Motion of Molecules at Plateau Region: Case of Propylene Glycol
Positronium annihilation measurements on normal and deuterated propylene glycols have been performed at the temperature range (14-325) K. The so-called “plateau region” in the dependence of the ortho-positronium lifetime on temperature has been observed at temperatures T > 270 K. Free volume differences between normal and deuterated propylene glycols have been observed at ≈ 100 K and ≈ 225 K. Assuming a linear expansion of propylene glycol at T > 260 K, we can estimate the velocity of moving molecules or part of them that surround a free volume. It appears to be 2.5 cm/s (0.25 Å/ns) in average.
Jozef Krištiak, Jan Kuriplach and Pradeep K. Pujari
V. Majerník et al., "Motion of Molecules at Plateau Region: Case of Propylene Glycol", Materials Science Forum, Vol. 733, pp. 80-83, 2013