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.
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A close look at polymer degree of crystallinity versus polymer crystalline quality
In the broader polymer field, the term ‘crystallinity’ is often used rather loosely. However, increasingly, it becomes critical to clearly distinguish between degree of crystallinity, which provides the fractional amount of crystalline phase in a polymer, and the crystalline quality, which describes the perfection of the crystalline moieties that may form in a polymer. The reason is that these different structural features dictate important properties of plastic materials, including the mechanical properties of commodity polymers and the behavior of macromolecular ferroelectrics; they also determine which photophysical processes occur in semiconducting polymers. Hence, rigor needs to be applied when establishing structure/processing/property interrelations; and it should become a general practice that specific functions are clearly attributed to the degree of crystallinity, the crystalline quality or a combination of the two. In this perspective,
- NSF-PAR ID:
- 10452331
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Polymer International
- Volume:
- 72
- Issue:
- 10
- ISSN:
- 0959-8103
- Page Range / eLocation ID:
- p. 855-860
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The multiscale morphology and device performance of printed semiconducting polymers are highly sensitive to the substrate/ink interfacial properties during solution coating. There is an urgent need for general design rules correlating the substrate properties and conjugated polymer (CP) morphology, which do not yet exist. Dynamic surfaces are particularly promising for templating highly crystalline and highly aligned conjugated polymer thin films and have been shown in recent studies. Herein, we implement the dynamic-templating method using a series of liquid-infused nanoporous substrates as a tool to study the impact of template reconfigurability and chemistry on the multiscale morphology of conjugated polymer thin films, using a high performing donor–acceptor polymer (DPP-BTz) as a model compound. By quantifying the enthalpy of adsorption, we demonstrate that the strength of template–CP interactions directly measures the effectiveness of dynamic surfaces in promoting conjugated polymer crystallization and alignment. We further show that the enthalpy of interactions increases by enhancing the template dynamics and is sensitively modulated by template chemistry. Specifically, increasing the template–CP interactions leads to a larger domain size and higher degree of crystallinity in templated conjugated polymer thin films prepared by meniscus-guided solution coating. This observation validates our hypothesis that dynamic templates function by promoting the nucleation of conjugated polymers. We also demonstrate that such dynamic-template-dependent morphology is independent of coating speed. Notably, the enhanced morphological properties modulate the charge carrier mobility in field-effect transistors (FETs) over an order of magnitude reaching a hole mobility of 2.8 cm 2 V −1 s −1 . This work is a significant step towards establishing general guidelines on how the substrate–ink interfacial properties influence morphology and performance of solution coated CP thin films.more » « less
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