Effects of Poly(3-hexylthiophene) Molecular Weight and the Aging of Spinning Solution on the Electrospun Fiber Properties

The electrospinning technique has been considered an attractive route for processing conjugated polymers in a significant quantity for large-scale applications. The processing-structure-property relationship of the electrospinning process for conjugated polymers is not well understood. Here, we report the electrospinning of poly(3-hexylthiophene) (P3HT) for three different molecular weights of P3HT: 31, 58, and 83 kDa. Chloroform was used as a solvent, and a high molecular weight poly(ethylene oxide) (PEO) was utilized to facilitate the processing of P3HT. The electrospinning was performed on the freshly prepared and 24 h aged spinning solutions. The aging of the spinning solution led to the self-assembly of P3HT chains, particularly with dominant H-aggregation for 83 kDa P3HT. The structure development and properties of the fibers were investigated, including the single-fiber electrical conductivity measured using a custom-built setup. The electrical conductivity has been found to be increasing with increasing molecular weight, and as high as a five-fold enhancement in single fiber electrical conductivity was obtained compared to the fiber from the freshly-prepared solution. Despite a 25% PEO concentration in the fibers, the maximum electrical conductivity of a single fiber was found to be ≈2.7 X 10^(-5) S/cm, similar to the pristine P3HT thin films. Our study provides an additional understanding of P3HT structure development in electrospun fibers as a function of polymer molecular weight and processing steps and relates that to fiber properties.