Glass Transition in Bulk and Confined Geometries
The investigation of the static and dynamic properties of glass forming polymers
in a thin film is of great interest for technological applications such as
protective coating of microelectronic surfaces, biological fluids in membrane,
thin resist film, etc. The ability to alter the physical properties of thin
films by tuning film-substrate interactions represents a tremendous opportunity
for the design and fabrication of advanced materials. This size scale is
comparable with the dimension of a single polymer molecule. Thus a large portion
of molecules will be in close proximity to an interface. Studies have shown
that the dynamics depends strongly on the nature of the confining wall, the
interface, a parameter that rather difficult to control in an experiment.
Hence, the development of a consistent and quantitative framework for modeling
thin films is one of the outstanding challenges in the engineering and physical
sciences. In our group we use a number of simulation techniques to tackle this
problem. Especially the application of the newly developed
Density of States Monte Carlo technique is
of great help. This new flavor of multicanonical or umbrella simulation was
originally proposed by the group of David Landau for lattice systems and has
since been generalized to particle based systems under active contribution
from our group. With this technique simulations very close to the actual glass
transition become possible. Especially all thermodynamic properties can be calculated.
A related question which is under heavy discussion is the influence of confinement (or nano-scales) to such a system. We are looking at organic polymer systems in carbon nanotube and the variation of glass transition temperature with the diameter of the nanotube.