What can be learned from the rotational motion of single molecules in a polymer melt near the glass transition?

¹  Department of Chemistry, Katholieke Universiteit Leuven - 3001 Leuven, Belgium
²  Institute of Physics, Johannes-Gutenberg University - 55099 Mainz, Germany

Received: 17 April 2007
Accepted: 25 June 2007

Abstract

We develop a framework for the interpretation of single-molecule (SM) spectroscopy experiments of probe dynamics in a complex glass-forming system. Specifically, from molecular dynamics simulations of a single probe molecule in a coarse-grained model of a polymer melt, we show the emergence of sudden large angular reorientations (SLARs) of the SM as the mode coupling critical temperature is closely approached. The large angular jumps are intimately related to meta-basin transitions in the potential energy landscape of the investigated system and cause the appearance of stretched exponential relaxations of various rotational observables, reported in the SM literature as dynamic heterogeneity. We show that one can determine parameters predicted by the mode coupling theory from SM trajectory analysis and check the validity of the time temperature superposition principle.