Evidence for frequency dependent diffusion in hydrogel

Abstract

The electrical response of a hydrogel to an external periodic voltage is investigated by means of the impedance spectroscopy technique. We show that the experimental data, obtained in the linear regime, for the real and imaginary parts of the electric impedance can be interpreted using the Poisson-Nernst-Planck model, taking into account the frequency dependence of viscosity and the non blocking character of the electrodes. We estimate the parameters (ion density, electrode conductivity, and diffusion coefficient) when varying the quantity of salt in the hydrogel. Our experimental data indicate that the bulk density of ions increases with the salt concentration, tending to a saturation value, whereas the electrode conductivity is independent of it. Finally, the parameters defining the dispersion of the diffusion coefficient depend weakly on the salt concentration.

Bioinspired Color-Changeable Organogel Tactile Sensor with Excellent Overall Performance

“…In addition, the amplitude of the RCR under high frequency is considerably lower than that under low frequency due to its viscosity-frequency dependence (Figure S5). 43 Furthermore, the reliability of the PAAm organogel under cyclic loading has been evaluated. As shown in Figure 2D, only a decrease (0.5%) of the RCR amplitude is observed after 1000 load-unloading cycles, indicating its reliability for long-term applications.…”

Frequency-Dependent Dielectric Permittivity in Poisson–Nernst–Planck Model

“…One of the challenges of such data analyses happens at the moment of selecting an expression for the impedance which compiles all the diversity of possible profiles in a wide frequency range. In an overview of dielectric spectroscopy studies, it is often assumed that the effects of ions prevail in low frequency regions, and it is often studied by employing the Poisson–Nernst–Planck (PNP) in the usual form and other approaches involving the frequency-dependent diffusion constant, frequency-dependent dielectric effect, − and the anomalous Poisson–Nernst–Planck (PNPA) models, − when it comes to the case of electrolytic cells or ionic cells. On the other hand, effects involving polarization inertia of molecules are often approached by the classic Debye model, non-Debye dielectric relaxation models, , among others.…”