102,280 research outputs found
Nematic ordering in a cell with modulated surface anchoring: effects of flexoelectricity
No full text
Electric response of asymmetric electrolytic cells to small AC signals
No full textWe present an extended theory for the electric response of an electrolytic cell with two different electrodes to a small amplitude external ac stimulus. In this case, the two electrodes limiting the cell are different in the sense that the spatial dependencies of the dynamical quantities characterising the system have not a well defined symmetry, with respect to the electrodes. This requires extending the Poisson-Nernst-Planck model to solve the fundamental equations allowing for the analytical determination of the electric impedance of the cell. The new theoretical framework opens the pathway to describe asymmetric electrolytic cells limited by conductive or adsorbing-desorbing boundaries
Independence of the effective dielectric constant of an electrolytic solution on the ionic distribution in the linear Poisson-Nernst-Planck model
No full textWe consider the influence of the spatial dependence of the ions distribution on the effective dielectric constant of an electrolytic solution. We show that in the linear version of the Poisson-Nernst-Planck model, the effective dielectric constant of the solution has to be considered independent of any ionic distribution induced by the external field. This result follows from the fact that, in the linear approximation of the Poisson-Nernst-Planck model, the redistribution of the ions in the solvent due to the external field gives rise to a variation of the dielectric constant that is of the first order in the effective potential, and therefore it has to be neglected in the Poisson's equation that relates the actual electric potential across the electrolytic cell to the bulk density of ions. The analysis is performed in the case where the electrodes are perfectly blocking and the adsorption at the electrodes is negligible, and in the absence of any ion dissociation-recombination effec
Significance of small voltage in impedance spectroscopy measurements on electrolytic cells
No full textWe investigate, theoretically, for what amplitude of the applied voltage to an electrolytic cell the concept of impedance is meaningful. The analysis is performed by means of a continuum model, by assuming the electrodes perfectly blocking. We show that, in the low-frequency range, the electrolytic cell behaves as a linear system only if the amplitude of the measurement voltage is small with respect to the thermal voltage V(T)=k(B)T/q, where k(B)T is the thermal energy, and q is the modulus of the electrical charge of the ions, assumed identical except for the sign of the charge. On the contrary, for large frequency, we prove that the amplitude of the applied signal has to be small with respect to a critical voltage that is frequency dependent. The same kind of analysis is presented for the case in which the diffusion coefficients of the positive ions is different from that for negative ions, and for the case where surface adsorption takes place
- …
