Electrocapillarity, electrical double-layer

More information about the ubiquitous presence in seawater of natural organic surfactants has been obtained by the use of seawater/solid interfaces than from studies of the interface between seawater and air. For practical reasons, it is usually very much simpler to study the adsorption of organic matter from solution onto solid surfaces, where a variety of powerful techniques such as electrocapillarity, electrical double-layer capacitance measurements, electrophoresis and ellipsometry can be used to study the progress of adsorption and the nature of the adsorbed layer. Neihof and Loeb (1972, 1974) and Loeb and Neihof (1975, 1977) have demonstrated by electrophoresis and ellipsometry that a wide variety of solid surfaces become covered by a strongly adsorbed film of polymeric acids upon exposure to seawater. Hunter (1977) found the same type of effect and has shown by electrophoretic studies at different pH and metal ion concentrations that phenolic and carboxylic groups are probably responsible. This adsorbed organic material seems hkely to represent an important part of the natural surfactants in seawater and, as such, will adsorb at the air/sea interface as well. 

The thermodynamic theory of electrocapillarity considered above is simultaneously the thermodynamic theory of the electrical double layer and yields, in its framework, quantitative data on the double layer. However, further clarification of the properties of the double layer must be based on a consideration of its structure. 

Gilkes RY (1990) Mineralogical insights into soil productivity An anatomical perspective. Proc 14th Congress of Soil Science, Kyoto, Japan. Transaction Plenary Papers pp 63-75 Grahamme DC (1947) The electrical double layer and the theory of electrocapillarity. Chem Rev 41 441-501n... 

We start this chapter with electrocapillarity because it provides detailed information of the electric double layer. In a classical electrocapillary experiment the change of interfacial tension at a metal-electrolyte interface is determined upon variation of an applied potential (Fig. 5.1). It was known for a long time that the shape of a mercury drop which is in contact with an electrolyte depends on the electric potential. Lippmann1 examined this electrocapillary effect in 1875 for the first time [68], He succeeded in calculating the interfacial tension as a function of applied potential and he measured it with mercury. 

The Electrical Double Layer and the Theory of Electrocapillarity. Chemical... 

Grahame, D. C. 1947. The electrical double layer and the theory of electrocapillarity. Chem. Rev. 41 441-501. 

D.C. Grahame. The Electrical Double Layer and the Theory of Electrocapillarity, Chem. Rev. 41 (1947) 441. (A classical review.)... 

See, e.g., D. C. Grahame, The electrical double layer and the theory of electrocapillarity, Chem. Rev. 41 441 (1947) C. W. Outhwaite, Modihed Poisson-Boltzmann equatioh in electric double layer theory based on the Bogoliubov-Born-Green-Yvon integral equations, J.C.S. Faraday 7/74 1214 (1978) and the references cited therein. 

Electrocapillarity and the Electric Double Layer Structure at Oil/Water Interfaces... 

Experimentally, the electrical double-layer affect is manifest in the phenomenon named electrocapillarity. The phenomenon has been studied for many years, and there exist thermodynamic relationships that relate interfacial surface tension between electrode and electrolyte solution to the structure of the double layer. Typically the metal used for these measurements is mercury since it is the only conveniently available metal that is liquid at room temperature (although some work has been carried out with gallium. Wood s metal, and lead at elevated temperature). 

Electrocapillary phenomena at the interface between two immiscible electrolyte solutions, which we will call the oil/water (O/W) interface for short, were studied first by Guastalla [1], then by Blank and Feig [2,3], Watanabe et al. [4, 5], Dupeyrat et al. [6, 7], Joos et al. [8,9], Gavach et al. [10-12], and Spumy [13]. Watanabe et al. applied the electrocapillary equations such as the Lippmann-Helmholtz equation to elucidate the double layer structure of the interface, whereas others [2,3,6,7] made a distinction between electrocapillarity and electroadsorption. Koryta et al. [14] have discussed the electric polarizability of the oil/water interface on the basis of the transfer Gibbs energies of ions from one solvent (the aqueous phase) to the other (the oil or organic phase). 

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