Voltage-induced instability

The first model of membrane electroporation was suggested by Crowley [1]. In Crowley s model the membrane is viewed as the isotropic elastic material. The necessary background for understanding its voltage-induced instability was discussed in Section II. Crowley s approximation for the elasticity energy term in Eq. (7) is... 

Several cases of dielectric, hydrodynamic, and flexoelectric instabilities and domain structures have been observed and extensively studied in CLCs. Their appearance depends on the initial orientation of molecules, the physical parameters of the material, and the applied electric field. In CLCs with positive dielectric anisotropy Ae > 0, an electric field applied along the helix axis of a planar (Grandjean) texture can induce a two-dimensional spatially periodic deformation which has the form of a square grid [96], The period and threshold voltage of this field-induced instability depend on the elastie constants, the dieleetric anisotropy, and the sample thickness [97],... 

An active mixer based on an oscillating EOF induced by sinusoidal voltage ( 100 Hz, 100 V/mm) was devised and modeled for mixing of fluorescein with electrolyte solutions. This is termed as electrokinetic-instability micromixing, which is essentially a flow fluctuation phenomenon created by rapidly reversing the flow. Various microchips materials (PDMS, PMMA, and glass) and various electrolytes (borate, HEPES buffers) have been used to evaluate this method of micromixing [480]. 

It has been Icnown for years that a decrease in the phase transition temperature of azobenzene containing LC is induced by trans -cis photoisomerization (23). Smectic LC of 4-alkyl-4 -cyano-biphenyl is subjected to phase transition by photoisomerization of azobenzene leading to a reversible change in the threshold voltage for electrohydrodynamic instability (24). None of them described the concept of image amplification. 

Abstract A systematic overview of various electric-field induced pattern forming instabilities in nematic liquid crystals is given. Particular emphasis is laid on the characterization of the threshold voltage and the critical wavenumber of the resulting patterns. The standard hydrodynamic description of nematics predicts the occurrence of striped patterns (rolls) in five different wavenumber ranges, which depend on the anisotropies of the dielectric permittivity and of the electrical conductivity as well as on the initial director orientation (planar or homeotropic). Experiments have revealed two additional pattern types which are not captured by the standard model of electroconvection and which still need a theoretical explanation. 

Flexocoefficients have also been obtained from the threshold voltages and wave numbers of electric field-induced flexoelectric instabilities (which are discussed in more detaii in Chapter 4 by Buka et al. ) for ClPbislOBB and for the molecule 4-((3-(4-(4-(decyloxy) benzoyloxy)benzoyloxy) phenylimino) methyl)-3-hydroxyphenyl 4-(6-(4 -cyanobiphenyl-4-yloxy)hexyloxy) benzoate (BCCB), which is a dimer composed of a calamitic and a BC molecule. In both cases the flexocoefficients were found to have the same order as that of calamities. 

At a certain critical voltage the destabilising shear-induced torque My = a.i dvj dx), which comes from the interaction of a field driven charged volume of a liquid with the director, becomes large enough to equalise the stabilising elastic torque. This balance of the elastic and hydrodynamic torques is the condition for the onset of instability ... 

From experiments on planar bilayer membranes (BLM), it was known that lipid bilayers were not able to withstand an increase in the applied voltage above a threshold value. A conductive state followed by a rupture was observed for values of the order of 200 mV. Electropulsation induces a transmembrane potential modulation, bringing a similar membrane instability. Indeed experiments on pure lipid vesicles showed that upon the field pulse the lipid bilayer could become leaky. This was observed on line by the associated increase in conductance of a salt-filled vesicle suspension [26]. But larger molecules could leak out and be directly detected outside the vesicles as observed with radiolabelled sucrose [27] or fluorescent dyes [28]. A very fast detection of the induction of membrane leakage is obtained by electrical conductance and light scattering... 

The condition expressed by Eq. (3.19) is no longer valid as type 11 electrode materials have narrow nonstoichiometric domains (Fig. 3.7). When the host lattice contains a transition-metal element M, the electrons injected in the insertion process are distributed in the empty d orbitals. The decrease in the formal oxidation state results in a change of either the ionic radius of the coordination shell symmetry (Jahn-Teller effect), inducing strains on the (77) framework. This situation is expressed as a strong positive interaction term proportional to the number of intercalated species (Eq. 3.19). It appears that the existence of a maximum of potential V(x) implies some instability in the [e-2] domain. As a consequence, the voltage composition curve shows a plateau in the forbidden composition range due to the equilibrium of the two pseudo-phases. 

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