This award supports theoretical research and education with the goal to understand how living organisms create the exquisitely controlled microarchitectures of biomineralized structures that lead to their extraordinary materials properties. A main focus of the work is on nacre, or mother-of-pearl, which has a highly controlled and organized microstructure that gives rise to remarkable strength and toughness - nacre is 3000 times tougher than the aragonite mineral that constitutes 95% of it. No synthetic composites outperform their components by such large factors. The aragonite tablets in nacre are highly oriented, and the standard paradigm in the field is that the crystal orientations are controlled by molecular-scale chemical templation. However, recent work by the PI and her experimental collaborators presents strong evidence that in nacre, the orientational ordering arises from nonlinear dynamical processes. This award supports research to: (1) extend a theoretical model developed by the PI for dynamical establishment of aragonite tablet crystal orientation in nacre to encompass both sheet and columnar nacre, enabling more comprehensive comparison between theory and experiments on a variety of organisms, (2) investigate other aspects of nacre architecture that could be due to dynamical self-organization processes similar to those in other condensed matter systems and materials, (3) work to understand better the design principles that these highly organized and complex structures are exploiting, and (4) investigate the implication of new experiments probing the architecture and properties of other biomineral systems with remarkable toughness, such as sea urchin tooth. Members of underrepresented groups will be actively recruited to participate in this research project.
NON-TECHNICAL SUMMARY This award supports theoretical research and education with the goal to understand how living organisms create the exquisitely controlled microarchitectures of biomineralized structures that lead to their extraordinary materials properties. A main focus of the work is on nacre, or mother-of-pearl, which is produced by some mollusks as an inner shell layer. It is a remarkable material that has a highly controlled and organized structure that gives rise to remarkable strength and toughness - nacre is 3000 times tougher than the aragonite mineral that constitutes 95% of it. No synthetic composites outperform their components by such large factors. The PI will develop models to understand the physical processes that lead to the well organized internal structure of nacre and other biomineral systems that exhibit remarkable materials properties. The PI has the advantage of access to experimentalists working on these materials. An improved understanding of how living organisms make materials with remarkable properties can lead to the discovery of new materials with enhanced performance for a wide range of technological and industrial applications.
Members of underrepresented groups will be actively recruited to participate in this research project.
The main research focus of the project was to work to understand the fundamental physical principles underlying the properties of biominerals. Biominerals are fascinating to study because of their remarkable resistance to fracture and because of their biological imporance. The theoretical work supported by the grant made progress on several different aspects of this problem. First, a theory was developed that enables experimentalists using x-ray photoemission spectroscopy (an advanced microscopy technique) to obtain quantitative information about the orientations of the crystal tablets that form the hard shells of molluscs. This work enables the determination of unprecedented information about the organization of the structure on length scales ranging from nanometers to microns. Second, theoretical modeling was used to interpret the experimental results on the structure of shells to new understanding about the dynamical and kinetic processes that occur during shell formation. In addition to the work on biominerals, the grant supported some other projects on the self-organizing properties of some other soft-matter and statistical mechanical systems. One such project was an experimental-theoretical collaboration with a group at the University of Chicago on the self-assembling properties of compressed nanomembranes composed of nanoparticles on the surface of water. The theoretical work showed that an unusual complex pattern of mini-folds in the nanomembranes can be understood by considering the possibility that the nanoparticles are temporarily mobile, so that entropy plays an important role in determining the properties of the structure. The grant also supported activities aimed to broaden the impact of the grant. First, the undergraduate and graduate students who were supported learned valuable quantitative skills, and also learned about working in experimental-theoretical collaborations. The PI also participated in a variety of outreach activities for elementary and middle-school students as well as for the general public.
