Local dielectric spectroscopy of near-surface glassy polymer dynamics

A noncontact scanning probe microscopy method was used to probe local near-surface dielectric susceptibility and dielectric relaxation in polyvinyl acetate near the glass transition. Dielectric spectra were measured from 10(-4) to 10(2) Hz as a function of temperature. The measurements probed a 20 nm thick layer below the free surface of a bulk film. A significant change in the fragility index and moderate narrowing of the distribution of relaxation times were found in the near-surface layer. In contrast to results for ultrathin films confined on or between metallic electrodes, no reduction in the dielectric strength was found, inconsistent with the immobilization of slower modes.     

Local polarization fluctuations in an aging glass

Polarization fluctuations were measured in nanoscale volumes of a polymer glass during aging following a temperature quench through the glass transition. Statistical properties of the noise were studied in equilibrium and during aging. The noise spectral density had a larger temporal variance during aging; i.e., the noise was more non-Gaussian, suggesting stronger correlations during aging.