Dynamics At or Near Interfaces

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In thin polymer films, effects due to confinement and to interfacial interactions are responsible for different physical phenomena not generally encountered in bulk materials. These effects include changes in the glass transition temperatures of polymers with decreasing film thickness and changes in the critical phase separation temperatures of A/B polymer blends with film thickness. This proposal has two general goals. In the first, an understanding of the nature of the interactions between polymers and surfaces and the manner in which these interactions affect properties such as local friction, viscosity and translational dynamics of chains is developed. Long and short-range intermolecular forces can have a destabilizing effect on polymer thin films and these effects, together with enthalpic and entropic interactions, influence the stability of thin film polymer blends in ways that are not well understood. The second part of this proposal examines these effects in homopolymer/homopolymer blends and in copolymer/homopolymer blends.In the future, polymer thin films will play an increasingly important role in technologies that, historically, have not involved the use of "soft" materials. Technologies include organic light emitting diodes, sensors, such as electronic noses, and whole cell adhesion sensors. In each of these technologies, specific properties of the polymer are critical. For example, in organic light emitting diodes the electronic and optical properties of the polymer are important whereas for the whole cell adhesion sensors the ability to "tune" adhesive properties of the polymer is critical. The advantage of using polymer thin films over non-polymeric materials in some technologies is that polymers are cheap and easy to fabricate. Moreover, it is potentially easier to "tailor" properties of polymers because of the wide range of molecules that can be synthesized. A fundamental understanding of the properties of polymer thin films will be necessary for the overall success of the use of "soft" materials in many future technologies.