ИСТИНА

Small angle X-ray scattering (SAXS) technique using synchrotron radiation is very suitable and unique tool for characterization of the supramolecular structure of biopolymer materials in different forms.1 In this work we studied the structure of chitosan-based composite materials in the powder, aerogel and film form by means of SAXS. The composite materials were prepared using metal vapor synthesis technique as described previously.2 Various polymer matrices either containing metal nanoparticles (gold or silver) or not were evaluated. To study dimensional characteristics of the composites the model-fitting analysis for SAXS results using simulation programs from ATSAS software was used.3 When modeling the SAXS calculated curves, the scattering models based on the microscopy results were postulated. As a result, the dimensional characteristics of chitosan units (fibrils in case of aerogel and globule-like structures in case of films) were determined. For metal nanoparticles (gold or silver) in different polymer matrices (powder, film, and aerogel) the volume size distribution function was calculated from difference curves, representing the scattering only from metal particles. During the modeling process, metal nanoparticle was represented as single rigid sphere with a characteristic diameter that did not interact with others. The modeling results showed an asymmetric size distribution function for all scattering objects (such as chitosan units and metal nanoparticles) containing several fractions with characteristic sizes. SAXS analysis revealed that nanoparticles in chitosan powder are agglomerated into metastable aggregates from few to several thousand individual particles. During the films and aerogels formation from chitosan-based powder composites redispersion of aggregated metal nanoparticles occurred.