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. Proton-conducting polymers, such as sulfonated poly(ether ether ketone) (SPEEK), are of great industrial interest. Such protonexchange membranes show high tendencies for water and water vapor uptake.The incorporation of water not only leads to mass and dimensional changes,but also to changes in conductivity by several orders of magnitude. Bothproperties highly impact the potential application of the materials and,therefore, have to be known precisely. As hydration is diffusion controlled,thin films may behave differently to bulk specimens. However, thedetermination of small mass changes occurring in thin-film samples is verychallenging. In this work, a new measurement setup is presented to simultaneouslycharacterize the mass change and the conductivity of thin polymer films. Themass change is measured by resonant piezoelectric spectroscopy (RPS) with ananobalance, which is based on high-precision piezoelectric resonators operating in thickness-shear mode (TSM). The mass resolution of thisnanobalance is ±7.9 ng. Electrochemical impedance spectroscopy andan interdigitated electrode array are used for conductivity measurements.The approach is validated by comparing two SPEEK films with differentdegrees of sulfonation (DS). The relative humidity (RH) in the measurement setup was changed stepwise within the range ∼ 2 % &lt; RH &lt; ∼ 85 %. For both material compositions,DS = 0.5 and DS = 0.9, the mass uptake, the hydration number and theproton conductivity are presented and discussed depending on RH. This newly designed experimental setup allows for in situ characterization of theproperties mentioned above; it can monitor not only the data for thestationary state, but also the dynamics of the hydration. To the authors'knowledge this is the first simultaneous and in situ measurement device forsimultaneously sensing mass and conductivity change due to hydration ofpolymeric thin-film materials.

journal of sensors and sensor systems

In situ analysis of hydration and ionic conductivity of sulfonated poly(ether ether ketone) thin films using an interdigitated electrode array and a nanobalance