Conjugated Polymer Assemblies on Carbon Nanotubes

The assembling behavior of four thiophene-containing conjugated polymers, regioregular poly(3-hexythiophene) (rr-P3HT), poly(3,3-didodecylquaterthiophene) (PQT-12), poly(2,5-bis(3- tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-14), and poly(2,5-bis(3-tetradecylthiophen-2-yl)thiophen-2-yl)thiophen-2-ylthiazolo[5,4-d]thiazole) (PTzQT-14), on carbon nanotubes was investigated through microscopic studies of nanowire formation and theoretical simulation. It is found that polymer backbone rigidity and shape influence the attachment mode on carbon nanotubes. rr-P3HT and PQT-12 have a zigzag backbone structure that allows a thermodynamically stable coaxial attachment on CNTs, providing an ordered growth front for the nanowire formation. In contrast, fused rings in PTzQT-14 and PBTTT-14 create a stair-step like backbone structure that causes a kinetically controlled wrapping conformation on CNTs, generating a twisted growth front that hinders the nanowire formation. In addition, the rigidity of polymer backbone influences the wrapping mode. Polymers with more flexible backbones (i.e., PBTTT-14) would take a dense irregular wrapping mode on CNTs. The CNT diameter plays an important role in the nanowire formation when CPs attach to the CNT in the wrapping mode. Larger nanotubes with smaller surface curvature provides a less twisted polymer growth front, allowing the formation of CPNWs.