Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films
| Autor: | Erfan Mohammadi, Gregory M. Newbloom, Joseph Strzalka, Fengjiao Zhang, Lilo D. Pozzo, Ge Qu, Jianguo Mei, Ying Diao, Xikang Zhao |
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| Rok vydání: | 2017 |
| Předmět: |
chemistry.chemical_classification
Morphology (linguistics) Materials science Crystallization of polymers Stacking Nanotechnology 02 engineering and technology Polymer engineering.material Conjugated system 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Coating chemistry engineering General Materials Science Thin film Composite material 0210 nano-technology Anisotropy |
| Zdroj: | ACS Applied Materials & Interfaces. 9:27863-27874 |
| ISSN: | 1944-8252 1944-8244 |
| DOI: | 10.1021/acsami.7b08133 |
| Popis: | Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor-acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiophene-co-thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π-π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. We further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front. |
| Databáze: | OpenAIRE |
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