Oligoaniline-assisted self-assembly of polyaniline crystals.

Abstract

The conductivity and charge transport mobility of conjugated polymers (CPs) are largely correlated with their degree of crystallinity, rendering the crystallization of CPs an important endeavour. However, such tasks can be challenging, especially in the absence of sidechain functionalization. In this study, we demonstrate that the incorporation of a small amount of oligomers, specifically tetraaniline, can induce crystallization of the parent polymer, polyaniline, through a single-step self-assembly process. The resulting crystals are compositionally homogeneous because the oligomers and their parent polymer share the same repeating unit and are both electroactive. Mechanistic studies reveal that the tetraaniline forms a crystalline seed that subsequently guides the assembly of polyaniline due to their structural similarities. Applying this oligomer-assisted crystallization approach to polyaniline with defined molecular weights resulted in single crystalline nanowires for 5000 Da polyaniline, and nanowires with strong preferential chain orientation for those with molecular weights between 10 000 and 100 000 Da. Absorption studies reveal that the polymer chains are in an expanded conformation, which likely contributed to the high degree of packing order. Two-probe, single nanowire measurements show that the crystals have conductivity as high as 19.5 S cm-1. This method is simple, general, and can potentially be applied to other CPs.