Study of dc conductivity, transport mechanism, and dielectric relaxation in cassava starch membranes plasticized with glycerol
In the current work, we studied dc conductivity and its relaxation in glycerol-plasticized starch membranes at various concentrations using impedance spectroscopy in frequency ranges between 20 Hz and 3 MHz and temperature ranging from 303 K to 423 K. We observed thermally activated dc conductivity following the Arrhenius model: $$ \ln σ = \ln σ_o - E_σ /k_BT $$, where the activation energy, E σ , diminished as glycerol increased. Non-Debye relaxation phenomena were observed in the actual portion of the conductivity as a function of the frequency, $$ σ ′ ≤ft( ω \right)∼ ω^n≤ft( n ≈ 1 \right) $$. Also, the symmetry of the relaxation peak observed in the imaginary part of the electric module remained unaltered as a function of temperature and glycerol content in the membranes, corresponding to a constant exponent, β = 0.80 ± 0.02, if we assume the $$ Φ (t) = \exp ≤ft[ - ≤ft( t/τ \right)^β \right] $$ correlation function in the ionic transport. The angular velocity, ω p , registering the maximum peak, $$ M_\max ^′ ′ $$, was fitted to the Arrhenius model, $$ \ln ω = \ln ω_ o - E_ω /k_ B T $$, finding great similarity between E ω and E σ values for each sample, indicating that the corresponding ionic processes have the same origin, in other words, due to the correlated jump of the charge carriers. The independence found between n and β indicates that the correlation processes or cooperative effects among ions in these materials deviate from the empirical description expressed by Ф( t ). However, these processes were identical when varying temperature glycerol content in the membranes, as suggested by the M ″( ω ) spectra.