Dielectric relaxation in water

Kakizaki, M. and Hideshima, T., Effect of distribution of free volume on concentration dependence of dielectric relaxation in water mixtures with poly(ethylene glycol) and glucose, Jpn. J. Appl. Phys., Part 1, 1998, 37, 900. 

M. Neumann, Dielectric relaxation in water. Computer simulations with the TIP4P potential, J. Chem. Phys., 85 (1986) 1567-1580. 

Dielectric relaxes in water. Basic neutralization time for polar media. 

Solvated electron formed in water. Longitudinal dielectric relaxation in water. Molecular vibration. 

In measurements of the dielectric relaxation of water adsorbed on acetylated wood, a large change in the activation enthalpy and entropy of dielectric relaxation was found to occur at 6 % moisture content (Zhao etal., 1994), this presumably being attributable to the onset of formation of capillary water in the cell wall. 

Paddison et al. performed high frequency (4 dielectric relaxation studies, in the Gig ertz range, of hydrated Nafion 117 for the purpose of understanding fundamental mechanisms, for example, water molecule rotation and other possible processes that are involved in charge transport. Pure, bulk, liquid water is known to exhibit a distinct dielectric relaxation in the range 10—100 GHz in the form of an e" versus /peak and a sharp drop in the real part of the dielectric permittivity at high / A network analyzer was used for data acquisition, and measurements were taken in reflection mode. 

A simplified version of this model, termed the hybrid model (VIG, p. 305) [32-34, 39] (see also Section IV.E) was proposed for the case of a small cone angle p. In this model the rotators move freely over the barrier U0 as if they do not notice the conical surface the librators move in the diametric sections of a cone—that is, they librate. The hybrid model was widely used for investigation of dielectric relaxation in a number of nonassociated and associated liquids, including aqueous electrolyte solutions (VIG, p. 553) [53, 54]. The hat model was recently applied to a nonassociated liquid [3] and to water [7, 12c]. 

M. S. Skaf, T. Fonseca and B. M. Ladanyi, Wave-vector-dependent dielectric relaxation in hydrogen-bonding liquids a molecular-dynamics study of methanol, J. Chem. Phys., 98 (1993) 8929-45 B. M. Ladanyi and M. S. Skaf, Wave vector-dependent dielectric relaxation of methanol-water mixtures, J. Phys. Chem., 100 (1996) 1368-80 M. S. Skaf, Molecular dynamics simulations of dielectric properties of dimethyl sulfoxide Comparison between available potentials, J. Chem. Phys., 107 (1997) 7996-8003. 

The dielectric relaxation of water (Hasted, 1973) can be characterized by a relaxation time m = 9-3 X 10-12 s at 293 K with activation energy 20 kj mol-1. The spread of relaxation times is remarkably small for such a complicated liquid. The data are interpreted in terms of rotation by water molecules having two hydrogen bonds, the spread of relaxation times showing that symmetrically hydrogen bonded and asymmetrically hydrogen bonded water molecules have slightly different relaxation times. 

Measurements of the dynamic properties of the surface water, particularly NMR measurements, have shown that the characteristic time of the water motion is slower than the bulk water value by a factor of less than 100. The motion is anisotropic. There is litde or no irrotadonally bound water. Study of a protein labeled covalently with a nitroxide spin probe (Polnaszek and Bryant, 1984a,b) has shown that the diffusion constant of the surface water is about 5-fold below the bulk water value. The NMR results are in agreement with measurements of dielectric relaxation of water in protein powders (Harvey and Hoekstra, 1972). 

Chan, R.K., Pathmanathan, K., and Johari, G.P. Dielectric relaxations in the liquid and glassy states of glucose and its water mixtures, /. Phys. Chem., 90, 6358,1986. 

All protic solvents undergo multiple relaxation processes due to the presence of hydrogen bonding. In the case of water and formamide (F), the data can be described in terms of two Debye relaxations. For the alcohols and A-methyl-formamide (NMF), three Debye relaxations are required for the description. In all of these solvents, the low-frequency process involves the cooperative motion of hydrogen-bonded clusters. In the case of water and the alcohols the high-frequency process involves the formation and breaking of hydrogen bonds. The intermediate process in the alcohols is ascribed to rotational diffusion of monomers. Studies of dielectric relaxation in these systems have been carried out for the -alkyl alcohols up to dodecanol [8]. Values of the relaxation parameters for water and the lower alcohols are summarized in table 4.5. 

For most polar liquids, (e /Eo) < 1. As a result, the solvation time, Xg, is shorter than the dielectric relaxation time, Td- Since water is by far the most important solvent for biological systems, in the next section we will discuss some recent results on the solvation dynamics and dielectric relaxation of water. 

To explain the bimodal dielectric relaxation in aqueous protein solutions, Nandi and Bagchi proposed a similar dynamic exchange between the bound and the free water molecules [21]. The bound water molecules are those that are attached to the biomolecule by a strong hydrogen bond. Their rotation is coupled with that of the biomolecule. The water molecules, beyond the solvation shell of the proteins, behave as free water molecules. The free water molecules rotate freely and contribute to the dielectric relaxation process, whereas the rotation of the doubly hydrogen-bonded bound water molecules is coupled with that of the biomolecule and hence is much slower. The free and bound water molecules are in a process of constant dynamic exchange. The associated equilibrium constant, K, can be written as... 

Foodstuffs contain much water. Many people believe the water content is responsible for the microwave heating of food. According to Fig. 1.15, dielectric relaxation of water and corresponding dielectric losses are quite negligible for ionic solutions. Conduction losses are preponderant. Ionic species such salts (sodium chloride) induce dielectric losses in soup and microwave heating results from ionic conduction. 

Polymers that contain the amide group, such as chitin and CS, usually show a low temperature mechanical and dielectric relaxation in the vicinity of -70 °C (at 1 Hz) [43] which is commonly called water relaxation since it is sensibly affected by changes in the moisture content of the polymer. Typically the peak intensity, very low when samples are dried, increases with increasing moisture content, whereas correspondingly the peak maximum shifts to lower temperatures. This relaxation has been assigned as the f)-wet relaxation attributed to the motion of water-polymer complex in the amorphous regions [20, 21]. 

DIELECTRIC RELAXATIONS IN NEUTRALIZED AND NONNEUTRALIZED CHITOSAN THE STRONGER WATER CONTENT EFFECT ON THE a-RELAXATION AND THE GLASS TRANSITION PHENOMENON... 

Jonquieres, A. and Fane, A. 1998. Modified BET models for modeling water vapor sorption in hydrophilic glassy polymers and systems deviating strongly from ideality. J. Appl. Polym. Sci. 67 1415—1430. Jonscher, A.K. 1983. Dielectric Relaxation in Solids. London, U.K. Chelsea Dielectric Press. 

Figure 4 shows typical variations of the dielectric relaxation with water content as recorded along a line stretched across I( /o) and directed towards the 100% water vertex of the pseudo-ternary phase diagram, that is for systems characterized with a fixed ratio of combined surface-active agents to hexadecane and enriched gradually with water. While dielectric relaxation phenomena are hardly detectable at low water contents, systems characterized with higher water contents exhibit striking dielectric relaxations, the dielectric increment (e - e ) increasing drastically as p approaches the critical value corresponding to the transparent-to-turbid transition. The increase in (G - e ) results from the drastic increase in the low frequency permittivity whose variations with p are plotted in Figure 5a. While at low water contents, increases slowly and almost linearly with p, it displays a divergent behavior in the vicinity of the border line F. Simi-...

In summary, the results of both techniques indicate that treatment of experimental data in terms of the coexistence of structurally different water layers within the pool is probably an oversimplification. Water seems to be present as one pseudo-phase, whose properties change continuously as more water is solubilized. At high W/S these properties are akin, but not equal to those of water in electrolyte solutions. This conclusion agrees with IR and NMR studies of water within reverse aggregates of ionic and nonionic surfactants [17,25-28,58,59,64], fluorescence measurements in RMs [6,7], NMR studies of concentrated salt solutions [5,9], IR results of HOD in bulk aqueous phase [82-84], theoretical calculations on molecular dynamics of water [76], dielectric relaxation of water in hydrated phospholipid bilayers [30], and meas-... 

Y. Feldman, N. Kozlovich, I. Nir, and N. Garti 1995 Dielectric relaxation in sodium bis 2(ethyl hexyl) sulfosuccinate-water-decane microemulsions near the percolation temperature threshold, Phys. Rev. E 51, 478-491. 

C R0nne, L Thrane, P-O Astrand, A Wallqvist, KV Mikkelsen, SR Keiding. Investigation of the temperature dependence of dielectric relaxation in liquid water by THz reflection spectroscopy and molecular dynamics simulation. J Chem Phys 107 5319-5331, 1997. 

Fig. XIV-2. Dielectric relaxation spectrum of a water-in-oil emulsion containing water in triglyceride with a salt concentration of 5 wt % at a temperamre of 25°C. The squares are experimental points and the lines are fits to Eq. XIV-4. (From Ref. 9.)...

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