A non-contact scanning-probe-microscopy method was used to probe local near-surface dielectric susceptibility and dielectric relaxation in poly-vinyl-acetate (PVAc) near the glass transition. Dielectric spectra were measured from 10-4 Hz to 102 Hz as a function of temperature. The measurements probed a 20 nm thick layer below the free-surface of a bulk film. A small (4 K) reduction in glass transition temperature and moderate narrowing of the distribution of relaxation times was found. In contrast to results for ultra-thin-films confined on or between metallic electrodes, no reduction in the dielectric strength was found, inconsistent with the immobilization of slower modes.
@article{arxiv.0707.1803,
title = {Local dielectric spectroscopy of near-surface glassy polymer dynamics},
author = {P. S. Crider and M. R. Majewski and Jingyun Zhang and H. Oukris and N. E. Israeloff},
journal= {arXiv preprint arXiv:0707.1803},
year = {2009}
}