The Role of Electric Double Layers

Hunter, R. J., Zeta Potentials in Colloid Science Principles and Applications, Academic Press, London, 1981. (Advanced level. The focus of this book is on the role of electrical double layers and zeta potential on electrophoresis and electroviscous effects. This volume presents some details on electrical double layers around nonspherical particles not discussed in the present book.)... 

Another difference lies in the role of electric double-layer repulsion, which is often a key factor in stabilizing aqueous foams with ionic surfactants. The adsorption of ionic surfactant at the liquid surface leads to the formation of a charged surface and a diffuse layer of counterions. As the foam lamellae thin because of the drainage of liquid, these counterions begin to repel each other and retard further thinning. Because ionization is not possible in nonpolar solvents, this double-layer mechanism is not operative in nonpolar foams. 

On the basis of experimental evidence and taking into account the role of electrical double layers on contact angles and flow patterns, one can certainly argue that the most successful conditions for multilayer Y-type LB deposition take place at a pH equal to the pX of the carboxylic acid, with a subphase where a minimum concentration of a... 

The Role of Electrical Double Layers (EDLs) and their Biological... 

In fluid lubrication the importance of wettability and the role of electrical double layers are discussed. Solid lubricants are more effective as protective films and as an example the use of monolayers of... 

The static - double-layer effect has been accounted for by assuming an equilibrium ionic distribution up to the positions located close to the interface in phases w and o, respectively, presumably at the corresponding outer Helmholtz plane (-> Frumkin correction) [iii], see also -> Verwey-Niessen model. Significance of the Frumkin correction was discussed critically to show that it applies only at equilibrium, that is, in the absence of faradaic current [vi]. Instead, the dynamic Levich correction should be used if the system is not at equilibrium [vi, vii]. Theoretical description of the ion transfer has remained a matter of continuing discussion. It has not been clear whether ion transfer across ITIES is better described as an activated (Butler-Volmer) process [viii], as a mass transport (Nernst-Planck) phenomenon [ix, x], or as a combination of both [xi]. Evidence has been also provided that the Frumkin correction overestimates the effect of electric double layer [xii]. Molecular dynamics (MD) computer simulations highlighted the dynamic role of the water protrusions (fingers) and friction effects [xiii, xiv], which has been further studied theoretically [xv,xvi]. 

The role of electrochemical double layer capacitors (EDLCs) in technologies to store electricity is an important [4], but compared to lithium-ion batteries, stiU an underestimated issue. In terms of energy densities, still the Hthium-ion batteries are the better choice ( 100 Whkg vs up to 5 Whkg for EDLCs), but in terms of power densities, the EDLCs are in a much better position and may reach values above 10 000 Wkg"T Another disadvantage of EDLCs might be the faster... 

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. 

More detailed and advanced information on these forces can be found in the book by Israelachvili (1991), which is devoted completely to intermolecular and surface forces. Here, we focus on the essential basic information and examples. Before we proceed to a physical explanation of these forces and the necessary equations, it is useful to explore the role played by the van der Waals forces in colloid stability since this theme reappears in our discussions of electrical double-layer forces in Chapter 11 and polymer-induced forces in Chapter 13. 

Though not discussed in this book, the role of non-aqueous solvents in determining the structures and properties of electrical double-layer has been the subject of numerous studies dating from 1920s. For the recent results, see, for example, Trasatti, S. Electrochim. Acta 1987, 32, 843 Borkowska, Z. J. Electroanal. Chem. 1988, 244, 1 Bagotskaya, I.A., Kazarinov, V.E. J. Electroanal. Chem. 1992, 329, 225. 

Tphe discreteness-of-charge effect (discrete-ion effect) is a general char-acteristic of electric double layers in aqueous media (I) and therefore should manifest itself in ionized monolayers. In a number of papers (2,3,4,5), one of the authors and co-workers investigated the role of this... 

There are many questions remaining and many puzzUng, unexplained effects such as the effect of cation size and valence on film stability. These questions point to the need to develop a better understanding of the crystal-like structure of LB films, the role of molecular and structural forces in creating these structures, and the nature and stability of electrical double layers subject to mechanical perturbations in the underlying subphase. 

Several interfacial phenomena may be considered when dealing with colloidal dispersions (i) Charge separation and formation of electrical double layers, (ii) Wetting of powders and the role of surfactants, (iii) Adsorption of surfactants and polymers at the solid/liquid and liquid/liquid interfaces. 

A logical division is made for the adsorption of nonelectrolytes according to whether they are in dilute or concentrated solution. In dilute solutions, the treatment is very similar to that for gas adsorption, whereas in concentrated binary mixtures the role of the solvent becomes more explicit. An important class of adsorbed materials, self-assembling monolayers, are briefly reviewed along with an overview of the essential features of polymer adsorption. The adsorption of electrolytes is treated briefly, mainly in terms of the exchange of components in an electrical double layer. 

Splelman L A and Friedlander S K 1974 Role of the electrical double layer In particle deposition by convective diffusion J. Colloid. Interfaoe. Sol. 46 22-31... 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

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