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SCOPE AND TOPICS The mechanisms of action for mesoscale functional systems involve:1. Separation into multiple domains, which may be a gross part of the structure (as in layered cuprates or proteins) or result from local (nanoscale) stochastic or collective composition fluctuations (as in alloys and solutions) 2. In solid state systems, complexity in the form of deviations of the chemical formula from the unit cell stoichiometry that are the origin of local elastic stress 3. Two or more coexisting/competing conformations for all or part of the structure that correspond to local minima in the total free energy landscape that determines the local and global arrangement of atoms so that the system exhibits static and/or dynamic nanoscale heterogeneity 4. Strong coupling between the elastic stress, local and global structure, and other degrees of freedom, e.g., charge, spin, etc. 5. A division of the overall function into sub-functions that reside in the different domains, creating an engine 6. The relative energies of the different conformations in the landscape are altered in response to microscopically reversible changes in local properties such as composition, charge/spin ordering, energy inputs, etc. 7. This engine is driven by cycling among the various conformational states in response to these changes Sessions: Functional Physical, Chemical, and Biological Systems Described. This first session will set the tone by describing examples of functional systems, what is known about their mechanisms, and the key issues in their further elucidation. The Current State-of-the-Art of Elastic and Other Local Forces and Entropy. It has recently become clear that elastic forces on multiple length scales, especially when acting on impurity sites or other inhomogeneities such as localized charges and interfaces, constitute some of the most important drivers for these phenomena. From the other direction, entropy must also play a critical role in systems with multiple conformations of near equivalent energies. The importance of the entropy of the solvent in solutions is already well known and may also have analogies in solids exhibiting inhomogeneities. Intrinsic Phase Separation, Heterogeneity, and Interfaces in Hard Solids and Soft Molecules. Lattice distortions are an easily measured characteristic of complex solids. Collective action between them, which may only be implied because it is often difficult to measure, will result in heterogeneities and nanophase separations. This phase separation will also create interfaces between the domains with unique structures and properties that may be negligible in extent if the phase interfaces are well matched or could involve the majority of the atoms. In soft materials multiple, competing conformations originate in the primary structure (or its equivalent) and the interactions of the constituent atoms and functional groups with each other and with the medium. The engine concept also derives from the different properties of the different conformations of the domains/molecule and their unique contributions to the mechanism of action. Coupling Between the Elastic, Bonding, Charge, Spin, Composition, and Other Degrees of Freedom. An essential aspect of a complex material is strong coupling among its elastic and other degrees of freedom. The different conformations and heterogeneity thus drive and are driven by charge/spin separation and ordering and chemical states. Although this coupling is arguably the most important characteristic of functional materials, its mechanisms in many systems are only poorly understood. An examination of the coupling processes in a variety of systems ranging from those where it is obvious to ones where it is obscure will advance this area. The Dynamic Energy Landscape; Where, Why, and How. The local energy landscape that determines the behavior and local energy for each atom and its division into a particular conformation (or interface) is determined by summing all of the different components of the total free energy. The critical characteristics of this landscape in a functional material are that it exhibits multiple local minima of comparable energies and that their relative energies can be altered by some other change in the system, such as charge ordering or phosphorylation. This accomplishes two tasks, an amplification of the process that causes this modification of the landscape so that a small stimulus can produce an anomalously large response in the system, and the means for linking ostensibly uncoupled steps in the reaction sequence. Mesoscale Engines: Technology and Applications. Nanoscale fabricated heterostructure engines, including immobilized enzymes and biomolecule-based sensors and separation media, are already the basis for certain technologies. An examination of these provides a foundation for extending the controlled synthesis and application of intrinsically heterogeneous functional systems. Retrospective and spontaneous discussions: Jim Krumhansl, Alex Muller, Hans Frauenfelder, et al. (Walter Kohn?) These will be distributed throughout the meeting. Symposium on Heterogeneous Aspects of Cuprates To include: Keynote Speaker: K. Alex Muller, "A metallic phase in lightly doped La1-xSrxCuO4 observed by electron paramagnetic resonance." Institute for Complex Adaptive Matter Workshop on Lifelike Matter: Emergent Functionality From the Standpoint of Template Controls on Energy Landscapes Zeolites, clathrates, mesoporous materials, organic-inorganic composites, organic host-guest compounds, and proteins have a number of features in common: 1. A large number of structures are accessible for a given composition. They are intrinsically heterogeneous in the sense of having a tightly bonded and relatively hydrophobic framework (organic or inorganic) and heavily hydrated hydrophilic regions containing ions and small molecules. 2. There is order on several length scales: local chemical bonding, interfaces between hydrophobic and hydrophilic regions, hydrated ions in channels, channel topology, intergrowths and folding... 3. Ions in channels are mobile but more constrained than in aqueous solution. There are common questions of their transport mechanisms and kinetics. 4. Synthesis is by "structure direction"- small molecules, surfactants or enzymes 5. The materials themselves are often catalytic - at surfaces, in pores, or at enzyme active sites The purpose of the workshop is to explore what concepts can be applied across the whole wide class of materials, to overcome issues of jargon, and to explore how one field can benefit another. Examples of questions might be: 1. How does one adapt the concepts and predictions of energy landscape formalism from protein folding to zeolites and mesoporous materials? Is there quantitative insight to be gained? 2. Can the inorganic/organic materials be used as tractable models for some biological functions? 3. Does a water molecule see similar environments as it moves along ion channels in a protein and a zeolite? Are ideas of hydration similar, qualitatively and quantitatively? |
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LOS ALAMOS NATIONAL LABORATORY |