(217bk) Confinement and Antiplasticization in Hydrated Thin Ionomer Films

The knowledge of hydration behavior is truly beneficial for molecular level understanding and advanced level designing of ionomer (~2-30 nm thick layer)-catalyst interface in fuel cells. When the film thickness approaches to several tens of nanometers, the interfacial properties determine the mechanical and transport properties. Strong confinement effect restricts the mobility of the polymer chains. The unique hydration behavior arises from relative interaction among water, polymer and substrate. The water distribution governs the film density and rigidity. There is a large database available for ionomer membranes. However, very little is known about thin films. The typical tensile stress-strain based measurements of mechanical properties are challenging as making free standing ultrathin films are difficult Fluorescence, being a sensitive technique offers convenient way to predict the stiffness of sulfonated Radel films (on SiO₂ substrate) as a function of thickness, relative humidity (RH) and ion exchange capacity (IEC).  The dye employed here is CCVJ, a rotor probe sensitive to viscosity of microenvironment. Simultaneous measurement of water uptake, swelling, density and dielectric properties offers useful insight about confinement effect on hydration and mechanical properties of thick and thin s-Radel films.