Capacitive Humidity Sensor with a Rapid Response Time on a GO-Doped P(VDF-TrFE)/LiCl Composite for Noncontact Sensing Applications

Abstract

Humidity-sensing devices are widely utilized in various fields, including the environment, industries, food processing, agriculture, and medical processes. In the past few years, the development of noncontact sensors based on moisture detection has increased rapidly due to the COVID-19 pandemic. Moisture-detection, noncontact and breath-monitoring sensors have promising applications in various fields. In this study, we proposed a rapid-response graphene oxide (GO)-doped P(VDF-TrFE)/LiCl nanocomposite-based moisture sensor fabricated on an interdigitated electrode. The synthesis of GO/P(VDF-TrFE)/LiCl resulted in a porous structure with nano-sized holes due to the effect of LiCl. Moreover, doped GO improved the conductivity of the sensing film. The created nanoporous structure improved the recovery time better than the response time, with the times being 4.8 s and 7.8 s, respectively. Not only did our sensor exhibit rapid response and recovery times, it also exhibited a high sensitivity of 1708.8 pF/%RH at 25% to 93%RH. We also presented a real-time breath-monitoring system for noncontact sensing applications based on GO-doped P(VDF-TrFE)/LiCl composites. The results revealed that GO-doped P(VDF-TrFE)/LiCl is a good candidate for fabricating real-time moisture-detection noncontact sensing devices.

Boosting the Sensitivity and Hysteresis of a Gel Polymer Electrolyte by Embedding SiO2 Nanoparticles and PVP for Humidity Applications

“…Therefore, the frequency at which the impedance modulus changes its slope acts as a threshold frequency. This behaviour change can also be observed in Figure 1b, where, Gels 2024, 10, x FOR PEER REVIEW 8 of 23 Following the analysis of the exhibited humidity-sensing responses at different frequencies, the capacitance sensitivities of the sensors to changes in relative humidity in the ambient chamber at 25 °C have been calculated using Equation ( 3), as typically used [1,13,34,40,41]: As illustrated in Figure 4, the impedance responses of the fabricated humidity sensors exhibit a decreasing trend with relative humidity; meanwhile, the capacitance responses reveal an increasing trend due to the relative humidity increase. The exhibited impedance and capacitance behaviours could be ascribed to the enhancement of ion conduction resulting from the interaction of the sensing layer with water molecules.…”

“…Following the analysis of the exhibited humidity-sensing responses at different frequencies, the capacitance sensitivities of the sensors to changes in relative humidity in the ambient chamber at 25 • C have been calculated using Equation (3), as typically used [1,13,34,40,41]:…”

“…Finally, Figure 10 and Table 2 compare the SiO 2 PVA:PVP 25% capacitors' sensing properties with those previously exhibited in the SOA. Figure 10 shows that, when compared with some recently reported capacitive humidity sensors based on pyromellitic dianhydride (PMDA)-oxydianiline (ODA)/TiO 2 [13], polyaniline (PANI)/1% Cu-ZnS [33], poly(ionic liquid) [44], PPy/graphene oxide (GO) [9], graphene oxide quantum dots (GOQD)/Nafion [11], PVA/cellulose acetate butyrate (CAB) [6], keratine/1% carbon fibres (CF) [10], graphenecarbon nanotube (CNT)-silicone adhesive (SA) [34], PVDF-BaTiO 3 [15], GO-doped poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/lithium chloride (LiCl) [41], or PVP+CAB [8], the SiO 2 PVA:PVP 25% -CILGPE capacitor has relevant detection parameters. These prior studies combine nanofillers or salts with polymers or use ILs to enhance sensitivity and hysteresis in humidity sensors.…”

Sensing Performance Enhancement Based on High-Frequency Polarization of Materials

“…Acceleration of the response process can also be realized by functional materials in that the surface provides forces for attracting target molecules’ motion, such as hydrogen bonds. Furthermore, materials’ nanostructure features such as pores or a high SAA accelerate its pathway transfer, which also significantly reduces response time (Figure o) . Constructing an interplay relationship that aligns material characteristics with performance, guided by specific scenario considerations and requirements, facilitates the engineering approach in the development of sensing systems.…”