(671a) Mechanics of Ultra-Thin Polymer Glasses

The mechanical properties of polymer glasses have been studied classically due to their importance in numerous technologies; however, there is an increasing need and demand to characterize these properties in films with thickness approaching the size scale of an individual polymer chain. We present recent results that use two experimental methods developed in our research group, called The Uniaxial Tensile Tester for Ultra-Thin films (TUTTUT) and Tensile tester for Ultra-thin Freestanding Films (TUFF). These methods allow for the direct measurement of the complete stress-strain relationship for uniaxial stretching of polymer films as thin as 10nm in both dry and liquid-based environments. We present the results of two studies. The first focuses on understanding the inter-relationship between polymer molecular weight, polydispersity, and thickness in controlling mechanical strength. Our findings reveal new quantitative understanding of the role of entanglements and surface mobility in defining polymer stiffness and strength. The second study focuses on understanding the role of nanostructure morphology in defining the mechanical response of block copolymer films. We use solvent vapor annealing processes to access a range of morphologies for block copolymer materials at a fixed segmental volume fraction. Our results decouple the influence of morphology from compositional volume fraction on mechanical properties, while also demonstrating new mechanisms for enhancing the ductility and toughness of ultra-thin films through interactions with water. Collectively, the results of these two studies not only advance the fundamental knowledge of polymer physics but also provide new guidance for designing ultra-thin film materials with enhanced performance.