Heat capacities and related thermal data for diethyl phthalate crystal, glass, and liquid to 360 K

Abstract

Experimentally determined heat capacity valu es, precise to within 0.1 percent, and related thermal data are reported for quenched and annealed diethyl phthalate glasses from ]0 oK to the glass transformation te mperature, Tg (around 180 O K) , for the liquid from T" to 360 oK, and for the crystal from 10 oK to the melting temperature (269.9 O K). The mole fraction of liquid·soluble, solid·insoluble impurity in the sample as determined by fractional melting was 0.0012. Co mmon thermodynamic properties calc ulable from the experimental data are reported. The heat capacities of the two glasses differ by more than the uncertainty of the meas urements, and both lie below that of the crystal in the range from 30 to 75 oK. At low temperatures, just above 10 oK, the heat capacities of the glasses rise as much as 8 percent above that of the crystal.

Orientation polarization from faster motions in the ultraviscous and glassy diethyl phthalate and its entropy

“…By using the calorimetric data from Chang et al, 3 Goldstein 13,14 had shown that entropy S exc of annealed diethyl phthalate glass 3 over the entropy of its crystal phase is 22.25 J / mol K at ͑adiabatic calorimetric͒ T g of 178 K. The 0 K entropy of the annealed glass is 20.17 J / mol K and thus the increase in S exc from 0 K to T g for the annealed glass is 2.1 J / mol K. For a diethyl phthalate glass formed by quenching, 3 the increase in S exc over the 0 K value is 3.64 J / mol K higher than the annealed glass at T near T g of 178 K ͑Table I of Ref. 14͒ and at T = 180.8 K, it is 1.7 J / mol K. The increase in the entropy of the quenched glass over the annealed glass is due to several factors: ͑i͒ the entropy difference from greater anharmonicity of vibrational displacement, ͑ii͒ the difference in the vibrational frequencies of the glass and crystal phases, ͑iii͒ the change in the number of configurational states that involve only the ␤-relaxation motions, and ͑iv͒ the loss in the annealed glass of available configurations from the unfrozen modes of molecular motions that show up as the high-frequency tail of the ␣-relaxation time distribution in the dielectric spectra.…”

“…5͑A͒, for the quenched glass using the diethyl phthalate entropy data for a "quenched glass" reported by Chang et al 3 The ratio ⌬⑀ ␤ / ͓S exc ͑T͒ − S exc ͑0͔͒ is also plotted against T in Fig. 5͑B͒, where S exc ͑T͒ is the excess entropy at T K and S exc ͑0͒ is the excess entropy at 0 K. Since the available entropy data are at 5 or 10 K temperature intervals, with a 20 K gap in the glass and ultraviscous liquid entropy data over the time-dependent, glass-softening or T g range, the S͑T͒ and S exc ͑T͒ values for the temperature at which ⌬⑀ ␤ was measured were interpolated from Chang's data by a cubicspline method.…”

“…͑B͒ The ratio ⌬⑀ ␤ / ͓S exc ͑T͒ − S exc ͑0͔͒ is plotted against the temperature. The entropies at each temperature were found by interpolating entropy data of the "quenched glass" taken from Table VI of Chang et al 3 and using the S exc ͑0͒ value given in that paper. The values of the ratios at the actual data points of Chang et al are indicated by filled circles.…”

“…Because of this similarity between the dielectric and thermodynamic features, we intended to study the relaxation strength of a molecular glass whose heat capacity and entropy had been already measured. Chang and Bestul 2 had reported such data for o-terphenyl and Chang et al 3 have reported the data for diethyl phthalate 3 in the glass, liquid, and crystal states. But, as the dipole moment of o-terphenyl is extremely small, the relaxation strength due to these fast motions in its glassy and ultraviscous liquid states is extremely small and could not be measured accurately enough to investigate the effect observed earlier.…”

Heat capacities of polyethylene from 2 to 360 K. I. Standard samples of linear and branched polyethylene whole polymer

“…The measuring procedures and methods of data treatment were discussed in more detail in another paper [24].…”