Role of Non-Equilibrium Pinned Layers on the Thermodynamics of Confined Polymer Blends

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This work will judiciously combine experiments and theory to probe the role of pinned polymer layers, which are known to form at wetting substrates, on the apparent thermodynamics of confined polymer mixtures. This research is motivated to study this issue since recent experiments on the phase behavior of confined polymer blends, which utilize a variety of complementary tools, suggest that the phase separation ["binodal"] temperatures are hardly affected on confinement. These conclusions are in qualitative disagreement with existing equilibrium theories, which uniformly predict a strong stabilization of the phase mixed state on confinement. Since equilibrium scenarios do not appear to explain these results, it is conjectured that the experimental findings arise from the well known fact that melt chains in the immediate vicinity of a wettable substrate are effectively pinned to this boundary over the time scale of the experiments. It then naturally follows that the apparent thermodynamics of the remaining, non-pinned, chains are affected by the presence of this pinned layer, thus providing a means of rationalizing the experimental results. This research will use thin polymer mixtures and polymer blends filled with nanoparticles to exhaustively probe this speculation. Small angle neutron scattering and quasi-elastic neutron scattering experiments will be complemented with theory and simulations, to delineate the existence of this pinned polymer layer, and to incisively understand its consequences on the phase behavior of an overlayer of a polymer blend. These activities are strongly coupled to the development of two new courses, titled "Introduction to Nanomaterials" and "Multiscale Modeling of Complex Fluids," which will be offered to senior undergraduate students. The PI will also partner with the Junior Museum in Troy to develop IMAX style movies, aimed at K-12 children, on the behavior of polymers, especially in the vicinity of surfaces.%%%Polymeric materials find use in a myriad of thin film applications, such as paints, lubricants, barrier coatings, in nanolithography and in proposed optoelectronic devices. The proposed research conjectures that a near-surface layer, which is pinned on macroscopic time scales, profoundly affects the thermodynamic properties of confined polymers. These pinned layers could also strongly alter the structure and hence the mechanical, thermal and electrical properties of these thin films. These conclusions, if verified, could impact the design and use of polymers in these wide variety of current and future applications. The educational and outreach activities target students from kindergarten to the advanced graduate: these activities will stress the importance of fundamental surface science and polymers in everyday life.***