Biomimetic Integration of Organic and Inorganic Phases into Composite Materials

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Abstract DMR-9634396 Stucky A team of investigators from University of California, Santa Barbara, in collaboration with researchers at DuPont, propose to develop methods for defining patterning in inorganic/organic composite materials in order to control shape, strength, and thermal transport. The biomimetic patterning that is sought includes both the spatial relationships between the organic and inorganic phases and the long-range hierarchical ordering of the resulting macrostructures. A known method of creating composite materials with well defined patterning is the cooperative assembly of organic surfactants and molecular inorganic species into mesocomposites. In this synthesis, the patterning in the final product is under control of the inorganic/organic interface. The proposed research will address the use of polymer-surfactant assemblies and polymerized inorganic phases to create materials with patterning on longer length scales. Particular emphasis will be placed on using inexpensive calcium carbonate or calcium sulfate as the inorganic phase. The exceptional fracture resistance of sea shells, which are a composite of calcium carbonate and only 1-2% organic material, demonstrates that even inorganic materials that are inherently brittle can be used to form tough composite materials. One of the major determinants of the toughness of shells is the long-range pattering of tabular aragonite crystals in an organic matrix. The process by which the red abalone controls the formation of this structure will be investigated to understand how this complex, tough composite material is synthesized, and knowledge obtained from the biosynthetic system will be applied to the synthesis of composite materials. While patterning on the micrometer length scale in biological systems is thought to be under control of the templating organic species, patterning on longer length scales is believed to be due to a reaction-diffusion mechanism. This research will address composite patterning by nonlinear dynamic reactions, including clock reactions and reaction-diffusion reactions, by tailoring the conditions to the growth of appropriate solid materials. The results of these studies will provide methods for controlling the three-dimensional properties of inorganic/organic composite materials by defining the patterning of the inorganic and organic phases over well defined length scales. %%% One of the accomplishments of nature that has not been emulated by man is the simultaneous synthesis and shaping of constructed objects. The spider and silkworm synthesize silk as they spin it; the molluscs prepare calcium carbonate directly in the desired architecture. The research described in this proposal explores the integration of organic and inorganic phases into patterned composite materials using inorganic/organic interfaces and non-equilibrium chemistry. The premier polymer science and technology which has been developed over many decades at DuPont Central Research and Development will be combined with the academic bio and materials science capabilities at the University of California, Santa Barbara, to provide an industrial, high technology environment for the training of students and execution of the research. In these studies, in vivo biological studies are used to guide the development of the in vitro biomimetic chemistry. The biomimetics approach is interpreted as being well beyond visual similarities or the two-dimensional coating of surfaces, but is viewed in terms of the three- dimensional, long range patterned control of composition, hierarchical structure and nanophase space properties. Organic and inorganic cooperative control of composite assembly, polymer structure direction of patterned inorganic organization, and space time nonequilibrium syntheses will be investigated to achieve this goal. The approaches outlined above, taken in the context of a molecular level understanding of the often elaborate and highly long range ordered assembly of biomateria ls, will lead to the practical design of technologically useful materials with specific properties over sharply defined length scales.