Implications of Thermal Annealing on the Benzene Vapor Sensing Behavior of PEVA-Graphene Nanocomposite Threads

Abstract

The effect of thermal treatments, on the benzene vapor sensitivity of polyethylene (co-)vinylacetate (PEVA)/graphene nanocomposite threads, used as chemiresistive sensors, was investigated using DC resistance measurements, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). These flexible threads are being developed as low-cost, easy-to-measure chemical sensors that can be incorporated into smart clothing or disposable sensing patches. Chemiresistive threads were solution-cast or extruded from PEVA and <10% graphene nanoplatelets (by mass) in toluene. Threads were annealed at various temperatures and showed up to 2 orders of magnitude decrease in resistance with successive anneals. Threads heated to ≥80 °C showed improved limits of detection, resulting from improved signal-noise, when exposed to benzene vapor in dry air. In addition, annealing increased the speed of response and recovery upon exposure to and removal of benzene vapor. DSC results showed that the presence of graphene raises the freezing point, and may allow greater crystallinity, in the nanocomposite after annealing. SEM images confirm increased surface roughness/area, which may account for the increase response speed after annealing. Benzene vapor detection at 5 ppm is demonstrated with limits of detection estimated to be as low as 1.5 ppm, reflecting an order of magnitude improvement over unannealed threads.

Ultra‐Fast Benzene Gas (C6H6) Detection Characteristics of Cobalt‐Doped Aluminum Oxide Sensors

“…There were no cobalt peaks (impurity phases) in the XRD patterns. This implies that the cobalt is almost dissolved to the aluminum matrix when the volume fraction of cobalt is lower than a certain value [36,37] . From XRD assessment, the strain is increased and lattice distortion is more, [38] implying lattice disorder [39] .…”

“…The lattice disorder increases the active sites for adsorption and desorption (gas sense) [40]. In fact, the aluminum-based nanoparticles are obtained at higher annealing temperature but the nanoparticles are prepared on low temperature due to hydroxide precursor solution in our work [36]. Structural parameters are tabulated in Table2.Figure2(a-c) establishes γ-Al 2 O 3 and Co-Al 2 O 3 oxide particle pre-structure and arrangement.…”

“…This implies that the cobalt is almost dissolved to the aluminum matrix when the volume fraction of cobalt is lower than a certain value. [36,37] From XRD assessment, the strain is increased and lattice distortion is more, [38] implying lattice disorder. [39] The lattice disorder increases the active sites for adsorption and desorption (gas sense).…”

“…[40] In fact, the aluminum-based nanoparticles are obtained at higher annealing temperature but the nanoparticles are prepared on low temperature due to hydroxide precursor solution in our work. [36] Structural parameters are tabulated in Table 2.…”