Dielectric constant sample cells

Since low volumes of solution and low analyte concentrations are involved in samples from works of art and archaeological pieces, low-volume cells (1-2 mL) can also be used coupled with micro- and ultramicroelectrodes. These last provide high sensitivity and allow operation with electrolytes of low dielectric constant or even work without supporting electrolytes [87, 88]. 

We will see that in the steady state of the blocking cells, we can extract partial conductivities, and from the transients chemical diffusion coefficients (and/or interfacial rate constants). Cell 7 combines electronic with ionic electrodes here a steady state does not occur but the cell can be used to titrate the sample, i.e., to precisely tune stoichiometry. Cell 1 is an equilibrium cell which allows the determination of total conductivity, dielectric constant or boundary parameters as a function of state parameters. In contrast to cell 1, cell 2 exhibits a chemical gradient, and can be used to e.g., derive partial conductivities. If these oxygen potentials are made of phase mixtures212 (e.g., AO, A or AB03, B203, A) and if MO is a solid electrolyte, thermodynamic formation data can be extracted for the electrode phases. 

One can measure the dielectric constant e of gases, liquids and solids by placing the sample in a capacitance cell. From measuring e as a function of temperature, one routinely gets the scalar first-order electric dipole susceptibility... 

The nature of the tracer dictates the detection system. For the liquid phase, quite often the tracers (e.g., NaCl, H2S04, etc.) are such that the detection probe is directly inserted into the reactor and continuous monitoring of the concentration at any fixed position is obtained by means of an electrical conductivity cell and a recorder. In this case, no external sampling of liquid is necessary. If the tracer concentration measurement requires an analytical procedure such as titration, etc., sampling of the liquid is required. For the solid phase, a magnetic tracer is sometimes used. The concentration of a solid-phase tracer can also be measured by a capacitance probe if the tracer material has a different dielectric constant than the solid phase. In general, however, for solid and sometimes gas phases, some suitable radioactive tracer is convenient to use. The detection systems for a radioactive tracer (which include scintillation counters, a recorder, etc.) can be expensive. Some of the tracers for the gas, liquid, and solid phases reported in the literature are summarized in Table 3-1. 

Figure 5. (A2) Various spectral quantities related to liquid water in the mid-IR region. Experimental values of log(/Q(i )//(i )) are shown in the case of an absorption set-np with a 1 p,m thick sample and of an ATR cell with an immersed portion of the crystal about 3 cm long (41). The optical constants n and k are also displayed together with the imaginary dielectric constants e".

Dielectric measurements on thin films were made using a two-fluid cell technique as per ASTM D 150. The advantage of the two-fluid cell is that measurement of dielectric constant is independent of sample thickness, electrode spacing, and electrode area. Thin films can be stacked to increase testing accuracy. The reproducibility of the dielectric constant measurement using the two-fluid cell was 2%. 

The liquid displacement method, described in ASTM D1531-62, is in fact the only proper method for accurate dielectric constant measurements on the thin (about 0.2 mm) foil samples. A gold plated ERA liquid cell with an electrode spacing of 1.435 inn was used for these measurements. The measuring... 

If Cg is relatively large compared to C, then the response of Cp will be dependent mainly on. Cg can be increased by decreasing wall thickness and Cs decreased by increasing the distance between the walls of the cell. Since the dielectric constant of the sample will alter Cg, the instrument response will follow the dielectric constant. Figure 5.16 indicates the type of nonlinear, but smooth, response obtained with a commercially available oscillometer for compounds of varying dielectric constant. 

This chapter is concerned with experimental measurements of flexo-electric coefficients. After a brief introduction to flexoelectricity in nematic liquid crystaJs, some applications exploiting the flexoelectric effect and the influence of this effect on electrohydrodynamic instabilities are pointed out. Flexoelectricity axises in samples with a splay-bend distortion in the director field and as such its measurement is not as direct as for dielectric constants. The theoretical background needed to analyse electro-optic experiments and extract the flexocoefficients is outlined in Section 2.2. Various experimental techniques that have been developed are described in Section 2.3. These involve cells in which the alignment of the nematic director is homeotropic, or planar or hybrid. In the first case, the interdigitated electrode technique is particularly noteworthy, as it has been used to establish several features of flexoelectricity (1) the effect can arise purely from the quadrupolar nature of the medium, and (2) the dipolar contribution relaxes at a relatively low frequency. 

Dark conductivities ap allow a number of conclusions [199, 200] and are thus measured first. Since Iq = a U a linear dependence (s 1) of the dark current Id on the voltage U indicates ohmic behavior, a superlinear dependence (s 2) the presence of space charge limited currents (SCLC). The constant a is directly proportional to the proportion of free to trapped charge carriers, the dielectrical constant of the sample, the electrical field constant and the mobihty of the charge carriers. Finally a is also determined by the cell geometry. As a is proportional to the mobility p of the charge carriers it is in certain cases possible to calculate p from the slope of the Id/U curve. The dark conductivity of an ohmic conductor varies with the temperature in an Arrhenius type fashion. The... 

Conductimetric and kinetic measurements were performed over a pressure range up to 700 atm. The sample cell is a field modulation cell modified for pressure work (7). The conductimetric cell constant is determined from dielectric calibration the constancy of which is checked after each pressure-run by remeasuring at 1 atm deviations for all measurements reported were always below 1 %. The necessary corrections for concentration due to compressibility were performed. 

Changes in cell-constant at high pressure are irrelevant for the kinetic measurements performed by electric field modulation techniques (8) the results of which are independent of cell geometry. The density of the benzene-chlorobenzene mixtures was calculated, assuming ideality, from the compressibility of the pure solvents. Measurements of the dielectric constant in the sample cell at different pressures yielded the change of dielectric constant with pressure (9D/9P), which is the important parameter for the description of electrostriction. The viscosity at different pressures was extrapolated from the pressure dependence for the pure solvents and the viscosity, at 1 atm, of the mixtures. 

The introduction of flexible, alicycUc Epidon structure in the PI backbone in combination with some flexible aromatic diamines reduces the inter- and intramolecular CTC interactions, and consequently the polarizability. This approach leads to transparent materials as revealed from the refractive index values (1.6-1.7) and optical gap energies ( > 3.26 eV). Also, the extinction coefficient evaluated by eUipsometry indicates that these semi-alicyclic Pis do not absorb visible light. The dielectric constant values for the samples containing ether bridges in the structural unit are lower than the classic dielectrics, namely 2.8 at 1 MHz. Moreover, their good transparency can be exploited in many applications such as LCDs or cell culture substrates. For these goals, the... 

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