Monohydroxy alcohols show a structural relaxation and at longer time scales a Debye-type dielectric peak. From spin-lattice relaxation experiments using different nuclear probes an intermediate, slower-than-structural dynamics is identified for n-butanol. Based on these findings and on diffusion measurements, a model of self-restructuring, transient chains is proposed. The model is demonstrated to explain consistently the so far puzzling observations made for this class of hydrogen-bonded glass forming liquids.

Dielectric loss spectra covering 13 decades in frequency were collected for 2-ethyl-1-hexanol, a monohydroxy alcohol that exhibits a prominent Debye-like relaxation, typical for several classes of hydrogen-bonded liquids. The thermal variation of the dielectric absorption amplitude agrees well with that of the hydrogen-bond equilibrium population, experimentally mapped out using near infrared (NIR) and nuclear magnetic resonance (NMR) measurements. Despite this agreement, temperature-jump NIR spectroscopy reveals that the hydrogen-bond switching rate does not define the frequency position of the prominent absorption peak. This contrasts with widespread notions and models based thereon, but is consistent with a recent approach.

Liquid monohydroxy alcohols exhibit unusual dynamics related to their hydrogen bonding induced structures. The connection between structure and dynamics is studied for liquid 1-propanol using quasi-elastic neutron scattering, combining time-of-flight and neutron spin-echo techniques, with a focus on the dynamics at length scales corresponding to the main peak and the pre-peak of the structure factor. At the main peak, the structural relaxation times are probed. These correspond well to mechanical relaxation times calculated from literature data. At the pre-peak, corresponding to length scales related to H-bonded structures, the relaxation times are almost an order of magnitude longer. According to previous work [C. Gainaru, R. Meier, S. Schildmann, C. Lederle, W. Hiller, E. Rössler, and R. Böhmer, Phys. Rev. Lett. 105, 258303 (2010)] this time scale difference is connected to the average size of H-bonded clusters. The relation between the relaxation times from neutron scattering and those determined from dielectric spectroscopy is discussed on the basis of broad-band permittivity data of 1-propanol. Moreover, in 1-propanol the dielectric relaxation strength as well as the near-infrared absorbance reveal anomalous behavior below ambient temperature. A corresponding feature could not be found in the polyalcohols propylene glycol and glycerol.

The spectral densities related to various relaxation processes of the glass former 2-ethyl-1-hexanol (2E1H), a monohydroxy alcohol, are probed using several nuclear magnetic resonance (NMR) experiments as well as via dielectric noise spectroscopy (DNS). On the basis of the spectral density relating to voltage fluctuations, i.e., without the application of external electrical fields, DNS enables the detection of the structural relaxation and of the prominent, about two decades slower Debye process. The NMR-detected spectral density, sensitive to the orientational fluctuations of the hydroxyl deuteron, also reveals dynamics slower than the structural relaxation, but not as slow as the Debye process. Rotational and translational correlation functions of 2E1H are probed using stimulated-echo NMR techniques which could only resolve the structural dynamics or faster processes. The experimental results are discussed with reference to models that were suggested to describe the dynamics in supercooled alcohols.

2-ethyl-1-hexanol (2E1H) was confined to the surface of a collagen matrix at various concentration levels c. Dielectric spectroscopy revealed that upon decreasing c, the alcohol's prominent hydrogen-bond mediated Debye-like relaxation broadens and turns nonexponential. This destabilization of the supramolecular association is accompanied by an increasing relative strength of the structural relaxation in 2E1H up to a point beyond which the two processes are merged when the solvent molecules are sufficiently diluted. These results demonstrate that the contribution of the Debye-like relaxation can be completely suppressed and concomitantly the limit of a simple, nonassociating liquid is reached. Confinement of the alcohol in a monolithic glass with nanoscopic pores subjected to different internal surface treatments is also demonstrated to bear a large impact on the relative strengths of the two processes.