BLANC - Blanc

Matériaux Biomimétiques Hiérarchiques obtenus par Congélation – NACRE

Submission summary

In recent years, the design of biomimetic materials and systems has been the focus of increased attention. The properties, functions, and structures encountered in nature are increasingly appealing for non-biological applications: control of the structure at different levels, adaptation to the environment, soft processing conditions, use of biodegradable materials, ability to self-repair, etc… The range of functions achieved by such biological routes is extremely wide: mechanical, structural, optical, chemical (energy conversion), transport. The solutions encountered in nature result from millions of years of evolution and can indeed be seen as an optimum for the targeted functions. Nacre is a school-case example for biomimetic inspiration. Its unique hierarchical architecture represents the optimum of how to overcome intrinsic materials weakness by hierarchical design. No structural engineering materials have such a hierarchy of structure, yet the message from biology here is clear – there is a need in the design of new materials to develop mechanisms at multiple length scales in order to create new hybrid materials with unique functional properties. A major obstacle to the development of biomimetic materials is the lack of processing routes to implement the bio-inspired designs into materials and systems. The process we introduce here to process nacre-like biomimetic hierarchical materials is a self-assembly process, inspired by a naturally occurring phenomenon, the freezing of sea ice, where the various impurities are expelled from the forming ice and entrapped within the channels between the lamellar ice crystals. Using ceramic particles instead of biological impurities, we take advantage of this natural segregation principle, while using ice as a natural and environmental-friendly templating agent. Freezing of the ceramic slurry yields an interpenetrating scaffold of ice and ceramic particles. After sublimation and sintering, a scaffold with a complex and often anisotropic porous microstructure generated during freezing is obtained. Materials obtained by this process exhibit striking similarities with the inorganic component of nacre replicating its hierarchical structure. Such hierarchy might be used either to promote a single property (e.g., mechanical strength), or to introduce several functionalities, associated with each of the degrees of hierarchy. Preliminary results of such ice-templated materials have shown dramatic improvements of structural properties. We believe that through the exposed freezing process we can control and tailor functional properties for a wide spectrum of applications. The proposed work is centred on the control, development and evaluation of the freezing route for processing biomimetic hierarchical materials exhibiting such improvements, and on the characterization of the resulting materials. A multiscale approach is necessary to apprehend the mechanisms taking place at all of the length scales. In particular, the core of the problem – the interaction between the particles and the solidification front– will be characterised both in situ (at several length scales) and ex-situ. To our knowledge, such comprehensive characterisation has never been undertaken. The knowledge gained from such experiments will be useful for other fields involved with crystal growth and design, from both a scientific point of view (phenomenological aspects) and a technical point of view, with the development of innovative electron and atomic force microscopies (including cryogenic studies) and tomography techniques during the project; benefits are expected for applications from microelectronics to metals processing and cryo-preservation of biological samples and organisms. The three-dimensional characterisation of the structures and the systems, covering the whole range of relevant length scales, is particularly innovating in these fields of research. The process being versatile in terms of nature of the materials being used, a major impact of the project could be expected for a wide range of applications, such as filtration, catalysis, gas pump, heat exchanger, etc… A transverse approach to the project aims at developing materials by design with an innovative and generic biomimetic approach, taking inspiration from the self-reinforcing nature of bone, which structure is permanently optimized to mach the stress state and provides the best possible functional response. The objective of this transverse approach is to develop a similar strategy of design for materials and engineering science, using state of the art 3D imaging technique and finite elements modelling. Materials obtained through the freezing route will be used, along with alternative materials exhibiting a variety of structures and morphologies.

Project coordination

Christian GUIZARD (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 350,000 euros
Beginning and duration of the scientific project: - 36 Months

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