Impact of Thermal Annealing on the Semicrystalline Nanomorphology of Spin-Coated Thin Films of Regioregular Poly(3-alkylthiophene)s as Observed by High-Resolution Transmission Electron Microscopy and Grazing Incidence X-ray Diffraction
The impact of thermal annealing on the growth of crystalline nanodomains of poly(3-alkylthiophene) (P3AT) in thin films (15–20 nm thick) was investigated as a function of length of alkyl side chain by combined low-dose high-resolution transmission electron microscopy (HR-TEM) and grazing incidence X...
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Veröffentlicht in: | Macromolecules 2012-07, Vol.45 (13), p.5575-5585 |
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Sprache: | eng |
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Zusammenfassung: | The impact of thermal annealing on the growth of crystalline nanodomains of poly(3-alkylthiophene) (P3AT) in thin films (15–20 nm thick) was investigated as a function of length of alkyl side chain by combined low-dose high-resolution transmission electron microscopy (HR-TEM) and grazing incidence X-ray diffraction (GIXD). Statistical analysis of the data yields the characteristic dimensions of the face-on oriented P3AT nanocrystals, i.e., average stem length l c along backbones and lateral dimension perpendicular to the stems l a along side chains. The following trends were identified: (i) in as-spin-coated films, the proportion of face-on oriented nanocrystals increases with the number of carbon atoms in the side chain, (ii) annealing favors the lateral in-plane growth of the nanocrystals along the side chain direction (a P3AT axis), (iii) for a given P3AT, the proportion of face-on oriented domains increases with annealing temperature, (iv) lateral growth along the a P3AT axis is most efficient for the longer octyl side chains, and (v) thermal annealing induces only modest lamellar thickening which is limited by the poor slide diffusion of π-stacked P3AT chains as opposed to lateral growth favored by weak van der Waals interactions between layers of n-alkyl side chains. The increase in the population of face-on oriented crystallites, observed when the length of the side chain increases, coincides with a corresponding decrease in the field effect mobility in annealed P3AT thin films. |
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ISSN: | 0024-9297 1520-5835 |
DOI: | 10.1021/ma300906v |