Communication: Supramolecular structures in monohydroxy alcohols: Insights from shear-mechanical studies of a systematic series of octanol structural isomers

Abstract

Communication: Slow supramolecular mode in amine and thiol derivatives of 2-ethyl-1-hexanol revealed by combined dielectric and shear-mechanical studies

Communication: Slow supramolecular mode in amine and thiol derivatives of 2-ethyl-1-hexanol revealed by combined dielectric and shear-mechanical studies

“…This is at odds with the common observation where decrease in the intensity of the dielectric Debye relaxation is followed by a decreased separation between the alpha and the Debye relaxation (e.g., Ref. 25). The invariant time scale separation could suggest that the size of the supramolecular structures is comparable in the three systems, but this is very speculative.…”

“…49 A crossover from an intermediate to the terminal power law reported for shortchain polymers, polymeric liquids, or monoalcohols (ν 0.7 ) is an evidence of an additional slow supramolecular organization/dynamics. [23][24][25]42,50 In the present study, due to resolution limits of the PSG technique, we were not able to clearly observe the change of the frequency dependence of G ′ and G ′′ at modulus values lower than 1 MPa. However, the power law of the lowfrequency part of the mechanical loss shear spectra for amine (ν 0.85 ) and thiol (ν 0.93 ) shows that they display an intermediate behavior between the one reported for non-associating and associating liquids.…”

“…Typically, diluting or modifying the position of the hydroxyl group in the alkyl chain backbone produces differences in the separation between the alpha-and the Debye processes. 25,35 The combined dielectric and shear mechanical results presented in the preceding paragraphs clearly show that there is a slow relaxation (Debye) mode in the amine. For the thiol, the signatures are subtle; however, it seems suggestive that there is also a slow process in the thiol even if it is weak in strength.…”

“…[18][19][20][21] It was earlier believed that the Debye relaxation a) Electronic address: kadrjano@us.edu.pl was only seen in the dielectric signal but with improved experiments and data analysis it has over the last 10-15 years been detected also by other experimental techniques, such as mechanical spectroscopy, dynamic light scattering, and nuclear magnetic resonance. [22][23][24][25][26] The origin of the Debye relaxation in monohydroxy alcohols has been hotly discussed and intensively upgraded throughout the last century. 27 Today the consensus is that the process is due to slow dynamics in supramolecular hydrogen bonded structures.…”

On the non-exponentiality of the dielectric Debye-like relaxation of monoalcohols

“…For long time the observation of the Debye-like process by other techniques than dielectric spectroscopy remained elusive, but slow dynamics additional to that of the structural relaxation have already been reported by a number of techniques [10][11][12][13][14][15] and most revealingly by shear modulus measurements [16][17][18]. Moreover, very recently and aided by complex viscosity η * (ω) representation of shear data, authors have reported for the first time the presence of an additional process, intermediate between those previously indentified [19].…”