Multi-scale Modeling of Polymer Thin Films towards Predicting Thermomechanical Behaviors of Nanomaterials under Nanoconfinement.

摘要

As the characteristic dimensions of polymer thin films become increasingly miniaturized in nanotechnological applications, such as nanoelectronics, coating, biosensors and functional nanocomposites, there is a growing need for understanding and predicting their thermo-mechanical responses. Nanoscale polymer thin films exhibit strong confinement effects on the key materials properties that diverge significantly from their bulk responses, such as glass-transition and elastic properties. While some progress has been made towards understanding the nanocofinement behaviors of polymer thin films and nanocomposites over the past two decades, predicting their properties is very challenging as they are greatly influenced by many factors, such as interfacial energy, cohesive interaction, and molecular weight, giving rise to the presence of interfaces and free surfaces at the nanoscale. To overcome these critical issues, in this dissertation, we have employed a novel simulation-based multi-scale modeling approach to investigate the thermo-mechanical responses of polymer thin films under nanoconfinement. In particular, we have developed a scale-bridging computational technique, called the thermo-mechanically consistent coarse-graining (TCCG) method, which employs a bottom-up modeling approach starting from all-atomistic molecular dynamics (AA-MD) simulations to obtain key materials parameters that are validated by experiments. Built upon our TCCG approach, we are able to investigate how the interface and free surface affect the glass-transition and mechanical behaviors of polymer thin films under nanoconfinement. We have also established a multi-scale modeling framework allowing the prediction of the glass transition and mechanical interphase properties of polymer-based nanocomposites as a function of interfacial energy and filler volume fraction by drawing the analogy between thin films and composites. Our multi-scale modeling framework and simulations explain the recent experimental observations on polymer nanostructures, and break new ground in predicting key structure-property relationships for polymer nanomaterials.