Group adsorption energies.additivity values

Thus, the determination of Qi and Ci values on the basis of measurements carried out at ordinary temperatures in these cases becomes difii-cult. In such cases, however, one can approximately estimate the additional contribution of the energy of specific interaction arising from TT-bonds or the functional groups at a somewhat higher a—e.g., when values of a correspond to 1 molecule per cavity. AQspecific is determined by subtracting the heat of adsorption of the reference molecule (incapable to specific interaction) from the heat of adsorption of the specifically adsorbed molecule 10, 28S0). Both molecules must have similar geometry, close values of polarizability and of heat of adsorption on nonspecific adsorbent (6). 

In addition to the value of ViF, one can also obtain an estimate for two other terms. The value of Of is small, because in the absence of an adsorption film, the contact can be regarded as direct, almost an ideal one. Although Of is small, it is still nonzero, as it would have been in the case of a complete cohesion of two surfaces, such as in the coalescence of two liquid droplets. There are two issues that introduce some uncertainty. First, the screening of the glass with methyl groups may be incomplete. Second, the surface of particles (fused glass) may not necessarily be a molecularly smooth spherical surface. For this reason, the value of Of assumes finite positive values on the order of tenths and even units on mJ/m. This is further confirmed by the observed spread in the 14F values for various specimens from 18 to 22 mJ/m. The sum X Acjf( ) = X + X = 12 now yields an approximate estimate for the surface free energy, 0,2. The reliability of this estimate is biased by the mentioned uncertainty in Cf and the 10% variation in the experimental values of p, and F. For the nonpolar solid phase, we therefore find a quantitative estimate of 012 = ( sg 20 mJ/m with the precision down to a few mJ/m. ... 

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