Novel gigahertz frequency dielectric relaxations in chitosan films

作者：Kumar Krishnan Siva; Prokhorov Evgen; Ramirez Marius; Hernandez Landaverde Martin A; Zarate Trivino Diana G; Kovalenko Yu; Sanchez Isaac C; Mendez Nonell Juan; Luna Barcenas Gabriel^*

来源：Soft Matter, 2014, 10(43): 8673-8684.

DOI：10.1039/c4sm01804d

Molecular relaxations of chitosan films have been investigated in the wide frequency range of 0.1 to 3 x 10(9) Hz from 10 degrees C to 110 degrees C using dielectric spectroscopy. For the first time, two high-frequency relaxation processes (in the range 10(8) to 3 x 10(9) Hz) are reported in addition to the low frequency relaxations alpha and beta. 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 degrees C to 54 degrees C with negative activation energy; this observation is traceable to hydrogen bonding reorientation. At temperatures above the glass transition temperature (54 degrees 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.

• 出版日期2014