Effects of electric field on thermodynamics and ordering of a dipolar liquid

The viscous consequence of different trends in clustering of 1,2-diol and 1,n-diol molecules

This paper presents the molecular basis for the quite different behavior of the viscosity of 1,2- and 1,n-diols in dependence of the length of the alkyl part of the molecules of these compounds. The experimental data on the dipolar orientational effects revealed a decidedly different role of that part of the molecules in creating a microstructure of both the hydrogen-bonded liquids. In the case of 1,n-diols, an increase in the alkyl radical length, i.e. an increasing of the distance between the OH groups within the molecule, highly stimulates molecular self-assembly in form of gradually longer and wider ribbon-like clusters. This effect yields a quite important increase in the viscosity of 1,n-diols as n increases. In the case of 1,2-diols, due to gradual separation of the hydrophilic and hydrophobic parts of the molecules, the situation is quite different. Two OH groups situated on one of the ends of the hydrocarbon radical form the clusters of a micelle-like shape, however, the dipole moment is not compensated. Along with an increase in the hydrocarbon part in 1,2-diol molecules, one only observes an increase in the intermolecular consolidation within the micelle-like entities. This manifests as a gradual decrease in the polarity of these clusters. So, actually, there are no relevant reasons for essential differences of viscosities in the series of 1,2-diols.

Unifying different interpretations of the nonlinear response in glass-forming liquids

This work aims at reconsidering several interpretations coexisting in the recent literature concerning nonlinear susceptibilities in supercooled liquids. We present experimental results on glycerol and propylene carbonate, showing that the three independent cubic susceptibilities have very similar frequency and temperature dependences, for both their amplitudes and phases. This strongly suggests a unique physical mechanism responsible for the growth of these nonlinear susceptibilities. We show that the framework proposed by two of us [J.-P. Bouchaud and G. Biroli, Phys. Rev. B 72, 064204 (2005)PRBMDO1098-012110.1103/PhysRevB.72.064204], where the growth of nonlinear susceptibilities is intimately related to the growth of glassy domains, accounts for all the salient experimental features. We then review several complementary and/or alternative models and show that the notion of cooperatively rearranging glassy domains is a key (implicit or explicit) ingredient to all of them. This paves the way for future experiments, which should deepen our understanding of glasses.

Nonlinear dielectric effects in liquids: a guided tour

Dielectric relaxation measurements probe how the polarization of a material responds to the application of an external electric field, providing information on structure and dynamics of the sample. In the limit of small fields and thus linear response, such experiments reveal the properties of the material in the same thermodynamic state it would have in the absence of the external field. At sufficiently high fields, reversible changes in enthalpy and entropy of the system occur even at constant temperature, and these will in turn alter the polarization responses. The resulting nonlinear dielectric effects feature field induced suppressions (saturation) and enhancements (chemical effect) of the amplitudes, as well as time constant shifts towards faster (energy absorption) and slower (entropy reduction) dynamics. This review focuses on the effects of high electric fields that are reversible and observed at constant temperature for single component glass-forming liquids. The experimental challenges involved in nonlinear dielectric experiments, the approaches to separating and identifying the different sources of nonlinear behavior, and the current understanding of how high electric fields affect dielectric materials will be discussed. Covering studies from Debye's initial approach to the present state-of-the-art, it will be emphasized what insight can be gained from the nonlinear responses that are not available from dielectric relaxation results obtained in the linear regime.

Does water belong to the homologous series of hydroxyl compounds H(CH2)nOH?

The main objective of this paper is to find a source of anomalously high value of the equilibrium permittivity of water. The source is identified to be the unusually high deformation polarizability. The conclusion follows from the analysis of the behavior of the orientational entropy increment induced by an external electric field applied to the liquids belonging to the homologous series of hydroxyl compounds H(CH₂)_nOH at the end of which water is located. The finding reflects the "indecision" of water about its dielectric relationship with the alcohol family: the value of the permittivity of water absolutely does not fit into alcohols (is too high), while the dipolar orientation effects (which normally determine the permittivity level) fit into alcohols quite well. It results from the presented experimental data that among all the diversity of intermolecular hydrogen-bonded structures existing in liquid water, predominant are the polar entities, i.e. the structures which more or less resemble the chains. Otherwise, the dipolar orientational effects would behave in a quite different way than what is observed in the experiment. The result is convergent with the conclusion of Wernet et al., based on the high-performance X-ray studies of water (Science, 2004).