Dielectric spectroscopy of liquid

It should, however, be noted that there exist rather complex and nontransparent descriptions made [15] in terms of the absorption vibration spectroscopy of water. This approach takes into account a multitude of the vibration lines calculated for a few water molecules. However, within the frames of this method for the wavenumber1 v < 1000 cm-1, it is difficult to get information about the time/spatial scales of molecular motions and to calculate the spectra of complex-permittivity or of the complex refraction index—in particular, the low-frequency dielectric spectra of liquid water. 

Previous findings on the actual microemulsion are given in references (9 17) where the system s phase map vs.concentration in the temperature interval (-20°C + 80°C), viscosity measurements,dielectric analysis of liquid samples against both concentration and frequency, the thermally stimulated dielectric polarization release (TSD), electro-optical phenomena, light scattering, Raman spectroscopy and sound propagation investigations are reported. 

Kremer, E. (1997), Broadband dielectric spectroscopy on collective and molecular dynamics in ferroelectric liquid crystals, in Dielectric Spectroscopy of Polymeric Materials—Eundamental and Applications, Runt, J. P. and Eitzgerald, J. J., eds., ACS, Washington, DC, pp. 423 44. 

C M. Haws, M. G. Oatk. and G. E Attard. Dielectric relaaatioa spectroscopy of liquid crystalline aide chain polymert. Side Ckem Liquid Cryjtul Pofymen (G. B. Ardk, ed.X Rlackic. Chapman ft Hall. New York. 1989, p. 196. 

Dantras, E., Dandurand, J., Lacabanne, C., Laffont, L., Tatascon, J.M., Archambeau, S., Seguy, I., Destruel, P., Bock, H., Fouet, S. HRTEM, TSC and broadband dielectric spectroscopy of a discotic liquid crystal. Phys. Chem. Chem. Phys. 6, 4167-4173 (2004)... 

The dipole moment of a molecule can be obtained from a measurement of the variation with temperature of the dielectric constant of a pure liquid or gaseous substance. In an electric field, as between the electrostatically charged plates of a capacitor, polar molecules tend to orient themselves, each one pointing its positive end toward the negative plate and its negative end toward the positive plate. This orientation of the molecules partially neutralizes the applied field and thus increases the capacity of the capacitor, an effect described by saying that the substance has a dielectric constant greater than unity (80 for liquid water at 20°C). The dipole moments of some simple molecules can also be determined very accurately by microwave spectroscopy. 

Rotational motion is spinning of the entire molecule around an axis in three-dimensional space. Figure 10 illustrates the rotational motion of a water molecule. Rotational motion occurs in liquid and gas phases of water and, to a limited extent, through defects in the solid phase (ice). Rotational motion of water molecules can be measured using NMR and dielectric spectroscopy (Belton, 1994). 

When a chain has lost the memory of its initial state, rubbery flow sets in. The associated characteristic relaxation time is displayed in Fig. 1.3 in terms of the normal mode (polyisoprene displays an electric dipole moment in the direction of the chain) and thus dielectric spectroscopy is able to measure the relaxation of the end-to-end vector of a given chain. The rubbery flow passes over to liquid flow, which is characterized by the translational diffusion coefficient of the chain. Depending on the molecular weight, the characteristic length scales from the motion of a single bond to the overall chain diffusion may cover about three orders of magnitude, while the associated time scales easily may be stretched over ten or more orders. 

Liquids are difficult to model because, on the one hand, many-body interactions are complicated on the other hand, liquids lack the symmetry of crystals which makes many-body systems tractable [364, 376, 94]. No rigorous solutions currently exist for the many-body problem of the liquid state. Yet the molecular properties of liquids are important for example, most chemistry involves solutions of one kind or another. Significant advances have recently been made through the use of spectroscopy (i.e., infrared, Raman, neutron scattering, nuclear magnetic resonance, dielectric relaxation, etc.) and associated time correlation functions of molecular properties. 

The attenuation of ultrasound (acoustic spectroscopy) or high frequency electrical current (dielectric spectroscopy) as it passes through a suspension is different for well-dispersed individual particles than for floes of those particles because the floes adsorb energy by breakup and reformation as pressure or electrical waves josde them. The degree of attenuation varies with frequency in a manner related to floe breakup and reformation rate constants, which depend on the strength of the interparticle attraction, size, and density (inertia) of the particles, and viscosity of the liquid. 

Thus far, we have avoided reference to perhaps the most commonly used estimate for the polarity The dielectric constant of the pure liquid. The dielectric constant can be determined from a range of experiments, including capacitance [211] and dielectric reflectance spectroscopy [212]. While the dielectric constant does not characterize the solvent environment as fully as multiparameter LEER approaches, it is simple to measure and accurate values are available for an enormous number of solvents [213]. 

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

The successful development of the time-domain dielectric spectroscopy method (generally called time-domain spectroscopy, TDS) [79-86] and broadband dielectric spectroscopy (BDS) [3,87-90] have radically changed the attitude towards DS, making it an effective tool for investigation of solids and liquids on the macroscopic, mesoscopic, and, to some extent, microscopic levels. 

Since the late nineteenth century, dielectric spectroscopy has been used to monitor dynamical properties of solid and liquid materials. At that time, dielectric measurements were performed either at a single frequency or in a very limited frequency range now, however, measurement technique and instrumentation have developed to such an extent that dielectric spectroscopy is today a well-established method to probe molecular dynamics over a broad range in frequency or time (cf. reviews by Johari [1], Bottcher and Bordewijk [34], Williams [35,36], and Kremer and Schonhals [37]), even with commercially available equipment. Including the latest developments, one can even say that nowadays dielectric spectroscopy is the only method that is fully able to realize the idea of 0- to 1-THz spectroscopy. In data sets that cover the range of up to 10 6—1013 Hz—that is, from ultra-low frequencies up to the far infrared—the full range of reorientational dynamics in... 

On some time scale, all liquids display viscoelasticity. Newtonian liquids like water have viscosity independent of shear rate over ordinary ranges of measurement (10 s < 7 < 10 s ). Dielectric spectroscopy reveals that water molecules respond to an oscillating electric field at a frequency of 17 GHz at room temperature. Hence, at shear rates of order 10 s water would be expected to be viscoelastic, and have a shear thinning apparent viscosity. 

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