Understanding the Deformation of Polymer Thin Films Under Hydration

Understanding the impact of interfaces and surfaces on hydrophilic/amphiphilic polymers including ionomers is of increasing interest as functional polymer coatings and thin-film devices become more ubiquitous. In these thin-film systems, confinement and interfacial energy impact a variety of properties including Tg, modulus, and morphology; the degree of hydration will also significantly impact these properties. Because of this, the characterization of mechanical properties for polymer thin films and networks under hydration remains a challenge. Here, we report the swelling-induced deformation of model hydrogel and block copolymer films as a function of thickness, cross-linking, and surface functionalization to understand the effect of confinement and surface interactions on polymer swelling and swelling-induced stresses. A cantilever bending method is used to characterize the mechanical response which is correlated to morphology using in-situ grazing incidence x-ray scattering. The results and techniques are applicable to understand the structure-functionality of a wide variety of polymers, including hydrogels, ion-conducting polymers for energy conversion, and block copolymers.