Controlling microstructure in poly(3-hexylthiophene) nanofibers

We demonstrate the ability to control the microstructural order of self-assembled nanofibers of poly(3-hexylthiophene) (P3HT) and link structure differences with formation conditions. We control the crystallization conditions of the P3HT chains through the use of various solvents and show that distinct differences in overall organization occur between nanofiber samples. We also show for the first time that a reorganization of the chains in a nanofiber can occur after heating in solution. This only occurs if the degree of order in the nanofiber is very high. This reorganization leads to P3HT crystals with a larger pi-stacking distance than the usually observed 0.38 nm and this structure can be repeatably obtained. We characterize the nanofibers' microstructure through UV-Vis absorbance, powder X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The amount of microstructural order follows a clear trend with increasing solvent quality. We demonstrate three separate causes for the microstructure variability; (1) the fractionation of polymer chains due to solubility differences, (2) chain conformational differences due to solvent interactions, and (3) the kinetics of formation.