Effect of adding nanometre-sized heterogeneities on the structural dynamics and the excess wing of a molecular glass former

TL;DR

This study investigates how adding nanometre-sized heterogeneities (POSS molecules) to glycerol influences its relaxation dynamics and excess wing, revealing broadening and slowing of alpha relaxation and an increased secondary relaxation.

Contribution

It provides experimental evidence on how nanometre-sized heterogeneities affect glassy dynamics and secondary relaxations in a molecular glass former.

Findings

Broadening of alpha relaxation with POSS addition

Significant slowing down of alpha-relaxation time

Enhanced secondary relaxation (excess wing)

Abstract

We present the relaxation dynamics of glass-forming glycerol mixed with 1.1 nm sized polyhedral oligomeric silsesquioxane (POSS) molecules using dielectric spectroscopy (DS) and two different neutron scattering (NS) techniques. Both, the reorientational dynamics as measured by DS and the density fluctuations detected by NS reveal a broadening of the alpha relaxation when POSS molecules are added. Moreover, we find a significant slowing down of the alpha-relaxation time. These effects are in accord with the heterogeneity scenario considered for the dynamics of glasses and supercooled liquids. The addition of POSS also affects the excess wing in glycerol arising from a secondary relaxation process, which seems to exhibit a dramatic increase in relative strength compared to the alpha-relaxation.