Multi-scale Phenomena in Macromolecular Fluids and Nano-Composite Materials

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The goal of this research is the development of a mathematicaltheory, models, and computational tools which underpin the design andof macromolecular materials and nano-composites. These materials arecomprised of anisotropic molecules (nematic polymers), which undergo aspontaneous disorder-order transition above a critical concentration.Materials made from nematic polymers achieve their properties throughthe collective molecular alignment structure. Specific molecularelements yield diverse property enhancements, from strength (theDupont product Kevlar and spider silk), to electrical conductivity(carbon tubes and conducting polymers), to barrier penetrationproperties (discotic clay platelets). The major technologicalchallenge is to extend results with fibers to other geometries such asfilms and molds. However, in typical laminar processing flows, themolecular response is highly sensitive to flow type and strength, andto molecular properties such as shape and concentration. In additionto complex dynamics, during flow processing there is a spatialconflict between interior flow response and molecular anchoringconditions at solid boundaries. The result is that instead of auniform molecular orientational distribution, as in fiber processingflows, film and mold flows always generate morphology on length scalesbetween the molecules and the processing devices. These ubiquitousstructures are not understood, either theoretically or experimentally,yet they dictate the effective properties of the end-use materials.The research supported by this award will help to understand the dynamicsand structures that occur in typical laminar flows of nematicpolymers.Modern high-performance materials and nano-composites are primarilydesigned with simple elements, from rod-like to platelet molecules.Remarkable property enhancements have been achieved thus far inlaboratory-scale experiments, with increased strength and durability,the ability to shield heat or gases, and to tune electromagnetic wavetransmission. The technological challenge is to scale theseexperimental results to industrially viable processes and materials.The challenge to mathematics and computational science is to build asolid foundation of theory, modeling, and simulation tools from whichto design and control the processes and final material properties.The theory of flowing molecules in confined spaces is still unable topredict and control the molecular structure created during flowprocessing. Yet micron-scale molecular structures always occur inprocessed films and molds of nano-composites. Furthermore, the bulkmaterial performance properties as well as their failure and damagemodes are dominated by the molecular structures generated inprocessing. The award will support a research program combiningtheory, modeling, simulations, and comparisons with laboratory data inthe dynamics and structure properties of nematic polymer materials andnano-composites in processing flows. These results will be the basis for the next phase of the materials pipeline, where bulk materialproperties are deduced from the molecule properties.