Tuning the nano-scale aggregate structure of conjugated block copolymers for enhanced single-walled carbon nanotube dispersion and thermoelectric applications

Abstract

Herein, conjugated block copolymers with insulating segments are strategically designed to modulate the aggregation behavior of the conjugated polymer (CP) and its interaction with single-walled carbon nanotubes (SWCNTs). The poly(thienylene vinylene) (PTV) derivative, poly[3,4-bis(2-ethylhexyl)thienylene vinylene] (P3,4EHTV; P0), is employed as the conjugated block. Three insulating blocks with varying degrees of hydrophobicity, including poly(ethyl oxide) (PEO), polystyrene (PS), and poly(pentafluoro styrene) (PFS), are introduced to obtain block copolymers P3,4EHTV-b-PEO (P1), P3,4EHTV-b-PS (P2), and P3,4EHTV-b-PFS (P3), respectively. Due to its optimized polymer aggregation structure, the P2/SWCNT nanocomposite thin film exhibits an electrical conductivity and power factor of 946.0 ± 23.7 S cm⁻¹ and 258.7 ± 15.8 μW m⁻¹ K⁻², respectively. The small, loosely packed P2 agglomerates with sufficient intermolecular interactions of the P3,4EHTV blocks allow for effective debundling of the SWCNTs, while the PS block provides steric hindrance for stabilizing the P2-wrapped SWCNTs, thereby achieving the most effective SWCNT dispersion. Further, the effects of insulating block length are investigated by fabricating two additional conjugated block copolymers with medium and high PS molecular weights (P2-M and P2-H). The P2-M/SWCNT nanocomposite film demonstrates improved molecular arrangement at the inter-tube junctions and stronger interfacial interactions, thereby achieving the highest electrical conductivity and power factor of 1023.7 ± 33.5 S cm⁻¹ and 298.8 ± 22.2 μW m⁻¹ K⁻², respectively. These findings highlight the role of conjugated block copolymer architecture in tuning the aggregation structure and modulating the CP–SWCNT interactions, thus providing a rational molecular design strategy for high-performance CP/SWCNT thermoelectric nanocomposites.