Towards additive manufacturing of semiconducting polymers : hot-melt extrusion of PCL:P3HT blends

Abstract

Additive manufacturing of organic π-conjugated compounds via dry processing remains an ongoing challenge due to the unique thermo-mechanical properties of these materials. In this study, we propose the use of poly(ε-caprolactone) (PCL), a thermoplastic polymer well-suited for hot-melt extrusion, as a matrix to facilitate the extrusion of poly(3-hexylthiophene-2,5-diyl) (P3HT). We investigate the PCL-P3HT blends as a model to better understand its behavior during hot-melt extrusion. Thermal and rheological characterizations enable us to identify a "printability window," defined as the temperature range (80–140 °C) where the blends exhibit optimal rheological properties for extrusion. Within this temperature range, the blends demonstrate shear thinning and thixotropic behavior, ensuring suitable printability and high print fidelity. The blends exhibit a composite-like behavior, with P3HT maintaining its aggregated state throughout the processing within this temperature range. The microstructure of the extruded architectures is characterized using UV-visible spectroscopy, revealing characteristic bands at 520, 580, and 610 nm, indicative of aggregated P3HT. Further confirmation of the P3HT aggregation state is provided by optical and fluorescence microscopy, as well as AFM-IR analyses conducted on both the surface and cross-section of the extruded architectures highlighting the sub-micron-scale phase separation between PCL and P3HT. Our results demonstrate the effectiveness of blending an organic π-conjugated compound, traditionally challenging to process via dry processing, with a thermoplastic matrix commonly used in hot-melt extrusion. This approach successfully combines the flexibility and ease of processing offered by PCL with the semiconducting properties of P3HT, thereby paving the way for the fabrication of more complex and functional 3D-printed optoelectronic devices.