Confinement effects on the excess wing in the dielectric loss of glass-formers

We present results from dielectric spectroscopy on four molecular glass-formers, both in bulk and in confined geometry. For systems exhibiting a well-resolved secondary (beta) relaxation, the confinement induces a relative enhancement (compared to the main a relaxation) of the effective dielectric strength of the beta process. In bulksystems without a well-separated beta process a similar relative enhancement is found also for the contribution to the dielectric loss identified as the excess wing. The latter effect results in a bimodal loss, which suggests that the excess wing should be attributed to a relaxation process separate from, and thus not a feature of, the alpha relaxation. The results hence provide an explanation for the much debated excess wing often observed in the dielectric response of glass-formers.