Solid surfaces, heterogeneity surface tension

This method has been employed to measure the critical wetting surface tensions of particles of sulfur, silver iodide, methylated glass beads, quartz, paraffin-wax-coated coal, and surfactant-coated pyrite. Generally. Fuerstenau and coworkers [106-115] found that the film flotation technique is sensitive to the surface hydrophobicity and the heterogeneity of the particles. It was found that particle size, particle shape, particle density, film flotation time, and the nature of the wetting liquids have negligible effects on the results of film flotation. But the liquid and the solid particles used in the experiments must not have any chemical interactions. 

In a praetical sense, it is not necessary to eliminate completely all evidence of roughness and heterogeneity. If the average contact angle and liquid surface tension measurements for a variety of liquids all give the same solid surface tension via the equation of state (11. then effectively the surface is sufficiently smooth and homogeneous. The required level of accuracy will determine the acceptable solid surface quality. 

In 1958 Cahn and Hilliard proposed a phenomenological theory for surface and interfacial tensions that was based on a general formalism for heterogeneous systems. It has a certain analogy with the descriptions of non-uniformities in magnetic and ferro-electric domains in solids. The basic idea was that the loeal Helmholtz energy density per molecule / is expanded in a Taylor series about, the corresponding quantity in a uniform phase. Mathematically,... 

The overall conclusion is that the present problem is not solved the main culprit is a lack of information on the submicroseopic properties of the solid surface, and the real world is very mueh more complex than discussed so far think of the influences of the line tension (which intermingles in a complicated fashion with surface roughness and heterogeneity) and surfactants (which may lead to continuing changes even after the application of a force has been stopped). 

In an attempt to lower their surface energy, solids almost always will adsorb small molecules, such as H2O or O2, on their surfaces. Molecules which form molecular solids have much smaller surface tensions than other solids. The study of surfaces is a difficult one, it can be seen. Fortunately a number of very special experimental methods have been developed, and surfaces may be studied in great detail. Such studies are useful in many important practical areas, such as adhesion, lubrication, corrosion and adsorption. However, the most important area is probably heterogeneous catalysis. 

Current theories to explain hysteresis of contact angles are primarily based on the concepts of surface roughness, surface heterogeneity, friction, and adsorption phenomena. Unintentional adsorption, or contamination—the result of inadequate experimental technique—is, however, the most frequent explanation. As all systems involving solids are subject to the reasons indicated above for hysteresis, we chose the system mercury-benzene-water, which should be affected only by adsorption phenomena, controllable under proper experimentation. An additional advantage is the fact that all interfacial tensions involved can be measured. 

Wang J, Bratko D, Luzar A (2011) Probing surface tension additivity on chemically heterogeneous surfaces a molecular approach. Proc Natl Acad Sci USA 108(16) 6374—6379 Leroy F, dos Santos D, Muller-Plathe F (2009) Interfacial excess fiee tmeigies of solid-liquid interfaces by molecular dynamics simulation and thermodynamic integratirai. Maciomol Rapid Commun 30(9-10) 864—870... 

---