The free-volume model, which has been useful for describing the behavior of the viscosity $\ensuremath{\eta}$ of dense liquids and glasses, is extended to account for their thermodynamic behavior as well. Experimental results for the heat capacity ${C}_{p}$ and the volume $\overline{v}$ show that the system falls out of complete, metastable thermodynamic equilibrium at the glass transition temperature ${T}_{g}$. As a first step in understanding these universal phenomena, a theory of the underlying metastable phase, the amorphous phase, is developed. Recent molecular-dynamic calculations demonstrating the existence of a cellular structure in liquids and the properties of the local free energy of the molecular cells permit us to formulate more precisely and justify in more detail the standard free-volume model. In particular, it is possible to define the free volume and distinguish solid-like and liquidlike cells. This leads to the introduction of percolation theory, which is used to describe the gradual development of the communal entropy of the amorphous phase. We then determine the probability distribution of the cellular volume as a function of the fraction of liquidlike cells, $p$. The equilibrium liquid-glass transition is associated with the increase of $p$ with temperature. This occurs via a phase transition which is most probably first order. The results of our theory give a generalized equation for the viscosity which agrees accurately with experimental results at all temperatures. Results for ${C}_{p}$ and $\overline{v}$ are also obtained. This equilibrium theory can provide the basis for a relaxation theory of the kinetic effects observed around and below ${T}_{g}$. The relationship between the entropy theory and the free-volume model is also clarified.

Liquid-glass transition, a free-volume approach

The previously described least‐squares derivation of nonbonded potential parameters from crystalline aromatic hydrocarbons was extended to include nonaromatic hydrocarbons. Further evidence was obtained that no specially large energy effects are present in the aromatic crystal structures with their π‐electron systems. A better separation of the nonbonded energy into C···C, C···H, and H···H components was obtained when the observational equations for the aromatic and nonaromatic structures were combined. The potentials obtained from the combined observational equations gave better fits to the nonaromatics than to the aromatics. Evidence is presented favoring an H–C–H angle of less than 106° in crystalline n‐pentane and n‐hexane. The parallel packing of molecular chains in the n‐hexane crystal and the nonparallel packing in the n‐pentane crystal were reproduced by a steepest descent minimization of the lattice energy using the observed lattice constants.

Nonbonded Potential Parameters Derived from Crystalline Hydrocarbons

Relaxation processes in crystalline polymers: experimental behaviour — a review

Resolution in 13C NMR of organic solids using high-power proton decoupling and magic-angle sample spinning

Many liquids have heat capacities that substantially exceed those of the corresponding crystal, and this discrepancy magnifies in the supercooled regime. Thus, liquid entropy declines more rapidly with temperature than does crystal entropy, and the former paradoxically seems to fall below the latter for temperatures below the Kauzmann point TK. Although laboratory glass transitions inevitably intervene to prevent observation of this entropy crossing, it has often been argued that a second‐order ‘‘ideal glass transition’’ in principle should occur at TK. The inherent structure theory of condensed phases has been modified to describe supercooled liquids, and has been applied to this Kauzmann paradox. The conclusion is that an ideal glass transition of the type normally associated with the Kauzmann phenomenon cannot occur for substances of limited molecular weight and with conventional intermolecular interactions. This result also subverts theoretical expressions for shear viscosity (such as the Tamman–Vogel...

Supercooled liquids, glass transitions, and the Kauzmann paradox

Heat capacities and thermodynamic properties of globular molecules. i. adamantane and hexamethylenetetramine1

Experimentally determined heat capacity values, precise to within 0.1 percent, and related thermal data are reported for quenched and annealed diethyl phthalate glasses from 10 °K to the glass transformation temperature, Tg (around 180 °K), for the liquid from Tg to 360 °K, and for the crystal from 10 °K to the melting temperature (269.9 °K). The mole fraction of liquid-soluble, solid-insoluble impurity in the sample as determined by fractional melting was 0.0012. Common thermodynamic properties calculable from the experimental data are reported. The heat capacities of the two glasses differ by more than the uncertainty of the measurements, and both lie below that of the crystal in the range from 30 to 75 °K. At low temperatures, just above 10 °K, the heat capacities of the glasses rise as much as 8 percent above that of the crystal.

/pdf/heat-capacities-and-related-thermal-data-for-diethyl-20wzsk1kli.pdf

Heat Capacities and Related Thermal Data for Diethyl Phthalate Crystal, Glass, and Liquid to 360 °K.

Heat capacities of two high density linear polyethylene samples were measured from 2 to 360 K. By incorporating the results from the previous work of this series, thermodynamic properties of completely crystalline linear polyethylene may be estimated. Cp , H - H0, S and - (G - H0) at 298.15 K for crystalline linear polyethylene are estimated to be 22.60 J K-1 mol-1, 3544 J mol-1, 23.02 J K-1 mol-1 and 3319 J mol-1, respectively. Spontaneous adiabatic temperature drifts were observed in both samples near 240 K. These drifts may be attributed to the enthalpy relaxation phenomena occurring in the glass transformation region.

/pdf/heat-capacities-of-polyethylene-from-2-to-360-k-ii-two-high-4m5sp6rktt.pdf

Heat Capacities of Polyethylene from 2 to 360 K. II. Two High Density Linear Polyethylene Samples and Thermodynamic Properties of Crystalline Linear Polyethylene.

Heat capacities of tetramethylammonium chloride and bromide were determined by low‐temperature adiabatic calorimetry from 5° to 350°K Derived thermodynamic properties were then calculated Two transitions were found in the chloride: a sharp, apparently first‐order transition occurs at 7576°K with an entropy of transition of 037 cal mole—1 °K—1 and a lambda‐shaped transition at 18485°K with an entropy increment of 014 cal mole—1 °K—1 No anomaly has been observed in the bromide Molal values of heat capacity, entropy, and free energy function at 29815°K for the chloride and the bromide are: 3751, 3864, 4558, 4799, and —2336, —2536 cal mole—1 °K—1, respectively

/pdf/heat-capacities-and-thermodynamic-properties-of-two-3zuyy8mbxg.pdf

Shu-Sing Chang

Papers

Heat capacities and thermodynamic properties of globular molecules. i. adamantane and hexamethylenetetramine1

Heat Capacities and Related Thermal Data for Diethyl Phthalate Crystal, Glass, and Liquid to 360 °K.

Heat Capacities of Polyethylene from 2 to 360 K. II. Two High Density Linear Polyethylene Samples and Thermodynamic Properties of Crystalline Linear Polyethylene.

Heat Capacities and Thermodynamic Properties of Two Tetramethylammonium Halides

Heat capacities and thermodynamic properties of globular molecules. ii. triethylenediamine1