On the relationship between matric potential and dielectric properties of organic free soils: a sensitivity study

2009 ◽  
Vol 46 (10) ◽  
pp. 1202-1215 ◽  
Author(s):  
Norman Wagner ◽  
Alexander Scheuermann
Keyword(s):  
Dielectric Relaxation ◽  
Low Frequency ◽  
Bound Water ◽  
Frequency Dispersion ◽  
Strong Relationship ◽  
Sensitivity Study ◽  
Relative Dielectric Permittivity ◽  
Relaxation Processes ◽  
Matric Potential ◽  
Relaxation Effects

High-frequency electromagnetic determination of moisture in porous media, (e.g., soil) is based on the strong relationship between volumetric water content and relative dielectric permittivity. In particular, in fine-grained soils the movement of water is influenced by different surface-bonding forces due to interface processes. The interface effects lead to a number of dielectric relaxation processes (free- and bound-water phase, Maxwell–Wagner effect, counterion relaxation effects). These relaxation processes are the reason for the strong frequency dependence of the electromagnetic material properties below 1 GHz. The matric potential is a measure of the bonding forces on water in the soil. Based on a thermodynamic relationship between soil matric potential and dielectric relaxation behaviour of water in different binding states, a broadband dielectric relaxation model was developed that considers low-frequency dispersion up to 1 MHz as well as losses due to direct-current conductivity. The sensitivity of the model on soil suction was systematically analyzed based on a pedotransfer function (PTF) for soil textures ranging from pure sand up to pure clay. The results are compared with known empirical and semiempirical calibration functions, as well as theoretical mixing models.

Study of the Molecular Mobility of Polysaccharide Solid Thin Layers by Dielectric Relaxation Spectroscopy

1997 ◽  
Vol 500 ◽  
Author(s):  
K. Liedermann ◽  
L. Lapčík ◽  
S. Desmedt
Keyword(s):  
Dielectric Relaxation ◽  
Low Frequency ◽  
Thin Layers ◽  
Side Chain ◽  
Relaxation Processes ◽  
Dielectric Relaxation Spectroscopy ◽  
Frequency Range ◽  
Polar Groups ◽  
Calculated Activation Energy ◽  
Β Relaxation

ABSTRACTTemperature dependence of measured dielectric relaxation spectra (DRS) in the frequency range 20 Hz - 1 MHz of hydroxyethylcellulose (HEC) are in the temperature range 100 – 350 K. of Arrhenius character with one relaxation process at 150 – 250 K. This process reflects most probably β-relaxation of the side chain groups. Calculated activation energy of this process was 5730 kJ/mole. Four types of polysaccharides were studied at 293 K temperature: hyaluronic acid (HA), chondroitin sulfate (CHS), HEC and carboxymethylcellulose (CMC), in the low-frequency range 10−5 - 100 Hz. Measured dielectric spectra were interpreted as sum of one A.C. conductivity process and of up to two relaxation processes. The relaxation processes were described by means of the Havriliak-Negami formula and their parameters were related to the molecular structure of the polymers. The low value of a in CHS is related to its strong coupling due to the presence of two polar groups in its monomeric unit, whereas low values of α × β are interpreted as being due to the strong steric hindrances caused by long pendants present in HEC.

Low Frequency Dispersion of a Molecular Crystal

1977 ◽  
Vol 32 (5) ◽  
pp. 515-516
Author(s):  
B. Hinopoulos ◽  
P. U. Sakellaridis
Keyword(s):  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Molecular Crystal ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Lattice Defects ◽  
Dielectric Behaviour ◽  
Crystalline Sample ◽  
Dielectric Relaxation Process

Abstract The dielectric behaviour of solid 1,4-Butandiol has been studied. A region of low frequency dispersion has been ob­ served. In a crystalline sample treated to have more lattice faults, the losses were increased. The effect is attributed to a dielectric relaxation process existing in connection with the lattice defects.

Dielectric Relaxation of Chitosan Films

2013 ◽  
Vol 685 ◽  
pp. 336-339 ◽  
Author(s):  
E.I. Bobritskaya ◽  
R.A. Castro ◽  
Yu.A. Gorokhovatsky ◽  
D.E. Temnov
Keyword(s):  
Acetic Acid ◽  
Dielectric Relaxation ◽  
Bound Water ◽  
Relaxation Processes ◽  
Dielectric Spectra ◽  
Chitosan Films ◽  
Second Peak

Dielectric spectra of pure chitosan films and chitosan films with different fillers were obtained. Two relaxation processes in 200 – 500 K temperature intervals were observed: wide β - peak in the region of 290 K and  - peak in the region of 390 K. The first peak due to the presence of the polymer-bound water and/or acetic acid and disappears when filler injected into the polymer. The second peak may be associated with the activation of the nonohmic conductivity.

scholarly journals Supercooled interfacial water in fine-grained soils probed by dielectric spectroscopy

2013 ◽  
Vol 7 (6) ◽  
pp. 1839-1855 ◽  
Author(s):  
A. Lorek ◽  
N. Wagner
Keyword(s):  
Specific Surface ◽  
Dielectric Relaxation ◽  
Water Content ◽  
Low Frequency ◽  
Relaxation Processes ◽  
Martian Surface ◽  
Fine Grained ◽  
State Of Water ◽  
Key Factor ◽  
Physical And Chemical

Abstract. Water substantially affects nearly all physical, chemical and biological processes on the Earth. Recent Mars observations as well as laboratory investigations suggest that water is a key factor of current physical and chemical processes on the Martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid-like state of water on Martian analogue soils for temperatures below 0 °C. To this end, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine-grained soils in the frequency range from 10 Hz to 1.1 MHz at Martian-like temperatures down to −70 °C. Two Martian analogue soils have been investigated: a Ca-bentonite (specific surface of 237 m2 g−1, up to 9.4% w / w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m2 g−1, up to 7.4% w / w). Three soil-specific relaxation processes are observed in the investigated frequency–temperature range: two weak high-frequency processes (bound or hydrated water as well as ice) and a strong low-frequency process due to counter-ion relaxation and the Maxwell–Wagner effect. To characterize the dielectric relaxation behaviour, a generalized fractional dielectric relaxation model was applied assuming three active relaxation processes with relaxation time of the ith process modelled with an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid-like water content by means of the Birchak or CRIM equation. There are evidence that bentonite down to −70 °C has a liquid-like water content of 1.17 monolayers and JSC Mars 1 a liquid-like water content of 1.96 monolayers.

Compensation phenomena in oil-resin mixtures: A new dielectric approach to percolative processes

1997 ◽  
Vol 12 (10) ◽  
pp. 2784-2793 ◽  
Author(s):  
O. Pagés ◽  
A. Lamure ◽  
C. Lacabanne ◽  
M. Odlyha ◽  
D. Craig
Keyword(s):  
Dielectric Relaxation ◽  
Dielectric Spectroscopy ◽  
Low Frequency ◽  
Relaxation Processes ◽  
Thermally Stimulated Currents ◽  
Critical Concentrations ◽  
Composite Systems ◽  
Percolation Phenomena ◽  
Percolation Thresholds ◽  
First Time

The methods of thermally stimulated currents (TSC) together with low frequency dielectric spectroscopy (LFDS) are combined for the first time to study percolation phenomena. These take place within oil-resin mixtures which constitute conductor/insulator-like composite systems. Each of these techniques is shown to describe selectively one of two different kinds of relaxation processes in the oil component: first, anelastic dipolar movements and second, the circulation of free charges. The separate qualitative interpretations of the combined TSC/LFDS experiments lead to convergent estimations of the percolation thresholds of the two basic materials in oil-resin mixtures. The latter appear as critical concentrations for which the dielectric relaxation processes either comply suddenly with compensation laws or pre-existing compensation phenomena change in nature.

scholarly journals Supercooled interfacial water in fine grained soils probed by dielectric spectroscopy

2013 ◽  
Vol 7 (2) ◽  
pp. 1441-1493
Author(s):  
A. Lorek ◽  
N. Wagner
Keyword(s):  
Specific Surface ◽  
Dielectric Relaxation ◽  
Water Content ◽  
Low Frequency ◽  
State Parameter ◽  
Relaxation Processes ◽  
Martian Surface ◽  
Temperature Range ◽  
Fine Grained ◽  
Key Factor

Abstract. Water as thermodynamic state parameter affects nearly all physical, chemical and biological processes on the earth. Recent Mars observations as well as laboratory investigations suggest that water is also a key factor of current physical and chemical processes on the martian surface, e.g. rheological phenomena. Therefore it is of particular interest to get information about the liquid like state of water on martian analog soils in the temperature range below 0 °C. In this context, a parallel plate capacitor has been developed to obtain isothermal dielectric spectra of fine grained soils in the frequency range from 10 Hz to 1.1 MHz at martian like temperatures down to −70 °C. Two martian analogue soils have been investigated: a Ca-Bentonite (specific surface of 237 m2 g−1, up to 9.4% w/w gravimetric water content) and JSC Mars 1, a volcanic ash (specific surface of 146 m2 g−1, up to 7.4% w/w). Three soil-specific relaxation processes are observed in the investigated frequency-temperature range: two weak high frequency processes (bound or hydrated water as well as ice) and a strong low frequency process due to counter ion relaxation and the Maxwell–Wagner effect. To characterize the dielectric relaxation behavior, a generalized fractional dielectric relaxation model is applied assuming three active relaxation processes with relaxation time of the ith process according to an Eyring equation. The real part of effective complex soil permittivity at 350 kHz was used to determine ice and liquid like water content by means of the Birchak or CRIM equation. There are evidence that Bentonite down to −70 °C has a liquid like water content of 1.17 monolayers and JSC Mars 1 a liquid like water content of 1.96 mono layers.

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

Sign in / Sign up

Export Citation Format

Share Document