Studies on interfaces using interaction potentials

The first information eoming from the application of the method regards the density profile across the interface. Density may be assumed to be constant in bulk liquids at the equilibrium, with local deviations around some solutes (these deviations belong to the family of cybotactic effects, on which something will be said later). At each type of liquid surface there will be some deviations in the density, of extent and nature depending on the system. 

A particular case is that of mobile surfaces, i.e., liquid/gas and liquid/liquid surfaces. Having liquids a molecularly grained sfructure, tiiere will always be at a high level of spatial deviation a local deviation of the surface from planarity. If there are no oflier effects, this deviation (sometimes called corrugation, but flic term is more convenient for other cases, like liquid/solid surfaces, where corrugation has a more permanent status) averages to zero. 

Jacopo Tomasi, Benedetta Mermucci, Chiara Cappelli 

The van der Waals regime locally corresponds to the large scale energy profile, with a smooth shape. 

The density profile for liquid/solid surfaces has been firstly studied for hard spheres on hard walls, and then using similar but a bit more detailed models. It is easy to modify die potential parameters to have an increment of the liquid density near the wall (adhesion) or a decrement. Both cases are physically possible, and this effect plays an important role in capillarity studies. 

To close this section on liquid surfaces, limited to a rapid examination of the several types of surface of more frequent occurrence, we report some general comments about the use of the standard approach on liquid stufaces. 

Jacopo Tomasi, Benedetta Mennucci, Chiara Cappelli 

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Use of Ultrasonic Vibration Potential To Monitor Coalescence. The complex chemical nature of crude oils makes it difficult to relate the dispersion behavior to the physicochemical properties at the crude-oil-water interface. In addition, the nonpolar and nontransparent nature of the oleic phase provides significant obstacles for studies of the interactions of the suspended water droplets in real systems. Recent development (28, 29) of electroacoustical techniques has shown considerable promise for electrokinetic measurements of colloidal systems and the direct monitoring of the rate and extent of coagulation (flocculation and coalescence) of water droplets in nontransparent water-in-oil media. The electroacoustic measurement for colloidal systems in nonpolar media is based on the ultrasound vibration potential (UVP) mode, which involves the applica-... 

From the positions of the maxima of the ionic density profiles relative to the minima of the ion-metal interaction potentials, they concluded that 1 is contact adsorbed and Li" " is not. Spohr [190] and later Perera and Berkowitz [191] obtained similar results by means of free energy calculations for 1 and simultaneous Li" " and 1 adsorption, respectively, on Pt(lOO), using the same interaction potentials. Eck and Spohr [77, 192] and Toth and Heinzinger [80] studied the adsorption of Li+ and several halide ions near the ab initio model of the mercury interface [40]. The liquid/ gas interface, contrary to metallic interfaces, is depleted in the interfacial region [193-195]. This is a consequence of the driving force towards fully hydrated ions. 

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