Surface characterization by contact angles

P Wittenbeck and A Wokaun, Plasma treatment of polypropylene surfaces Characterization by contact-angle measurements , J. Appl. Polym. Sci, 1993 50 187. 

There is a significant difference between the terms for the solid surface energy in Young s equation, yi3 or ysF and Yi and in Eqn. 4 of work of adhesion Wa. This is because in the former case, the solid is in equilibrium with phase 3, which may well be air saturated with vapour of Uquid 2 (see Wetting and spreading especially Fig. 1 therein), but for the latter the solid is in vacuo. The difference between these two terms is the spreading pressure, see Surface characterization by contact angles - polymers. 

Despite these considerations, the critical surface tension is an empirical parameter, often quoted and relatively easy to measure, which helps characterize the surface of a low-energy solid such as a polymer. Values of this are available from review articles and Bandrup and Immergut and Grulke s Polymer Handbookf A much-simplified practical routine based on the concept is used in ASTM D-2578 to test the surface of plastic film see Surface characterization by contact angles - polymers. 

Thirdly, a water break test should then be carried out by spraying distilled or deionized water on to the prepared surface (Surface characterization by contact angles -polymers and Wetting and spreading). Careful abrasion is needed until a continuous layer of water remains for 30 s without any breaks. Once dried, the surface will then be ready for bonding. 

See also Pre-treatments of polymers and Surface characterization by contact angles - polymers. 

The chemical changes caused by pre-treatments may be studied by the use of contact angle measurements (see Surface characterization by contact angles polymers) or preferably with surface techniques such as X-ray photoelectron spectroscopy (XPS). The topographical changes are best studied by means of Scanning electron microscopy (SEM) or Atomic force microscopy (AFM). 

Other methods of surface characterization are discussed in Infrared spectroscopy attenuated total reflection. Infrared spectroscopy RAIR, Surface characterization by contact angies - metais. Surface characterization by contact angles - polymers. Critical surface tension, and Electron probe microanalysis (EPMA). 

Notwithstanding these drawbacks and the delicate nature of the problem, the methods described in Surface characterization by contact angles-polymers may be employed. 

Related articles are Adsorption theory of adhesion. Contact angles and interfacial tension. Dispersion forces. Pre-treatment of metals prior to bonding. Roughness of surfaces. Surface characterization by contact angles-polymers. Surface energy and Wetting and spreading. 

Equation 4 applies to an interface across which only dispersion forces act if other forces act as well, there must be another negative term on the right-hand side, giving the further lowering of interfacial energy (see Contact angles and interfacial tension, Eqn. 2, and Surface characterization by contact angles - polymers, Eqn. 4). Over the years, it... 

Confining a liquid between weakly attractive lyophobic surfaces (characterized by contact angles above 90 ) at a sufficiently small separation will lead to spontaneous evaporation. This thermodynamic process is controlled by competition between bulk energetics (that favors the liquid phase) and surface energetics (that favors the vapor phase). The liquid-to-vapor transition occurs when the grand potential of the confined liquid and confined vapor are comparable [28, 34, 35] ... 

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