Surface region electrical double layer thickness

In a general sense, the swollen polymer films can be considered as a polymer, polyelectrolyte gel [3]. Various microscopic techniques have revealed a pronounced heterogeneity of the surface layer [151-159]. In this respect, one has to distinguish between macropores (whose diameter exceeds 10 nm considerably) and nanopores (which represent solvent molecules and ions between the polymer chains). Inside the macropores, the thermodynamic and transport properties of ions and solvent molecules practically do not differ from that of the contacting bulk solution. The space-charge regions (electric double layers) are formed at the interface between the polymer and solution phases whose thickness is much lower than the characteristic sizes of macroelements (fibrils, grains, and pores). The... 

The adsorption of the growth unit(s) into the surface adsorption layer. This step is likely to involve the partial dehydration of the growth unit(s). The adsorption layer is a region immediately adjacent to the surface of thickness < 1000 nm. It is that part of the electrical double layer of ionic crystals, termed the Stern layer, in which specific adsorption occurs. 

Fig.l Schematic representation of the electric double layer at a solid-liquid interface and variation of potential with the distance from the solid surface if/Q, surface potential potential at the Stern plane potential at the plane of share (zeta potential) 8, distance of the Stern plane from the surface (thickness of the Stern layer) k, thickness of the diffuse region of the double layer. 

When a metal electrode is placed in an electrolyte solution, an equilibrium difference usually becomes established between the metal and solution. Equilibrium is reached when the electrons left in the metal contribute to the formation of a layer of ions whose charge is equal and opposite to that of the cations in solution at the interface. The positive charges of cations in the solution and the negative charges of electrons in the metal electrode form the electrical double layer [4]. The solution side of the double layer is made up of several layers as shown in Fig. 2.7. The inner layer, which is closest to the electrode, consists of solvent and other ions, which are called specifically adsorbed ions. This inner layer is called the compact Helmholtz layer, and the locus of the electrical centers of this inner layer is called the inner Helmholtz plane, which is at a distance of di from the metal electrode surface. The solvated ion can approach the electrode only to a distance d2. The locus of the centers of the nearest solvated ion is called the outer Helmholtz plane. The interaction of the solvated ion with metal electrode only involves electrostatic force and is independent of the chemical properties of the ions. These ions are called non-specifically adsorbed ions. These ions are distributed in the 3D region called diffusion layer whose thickness depends on the ionic concentration in the electrolyte. The structure of the double layer affects the rate of electrode reactions. 

Fig. 1 Electroosmotic flow near the double layer region for (a) a homogeneous surface (C = -ICol)and(b) a homogeneous surface with a heterogeneous patch (C = + ICoD- Over the heterogeneous patch, the excess cations are attracted to the positive electrode resulting in an electroosmotic flow in the opposite direction to that over the homogeneous regions with an excess anion concentration. Arrows represent streamlines and 1/k refers to the characteristic thickness of the electrical double layer...

The surface conduction is the excess electric conduction tangential to a charged surface and originates from the excess counterions concentrations in the electrical double layer region near the solid-liquid interface. The corresponding electric conductivity is called the surface conductivity, /is, that is considered as the electric conductivity of a sheet of material of negligible thickness, with a unit m Specific surface conductivity values are of the order 10 10 for water in glass capillaries. 

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