Materials World Network: Controlling Properties of Polymers in Thin Films

Trustees Of Boston University, Boston

Investigators

Abstract

This Materials World Network brings together world-expertise on the experimental characterizations of polymer films (Boston University, USA and Universität Freiburg, Freiburg, Germany on the film stress and viscoelasticity, respectively) and computer simulations on the dynamics and structure of confined polymers (Institut Charles Sadron, Strasbourg, France) to seek for the possibility of a unified picture that can account for all the unusual properties observed of polymer films to date (namely the dynamics, residual stress and thermal expansivity), and at the same time attempt to relate these properties to the (out-of-equilibrium) polymer structures therein as well as the fabrication and/or post-fabrication processes producing them. By establishing such structure-property and processing-property relations, the Network aims to ultimately institute a strategy that can predict, design and tune the properties of polymer films. Because the structures of the polymer films that allegedly cause the unusual properties are metastable and change with time, a cross-linkable copolymer of polystyrene are used to freeze-in the structures and whereby their properties. This research is largely guided by several published experiments and a model conjectured by Reiter (the PI from Germany) and de Gennes portraying how a non-equilibrated polymer network structure engendered by rapid solvent evaporation could explain negative thermal expansivity. The results of this program are expected to substantiate this model, and additionally expand its relevance to the dynamical behaviors of the films. The resultant, more encompassing model will provide a pivotal platform upon which the structure-property and processing-property relations can be portrayed and/or formulated. Applications of polymer films are widespread. Success of this program leads to a simple strategy to design and fabricate polymer films with premeditated thermal expansion and/or dynamical properties. Having such ability significantly enhances our leverage to adapt these materials in a cost effective manner to the ever-changing demands on their properties by the applications employing them. Six PhD students are trained in this program, providing them an excellent training ground in the academically challenging and technologically relevant problem concerning the unusual properties of spin-coated polymer films. Members of the Network benefit from the international setting of the program. In particular, there are regular meetings and physical exchange between the PhD students besides frequent video conferences. This program actively engages undergraduate and high-school student participants. This award is jointly funded by the DMR Polymers Program and the DMR Office of Special Programs.