Carbon Nanotube Functionalization and Radiation Induced Enhancements in the Sensitivity of Standalone Chemiresistors for Sensing Volatile Organic Compounds

Chemical stress-induced alterations in the number-density and the architecture of conducting interjunctions impart chemiresistivity in conducting polymer composites (CPCs). Herein, marked enhancement in the chemiresistive response of CPCs is reported by maneuvering interfacial and percolation characteristics of carbon nanotube (CNT) based chemiresistors, through CNT functional group variation and high energy radiation exposure. Unfunctionalized (CNT-UF), hydroxyl functionalized (CNT-OH), amine functionalized (CNT-NH2), and carboxyl functionalized (CNT-COOH) carbon nanotubes, polydimethylsiloxane (PDMS), and γ radiation were used in different combinations to prepare PDMS/CNT chemiresistors. Even at the same ϕCNT, PDMS/CNT-NH2 chemiresistors exhibited significantly milder response against toluene vapors than PDMS/CNT-COOH chemiresistors, whereas PDMS/CNT-OH chemiresistors were unresponsive due to poor nanotube dispersion and low electrical conductivity. PDMS/CNT-COOH chemiresistors had the lowest surface energy, highest entanglement density, and highest critical strain for CNT–CNT structure breakdown under shear, suggesting superior interfacial interactions. Dielectric, CNT percolation, and XPS analysis also revealed marked variations in CPC properties with change in functional groups on CNT. The gel content of all irradiated chemiresistors increased with radiation dose; however, amine-functionalized CNT was found to inhibit interfacial radical combinations. With the increase in radiation dose, the chemiresistivity increased in a dose-dependent fashion, suggesting the possibility of interfacial grafts and immobilization of PDMS segments onto the CNT-COOH surface. The chemiresistivity of the PDMS/CNT-COOH chemiresistor was highly dependent on polymer–solvent interaction parameters. The chemiresistor displayed excellent sensitivity, reversibility, and reproducibility, underscoring its potential in monitoring hazardous volatile organic compounds.