Use of poly(amidoamines) as CO₂- and Si₂-sensitive material for gravimetric sensors

Abstract

A novel polymeric material of poly(amidoamine) [PAA] structure was used as sensor-coating for the detection of CO₂ and SO₂ in gaseous mixtures by means of gravimetric sensors. The PAA utilized for this work was an amorphous rubber-like material, purposely selected for the flexibility of its macromolecular structure, which favours the diffusion of analyte molecules through the polymeric layer. It was prepared and characterized in our laboratory by means of IR and NMR spectroscopy, DSC analysis, viscometric measurements and potentiometric titration with standard acids. The polymeric films were prepared by casting from dilute methanol solutions and their average thickness ranged between 0.40 and 0.80 μm. The morphology of the films was studied by means of SEM. Sorption experiments in the presence of CO₂ and SO₂ alternately were carried out in environments at controlled temperature and relative humidity (RH) levels. The response towards both CO₂ and SO₂ approached linearity. The limits of sensitivity towards both gaseous analytes were determined, and the dependence of the PAA Sorption on RH was investigated. The long-term stability of the material in normal atmospheric conditions was also considered. The Sorption phenomenon was completely reversible in the case of CO₂, while hysteresis was detected in the case of SO₂. The response times were on the order of 5 min for CO₂ and 7 min for SO₂.