Based on a thermodynamic approach, a mathematical model of charge transfer processes in the polymeric ionites (ion-exchange materials) during the water vapor sorption was developed. Theoretical dependences of the resistance of a polymeric ionite on the relative air humidity over the range 10-100% at physically reasonable values of the parameters of the system were obtained. The comparison of theoretical and experimental dependences has been performed. Possible reasons for and criteria of the phase transitions that lead to stepwise change of ionite resistance were discussed. The developed mathematical model adequately describes the available experimental data and allows formulating practical recommendations on selecting optimal polymeric coatings for the electrode units of molecular-electronic humidity gauges.
The sorption of water vapor by ion-exchange materials is studied using a model that incorporates the interplay between changes in the energy of dissociation of ion-exchange groups and the osmotic effect. It is shown that first-order phase transitions in which a thin film of a sorbed liquid transforms into a thick film are possible at realistic values of system parameters and at both high and low values of relative air humidity. A criterion for a phase transition is established and the reasons for it are discussed. The phase transitions obtained in this work are observed experimentally as hysteresis in water vapor adsorption-desorption curves. At the same time, hysteresis observed in earlier studies at both high and low relative air humidities was explained by relying on different models developed separately for high and for low ranges of humidity. This work allows us to explain these critical phenomena using a single mathematical model.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.