Dielectric measurement analyzer

Dielectric measurement analyzer (simultaneously with viscoelastic measurement)... 

Figure 4.64 Arrhenius plot of secondary relaxation in the AB cross-liked polymer COVTPU50St50. Modern apparatus, such as a dynamic mechanical spectrometer and a dielectric measurement analyzer, arc equipf>ed with analytical software to calculate the activation energy...

According to the results shown for this polymer, it is possible to confirm the hypothesis of Riggs et al. [129] concerning the existence of two mechanisms of water absorption. On the other hand it is interesting to note that the dielectric analysis of these polymers allow to know the importance of water sorption in this kind of polymers what is very important from technological an medical point of view. Therefore dielectric measurements on these kind of polymers result in a powerfull tool to analyze the effect of water absorption on the polymeric matrix and then to applications of these materials. 

Polymer properties are very often dependent on the polymer preparation. So, a good monitoring of the polymerization process is the key step to obtaining good and reproducible materials. The extent of the polymerization can be controlled in different ways. IR is the most usual [27,30] but is not very accurate and requires the extraction of samples to analyze. Recently, an in situ monitoring of PMR-15 processing has been provided by means of frequency-dependent dielectric measurements [33,34]. This non-destructive technique allows the characterization of all the steps of the curing process and thus they can be optimized. 

A Novocontrol Alpha-Analyzer (v=10 -10 Hz) was used for dielectric measurements, both at atmospheric and at high pressure. For atmospheric pressure measurements, a parallel plate capacitor separated by a quartz spacer (empty capacitance 90 pF) and filled by the sample was placed in the nitrogen flow Quattro cryostat (T= 100-3 60 K). For high pressure measurements, a sample-holder multi-layer capacitor (empty capacitance 30pF) was separated from the pressurizing fluid (silicon oil) by a Teflon membrane. The high pressure chamber (Cu-Be alloy), provided by UNIPRESS, was connected to a hydraulic pump able to reach 700 MPa, and controlled in the interval 195-360 K within 0.1 K by means of a thermally conditioned liquid flow. 

Fourier transform dielectric. spectrometer Viscoelastic measurement analyzer at constant humidity... 

The experimental setup for dielectric measurements in sorption columns is sketched in Figure 6.32. It consists mainly of an adsorption column filled with sorbent material, a capacitor inside the column connected to an impedance analyzer (HP 4192 A) and a (traditional) thermal conductivity detector (TCD) (Perkin Elmer, Germany) to detect changes in the concentration of the gas leaving the column. 

The motive for the present investigation is the question whether high fields promote proton jiomping in acid-base adducts and whether the reaction partners can be regarded as tautomers. According to conventional dielectric measurements by Polish authors such an equilibrium would be well-poised for the title compounds. Malecki analyzed the nonlinear dielectric effects in this system without concern for relaxation. ... 

These relations may offer useful information for analyzing the curing process of an epoxy resin system by the on-line dielectric measurement [16-21] which can provide the conductivity of the reactive system, because the viscosity or the relaxation time of the system can be calculated through these relations [Eqs. (1) and (5), or Eqs. (2) and (4)] from the conductivity directly detected during curing of the epoxy resin system before gelation [22,23]. 

Figure 4. Setup for high-pressure dielectric measurements G, supply for pressurising gas V, valves M, pressure gauge GMK, gas compressor TM, heating and cooling jacket T, T, thermocouples B, Bridgman piston A, autoclave K, capacitor I, electrical connection to heating block Pt, platinum resistance thermometer DVM, digital voltmeter S, recorder HP, Hewlett-Packard impedance analyzer C, computer R, Rj, regulators TMG, temperature registration DW, dewar.

For measurements in the frequency domain, capacitance bridges, impedance analyzers, frequency response analyzers, radio-frequency reflectometers and network analyzers are typically employed. Figure 1 shows schematically the frequency range of dielectric measurements covered by different techniques and equipments [17]. The principle of these measurements is as follows. The sample... 

Figure 1. Techniques and equipment for dielectric measurements. FRA means frequency response analyzer, TDS is time domain spectroscopy...

Independently of the specific dielectric technique used, the results of dielectric measurements are usually analyzed in the form of complex dielectric permittivity e(o ) = e w) — ie (w) at constant temperature by fitting empirical relaxation functions to e(o ). In the examples to be given later in this chapter, the two-shape-parameter Havriliak-Negami (HN) expression [22]... 

The number of measurable layers of a stack is limited only by the optical contrast between the different layers. In practice stacks of ten layers and more can be analyzed by ellipsometry. Further advantages of ellipsometry compared with other metrological methods are the non-invasive and non-destructive character of the optical method, the low energy entry into the sample, the direct measurement of the dielectric function of materials, and the possibility of making the measurement in any kind of optical transparent environment. 

Capacitive Sensors. This device usually consists of a capacitor which is formed either from two concentric cylinders or from a pair of parallel plates. The solid sample to be analyzed for moisture content is passed between these plates. Since w has a large dielectric constant, the w content of the sample causes a significant change in the dielectric constant of the solid, which is measured using bridge or frequency techniques. 

---