Fluoropolymer-based capacitive carbon dioxide sensor

Abstract

We describe a thin film sensor of carbon dioxide which relies on the change in capacitance of a fluoropolymer thin film caused by the difference in dielectric constants between air and carbon dioxide and by the preferred adsorption by the polymer of carbon dioxide compared to that of air. The fluoropolymer, Teflon AF 2400™, selectively adsorbs large quantities of CO2 with sufficient diffusivity to allow response times of a few seconds to be achieved. The sensor demonstrates completely linear response over its operating range from ppmv to 100% CO2. Sensor performance is currently limited by thermal drift and the need to remove all water vapour from the sample flow. Precision levels, currently at the level of 5–10 ppm, can be reduced to well below that of 1 ppm with proper redesign of the sensor. As part of these studies, the absolute solubilities of several compounds in Teflon AF 2400 were measured and are as follows (in units of µmoles cm−3 atm−1): air (16.6), CO2 (177), C2F6 (≈ 600), CF3CFH2 (≈ 800) and CF2ClCF2Cl (≈ 4500).

Novel amperometric carbon monoxide sensor based on multi-wall carbon nanotubes grafted with polydiphenylamine—Fabrication and performance

“…However, when the MWNT-g-PDPA-ME was coated with 0.5% Nafion, such interference from the gases was not detected at MWNT-g-PDPA-ME. The insignificant or no interference from the gases is attributed to the solubility and dielectric properties of the gases at a fluorinated polymer [28], Nafion coated on the MWNT-g-PDPA-ME. The dielectric constants of the gases are less than that of CO and hence do not show interfering signals at the Nafion film/gas interface.…”

Development of a New Wireless Chemical Sensor for CO<inf>2</inf> detection

“…Due to the large permeability of the Teflon AF 2400 thin film, atmospheric water vapor influences the performance of SAW gas sensors by causing shifts in the baselines and altering responses to the targeted vapors [3]. To investigate the effect of humidity changes, test atmosphere was varied to 5%, 20%, and 30%RH by humidifier and monitored by hygrometer at 25 o C. Three parallel response curves are observed from 50 to 300ppm CO 2 concentration, as shown in Figure 6(a).…”

“…The reflectors are located at different distances from SPUDTs to get different wave propagation lengths. The surface between the first and second reflectors is coated with Teflon AF 2400 sensitive film, which provides extremely high CO 2 solubility, permeability (from Dupont), and selectivity [3]. When the SPUDTs receive electromagnetic (EM) energy from network analyzer through antenna, SAW is generated on the surface and propagating toward reflectors.…”

Flexible sensorial system based on capacitive chemical sensors integrated with readout circuits fully fabricated on ultra thin substrate

“…Each CIM is able to detect diverse analytes depending from the diffusion capability of the particular gas into the dielectric matrix [11][12][13]. In fact, once the analyte is absorbed into the sensor, a combination of different mechanisms can take place.…”