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Thermodynamic properties of some cyclohexyl esters in the condensed state

“…As was noted previously, (14)(15)(16)(17) the large jumps of the heat capacity at the glass transition and fusion of the substances are caused mainly by removal of the prohibitions for the hole-formation process and the conformational conversions in liquids. The heat capacity jumps at fusion l cr C s,m (T fus ) are less than the heat capacity jumps at the glass transition l gl C s,m (T g ) for all esters, whereas the differences between the heat capacities of the metastable liquid and crystal at the glass-transition temperatures l cr C s,m (T g ) are more than the values of l gl C s,m (T g ) (table 6, figures 1 to 4).…”

“…Their conformational terms can be estimated on the basis of the energy differences between conformers of the compounds (18) calculated by the molecular mechanics method using the MM2 program with the force field described in reference 19. The energy differences between conformers of the esters in the gas state (20) are given in table 12. It was assumed that these differences are valid also for the liquid state.…”

“…The first comes from the conformational contributions which can be estimated as the entropies of mixing of the conformers S mix conf if it is assumed that the equilibrium conformational composition of the liquid at T g is frozen in the glass (16,17) (table 12). The second comes from the contributions from the overall orientational and positional disordering of the molecules in the glass in comparison with the crystal.…”

Thermodynamic properties of methyl esters of benzoic and toluic acids in the condensed state

“…The molar enthalpy of formation of holes, f H m (hole) = 3.64 kJ · mol −1 in the liquid methyl m-toluate at the glass transition temperature was calculated from equation (4) (3,24) The configurational entropy of liquid and glassy methyl m-toluate and the number of molecules in a co-operative domain according to the Adam-Gibbs theory can be evaluated from the data obtained. The temperature dependence of the configurational entropy S m (config) (figure 6a) was derived in a way similar to that proposed in reference 27 from the molar entropy of fusion fus S m and the heat capacity differences between the liquid (the glass below T g ) and the crystal by the following equation:…”

“…Previously, (2,3) a method was suggested to estimate the molar enthalpy of formation of holes f H m (hole) at the glass transition temperature on the basis of the heat capacity jump at the glass transition and the enthalpy of vaporization. Glass formation under fast supercooling of the liquid methyl m-toluate makes it possible to determine the value of f H m (hole) for this compound, too.…”