High swelling gels for sensing applications

Crosslinked hydrophilic polymers of different chemical structures can be used as sensor coatings for the detection of gaseous analytes. If their crosslink density is low, these materials behave in aqueous media as soft hydrogels with high swelling capacity. From a physico-mechanical standpoint, they are amorphous rubber-like materials, with high flexibility of their macromolecular chains. This property is particularly significant in view of applications in the sensors field, because it favours diffusion of the analyte molecules through the coating layer. This paper deals with the application of poly(ethylene glycols) (PEG)- and poly(N-vinylpyrrolidinone) (PVP)-based crosslinked resins as relative humidity (RH) sorbing materials, and of a poly(amidoamine)(PAA)-based resin as SO2-sorbing material. The electronic devices used for evaluating the sorption capability of these polymeric coalings were gravimetric resonant sensors. Resins of various crosslink density, and therefore of various swelling ratios in water, were purposely prepared and characterized. Thin coating layers, prepared by casting from dilute aqueous suspensions of the resins, previously micronized in water, were used for sorption experiments. All experiments were performed in controlled RH and temperature environments.