Heterogeneities of the dynamics close to the glass transition in van der Waals liquids in the bulk and in thin films
- Event time: 1:00pm
- Event date: 2nd December 2002
- Speaker: Didier Long (University of Edinburgh)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, for instance by measuring the diffusion coefficient of tagged particles, by NMR studies, dielectric hole burning or photobleaching experiments. By considering the thermally induced density fluctuations, we propose that the 3D glass transition is controlled by the percolation of small domains of slow dynamics, coexisting with domains of faster dynamics. We propose that the characteristic size of these heterogeneities is set by the competition between density fluctuations relaxation and individual molecular jumps, and derive a size (a few nanometers) comparable with that estimated by NMR. This model allows then to explain the important shift of the glass transitition temperature in thin polymer films which have observed over the past ten years. We will consider the case of suspended films and of strongly interacting films, as well as the cross-over between these two regimes.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..