Effect of POSS™ functionality on morphology of thin hybrid chitosan films

Abstract

Organic-inorganic hybrid films based on chitosan (Chi) and hydrophilic polyhedral oligomeric silsesquioxanes (POSS™) were prepared by alkaline precipitation of the dried blends. The effect of the POSS type and concentration on morphology and permeability of Chi/POSS hybrid films were evaluated by IR spectroscopy, solid phase NMR, SEM and AFM and by diffusion transport of low-molecular-weight electrolytes. In mechanically stable hybrid films, contents of octakis {[3-(2,3-dihydroxypropoxy)propyl]dimethylsilyl}-POSS™ (DL-POSS),octakis(trimethylammomum)-POSS™ (TMA-POSS) and octaammonium-POSS™ (OA-POSS) range between 0.625 and 2.5 mol% (in relation to amount of the deacetylated chitosan amino groups). The large POSS molecules (approx. 2-3 nm) influenced the packing the chitosan chains on a nanoscale due to multiple intermolecular bonds and changed the heterogeneity of hybrid films. The electrolyte (HCl, NaCl and NaOH) transport through the films depended on the POSS type, its content, and the preparation method. With increasing POSS content, the permeabilities tended to increase across the hybrid films with the cross-linker (ethyleneglycol diglycidyl ether, 75 mol%), which was added into a precursor film before its drying and alkaline treatment. In contrast, the electrolyte penetration usually decreased through the films cross-linked after their drying and alkaline precipitation. The dependence of the diffusion permeability of Chi/POSS hybrid films on their morphology is discussed.