Dielectric relaxations in chitosan solution with varying concentration and temperature: analysis coupled with a scaling approach and thermodynamical functions

Abstract

The dielectric properties of chitosan in an aqueous solution with no added salts have been measured as a function of concentration and temperature in the frequency range from 40 Hz to 110 MHz, respectively. After reducing the contribution of the electrode polarization effects, the dielectric spectra of chitosan semidilute solutions show two relaxations at 100 kHz and MHz, respectively. The observed two dielectric relaxations have been strictly analyzed using the Cole-Cole function and the possible relaxation mechanisms were attributed to the fluctuation of condensed counterions and free counterions, respectively. The dependence of the dielectric increment and relaxation time on concentration was interpreted in light of the scaling properties of polyelectrolyte solutions. It was found that the dependence of relaxation time on the C p follows the expected exponents of the scaling laws, both in the low-frequency and high-frequency cases. The good agreement between experimental results and theoretical analysis suggests that the low-and high-frequency relaxation mechanisms are the fluctuation of condensed counterions and free counterions, respectively. In addition to this, this analysis gives further support to the scaling approach of the dynamic behavior of polyelectrolytes. The temperature dependence of the dielectric spectrum of chitosan solutions showed that the low-and highfrequency dielectric increment generally decreases with the rise of temperature, which is considered to be due to the acceleration of the reorientation motion of the counterions. Moreover, the thermodynamic parameters, such as activation free energy E a , activation enthalpy change DH and activation entropy change DS of low-and high-frequency were calculated from the relaxation time, and discussed from the microscopic thermodynamical view.

Dielectric relaxations of poly(acrylic acid)-graft-poly(ethylene oxide) aqueous solution: Analysis coupled with scaling approach and hydrogen-bonding complex

“…4, a widely distributed relaxation can be observed in the frequency range from 100 kHz to 100MHz, and the frequency of this relaxation increases with concentration as shown by the arrow. Moreover, it should be noted that the steep rise in permittivity at low frequency is attributed to the effect of electrode polarization (EP), which should be removed from the spectra before dielectric analysis because the EP often obscures the relaxations in the low-frequency range [23,32].…”

“…x , where C x and G x denote the measured capacitance and conductance, respectively. The raw data measured were corrected according to Schwan's method [32,33], based on the following equations:…”

“…By fitting the expression Eq. (4), including both the electrode polarization and the effective dielectric relaxation, to the raw experimental data over the whole frequency range, the EP term (Aω −m and Bω −n ) and the dielectric parameters of each relaxation process can be determined [32].…”

“…Then, new ε and ε curves free of the EP effect were derived by mathematically subtracting Aω −m from the permittivity and the Bω −n from the dielectric loss, respectively. Finally, fitting simultaneously the new ε and ε curves, the effective dielectric parameters of the relaxations were determined [32]. The optimized fitting curve was guaranteed by the nonlinear least-squares method.…”

Chitosan–Gold–Lithium Nanocomposites as Solid Polymer Electrolyte

“…Also it was very large for lithium containing nanocomposites, indicating higher electrode polarization. 34 The values at high frequency (10 6 Hz) for chitosan film, chitosan-1 mM Au film, chitosan-50% LiClO 4 film and chitosan-1 mM Au-50% LiClO 4 film are 0.77, 2.36, 109 and 12 respectively. These results indicated that these chitosan nanocomposites have greater charge storing capacity than chitosan film.…”