Nanoscale Distributions of Glass Transition Temperature and Physical Aging in Confined Polymers and Polymer Nanocomposites: Fluorescence Studies

摘要

Over the past decade, there has been significant study of the glass transition temperature, Tg, of confined polymers, often as thin films, and polymer nanocomposites (NCs). Most studies have been performed on films supported on a substrate with a free surface (polymer-air interface) opposite the polymer-substrate interface. These studies have generally found a reduction of Tg with decreasing thickness in ultrathin films except when attractive polymer-substrate interactions, e.g. hydrogen bonds, are present. With NCs, studies have reported the effect of nanofiller concentration on Tg. However, the NC studies have generally made little quantitative comment on nanofiller dispersion or average interparticle separation distance. The latter quantity is likely to be important in determining the deviation of Tg from the bulk value when there are attractive polymer-nanofiller interactions. At a sufficiently small interparticle spacing, of order 100 nm, all polymer chains in a NC could have their behavior modified by the proximity to the polymer-nanofiller interface.