Giovanni Barbero

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We discuss the influence of the ions dissolved in a liquid on the impedance spectroscopy of a cell. Our analysis is performed in the small-voltage regime, where the actual bulk density of ions is only slightly perturbed by the external electric field. In this framework, we show that the presence of the ions can be taken into account by a surface density of(More)
We evaluate the ionic relaxation time of a nematic cell subjected to a potential difference, V0 , very large with respect to VT=KBT/q=0.025 V, where KBT is the thermal energy, and q the electrical charge of the ions, assumed monovalent. The analysis is performed by assuming that the mobilities of the positive and negative ions are the same, and that the(More)
We investigate the cholesteric-nematic transition induced by an external bulk field in a sample of finite thickness ℓ. The analysis is performed by considering a tilted magnetic field with respect to the easy direction imposed by rigid boundary conditions inducing planar orientation. In the case of parallel orientation between the magnetic field and of the(More)
We analyze the models that account the ionic contribution to the complex dielectric constant of a nematic liquid crystal. We compare the predictions of the model of [Sawada, Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 318, 225 (1998)] based on the assumption that the electric field in the liquid coincides with the applied one, with the model of Macdonald(More)
The influence of the ions present in a liquid crystal on the dynamical response of a nematic slab submitted to a dc voltage is studied. The evolution of the system toward the equilibrium state is investigated by solving the continuity equation for the electric charge, taking into account the current of drift and of diffusion. Our analysis shows that the(More)
We present a general model to describe the influence of the ionic adsorption on the anisotropic part of the surface energy of a nematic liquid crystal in contact with a substrate. We show that in the limit of small adsorption energy, the exponential approximation for the electric field of ionic origin works well. In this limit, the dielectric and(More)
A liquid crystal (LC) cell has been made by using a standard sandwich configuration with one of the indium tin oxide (ITO) electrodes covered by a thin layer of tungsten trioxide (WO3). In this kind of cell optical polarization switching (observed under a crossed polarizer microscope) occurs for only one of the two polarities of an ac external applied(More)
The twist-bend nematic phase, N_{TB}, may be viewed as a heliconical molecular arrangement in which the director n precesses uniformly about an extra director field, t. It corresponds to a nematic ground state exhibiting nanoscale periodic modulation. To demonstrate the stability of this phase from the elastic point of view, a natural extension of the Frank(More)
The effect of the generation-recombination phenomenon on the electrical impedance of an electrolytic cell is investigated. We show that this phenomenon could be responsible for the appearance of a plateau in the real part of the impedance of the cell. The possibility to observe the plateau, arising from the generation-recombination phenomenon, is discussed(More)
We analyze in which experimental conditions the concept of electrical impedance is useful for an electrolytic cell. The analysis is performed by solving numerically the differential equations governing the phenomenon of the redistribution of the ions in the presence of an external electric field and comparing the results with the ones obtained by solving(More)