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For the past 25 years, we have researched a range of topics in the general area of diffusion and transport. The most significant development is a text book, published in 2005. “Kinetics, Transport, and Structure in Hard and Soft Materials” discusses the connection between structure and mechanisms of atomic or molecular transport in different classes of materials, from metals and semiconductors to network glasses, polymers and supercooled liquids.
The book is divided into four parts; Part I begins with a discussion the fundamentals of transport, wherein transport properties of a system of non-interacting particles are calculated and the phenomenon of Brownian motion introduced. The phenomenology of diffusion is also discussed wherein Fick's laws are introduced and solved for a range of practical cases involving mass transport. Elementary Statistical mechanics, involving Partition functions, probability distribution functions and correlation functions, is discussed to lay the foundation for the subsequent discussion of mechanisms of transport in different materials. Parts II and III focus on mechanisms of transport in crystalline materials and in structurally disordered materials. Chapters explain how the mechanism of diffusional transport of an atom or molecule is intimately connected to the spatial organization of neighboring structural elements and to its interactions with them. The book reviews factors that control temperature dependent long-range dynamics of glass-forming systems. Diffusion and viscoelasticity of polymer melts, transport (viscous flow and ionic diffusion) in inorganic network glasses, and dynamic heterogeneity in super cooled liquids are described. Part IV analyzes the development of instabilities, such as spinodal decomposition and Mullins-Sekerka instabilities, which lead to the morphological evolution of materials.
The publications, range from polymer-polymer diffusion to gas sorption in polymers. In the figure below, incoherent elastic neutron scattering measurements of a polymer blend demonstrates the influence of confinement on the mean square displacements. They decrease with film thickness.
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