This work represents a contribution to the design, preparation and characterization of nanocomposite materials based on biocompatible components. The effect of composition, filler geometry and polymer charge were highlighted and their role on the final properties of the nanocomposites was revealed. We combined some biopolymers (methylcellulose, alginate, chitosan) with two nanoclays (kaolinite sheets and halloysite nanotubes) to prepare nanocomposites by means of the casting method from water. The thermal stability, the surface wettability, the mechanical properties of the obtained films were studied. SEM micrographs highlighted the surface morphology of the biocomposite materials. X-ray data allowed us to correlate the mesoscopic structure to the properties of these nanocomposites.

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Crystal-chemical characterization of 281 gamets, representative of most geologic environments, has allowed distortion of the X, Y and Z polyhedra to be examined as a function of chemical composition, allowing us to understand the reasons for compositional preferences in nature. Pyralspites [with E(Mg,Fe,Mn) as the dom inant X cationsl and ugrandites (with Ca as the dominant X-cation) are separated by a significant compositional gap (1.5 to 2.1 Ca apfu). The existence and width of this gap have been explained on the basis of two different configurations for the X and Y polyhedra, corresponding to mainly ionic and mainly covalent bonding schemes, respectively. In the former configuration, occurring in pyralspitic gamets, the shared X-X and X-Y edges are shorter than the unshared ones; in the latter configuration, occurring in ugrandites, the opposite situation is present. Most structural parameters within (Mg,Fe,Mn)-Ca gamet solid-solutions show non-linear variations: this fact, together with spectroscopic (XANES) data, rules out the presence of domains with either pyralspitic or grossular configurations; thus, the same X cation shows a different bonding behaviour, depending on the gamet structure (pyralspitic or ugranditic) in which it occurs. The unit-cell edge and the fractional coordinates of the oxygen atom have been modelIed along the PYR-ALM, ALM-GRO and PYR-GRO joins. Positive excess volumes of mixing (L'!. V) are present along all three solid-solu tions. The L'!. V value increases, and its compositional dependence is progressively more symmetric, with increasing size difference between the component X cations. The maximum calculated L'!.V of mixing along the PYR-GRO join (-7.5 A3 per unit cell) is mainly due to the excess volume increase of the XOg polyhedron with increasing Ca substitution (-5.5 A3 per unit cell). The Y06 octahedron also shows an excess volume, but its contribution to the L'!. V of mixing is just enough to compensate for the negative L'!. V shown by the Z0 4 tetrahedron (-0.3 A3 per unit ce1I).

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