Dipolar potential

The frustration effects are implicit in many physical systems, as different as spin glass magnets, adsorbed monomolecular films and liquid crystals [32, 54, 55], In the case of polar mesogens the dipolar frustrations may be modelled by a spin system on a triangular lattice (Fig, 5), The corresponding Hamiltonian consists of a two particle dipolar potential that has competing parallel dipole and antiparallel dipole interactions [321, The system is analyzed in terms of dimers and trimers of dipoles. When the dipolar forces between two of them cancel, the third dipole experiences no overall interaction. It is free to permeate out of the layer, thus frustrating smectic order. 

Here, Hg(s) is the surface potential of mercury in contact with the solution phase S. The difference of metal and solution surface potentials, Hg(s) - s(Hg), is the dipolar potential difference, often written2 as g (dip) = gM(dip) - gs(dip), with the metal M here equal to Hg. 

Dipolar Potential Anisotropy of lipid headgroup dipoles in organized membrane Electrostatic... 

The polar lipid headgroup zone contains the phospholipid and steroid phosphorus-nitrogen, carbonyl, hydroxyl and hydration water moieties which combine to establish a substantial dipolar potential. This positive potential is of a magnitude of several hundred millivolts across the membrane headgroup zone. In the membrane hydrocarbon interior, the electrostatic field must be at least 450 to 750 mV (14) and controls ion current across the interior as we 1 1 as possibly influencing selective ion adsorption to the membrane surface. 

Synergic action of receptors Is preferred for maximization of an analytical signal. A concurrent reduction of dipolar potential and molecular packing will amplify any one receptoi—stimulant complexation in comparison to singular alteration of either parameter. 

While one cannot rule out that there are contributions of different origins to the hydration repulsion, the polarization contribution might be the dominant one, at least for not too small separations, and this can explain, as shown later in the paper, the quadratic dependence, determined experimentally by Simon and McIntosh,24 of the hydration repulsion on the surface dipolar potential. 

The Gruen—Marcelja model could relate the hydration force to the physical properties of the surfaces by assuming that the polarization of water near the interface is proportional to the surface dipole density.9 This assumption led to the conclusion that the hydration force is proportional to the square of the surface dipolar potential of membranes (in agreement with the Schiby—Ruckenstein model),6 a result that was confirmed by experiment.10 However, subsequent molecular dynamics simulations revealed that the polarization of water oscillated in the vicinity of an interface, instead of being monotonic.11 Because the Gruen—Marcelja model was particularly built to explain the exponential decay of the polarization, it was clearly invalidated by the latter simulations. Other conceptual difficulties of this model have been also reported.12 13... 

One can identify three physical phenomena which lead to the observed values of Ax- First, an ionic double layer can be established if the distance of closest approach for cations and anions to the interface is not the same. Second, if one of the components of the solution has a dipole moment, it may assume a preferred orientation at the interface, thereby giving rise to dipolar potential drop. Finally, the presence of the solute can change the orientation of water molecules at the interface from that present in the pure solvent. The fact that Ax is usually positive is evidence that the anion approaches the surface more closely than the cation. This is not difficult to understand given that anions are more weakly solvated than... 

A (j) is the potential drop due to the net free charge at the interface is the dipolar potential due to the metal phase, more specifically, to the electron overspill that occurs at the surface of the metal finally, is the dipolar potential due to the solution phase which arises because of the orientation of solvent molecules at the interface due to their proximity to the metal, and because of the unequal distances of closest approach of the cations and anions to the interface. is defined in the opposite direction to because the concept of the dipolar potential originates at the condensed phase vacuum interface where the definition of the potential drop is always from vacuum to the condensed phase. The dipolar potential arises for the same reasons as the surface potential x at the metal vacuum interface. However, it is not the same because of the effect that the proximity of the molecules and ions of the solution phase have on the electron overspill. 

In order to extend the above treatment to the metal solution interface, one must consider the effect of the solvent molecules adsorbed on the metal on the electronic overspill. Because the solvent molecules are polarizable, an induced dipole moment is established in the solvent monolayer, which acts to reduce the extent of overspill. As a result, the dipolar potential due to the metal is reduced by a factor corresponding to the optical permittivity of the monolayer, Sop. Recalling that this dipole potential is designated as one has at the PZC... 

In this paper we give an overview of the mean-field theory of phase transitions in coupled rotors with particular attention to the issues of reentiance, other quantum anomalies, and meta-stability. We comparatively analyze coupled planar rotors (two-dimensional model) and coupled linear rotors (three-dimensional). We show that the dipolar potential does not exhibit the reentrance anomaly, whereas the quadmpolar one does. The phase transition turns out to be second order in all cases except for the linear rotors in a quadmpolar potential where it is first order. We also investigate the effects of the crystal field in the case of the linear rotor model with quadmpolar potentials the crystal field causes the appearance of critical points which separate lines of the phase diagram where the transition is first order from regions where there is no... 

These processes alter the total dipolar potential field, the latter usually being envisioned as a trapezoidal electrostatic field, as shown in figure 9.6. 

Figure 9.6 The inherent dipolar potential of the membrane as a trapezoidal potential field extending across the plane of the BLM. An external voltage can skew the electric field to act as a driving force for ion translocation.

Solving the one-dimensional Poisson equation with the charge density profile p z) leads to the electrostatic (dipolar) potential drop near the interface according to... 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

This form of the functional assumes that the difference in the free energy of each ion transfer between water and organic phase is so large that each ion species is located either completely in water or completely in oil. Furthermore, formation of a spontaneous dipolar potential drop across the contact of the two solvents and its possible coupling with the ion distribution is not part of the model. 

The maximum electrical potential in the compact layer A < - includes a dipolar potential which is shown schematically as a narrow region at the sharp interface. A dipolar layer can be located not only in the compact layer but can also occupy part of the diffuse layer. The amplitude and sign of isPpg can differ from the total interfadal potential. Figure 4 illustrates four possibilities for potential distribution at ITIES. Generally, the dipolar potential depends on the total interfadal potential A <. ... 

To transpose these polar variables into dipolar variables, it is convenient to define the Peltier potential difference, notated with an uppercase pi (U), as the dipolar potential... 

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