Counter ions, surface properties

There is a significant scatter between the values of the Poiseuille number in micro-channel flows of fluids with different physical properties. The results presented in Table 3.1 for de-ionized water flow, in smooth micro-channels, are very close to the values predicted by the conventional theory. Significant discrepancy between the theory and experiment was observed in the cases when fluid with unknown physical properties was used (tap water, etc.). If the liquid contains even a very small amount of ions, the electrostatic charges on the solid surface will attract the counter-ions in the liquid to establish an electric field. Fluid-surface interaction can be put forward as an explanation of the Poiseuille number increase by the fluid ionic coupling with the surface (Brutin and Tadrist 2003 Ren et al. 2001 Papautsky et al. 1999). 

Clay minerals have a permanent negative charge due to isomorphous substitutions or vacancies in their structure. This charge can vary from zero to >200cmol kg" (centimoles/kg) and must be balanced by cations (counter-ions) at or near the mineral surface (Table 5.1), which greatly affect the interfacial properties. Low counter-ion charge, low electrolyte concentration, or high dielectric constant of the solvent lead to an increase in interparticle electrostatic repulsion forces, which in turn stabilize colloidal suspensions. An opposite situation supports interparticle... 

In addition to proton adsorption, interactions between the ions of the inert electrolyte (counter ions, section 10.3) and the oxide surface lead to ion pair formation which influences the electrochemical properties of the oxides and the determination of pKa values. Ion pair formation involves outer sphere surface complexes (see Chap. 11), e.g. 

In situ polymerization, and electrochemical polymerization in particular [22], is an elegant procedure to form an ultra thin MIP film directly on the transducer surface. Electrochemical polymerization involves redox monomers that can be polymerized under galvanostatic, potentiostatic or potentiodynamic conditions that allow control of the properties of the MIP film being prepared. That is, the polymer thickness and its porosity can easily be adjusted with the amount of charge transferred as well as by selection of solvent and counter ions of suitable sizes, respectively. Except for template removal, this polymerization does not require any further film treatment and, in fact, the film can be applied directly. Formation of an ultrathin film of MIP is one of the attractive ways of chemosensor fabrication that avoids introduction of an excessive diffusion barrier for the analyte, thus improving chemosensor performance. This type of MIP is used to fabricate not only electrochemical [114] but also optical [59] and PZ [28] chemosensors. 

Counter ion — A mobile ion that balances the charge of another charged entity in a solution. It is a charged particle, whose charge is opposite to that of another electrically charged entity (an atom, molecule, micelle, or surface) in question [i]. Counter ions can form electrostatically bound clouds in the proximity of ionic macromolecules and in many cases, determine their electric properties in solution [ii]. 

The products thereby obtained are anionic silane surfactants exhibiting excellent surfactant properties dependent on the ammonium counter ion. Some specimen are real foam boosters, too. For example an 1 wt. % aqueous solution of isopropylammonium sulfatohexyl trimetyl silane shows a surface tension of 21 mN m and a spreading ability of 65 mm. As being familiar for the nonionics the aqueous solution of... 

The anions of adsorbed mineral acids are loosely bound at the surface and form a diffuse cloud of counter ions around the surface of the carbon particles. When the second oxygen chemisorption occun on immersion in pure water, the bound counter ions are OH ions. Obviously, the counter ions can be exchanged for other negatively charged ions, the carbons have anion exchange properties. 

An important aspect of analyzing the double layer data in the presence of specific adsorption is the determination of the dielectric properties of the irmer layer. In the Grahame model for ionic adsorption [Gl], the adsorbed ions are assumed to have their charge centers located on the inner Helmholtz plane (iHp). Furthermore, the iHp is closer to the electrode surface than the oHp. This is due to the fact that the adsorbed ions replace solvent molecules on the electrode surface, whereas the counter ions on the oHp do not. Another feature of the following treatment is that the charge on the adsorbed ions is assumed to be located on the iHp. Accordingly, the potential drop across the inner layer is given by... 

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