Debye relaxation and 250 K anomaly in glass forming monohydroxy alcohols

Abstract

A previous dielectric, near-infrared (NIR), and nuclear magnetic resonance study on the hydrogen-bonded liquid 2-ethyl-1-hexanol [C. Gainaru et al., Phys. Rev. Lett. 107, 118304 (2011)] revealed anomalous behavior in various static quantities near 250 K. To check whether corresponding observations can be made for other monohydroxy alcohols as well, these experimental methods were applied to such substances with 5, 6, 7, 8, and 10 carbon atoms in their molecular backbone. All studied liquids exhibit a change of behavior near 250 K which is tentatively ascribed to effects of hydrogen bond cooperativity. By analyzing the NIR band intensities, a linear cluster size is derived that agrees with estimates from dielectric spectroscopy. All studied alcohols, except 4-methyl-3-heptanol, display a dominant Debyelike peak. Furthermore, neat 2-ethyl-1-butanol exhibits a well resolved structural relaxation in its dielectric loss spectrum which so far has only been observed for diluted monohydroxy alcohols.

Broadband dynamics in neat 4-methyl-3-heptanol and in mixtures with 2-ethyl-1-hexanol

“…9 In Fig. 1 we reproduce a spectrum from that work taken at 190 K. Here the Debye-like feature is rather weak.…”

“…For 4M3H the τ D /τ α ratio is only ∼3-5 at temperatures at which the structural relaxation times are in the nanosecond range. 9 Near the minimum of the spin-lattice relaxation time, the 1 H-T 1 times of 4M3H are considerably longer than those measured using the deuteron probe, as also observed for 2E1H. 17 This is due to differences in the dipolarly dominated proton-proton versus the quadrupolar coupling strength.…”

“…The liquid obtained from Alpha-Aesar (data taken from Ref. 9) shows a significantly smaller Debye process as compared to that obtained from Sigma-Aldrich. Drying the latter using a molecular sieve reduces the Debye relaxation strength, but only slightly.…”

“…In this respect, the behavior of (4M3H) 0.95 (2E1H) 0.05 resembles that of pure 4M3H. 9 However, one also recognizes that in the audio-frequency range the Debye process for the x = 0.05 sample is much more prominent than the structural relaxation, in contrast to what has been observed for neat 4M3H. 9 We analyzed the data for all concentrations x quantitatively in terms of Eq.…”

“…18 For monohydroxy alcohols with a small Debye-like feature such as 4-methyl-3-heptanol (4M3H), dielectric 5,6,9,[19][20][21] and calorimetric measurements 19,22,23 have been performed but work using other methods is scarce. 24 Apart from using dielectric spectroscopy, in the present work we report on the shear viscosity and volume expansivity of 4M3H and study this substance using several NMR techniques including relaxometry, diffusometry, and echo spectroscopy.…”