-casting process, as monitored using polarized Raman spectroscopy. These measurements point to the formation of a liquid-crystalline phase of P3HT solutions within a specific time period during solvent evaporation, which leads to a conducting channel. These conclusions are based on the angular dependence of polarized Raman scattering peaks, the anisotropy in the fluorescence background signal, analysis of the scattering-peak shape, and direct observations of the three-phase contact line in an optical microscope under crossed polarizers. These results shed new light on the evolution of chain alignment and thus materials nanostructure, specifically in solution-processed P3HT and more generally in pi-conjugated systems. They may further enable the design of improved materials and processes for this important class of polymers.