Spatial and temporal fluctuations of the electric polarization were imaged in polymer thin films near the glass
transition using electric force microscopy. Below the glass transition the fluctuations are quasi-static and spatial
fluctuations were found to quantitatively agree with predictions for thermal fluctuations. Temporal fluctuations appear
near the glass transition. Images of the space-time nanoscale dynamics near the glass transition are produced and
analyzed. Local, complex dielectric susceptibility was also studied, and shows that dynamics on the free-surface are
faster relative to the bulk.
A number of recent experiments and simulations give strong support for the idea that dynamics vary with position in glassy materials. Relaxation times appear to be correlated over a few nanometers, supportive of the notion of cooperatively rearranging regions (CRR). But details of the local cooperative dynamics are still mysterious, and certain issues, such as the heterogeneity lifetime, remain controversial. I will describe experiments in which molecular cooperativity was directly observed near the glass transition, through nanometer-scale probing of dipolar noise in polymer glasses. The dynamics and evolution of individual CRR was studied. The CRR were found to revisit a handful (2-4) of configurations up to hundreds of times. Statistical analysis of the noise give information about the lifetime of the CRR, the local shape and evolution of the energy landscape, and the evolution from exponential to nonexponential response.
* E. Vidal Russell and N. E. Israeloff, Nature 408, 695 (2000).