Dielectric characterization of water

Dielectric Characterization of Water in Polyimide and Poly(amide—imide) Thin Films... 

The dielectric properties of water have been extensively used to determine moisture content in food systems. However, only veiy recently have we used the complex dielectric properties of emulsions in the microwave frequency region to characterize both emulsion type and water content [50-52], We have developed both a cavity resonance dielectrometer capable of operating at 8-11 GHz and an interference dielectrometer operating at 23.45 GHz. 

A. Water and Tissue Water. The dielectric properties of pure water have been well established from dc up to microwave frequencies, approaching the infrared (3). For all practical purposes they are characterized by a single relaxation process centered near 20 GHz at room temperature. Static and infinite frequency permittivity values are, at room temperature, close to 78 and 5, respectively. Hence, the microwave conductivity increase predicted by Eq. (1) is close to 0.8 mho/cm above 20 GHz, much larger than typical low-frequency conductivities of biological fluids which are about 0.01 mho/cm. The dielectric properties of water are independent of field strength up to fields of the order 100 kV/cm. 

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. 

Gelin K, Bodin A, Gatenhohn P, Mihranyan A, Edwards K, Strpmme M (2007) Characterization of water in bacterial cellulose using dielectric spectroscopy and electron microscopy. Polymer 48 7623-7631... 

D.W. Urry, S.Q. Peng, J. Xu, and D.T. McPherson, Characterization of waters of hydrophobic hydration by microwave dielectric relaxation. J Am Chem Soc 119,1161-1162,1997b. 

Increasingly, dielectric measurements are being used to characterize the water content of emulsions. One model for the dielectric constant of a suspension, ... 

Conventionally RAIRS has been used for both qualitative and quantitative characterization of adsorbed molecules or films on mirror-like (metallic) substrates [4.265]. In the last decade the applicability of RAIRS to the quantitative analysis of adsorbates on non-metallic surfaces (e.g. semiconductors, glasses [4.267], and water [4.273]) has also been proven. The classical three-phase model for a thin isotropic adsorbate layer on a metallic surface was developed by Greenler [4.265, 4.272]. Calculations for the model have been extended to include description of anisotropic layers on dielectric substrates [4.274-4.276]. 

Smith et al. [1.127] reviewed the dielectric relaxation spectroscopy (DRS) as a method for structural characterization of polymers and proteins providing, among others, information about the water content and states of water. 

Because cryosolvents must be used in studies of biochemical reactions in water, it is important to recall that the dielectric constant of a solution increases with decreasing temperature. Fink and Geeves describe the following steps (1) preliminary tests to identify possible cryosolvent(s) (2) determination of the effect of cosolvent on the catalytic properties (3) determination of the effect of cosolvent on the structural properties (4) determination of the effect of subzero temperature on the catalytic properties (5) determination of the effect of subzero temperature on the structural properties (6) detection of intermediates by initiating catalytic reaction at subzero temperature (7) kinetic, thermodynamic, and spectral characterization of detected intermediates (8) correlation of low-temperature findings with those under normal conditions and (9) structural studies on trapped intermediates. 

Third, the success of the composite HC-SD model described in Section IX implies the idea that liquid water presents as if a solution of two components. The main one comprises 95% of molecules (librators), which reorient rather freely in a deep potential well and are characterized by a broken H-bond. The second component comprises 5% of molecules, which are H-bonded and perform fast vibration. Molecules of the first group live much longer than those of the second group. Thus a physical sense of the HC model is clarified in Section X as that describing dielectric response of dipoles with broken H-bonds. 

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