To gain insight into a recent observation that the prominent, Debye-type relaxation process observed for a primary alcohol may not be the ␣-relaxation process associated with molecular diffusion of a liquid ͓Europhys. Lett. 40, 549 ͑1997͒, J. Chem. Phys. 107, 1086 ͑1997͔͒, the dielectric spectra of an uncrystallizable secondary alcohol, 5-methyl-2-hexanol, has been investigated by broadband spectroscopy. Measurements made over a temperature range from 110 to 298 K showed that three relaxation processes occur. Processes I and II have a non-Arrhenius variation of the relaxation rate with temperature, and process III an Arrhenius. Only process I, the slowest of the three, has a single relaxation rate, the other two, a broad distribution. The contribution to permittivity from process II was 0.8, i.e., ϳ3% of the static permittivity, and from process III, the fastest was 0.1, i.e., ϳ0.3%. It is argued that the mechanism of process I is the breaking followed by dipolar reorientation and reforming of the H-bonds in the intermolecularly H-bonded structure, and process II is that of the orientation of the other dipolar groups, such as the -OR group. Process III is the usual JohariGoldstein process. For 5-methyl-2-hexanol, the mode-coupling and another theory by Souletie and Bertrand ͓J. Phys. I 1, 1627 ͑1991͔͒ seem to agree with the relaxation rate of processes I and II, and predict temperatures for 10 Ϫ4 Hz relaxation rate, within a few degrees of that expected.
The extent of H bonding in alcohols may be reduced by sterically hindering its OH group. This technique is used here for investigating the reasons for the prominent Debye-type dielectric relaxation observed in monohydroxy alcohols ͓Kudlik et al., Europhys. Lett. 40, 549 ͑1997͒; Hansen et al., J. Chem. Phys. 107, 1086 ͑1997͒; Kalinovskaya and Vij, ibid. 112, 3262 ͑2000͔͒, and broadband dielectric spectroscopy of supercooled liquid and glassy states of 1-phenyl-1-propanol is performed over the 165-238 K range. In its molecule, the steric hindrance from the phenyl group and the existence of optical isomers reduce the extent of intermolecular H bonding. The equilibrium permittivity data show that H-bonded chains do not form in the supercooled liquid, and the total polarization decays by three discrete relaxation processes, of which only the slower two could be resolved. The first is described by the Cole-Davidson-type distribution of relaxation times and a Vogel-Fulcher-Tammann-type temperature dependence of its average rate, which are characteristics of the ␣-relaxation process as in molecular liquids. The second is described by a Havriliak-Negami-type equation, and an Arrhenius temperature dependence, which are the characteristics of the Johari-Goldstein process of localized molecular motions. The relaxation rate's non-Arrhenius temperature dependence has been examined qualitatively in terms of the Dyre theory, which considers that the apparent Arrhenius energy itself is temperature dependent, as in the classical interpretations, and quantitatively in terms of the cooperatively rearranging region's size, without implying that there is an underlying thermodynamic transition in its equilibrium liquid. The relaxation rate also fits the power law with the critical exponent of 13.4, instead of 2-4, required by the mode-coupling theory, thereby indicating the ambiguity of the power-law equations.
Electrooptic spectroscopy of an antiferroelectric liquid crystal is carried out over a range of frequencies from 1 Hz to 100 kHz. In the antiferroelectric SmC A phase two relaxation processes are found, one at the fundamental frequency of a mode and the second at twice the frequency of a different mode. A comparison of the results of the electro-optic spectroscopy with a theoretical study of the motion of the director of an antiferroelectric helix subject to a weak alternating field enables a determination of the origin of the relaxation processes in antiferroelectric phases.
Dielectric relaxation processes in an antiferroelectric liquid crystal ͑AFLC͒ have been investigated over a wide range of frequencies from 1 Hz to 1 GHz. The AFLC under investigation possesses a variety of different ferrielectric, ferroelectric, and antiferroelectric phases. Dielectric and polarization measurements under direct bias voltage have been made with a view to clarifying the origin of the high-temperature ferrielectric phase, which appears between the AF and smectic-C* phases. This phase is assigned to an unstable ferrielectric phase with q T parameter greater than 1/2 ͑according to the Ising model͒ or a doubly modulated incommensurate phase ͑according to the expanded Landau model͒. The results are also supported by conoscopy.
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