Graphical abstractHighlights► The size of amorphous SiO2 nanoparticles coincides for different test methods. ► Different measurement methods deliver different values for crystalline ZrO2 nanoparticles. ► The use of complementary methods is favourable.

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The keratin structure in the cortex of peacocks’ feathers is studied by X-ray diffraction along the feather, from the calamus to the tip. It changes considerably over the first 5 cm close to the calamus and remains constant for about 1 m along the length of the feather. Close to the tip, the structure loses its high degree of order. We attribute the X-ray patterns to a shrinkage of a cylindrical arrangement of β-sheets, which is not fully formed initially. In the final structure, the crystalline beta-cores are fixed by the rest of the keratin molecule. The hydrophobic residues of the beta-core are locked into a zip-like arrangement. Structurally there is no difference between the blue and the white bird.

Epoxy resin nanocomposites were prepared by curing bisphenol-F with an aliphatic amine in the presence of SiO 2 and ZrO 2 nanoparticles as inorganic fillers. Both types of particles were prepared with diameters of around 10 nm and 70 nm to study size effects in the nanocomposites. The nanoparticles showed a different constitution: while silica was amorphous and spherical in nature, zirconia was crystalline and non-spherical. Both nanoparticles were surface-functionalized with novel diethyleneglycol-based capping agents to increase the compatibility with the epoxy matrix. The organic functionalities were attached to the nanoparticle surface via phosphonic acid (zirconia) and trialkoxysilane (silica) anchor groups. The homogeneity of the distribution of surface-modified inorganic nano-sized fillers in the matrix up to 5.8 vol% in case of silica and 2.34 vol% in case of zirconia was determined by small-angle X-ray scattering and transmission electron microscopy. Mechanical properties such as hardness and storage modulus were increased with increasing filler content while thermal stability of the obtained materials was nearly unaffected after incorporation of nanoparticles.