title: Novel gigahertz frequency dielectric relaxations in chitosan films.
abstract: Molecular relaxations of chitosan films have been investigated in the wide frequency range of 0.1 to 3 × 10(9) Hz from -10 °C to 110 °C using dielectric spectroscopy. For the first time, two high-frequency relaxation processes (in the range 10(8) to 3 × 10(9) Hz) are reported in addition to the low frequency relaxations α and β. These two relaxation processes are related to the vibrations of OH and NH2/NH3(+), respectively. The high-frequency relaxations exhibit Arrhenius-type dependencies in the temperature range 10 °C to 54 °C with negative activation energy; this observation is traceable to hydrogen bonding reorientation. At temperatures above the glass transition temperature (54 °C), the activation energy changes from negative to positive values due to breaking of hydrogen bonding and water loss. Upon cooling in a sealed environment, the activation energies of two relaxation processes are nearly zero. FTIR and XRD analyses reveal associated structural changes upon heating and cooling. These two new high-frequency relaxation processes can be attributed to the interaction of bound water with OH and NH2/NH3(+), respectively. A plausible scenario for these high-frequency relaxations is discussed in light of impedance spectroscopy, TGA, FTIR and XRD measurements.
authors.affiliation: Cinvestav Queretaro, Libramiento Norponiente 2000, Queretaro, QRO 76230, Mexico. gluna@qro.cinvestav.mx.
authors.forename: Siva
authors.initials: S
authors.lastname: Kumar-Krishnan
authors.forename: Evgen
authors.initials: E
authors.lastname: Prokhorov
authors.forename: Marius
authors.initials: M
authors.lastname: Ramírez
authors.forename: Martín A
authors.initials: MA
authors.lastname: Hernandez-Landaverde
authors.forename: Diana G
authors.initials: DG
authors.lastname: Zarate-Triviño
authors.forename: Yu
authors.initials: Y
authors.lastname: Kovalenko
authors.forename: Isaac C
authors.initials: IC
authors.lastname: Sanchez
authors.forename: Juan
authors.initials: J
authors.lastname: Méndez-Nonell
authors.forename: Gabriel
authors.initials: G
authors.lastname: Luna-Bárcenas
mesh_terms: D048271:Chitosan / Q000737:chemistry*; D058266:Dielectric Spectroscopy; D008567:Membranes, Artificial; D008872:Microwaves
chemical_list: D008567:Membranes, Artificial; D048271:Chitosan