Since the mid 1990's there has been a sustained and intense interest in the glass transition (Tg) and the dynamical properties associated with the glass transition in thin polymer films and other confined materials. Our group (often in collaboration with others) has made a number of important contributions to this area. These contributions include:
- making the first measurements of the Tg value in thin free standing polymer films (1996)
- making the first measurements of dynamics in free standing films (1998)
- measuring the Mw dependence of Tg in free standing polymer films, and from those results suggesting two distinct mechanisms for Tg reductions (2000-2001)
- providing a link between thin film Tg measurements and the length scale for cooperative motions (2000)
- showing a direct correlation between Tg reductions and interfacial properties (2003)
- using rate dependent Tg measurements to show that confinements effect are only manifested in the slow dynamics
- showing the independence of Tg to sample atmosphere (led by Dalnoki-Veress' group)
The strong link to interfacial properties, especially those near the free surface, has resulted in our focusing significant efforts to direct measurements of the surface regions. These ongoing studies are highlighted by:
- Nanoparticle embedding studies to probe the near surface region of polymeric and non polymeric films. This extensive work includes effect of particle size, Mw of polymer, temperature (2008-2011)
- Use of relaxation of nanoscale deformations to probe the free surface region in polymers (PS, i-PMMA) (2008)