Surface Tension and Its Measurement

Surface science is an important branch of physical organic chemistry that studies the behavior and characteristics of molecules at or near a surface or interface. The interface can form between solids, liquids, gases, and combinations of these states. Complex apparatus has been developed to identify and quantify surfaces and interfaces. Polymer surfaces are of special interest in industrial and biological applications examples of the latter include dental implants and body part prosthetic devices. Modification of surfaces of these devices allows formation of controlled interfaces to achieve characteristics such as bondability and compatibility. 

Adhesion is an interfacial phenomenon that occurs at the interfaces of adherends and adhesives. This is the fact underlying the macroscopic process of joining parts using adhesives. An understanding of the forces that develop the interfaces is helpful to the selection of the right adhesive, proper surface treatment of adherends, and effective and economical processes to form bonds. This chapter is devoted to the discussion of the thermodynamic principles and work of adhesion that quantitatively characterize surfaces of materials. 

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A Couper, Surface Tension and its Measurement, chapter 1 in Investigations of Surfaces and Interfaces, Part A. B.W. Rossiter, R.C. Baetzold, Eds., Physical Methods of Chemistry Series, IXA, 2nd ed. Wiley (1993). (A fairly complete review also containing a section on non-equilibrium tensions.)... 

Ihis chapter has been adapted from Surface Tension and Its Measurement in Surface Treatment of Materials for Adhesion Bonding, S. Ebnesajjad C.E. Ebnesajjad 2006 Elsevier Inc. 

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

From the viscosity, as well as the phase equilibrium, surface tension, and density measurements it is evident that the system KF-K2M0O4-B2O3 is very complex. Beside the chemical reactions, the polymerization tendency of the melts, especially in the region of higher contents of boron oxide, makes this system difficult to study. 

For the application of this equation one has to measure surface energy (surface tension) and its dependence on electrode potential at constant activities of the different components. Precise measurements are restricted to liquid metals like mercury or gallium and their alloys. Classical experiments were made with the Lippmann electrocapillary meter. The measurement of the drop time or the drop frequency of a dropping mercury electrode is easier. 

Table 24.1a Information of the mean atomic cohesive energy b(0) (in bold case) derived from fitting the measured T-dependent surface tension, as shown in detail later in Sect. 24.4.2 with the measured surface tension and its temperature coefficient as listed in the first two columns...

The topic of capillarity concerns interfaces that are sufficiently mobile to assume an equilibrium shape. The most common examples are meniscuses, thin films, and drops formed by liquids in air or in another liquid. Since it deals with equilibrium configurations, capillarity occupies a place in the general framework of thermodynamics in the context of the macroscopic and statistical behavior of interfaces rather than the details of their molectdar structure. In this chapter we describe the measurement of surface tension and present some fundamental results. In Chapter III we discuss the thermodynamics of liquid surfaces. 

It was made clear in Chapter II that the surface tension is a definite and accurately measurable property of the interface between two liquid phases. Moreover, its value is very rapidly established in pure substances of ordinary viscosity dynamic methods indicate that a normal surface tension is established within a millisecond and probably sooner [1], In this chapter it is thus appropriate to discuss the thermodynamic basis for surface tension and to develop equations for the surface tension of single- and multiple-component systems. We begin with thermodynamics and structure of single-component interfaces and expand our discussion to solutions in Sections III-4 and III-5. 

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