Macromolecules, Vol.51, No.20, 8306-8315, 2018
Deformation Mechanism of Poly(3-alkylthiophene) Studied by in Situ X-ray Scattering and Texture Analysis
Understanding the deformation mechanism of conjugated polymers is essential for developing flexible or stretchable electronic devices. In this work, the mechanical properties of poly(3-dodecylthiophene) (P3DDT) and poly(3-hexylthiophene) (P3HT) are measured at different temperatures, and the underlying deformation mechanism is explored by using in situ X-ray scattering and pole figure. It is observed that the modulus and fracture strength of P3DDT decrease with increasing stretching temperature. The elongation at break of P3DDT exhibits a sharp increase when the stretching temperature reaches 45 degrees C. The general deformation process of the two polymers is in line with the traditional deformation mechanism established for flexible crystalline polymers with several special features. Well-defined yielding is not detected even at temperatures below the main-chain glass transition temperature, which corresponds to the microscopic observation of the absence of a well-defined lamellar-fibrillar transition. By analysis of the orientation features, P3DDT and P3HT show different orientation features at 30 degrees C while they exhibit similar c-axis orientation at 110 degrees C. Crystallographic slip is proposed to be the main deformation mechanism at 30 degrees C, while evidence for stress-induced melting and recrystallization is observed at 110 degrees C.