Apparent surface free energy

A number of reports have described theoretical calculations for superhydrophobic surfaces. Marmur [10] and Quere and co-workers [11,12] show the theoretical background for surface roughness. There are also many reports regarding creation of superhydrophobic surfaces using hthography [13], fractal structure of wax [14], chemical vapor deposition (CVD) of poly(tetrafluoroethylene) (PITH) [15] carbon nanotubes and web-like structures [16-18] and by coating hydrophobic silanes onto aluminum acetylacetonate [19] and so on. These micro-structured surfaces show a decrease in apparent surface free energies. 

To validate the values of surface free energy obtained from the hysteresis approach, Neumann [12,13], equation- of- state approach was also used. The apparent surface free energy in this approach is determined from the liquid advancing contact angle, its surface tension and constant P as ... 

Figure 15.3 Apparent surface free energy of pure PS layers deposited on glass plates.

Apparent Surface Free Energy Calculated for Glass Plates Covered with Pure PS Layers... 

Figure 15.9 Apparent surface free energy for the PS layers with various embedded polymer fillers deposited on glass slides.

The slow rate of transition from stage (h) to stage (d) in Figure 2 is an indispensable condition in the solvent-cast process of ultrafiltration membrane technology. Stage (d) is a kind of micro-phase separation, which is apparently metastahle. The transitions (h) to (c) and (c) to (d) are governed hy the mobility and the surface free energy of the particle. 

There remains the question of the physical-i.e., operational [9] -definition of the terms. It appears to the writers that the derivation as a force balance is merely intuitional, and, as a consequence, it leaves the quantities and yg o undefined operationally. Thus, if these be viewed as forces parallel to the solid surface, one must ask with what property of the solid they are to be identified. Unlike the case with liquids, there is for solids a surface or stretching tension (the work per unit stretching of the surface [20, 25, 28]), in general nonisotropic. If this is what is involved, liquid drops on a crystalline surface of low symmetry should not be circular in cross section this is apparently contrary to observation. From the thermodynamic derivation, however, we see that one is dealing with the work of exchanging one type of solid interface for another, and that surface free energies, not stretching tensions, are the proper quantities. 

A. Surface Free Energies. Surface free energies must dominate any explanation of the adhesion between different phases which are not mechanically linked. Current levels of understanding of adhesiveness are such that actual adhesive strengths are always much less (1-0.1%) than those predicted by thermodynamic analysis, and often there is apparently little correlation between the two. Further refinement of the theory of adhesiveness will require understanding of the importance of flaws in an adhesive joint and of the relative contributions of polar and dispersive Van der Waal s interactions. The following is an analysis of adhesion in terms of surface free energies. 

Where the parameter R is an averaged value of the apparent capillary radius of the thin porous layer (29). However, as shown in (33-35), Eq. [16] is valid only if a precursor duplex liquid (ilm is pre.sent ahead of the penetrating front of a liquid completely wetting the solid surface. Thus, from this equation it is clearly seen that the surface free energy of the substrate is not related to the rate of penetration of the liquid. Nevertheless, Eq. [16] is very useful for the determination of the R parameter of glass plates covered with the powder of the solid tested. Liquids most suitable for this purpose are the i-alkanes. like n-octane or n-decane. 

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