Surface energy typical values listed

For comprehensive listings of experimental surface tension values for a wide variety of polymers, the reader is referred to several excellent references 3,4-5. The surface tension of even the most polar polymers generally fall well below that of water (as shown in Figure 4) so that in terms of surface tension, polymers should be considered at best only mildly hydrophilic. Poljnners are low surface energy materials in comparison with other classes of materials by virtue of their low mass density and consequently a low interaction density, as is demonstrated in Table 1, which shows typical values for a range of different types of materials. 

Chemisorption and physisorption are usually studied by measuring (directly or indirectly) the coverage of a surface versus the temperature. The lower the temperature needed to reduce the coverage of a surface, the lower the energy of interaction between gas molecule and surface. Energies of interactions are usually listed as heats of adsorption, or A dsH. They are typically listed as positive numbers, although in all cases the process itself is exothermic. Table 22.3 lists some values for differ-... 

Surface energy figures for a range of fillers have been listed by Schlumpf [14]. Approximate ratios for some of these values to that of typical plastics are shown in Table 2.2. 

The raw output of a molecular structure calculation is a list of the coefficients of the atomic orbitals in each LCAO (linear combination of atomic orbitals) molecular orbital and the energies of the orbitals. The software commonly calculates dipole moments too. Various graphical representations are used to simplify the interpretation of the coefficients. Thus, a typical graphical representation of a molecular orbital uses stylized shapes (spheres for s-orbitals, for instance) to represent the basis set and then scales their size to indicate the value of the coefficient in the LCAO. Different signs of the wavefunctions are typically represented by different colors. The total electron density at any point (the sum of the squares of the occupied wavefunctions evaluated at that point) is commonly represented by an isodensity surface, a surface of constant total electron density. 

Shustorovich (5) has reviewed the detailed method and the equations for calculating heat of chemisorption and activation barriers by BOC. The multidimensional activation energies were calculated in the present work and the activation energies are listed in Table 1. The initial preexponential factors were estimated by transition-state theory, employing reasonable chemical assumptions about surface mobility. Dumesic et al. (3) summarized typical ranges of these values used in microkinetic analysis studies. For the reaction A +B —>C +D the preexponential factor is typically 10 s", assuming immobile surface intermediates without rotation. 

Finally, it must be noted that the values of critical surface tensions and surface free energies listed in Table 2.5 are for clean surfaces. In the typical bonding environment this is, of course, not the usual situation. The surfaces may be clean from the technologist s viewpoint but they are certainly not truly... 

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