Electrode potentials, contact angles

If a gas bubble adheres to an electrode surface being in contact with an electrolyte solution, the contact angle can be measured as an indicator of the interfacial tension and its change. The respective relationship is cos 6= (y ni - y,m)/ g,s with g, s, m referring to the gas, solution and metal phase respectively. It was initially observed by Mdller, that 6 changes with E [08M61]. Assuming that s and do not depend on the electrode potential a plot of relationship follows ... 

Figure16.6 (a) Schematicdrawingofexperimental set-upforthe evaluation of the interfacial tension under potential control, (b) Relative change in contact angle as a function ofthe potential after the substrate was inserted into (open circles) and pulled from the nitrobenzene phase. Insets are schematic drawings of the side views of the contact lines. The potential was described with respect to the Au/AuO f reference electrode.

Figure 2.1 (a) A schematic representation of the apparatus employed in an electrocapillarity experiment, (b) A schematic representation of the mercury /electrolyte interface in an electro-capillarity experiment. The height of the mercury column, of mass m and density p. is h, the radius of the capillary is r, and the contact angle between the mercury and the capillary wall is 0. (c) A simplified schematic representation of the potential distribution across the metal/ electrolyte interface and across the platinum/electrolyte interface of an NHE reference electrode, (d) A plot of the surface tension of a mercury drop electrode in contact with I M HCI as a function of potential. The surface charge density, pM, on the mercury at any potential can be obtained as the slope of the curve at that potential. After Modern Electrochemistry, J O M. 

Figure 1.5 Pyrite electrode at pH = 9.2 in 0.05 mol/L sodium tetraborate solution containing 1000 mg/L of three potassium alkykanthates. (a) Cyclic voltammograms at 4 mV/s (b) Contact angles measured after holding the electrode at each potential for 30s. Vertical lines are the reversible potential of the xanthate/dixanthogen couples (Gardner and Woods, 1977)...

Arce etal. [140, 141] have studied the dynamics of 1-dodecanethiol and bu-tanethiol SAMs on Au(lll), applying ex situ and in situ STM. The potential of zero charge for the thiol-modified Au(lll) electrode was determined for self-assembled monolayers of octade-canethiolate (—0.52 V), undecanethiolate (—0.49 V), propanethiolate (—0.3 V), and H, //,2//,2 //-perfluorodecanethiolate (1.04 V) ]142]. The potentials (expressed versus Ag]AgCl]saturated KCl electrode) were determined from the measurements of the contact angle for a droplet of 0.1 M NaCl04 aqueous solution. 

Figure 4. Photographs of bubble profiles superimposed on a voltammogram showing change in contact angle with electrode potential of copper in the presence of 2 X 103 M potassium diethyldithiophosphate as flotation collector. Conditions sweep rate, 50 mV Is pH 9.3 (0.25 M sodium borate). (Reproduced, with permission, from Ref. 1. Copyright 1975, Universita Degli Studi.)...

The contact angle of an electrolyte on a solid electrode changes when changing the potential. This effect was used by Morcos and Fischer, who measured the potential-dependent capillary rise of an electrolyte meniscus at the surface of a partially immersed metal plate 11551. The interfaeial energy at a solid elec-trode/solution interface can also be measured by the Wilhelmy plate method 1156,157],... 

The bubble break-off diameter depends on a current density and as it was shown by numerous experiments,71,76 77 it decreases with increasing current density. The fact that break-off diameter decreases with increasing current density is the result of varying electrode potential which affect the wettability and, hence, the contact angle supports the conclusion that (13) is a basic relationship to explain the dependence of the break-off diameter on the current density. Then, the bubble break-off diameter, d can be presented by... 

Electrolytic gas evolution is a dynamic phenomenon affected by interactions among all the process variables. The interaction of the potential, electrode, and electrolyte not only determines the rate at which gas is evolved, but also affects the contact angles of the bubbles that determine, in conjunction with the electrolyte surface tension, the fundamental forces binding the bubbles to the electrode. Since the process occurs at a surface, small quantities of impurities may have a large effect. The dynamics of bubble evolution... 

Silver electrodes become hydrophobic in the presence of ethyl xantate ions (EtOCS2 ), as they undergo a chemisorption process followed by silver xantate formation. This phenomenon was studied by voltammetry, FTIR, UW spectroscopy and contact angle measurements under controlled potential . ... 

Translation Translation and oscillation of the droplet are caused by contact angle variations at the three-phase contact line resulting from the application of an electrical potential between the droplet and an electrode that underlies only a portion of the droplet. The platform used to experimentally study these phenomena consists... 

Only a few reports deal with the contact angle measurements on PTh and PPy surfaces. It has been found that the measured contact angles of water on electrochemi-cally prepared films strongly depend on film thickness as well as on polymerization variables such as applied electrode potential, nature of the working electrode, electrolyte, solvent and temperature. It is far from obvious to conclude on the wettability of these surfaces but some trends can be drawn from literature. 

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