Quantifying the Mechanical Anisotropy in Poly(3-hexylthiophene) Nanofibers

Correlating the structure with nanomechanical property of semicrystalline conjugated-polymer crystal is of essential importance for the performance improvement and design of flexible electronic devices. Although it is well-known that the semicrystalline conjugated-polymer crystal exhibits anisotropic structure owing to the π–π and layer stacking of highly coplanar conjugated backbones, the structure–nanomechanical property relationship is missing. Here, we investigated the axial mechanical anisotropy of the P3HT nanofiber by using thermal shape-fluctuation analysis and a three-point bending test based on atomic force microscopy. Our results show that Young’s modulus in the layer-stacking direction (EL) is 1–2 orders of magnitude greater than that in the π-conjugated backbone direction (EB). We attribute this mechanical anisotropy to the π-stacking of the P3HT backbone, but the layer stacking will decrease EL, which weakens the mechanical anisotropy. Moreover, we demonstrated that the P3HT nanofiber shows ...