Free volume factor in supercooled liquid dynamics

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

“…3 in Ref. 21 whose size increases with the temperature, and the plot of the hole volume against T of different polymers and molecular materials show a qualitatively similar elbow shaped, [20][21][22][23][24][25] as the plot of ⌬⑀ ␤ observed here. These issues need to be resolved before interpreting the NMR studies of ␤ relaxation in terms of small-angle motions of all molecules in the structure.…”

“…More recently the same elbow shape has been observed in the corresponding plot of the hole volume measured by positron annihilation lifetime spectroscopy ͑PALS͒. [20][21][22][23][24][25] The plot of ␣ ␤ against the temperature in Fig. 3͑B͒ shows a shallow minimum at T immediately above T g in the 180-187 K range.…”

“…124, 044513 ͑2006͒ sion of the bulk state becomes higher on crossing T g , the population and/or size of the localized regions in an ultraviscous liquid increases, and ⌬⑀ ␤ and f m increases more rapidly. Independent studies by PALS measurement of polypropylene glycol-4000, 21 21 ͒ have shown a similar elbow-shaped plots of the hole volume against the temperature. Moreover, it has been inferred that small cavities of mean equivalent radius of 2.4 to 4.8 Å occur in ultraviscous liquid glyoerol at 250-275 K, and their limiting size is temperature dependent more at T Ͼ T g than at T Ͻ T g .…”

“…5 One of the characteristic features of the ␤ relaxation is that its relaxation strength increases with increase in the temperature T. 4,5,18 This means that as the number of molecules contributing to the availability of distinct configurations increases with increase in T, C p,exc and S exc and any contribution to volume should increase, and hence one would expect that the increase in the ␤-relaxation strength may be at least qualitatively related to C p,exc and S exc and possibly to free volume. Bartoš and co-workers [19][20][21][22][23][24][25] have studied a series of glasses, both molecular and polymeric and have found that as T is increased, the hole volume V h in the structures of the glass and ultraviscous liquid also increases slowly. It increases slowly in the glassy state and increases rapidly in the ultraviscous liquid or rubber state at T Ͼ T g , thus showing an elbowlike feature in its plot against T. Thus, two more quantities, namely, ͑d⌬⑀ ␤ / dT͒ p ͓see Ref.…”

Probing the cooperative dynamics varying the side-chain length of poly(alkyl acrylate)s: ESR experiments

“…This represents one of the reasons of the appeal exerted by molecular probe spectroscopy, as its recent application in the framework of dielectric spectroscopy also testifies [10]. With time resolved fluorescence measurements of doped malachite green molecules dissolved in different glass formers [11] and with positron annihilation lifetime spectroscopy studies [12] dynamic anomalies were enlightened in the range 1.15-1.4T g .…”