Molar cohesive energy

Table 2. Molar cohesive energy of various functional groups...

The advantage of Kanig s argument over other concepts consists in the establishment of a correlation between values ip and a and certain parameters that are easily found experimentally Aa, Cp (change in the heat capacity) at glass temperature, and molar cohesion energy at Tt. This allows both values, and a, to be calculated... 

Solubility Parameter. Increased attractive forces between molecules, as measured by a larger solubility parameter, requires more thermal energy to produce molecular motion. This results in an increase in the Tg with increasing cp. Eisenberg (1993) provides an equation that relates the molar cohesive energy density,o2p, to the glass transition by... 

This formula has been refined [77] for the calculation of the molar cohesive energy of noble gas crystals into ... 

Molar cohesive energy ECoh Al Gcoh Cohesive energy density coh... 

A serious objection against such a thermodynamic analogy, however, for identifying Lj SjTgj with the molar cohesion energy is twofold ... 

From the additive nature of the molar cohesive energy and molar volume of the ligand in a complex, it has been shown that the log(partition constant) of a complex MA is approximately n times that of the ligand HA (141) [cf. Eqs. (17) and (18)]. Then from Eq. (16) we see that Kni262) p26- Since pKa is almost the same for these aliphatic carboxylic acids, one may realize that / 26 and hence log Kn(262) should... 

Hayes Method. A relationship between polymer structure, glass transition temperature and molar cohesive energy (cohesive energy density multiplied by the molar volume) was found by Hayes (9) ... 

Table 21.1 shows the molar cohesive energies of functional groups in oligo-polyols and inPU. 

Here is the solubility of a dmg in water on the molar scale (M at 25 °C log s = 1.74 + logxssat for poorly soluble solutes, see above). The first term in Eq. (1.25) assumes that the dmg molecule has a molar cohesive energy similar to that of 1-octanol, so that the logarithm of the activity coefficient of the dmg in water should be equal to P°w, the logarithm of the distribution ratio between 1-octanol and water. This, in turn, can be related to the constitution and stmcture of the dmg (Hansch and Leo 1979). The second term, involving the molar entropy of fusion of the dmg molecule, is taken as zero for liquid solutes (at 25 °C) but non-zero for crystalline drugs. In summary, Eq. (1.25) predicted the aqueous solubility of 167 dmg and related organic solutes with a correlation coefficient of 0.994 and a standard deviation of 0.24 in log s. 

Table 1.10 shows the lattice energies, C/iatE, applicable at zero K, the molar cohesive energies of the molten salts, i.e., the products of the molar volumes Ve... 

Solubility parameters are measured in (MJ/m ) or (cal/sm ) (1 (MJ/m ) =2.054 (cal/sm ) °). The cohesive energy is equal in magnitude and opposite in sign to the potential energy of a volume unit of a liquid. The molar cohesive energy is the energy associated with all molecular interactions in one mole of the material, i.e., it is the energy of a liquid relative to its ideal vapor at the same temperature (see Chapter 5). 

If U is defined as the molar internal energy (the molar potential energy of a material relative to the ideal vapor at the same temperature), then the molar cohesive energy (the energy associated with the net attractive interactions of the material) is defined as U. As presented by Polak [9] ... 

Eskin and Nesterov (1966b, 1967b), Eskin (1973) have proposed a method to study the energy of polymer molecular cohesion based on critical opalescence in the P-I-LMWL system, In particular, on a careful study of the dependence = /( ) (Equation 17). The obtained quantities of the molar cohesion energy of a number of polymers arc in good agreement with the data yielded by other methods (Eskin, 1973, table 7.3). 

Polymers have been grouped into the following 10 categories aliphatic polyolefins, polystyrenes, polyvinyl halides, polyvinyl esters, cellulose esters, polyvinyl ethers, poly-ethers, aromatic polymers, copolymers and miscellaneous polymers. The molar cohesive energies (Eg) were calculated from their respective group increments according to the following equation ... 

Change in heat capacity in glass transition interval, AC is average value. Molar cohesive energy as calculated from Ref. (J62). 

Another approach to the characterization of the molecular mobility in the surface layers may be based on the measurements of the heat capacity of filled polymers. ° The increase in the specific heat capacity at the glass transition, ACp, is linked with the molar cohesion energy of the polymer, Wc, and the molar energy of formation of the holes, h, by the relationship ... 

For a liquid, the molar cohesive energy (Eco) can be defined as the molar energy required to disrupt all molecular interactions it is then possible to relate it with the heat of evaporation A/fvap by means of the following expression ... 

If one assumes that the cohesion energy is an additive parameter, then Eco is equal to the sum of the contributions of the various groups constituting the monomer unit. Hence, knowing the cohesion energy of each group, one should be able to calculate the actual value of Eco- As a matter of fact, the molar cohesion energies are not strictly additive, unlike what is called the molar attraction constant (F) ... 

COHESION ENERGY IN POLYMERS 17 Table 2.1. Molar cohesive energy of several important polymers... 

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