Contribution of polymeric swelling to the overall response of capacitive gas sensors

A new method for investigation of the swelling of polymers on exposure to gas or vapour has been devised and tested. It uses an optical profilometer (based on the chromatic aberration of a lens system) which is integrated into a computer-controlled gas-dosing and mixing setup. Gas and/or vapour conc...

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Bibliographic Details
Published in:Analytical and bioanalytical chemistry 2013-08, Vol.405 (20), p.6445-6452
Main Authors: Altenberend, U., Oprea, A., Barsan, N., Weimar, U.
Format: Article
Language:English
Subjects:
Airborne sensing
Analytical Chemistry
Biochemistry
Biomimetics
Characterization and Evaluation of Materials
Chemistry
Chemistry and Materials Science
Correlation
Crystals
Electrodes
Food Science
Gas sensors
Gas-detectors
Gases
Glass substrates
Humidity
Isotherms
Laboratory Medicine
Monitoring/Environmental Analysis
Polymeric composites
Polymers
Profilometers
Properties
Research Paper
Sensors
Silicon wafers
Silicone resins
Swelling
Vapour
Water content
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Summary:A new method for investigation of the swelling of polymers on exposure to gas or vapour has been devised and tested. It uses an optical profilometer (based on the chromatic aberration of a lens system) which is integrated into a computer-controlled gas-dosing and mixing setup. Gas and/or vapour concentration-dependent measurements have been carried out for thick layers of the polymers commonly used in gravimetric and capacitive gas sensors: poly(acrylic acid) (PAA), poly(vinyl pyrrolidone) (PVP), poly(ether urethane) (PEUT), and polydimethylsiloxane (PDMS). The thickness of PAA, PVP, and PEUT films changed significantly on exposure to humidity. These data have been used to derive the sorption isotherms of the respective polymers, which were found to be Henry or Flory–Huggins isotherms. Comparison of the geometrical (swelling) responses with capacitive responses revealed a strong correlation. The correlation, which occurs because both types of response are proportional to the water content of the polymer, is also valid for polymers with nonlinear gas responses. Finally the geometrical and electrical characteristics of the capacitive samples were used to explain the dependence of the capacitive response of different polymers on the concentration of the target gas or vapour. In this way was deduced that PDMS, which does not swell on exposure to humidity, swells in the presence of 2,3-dimethylpentane, for which no profilometer evaluations are yet available.
ISSN:1618-2642
1618-2650
DOI:10.1007/s00216-013-7023-x