Flexible Chemiresistive Cyclohexanone Sensors Based\non Single-Walled Carbon Nanotube–Polymer Composites

Abstract

We\nreport a chemiresistive cyclohexanone sensor on a flexible substrate\nbased on single-walled carbon nanotubes (SWCNTs) functionalized with\nthiourea (TU) derivatives. A wrapper polymer containing both 4-vinylpyridine\n(4VP) groups and azide groups (P­(4VP-VBAz)) was employed to obtain\na homogeneous SWCNT dispersion via noncovalent functionalization of\nSWCNTs. The P­(4VP-VBAz)–SWCNT composite dispersion was then\nspray-coated onto an organosilanized flexible poly­(ethylene terephthalate)\n(PET) film to achieve immobilizing quaternization between the pyridyl\ngroups from the polymer and the functional PET substrate, thereby\nsurface anchoring SWCNTs. Subsequent surface functionalization was\nperformed to incorporate a TU selector into the composites, resulting\nin P­(Q4VP-VBTU)–SWCNT, for the detection of cyclohexanone via\nhydrogen bonding interactions. An increase in conductance was observed\nas a result of the hydrogen-bonded complex with cyclohexanone resulting\nin a higher hole density and/or mobility in SWCNTs. As a result, a\nsensor device fabricated with P­(Q4VP-VBTU)–SWCNT composites\nexhibited chemiresistive responses (Δ<i>G</i>/<i>G</i>₀) of 7.9 ± 0.6% in N₂ (RH 0.1%)\nand 4.7 ± 0.4% in air (RH 5%), respectively, upon exposure to\n200 ppm cyclohexanone. Selective cyclohexanone detection was achieved\nwith minor responses (Δ<i>G</i>/<i>G</i>₀ < 1.4% at 500 ppm) toward interfering volatile organic\ncompounds (VOC). analytes. We demonstrate a robust sensing platform\nusing the polymer–SWCNT composites on a flexible PET substrate\nfor potential application in wearable sensors.