50 research outputs found
Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells
Intricate biomineralization processes in molluscs engineer hierarchical
structures with meso-, nano-, and atomic architectures that give the final
composite material exceptional mechanical strength and optical iridescence on
the macroscale. This multiscale biological assembly inspires new synthetic
routes to complex materials. Our investigation of the prism-nacre interface
reveals nanoscale details governing the onset of nacre formation using
high-resolution scanning transmission electron microscopy. A wedge polishing
technique provides unprecedented, large-area specimens required to span the
entire interface. Within this region, we find a transition from nanofibrillar
aggregation to irregular early-nacre layers, to well-ordered mature nacre
suggesting the assembly process is driven by aggregation of nanoparticles
(~50-80 nm) within an organic matrix that arrange in fiber-like polycrystalline
configurations. The particle number increases successively and, when critical
packing is reached, they merge into early-nacre platelets. These results give
new insights into nacre formation and particle-accretion mechanisms that may be
common to many calcareous biominerals.Comment: 5 Figure
Tuning hardness in calcite by incorporation of amino acids
Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure–property relationships of even the simplest building unit—mineral single crystals containing embedded macromolecules—remain poorly understood. Here, by means of a model biomineral made from calcite single crystals containing glycine (0–7 mol%) or aspartic acid (0–4 mol%), we elucidate the origin of the superior hardness of biogenic calcite. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules
Mosaic anisotropy model for magnetic interactions in mesostructured crystals
We propose a new model for interpreting the magnetic interactions in crystals with mosaic texture called the mosaic anisotropy (MA) model. We test the MA model using hematite as a model system, comparing mosaic crystals to polycrystals, single crystal nanoparticles, and bulk single crystals. Vibrating sample magnetometry confirms the hypothesis of the MA model that mosaic crystals have larger remanence (Mr/Ms) and coercivity (Hc) compared to polycrystalline or bulk single crystals. By exploring the magnetic properties of mesostructured crystalline materials, we may be able to develop new routes to engineering harder magnets
Sass, Stephen Louis
Also available as a printed booklet and from the Dean of Faculty website https://theuniversityfaculty.cornell.edu/Memorial Statement for Stephen Louis Sass, who died in 2019. The memorial statements contained herein were prepared by the Office of the Dean of the University Faculty of Cornell University to honor its faculty for their service to the university
Hierarchically Structured Hematite Architectures Achieved by Growth in a Silica Hydrogel
Biomineralization
strategies include the use of hydrogels to direct
the formation of composite, single-crystal-like structures with unique
structure–property profiles. Application of similar synthetic
approaches to transition-metal oxides has the promise to yield low-temperature
routes to hierarchically structured crystals that are optimized for
a range of applications. Here, growth of hematite (α-Fe<sub>2</sub>O<sub>3</sub>) within a silica hydrogel resulted in hierarchical,
mosaic crystals preferentially expressing catalytically active {110}
facets, which are absent in solution-grown controls. Quantitative
structural and compositional analysis reveals architectural changes
that begin with the incorporation of silicon into the hematite lattice
and propagate through to the nanoscale domain structure and assembly,
leading to microscale morphologies that show improved photocatalytic
performance. This work demonstrates the potential of applying bioinspired
crystallization techniques to design functional oxides with multiscale
architectural features