Sand2015-xxxxr Ldrd Project Number: 169249 Ldrd Project Title: Modeling the Coupled Chemo-thermo- Mechanical Behavior of Amorphous Polymer Networks Project Team Members

Amorphous polymers exhibit a rich landscape of time-dependent behavior including viscoelasticity, structural relaxation, and viscoplasticity. These time-dependent mechanisms can be exploited to achieve shape-memory behavior, which allows the material to store a programmed deformed shape indefinitely and to recover entirely the undeformed shape in response to specific environmental stimulus. The shape-memory performance of amorphous polymers depends on the coordination of multiple physical mechanisms, and considerable opportunities exist to tailor the polymer structure and shape-memory programming procedure to achieve the desired performance. The goal of this project was to use a combination of theoretical, numerical and experimental methods to investigate the effect of shape memory programming, thermo-mechanical properties, and physical and environmental aging on the shape memory performance. Physical and environmental aging occurs during storage and through exposure to solvents, such as water, and can significantly alter the viscoelastic behavior and shape memory behavior of amorphous polymers. This project – executed primarily by Professor Thao Nguyen and Graduate Student Rui Xiao at Johns Hopkins University in support of a DOE/NNSA Presidential Early Career Award in Science and Engineering (PECASE) – developed a theoretical framework for chemothermo-mechanical behavior of amorphous polymers to model the effects of physical aging and solvent-induced environmental factors on their thermoviscoelastic behavior. INTRODUCTION: Amorphous polymers exhibit a wide range of complex temperature-dependent and timedependent behaviors, from elastic and rubbery to viscoplastic and glassy. At high temperatures, polymer structure has high mobility and is in an equilibrium rubbery state. The mobility decreases with temperature, and cooling drives the initially rubbery material out of equilibrium and induces the glass transition. The glass transition mechanism can be exploited to achieve the shape memory behaviors. The programmed shape of these materials can be stored by the tremendous decrease in chain mobility and recovered to an original shape in response to an environmental trigger, such as heat and solvent, which increases the chain mobility. Modeling the shape memory effect of amorphous polymers requires modeling the temperature-dependent and time-dependent behaviors of the glass transition. Simultaneously, the investigation on shape memory behaviors of amorphous polymers can also enrich the understanding the glass transition. Shape memory polymers (SMPs) are smart materials that can memorize one or multiple temporary shapes and recover to their permanent shape in response to an environmental stimulus, SAND2015-1359R