Electrical double-layer structure presence

The effect of the phospholipids on the rate of ion transfer has been controversial over the last years. While the early studies found a retardation effect [6-8], more recent ones reported that the rate of ion transfer is either not retarded [9,10] or even enhanced due to the presence of the monolayer [11 14]. Furthermore, the theoretical efforts to explain this effect were unsatisfactory. The retardation observed in the early studies was explained in terms of the blocking of the interfacial area by the phospholipids, and therefore was related to the size of the transferring ion and the state of the monolayer [8,15]. The enhancement observed in the following years was attributed to electrical double layer effects, but a Frumkin-type correction to the Butler Volmer (BV) equation was found unsuitable to explain the observations [11,16]. Recently, Manzanares et al. showed that the enhancement can be described by an electrical double layer correction provided that an accurate picture of the electrical double layer structure is used [17]. This theoretical approach will be the subject of Section III.C. 

Of interest here is the question relating to the value for the slope coefficient, k, from equation (1), when surfactant structures incorporating both ionic (say sulphonate) and nonionic moieties are included together. The Ghanges in electric double layer effects imparted from salt addition might dominate the packing constraints and therefore the phase inversion process, or perhaps oxyethylene dehydration effects from the presence of toluene could also play a role. 

The ssDNA was immobilized stronger and faster on the GC surface in the presence of the lipid membrane than on a bare GC surface and using milder conditions [61]. The lipid membrane enhanced the stabihty of ssDNA towards desorption from the GC surface [61,62]. Moreover, the adsorption of ssDNA on BLM induced a conductance enhancement due to (1) structural changes (i.e., defect sites) within the membrane and (2) the increase in negative surface charge density of the membrane. The charge of the phosphate groups of ssDNA induced an increase of cation concentration in the electrical double layer [63]. 

Recently, Forsman developed a correlation-corrected PB model by introducing an effective potential between like-charge ions (Forsman, 2007). The effective potential at large ion-ion separation approaches the classical Coulomb potential and becomes a reduced effective repulsive Coulomb potential for small ion-ion separation. Such an effective potential represents liquid-like correlation behavior between the ions. For electric double layer with multivalent ions, the model makes improved predictions for the ion distribution and predicts an attractive force between two planes in the presence of multivalent ions (Forsman, 2007). However, for realistic nucleic acid structures, the model is computationally expensive. In addition, the ad hoc effective potential lacks validation for realistic nucleic acid structures. 

The structure electrical double layer at the silica-aqueous electrolyte interface was one of the earlier examined of the oxide systems. At the beginning the investigations were performed with application of electrokinetic methods next, with potentiometric titrations. The properties of this system were very important for flotation in mineral processing. Measurements proved that pHpZC and pHiep are equal to 3, but presence of some alkaline or acidic contaminants may change the position of these points on pH scale. Few examples, concerning edl parameters are shown in Table 3. Presented data concern a group of systems of different composition of the liquid phase and solid of a different origin. The latest measurements of this system takes into account the kinetics of the silica dissolution [152], and at zeta measurements, also the porosity of dispersed solid [155]. 

At the interface between O and W, the presence of the electrical double layers on both sides of the interface also causes the variation of y with Aq<. In the absence of the specific adsorption of ions at the interface, the Gouy-Chapman theory satisfactorily describes the double-layer structure at the interface between two immiscible electrolyte soultions [20,21]. For the diffuse part of the double layer for a z z electrolyte of concentration c in the phase W whose permittivity is e, the Gouy-Chapman theory [22,23] gives an expression... 

The value of o varies not only with the structure of the hydrophilic head group, but also with changes in the electrolyte content, temperature, pH, and the presence of additives in the solution. Additives, such as medium-chain alcohols that are solubilized in the vicinity of the head groups (Chapter 4, Section IIIA), increase the value of oq. With ionic surfactants, o decreases with increase in the electrolyte content of the solution, due to compression of the electrical double layer, and also with increase in the concentration of the ionic surfactant, since that increases the concentration of counterions in the solution. This decrease in the value of ao promotes change in the shape of the micelle from spherical to cylindrical. For POE nonionic surfactants, an increase in temperature may cause a change in shape if temperature increase results in increased dehydration of the POE chain. 

In Fig. 10.5b the barrier due to the stmctural component of the disjoining pressure is schematically represented for the case where its range of action is either smaller or greater than the thickness of the electric double layer. One of the ways of ensuring enhanced floatability in the presence of the structural component consists in the use of surfactants. Adsorption of... 

Photoredox reactions at organized assemblies such as micelles and microemulsions provide a convenient approach for modeling life-sustaining processes. Micelles are spontaneously formed in solutions in the presence of surfactants above a certain critical concentration. In aqueous solutions, the hydrophobic tails of the surfactant form aggregates with the polar head facing toward the aqueous environment, as depicted in Fig. 9. The hydrophobic core in micelles is amorphous and exhibits properties similar to a liquid hydrocarbon. The polar heads are also randomly oriented, generating an electrical double layer around the micelle structure. In this respect, surface properties of micelles can be somewhat correlated with the polarized ITIES. The structure of micelles is in dynamic equilibrium, in which monomers are exchanged between bulk solution and the assembly. 

We have considered here some of the physical factors involved in ion, electron, and proton transport in membrane structures, as well as the electric fields and electrical double layers that are intimately associated with these transport processes. In considering the membrane potential, which more accurately should be termed the transmembrane potential drop, it can be seen that the presence of membrane surface charges may be significant and could produce effects not expected from a consideration of Nernstian diffussion processes alone. For example, from Eq. (3) and the... 

Separation of apatite from dolomite using dodecylamine as the collector is enhanced by sodium chloride addition. Adsorption of the cationic collector on the apatite surface is attributed mostly to chemical Interactions. Sodium chloride, as indicated by zeta potential measurements, does not act as an indifferent electrolyte and affects the surface structure of apatite. However, in the case of dolomite, sodium chloride reduces the adsorption of the collector by compressing the electrical double layer. Satisfactory separation of apatite from its mixture with dolomite is achieved at pH 6.3 with dodecylamine collector In the presence of sodium chloride. 

Surface-activate ions of the supporting electrolyte not only change the chemical potential of the organic substance in the solution, but also effect the structure of the electric double layer, increasing or decreasing the adsorption of orgainc molecules. Thus, in the presence of anions, which decrease the mutual repulsion between the adsorbed cations of [(C3H7)4N] the adsorption of the latter cations increases. At the same time, the specific adsorption of Br and I anions decreases the adsorption of ethyl alcohol, phenol and of the salicylate anion [3]. 

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