Cohesive energy density 144 correlation volume

Volumes of activation can be unambiguously determined only from the pressure dependence of the rate constants. Attempts to obtain volumes of activation from the correlation of rate constants with the solubility parameter 22 or the cohesive energy density parameter (ced)23, which are related to the internal pressure of solvents, have not led to clear-cut results. 

Estimate pressure—volume—temperature (PVT) relations, cohesive energy densities, pair correlation functions, X-ray scattering curves, elastic constants, and other properties. 

Abraham also found that the free energies of transfer of t-butyl chloride between solvents correlated with the cohesive energy density of the solvent. This attribute of the solvent was introduced by Hildebrand and is defined as the heat of vaporization of the solvent divided by its molar volume, all minus an RT term [36]. It is reasonable that this correlation represents causality since the interaction of any solute with a solvent requires disruption of solvent-solvent interaction. Subsequent work in our laboratory suggests that... 

Many papers have been published regarding the gas permeation properties of polyimides(7-7). Polyimides are very useful polymers for the analysis of relations between gas permeation properties and polymer structure, because many different structures, based on diadds and diamines, can be prepared from existing compounds. We have previously reported relations between free volume or cohesive energy density and gas diffusivity(8,9). In this study, we prepared five kinds of polyimides and explored correlations between gas diffusivity and parameters such as stor e modulus, cohesive energy density, and free volume. These results were con iared with data from previous studies. We dso discuss the merits of the use of each of these parameters to correlate gas permeability properties of different polymers. 

The values of the properties which will be fitted by using equations 2.9 and 2.10 will be selected from available and apparently reliable experimental data whenever there are sufficient amounts of such data. Some important properties of polymers, such as the van der Waals volume (Chapter 3) and the cohesive energy (Chapter 5), are not directly observable. They are inferred indirectly, and often with poor accuracy, from directly observable properties such as molar volume (or equivalently density) and solubility behavior. When experimental data are unavailable or unreliable, the values of the properties to be fitted will be estimated by using group contributions. The predictive power of such correlations developed as direct extensions and generalizations of group contribution techniques will then be demonstrated by using them... 

Figure 15.5 shows the dependence of calculated cohesive energy on volume of the unit cell. Local density approximation of the exchange-correlation energy of electrons fails for these molecular systems. Minima at curves based on improved theory (Figure 15.5, small squares) correspond well to experimental quantities (diamonds) for argon and krypton (error of the order of 9%). For neon the error of the cohesive energy calculation equals to 39%. 

Fig. 1 Schematic description of cohesive and interfacial wear processes from the two terms non interacting model of friction (from [96]). Bulk ploughing involves the dissipation of the frictional work within a volume of the order of the cube of the contact radius. Interfacial shear corresponds to the dissipation of the frictional energy in much thinner regions and at greater energy densities. Cohesive wear processes (cracking, tearing, microcutting...) are governed by the cohesive strength of the polymer. Mechanisms such as transfer film formation correspond to interfacial wear and do not readily correlate with accessible bulk failure properties...

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