Cooperative Dynamics in Supported Polymer Films

摘要: Ultra-thin polymer films have ubiquitous technological applications, ranging from electronic devices to artificial tissues. These nanoconfined materials, typically with thickness less than 100nm, exhibit properties that are different their bulk counterparts. Despite extensive efforts, a definitive picture of nanoconfinement effects on dynamics, such as the glass transition temperature and fragility (two most important for amorphous processing) has yet emerge. In particular, property changes in dynamics supported comparison materials involve complex convolution boundary thermodynamic interactions, roughness compliance, addition finite size due confinement. this thesis, we consider molecular simulations substrate-supported, coarse-grained where these parameters (e.g polymer-substrate interaction) tuned separately determine how variables influence film dynamics. All significantly but all our observations can be understood unified framework through quantification constraining string-like collective motion within film. This scale serves measure cooperatively rearranging regions, hypothesized Adams-Gibbs theory describe relaxation. A challenge is cooperative dynamical not readily accessed experiments. Therefore, investigate relatively high mobility interfacial layers near polymer-air interface, whose ξ grows similar fashion We find precise scaling relation between average length L particle exchange displacements (strings). first direct evidence mobile layer related Moreover, links relaxation time via AdamGibbs relation, so directly connected temperature. Our findings consistent other recent studies, theoretically predicting or providing indirect evidences regarding motion.