Proton mobility and copper coordination in polysaccharide- and gelatin-based bioblends and polyblends
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Polysaccharide- and gelatin-based bioblends and polyblends were synthesized and characterized by complex impedance spectroscopy, proton nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Higher ionic conductivities of 7.9 × 10−5 S/cm at room temperature and 2.5 × 10−3 S/cm at 80 °C were obtained for the agar-chitosan polyblends. For all samples, the activation energies, calculated from the Arrhenius plot of ionic conductivity and from the onset of NMR line narrowing, are in the range 0.30–0.86 and 0.38–0.57 eV, respectively. The glass transition temperatures (T g NMR ) varied from 200 to 215 K, depending on the sample composition. The temperature dependence of the 1H spin–lattice relaxation revealed two distinct proton dynamics. The EPR spectra are characteristic of Cu2 ions in tetragonally distorted octahedral sites. Quantitative analysis of the EPR spin Hamiltonian g || and A || parameters revealed copper ions complexed by nitrogens and oxygens in the samples containing chitosan or gelatin and only by oxygens in agar-based ones. The in-plane π bonding is less covalent for the gelatin and chitosan blends. Results suggest that natural bioblends and polyblends are interesting systems to be used in materials science engineering.
KeywordsNatural macromolecules Bioblends Impedance Solid state NMR EPR
The financial support of the Brazilian agencies Capes, CNPq and FAPESP are gratefully acknowledged. Research was partially financed by the CeRTEV, Center for Research, Technology and Education in Vitreous Materials, FAPESP 2013/07793-6.
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