The morphological, structural, and electrical properties of poly(3-methylthiophene) polymer brush films grown on indium tin oxide up to 120 nm thick are reported. Optical spectroscopy experiments indicate that the average orientation of polymer chains is nearly isotropic at thicknesses below 10 nm and above 30 nm, and exhibits mild vertical anisotropy in between. Atomic force microscopy shows that the film surfaces consist of column-shaped domains with an average cross-sectional area (2.3 × 10 −3 μm 2 ) and density (200 μm −2 ) that are independent of film thickness. Analysis of the contact between printed Au electrodes and the polymer brush film shows that a small fraction of the film surface (i.e., the tallest columns) makes contact with the electrodes. The measured bulk resistivity along the columns is 1.4 × 10 5 Ω•cm, 2 orders of magnitude lower than typical values for spuncast poly(3-alkylthiophene) films, while the resistance along individual polymer chains in the columns is estimated to be 360 GΩ/nm per molecule, comparable to molecular wires that exhibit charge transport by intramolecular processes. The enhanced conduction is likely due to additional intramolecular transport pathways enabled by the electrode-polymer brush-electrode device architecture, establishing conjugated polymer brushes as a platform for studying the interplay among synthesis, morphology, and charge transport phenomena.
A highly sensitive amperometric gas-phase nitric oxide (NO) sensor based on a Pt working electrode chemically deposited on a Nafion film is described. The Pt electrode is chemically deposited on a Nafion 117 membrane by impregnating the film with Pt(NH3)42+ ions, which are then exposed to NaBH4 to precipitate conductive Pt metal. The sensor was characterized with a mass-flow controlled 1 ppm NO standard gas and has an electrochemical surface area of 34 ± 9 cm2, low limits of detection (4.3 ± 1.1 ppb) and a fast response time (<5s) toward changes in gas phase NO levels. Good correlation was found for measurements with the new amperometric Pt-Nafion sensor vs. chemiluminescence results for detecting the rates of NO released from CarboSil 2080A polymer films doped with S-nitroso-N-acetylpenicillamine (R = 0.999, m = 0.999, n = 6) and for electrochemical reduction of nitrite to NO (R = 0.999, m = 0.938, n = 3) mediated by a copper(II)-tri(2-pyridylmethyl)amine complex.
The
growth mechanism and polymer density in conjugated polymer
brush (CPB) films composed of poly(3-methylthiophene)
(P3MT) are characterized. X-ray photoelectron spectroscopy experiments
show that the initiation of aryl halide monolayers by Pd(PtBu3)2 produces disproportionated monolayer
initiators. Unlike disproportionated species formed during the solution-phase
initiation of aryl halides, which cannot mediate polymerization, the
surface-bound initiators catalyze polymerization to form CPB films
with a high grafting density (1.2 nm–2). Rutherford
backscattering spectrometry (RBS) experiments show that P3MT CPB films
have a characteristic monomer volume density (3.7 nm–3) that is indistinguishable from the volume density of spuncast poly(3-hexylthiophene)
films. Using these RBS and XPS results, characteristics of P3MT CPB
growth are obtained, including the turnover frequency (7.5 h–1) and polymer molecular weight (300 g/mol·nm).
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