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Load transfer in materials based on nanometric polysaccharide crystals – NANOPOLYS

Submission summary

Cellulose, chitin and starch are natural homopolymers that occur in various tissues with common feature bearing well-defined crystallites of nanometric sizes. Cellulose and chitin essentially have a role of tensile load bearing whereas starch is a compact form of carbohydrate storage. Due to a fairly rigid molecular backbone and an extensive network of hydrogen bonds, such crystals can be thermally stable up to nearly 400°C and resistant to solvents, making them an ideal elements for high-performance materials. The use of polysaccharide microcrystals of high aspect ratio in composite materials, now studied worldwide, has been initiated in CERMAV in the 1990's. The basic approach has been to mix them as fillers to dramatically improve the mechanical properties of soft matrices, especially above their glass transition temperature. Another approach developed in Kyoto University of Japan, is to impregnate contrast-matching resin into compacted microfibrillar sheet to obtain strong transparent, thermally stable sheet as a candidate for supporting material of flexible display for electronic devices. Methods to orientation of cellulose and chitin crystallites have been also developed in the last years using shear flow, elongational flow, magnetic or electric field. CERMAV scientisits played major role in each of those developments. Materials of different organization of crystals can be thus prepared. On the other hand, the mechanisms of load transfer in such nano-composites, and the role of interface properties, filler-filler interactions, and the contribution of morphology of individual particles have been only speculative. In this context, we plan to use polysaccharide microcrystals as probes to follow the load transfer in such materials. For this purpose, the following three interrelated subjects are identified 1. precise determiniation of stiffness tensor and spectral response of microcrystals We will start from simple model system using isolated single crystals with relatively large crystal size (20 nm ~) uni-axially oriented samples. X-ray diffraction combined with mechanical tests on such system will allow us to precisely measure the tensor elements of the crystals without ambiguity. Vibrational spectroscopy combined with mechanical tests will allow us to obtain information on molecular deformation related to local strain. Direct mechanical measurements on single particles using AFM as well as Inelastic X-ray and neutron scattering that allow us to evaluate elastic modulus from phonon velocity, will be also used to validate the measurements of stiffness tensor. 2. preparation of nano-composites with controlled organization and interface Nano composites with different interface and organization will be prepared to understand their contribution on filler-matrix and filler-filler load transfer mechanism in nano-composits. 3. load transfer analysis of nano-composites and biological samples Using the precise characteristics obtained in subject 1, the load and strain distribution in nano-composites will be analyzed using X-ray diffraction and vibrational spectroscopy. Originality and expected outcome The originality of the project with respect to the existing research lies in the fine analysis of the interface and mechanical response at nanoscopic level. The key to the success is the expertise at CERMAV for diverse source of crystalline polysaccharides and on handling of microcrystals, which allows us to vary the crystal morphology and sizes by choosing their biological origin. The understanding of load transfer at nanoscopic level will be a basis to develop a rational design of nano-composite. The research area of the project leader has been in line with classical subject of CERMAV, specialized in crystal structure analysis and surface modification. The sample preparation implicitly involved preparation of nano-composites, but the project aims to further focus on the aspect of materials science. The methods and concepts that will be developed in this project would be applicable to a wide domain of nano-composites or most polymers that inherently have structural heterogeneity at nano-scopic level.

Project coordination

Yoshiharu NISHIYAMA (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 150,000 euros
Beginning and duration of the scientific project: - 36 Months

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