RESUMO
Photocontrolled organic field-effect transistors (OFETs) containing a hybrid compound of fullerene C60 (n-semiconductor) with spiropyran (electrical conductivity photocontroller) as the active layer were fabricated for the first time. It was found that an OFET based on the hybrid compound, unlike the multilayer transistor (a device based on unmodified fullerene C60 and spiropyran in different layers), has higher transfer characteristics (source-to-drain current), charge carrier mobility in the active layer, and response rate to external influence, which makes them promising materials for the manufacture of optical memory elements.
RESUMO
This paper concerns the bulk and interfacial properties of a series of alkylated chitosans having different alkyl chain lengths grafted randomly along the main chitosan chain. Chitosan has a low degree of acetylation (5%); on chitosan derivatives, the role of the degree of grafting and of length of the alkyl chains are examined. The optimum alkyl chain length is C12 and the degree of grafting 5% to get physical gelation based on the formation of hydrophobic domains. The cross-linking is essentially controlled by the salt concentration: it is shown that 0.025 M AcONa is needed to screen electrostatic interchain repulsions. Hydrophobic interactions produce highly non-Newtonian behavior with large thinning behavior; this behavior is suppressed in the presence of cyclodextrins able to cap the hydrophobic alkyl chains. The interfacial properties of the chitosan derivatives were tested for the air/aqueous solution interfaces. Specifically, the role of their structure on the kinetic of film formation was examined showing that excess of external salt favors the stabilization of the interfacial film. The derivatives with a higher degree of substitution and longer alkyl chains are more efficient and give a higher elastic modulus compared to the model surfactant as a result of the chain properties.
