Wetting and contact angle

The effect of the chemical makeup of the adhesive/adherend system on contact angle and wetting is manifest through the influence of such chemistry on the surface free energies of the adhesive-air (or other fluid medium), adherend-air... 

Blake TD (1993) Dynamic contact angles and wetting kinetics. In Berg JC (ed) Wettability. Dekker, New York, pp 251-309... 

FINCH, J.A. and SMITH, G.W., Contact angles and wetting , in LUCASSEN-REYNDERS, E.H. (editor), Anionic Surfactants, 11, 317-384, Dekker (1981)... 

Contact Angles and Wetting Phenomena, Speclcd issue Adv. Colloid Interface Set 39 (1992), Th.F. Tadros, A.W. Neumann, Eds. (Papers presented at a symposium held in Toronto, June 1990.)... 

FIGURE 10.4 Cohesive energy plot of contact angle and wetting tension data for an epoxy coating. (From Hansen, C.M. and Wallstrom, E., J. Adhes. (http //www.tandf.co.uk), 15, 275-286, 1983. With permission.)... 

Assuming that no surface electrification is involved, the above group of equations are the basic thermodynamic relations for describing the equilibrium contact angle and wetting phenomena. In so far as details of molecular structure of the substances and surfaces play an important part, these purely thermodynamic equations would not be expected to suffice to permit us to describe the wetting, spreading, and adhesion of liquids on solids. 

Y. Yuan, T.R. Lee, Contact angle and wetting properties. In Surface Science Techniques, ed. by G. Bracco, B. Holst (Springer, Berlin, 2013), pp. 3-34... 

The fundamentals upon which most of these operations are based are surface phenomena. Surfaces are attracted to each other by van der Waals forces surfaces are repelled by the electrochemical double layer or by steric hindrance. Surface energies, contact angles, and wetting are important. 

The theoretical discussion of contact angle and wetting to this point has assumed implicitly that the solid surface in question is a smooth, ideal plane. In fact, of course, very few solid surfaces even begin to approach such a state. The finest polished glass surface, for example, will usually have asperities of 5 nm or more. Commonly encountered polished surfaces, will be much rougher by factors of 10-1000. The earliest, and still most useful, quantitative attempt to correlate the observed contact angle of a liquid on a solid with the surface roughness is the Wenzel relationship which proposes a thermodynamic relationship such that... 

The basic framework for the application of contact angles and wetting phenomena lies in the field of thermodynamics. However, in practical apphcations it is often difficult to make a direct correlation between observed phenomena and basic thermodynamic principles. Nevertheless, the fundamental validity of the analysis of contact angle data and wetting phenomena helps to instill confidence in its apphcation to nonideal situations. 

Having mentioned several times the use of surfactant solutions in wetting studies, we now consider specifically some of the effects their presence can have on contact angles and wetting. The action of surfactants derives from their adsorption at the various interfaces and the resultant modification of interfacial tensions. In terms of the Gibbs equation, the relationship between the specific adsorption of a solute, G, and surface tension is given by... 

Figure 7.19 Contact angle [70]. (a) Contact angle and wetting of solids, (b) Behavior of three-phase contact angle when the liquid drop placed on boundary of hydrophilic and hydrophobic material for octane drop on the...

Table 20.6. Contact angle and wetting conditions Conditions Contact angle Examples...

Yuan Y, Lee TR. Contact angle and wetting properties. In Bracco G, Holst B, editors. Surface science techniques. Springer Berlin Heidelberg 2013. p. 3-34. 

This volume provides essential reading for scientists and engineers concerned with problems involving surface effects associated with surface tension, contact angles, and wetting as outlined above. It is hoped that the information presented will clarify existing uncertainties and point the way to further advances and applications. 

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