This work was conducted on Pinctada maxima nacre (mother of pearl) in order to understand its multiscale ordering and the role of the organic matrix in its structure. Intermittent-contact atomic force microscopy with phase detection imaging reveals a nanostructure within the tablet. A continuous organic framework divides each tablet into nanograins. Their shape is supposed to be flat with a mean extension of 45nm. TEM performed in the darkfield mode evidences that at least part of the intracrystalline matrix is crystallized and responds like a 'single crystal'. The tablet is a 'hybrid composite'. The organic matrix is continuous. The mineral phase is thus finely divided still behaving as a single crystal. It is proposed that each tablet results from the coherent aggregation of nanograins keeping strictly the same crystallographic orientation thanks to a hetero-epitaxy mechanism. Finally, high-resolution TEM performed on bridges from one tablet to the next, in the overlying row, did not permit to evidence a mineral lattice but crystallized organic bridges. The same organic bridges were evidenced by SEM in the interlaminar sequence.

International audienceSheet nacre is a nanocomposite with a multiscale structure displaying a lamellar “bricks and mortar” microarchitecture. In this latter, the brick refer to aragonite platelets and the mortar to a soft organic biopolymer. However, it appears that each brick is also a nanocomposite constituted as CaCO3 nanoparticles reinforced organic composite material. What is the role of this “intracrystalline” organic phase in the deformation of platelet? How does this nanostructure control the mechanical behaviour of sheet nacre at the macroscale? To answer these questions, the mechanical properties of each nanocomponents are successively investigated and computed using spherical and sharp nanoindentation tests combined with a structural model of the organomineral platelets built from AFM investigations

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The thermal behaviour of Pinctada margaritifera nacre was studied at different temperatures by means of thermal gravimetric, thermo-mechanical and Rock-Eval analyses. From the mechanical point of view nacre exhibited a complete reversible behaviour up to 230 °C. The bio-aragonite allotrope was seen to be as stable as the abiotic aragonite up to 470-500 °C. It was also evidenced that the organic phase was keeping cracking oxygen functions at temperatures as high as 650 °C. Nacre thermal behaviour could be described following four distinctive stages and discussed in comparison with previous data obtained in oxidative conditions.

International audienceNacre (the pearly internal layer of molluscan shells) is an attractive nanocomposite displaying high mechanical properties, low density and a good biocompatibility with human bones. It is currently studied for both the prosthesis design and the creation of new organic/inorganic hybrid materials by mimicking biomineralisation processes. These exceptional mechanical properties are ascribed to its highly ordered layered 'bricks and mortar' microstructure and more particularly to the energy absorption ability of the mortar during crack propagation. However, this ability appears to be drastically reduced in presence of nano-shocks generated during friction by the dynamic solicitations. This paper compares two Finite Element simulations – a quasi-static compression test and a dynamic impact test – in order to consider the fracture mechanisms induced by friction. It reveals that cracks migrate from the mortar to the bricks, involving in the latter case, the formation of wear nano-debris. These numerical results are confronted with experimental results during friction

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Sheet nacre is a natural biocomposite with a multiscale structure including a mineral phase of calcium carbonate (97 wt.%)