Dielectric thermal analysis DETA

An alternative method of studying the molecular motions of a polymeric chain is to measure the complex permitivity of the sample, mounted as dielectric of a capacitor and subjected to a sinusoidal voltage, which produces polarization of the sample macromolecules. The storage and loss factor of the complex permitivity are related to the dipolar orientations and the corresponding motional processes. The application of the dielectric thermal analysis (DETA) is obviously limited to macromolecules possessing heteroatomic dipoles but, on the other hand, it allows a range of frequency measurement much wider than DMTA and its theoretical foundations are better established. 

The relaxation methods employed are Dynamic Mechanical Thermal Analysis (DMTA) and Dielectric Thermal Analysis (DETA). Generally in both cases a single excitation frequency is used and the temperature is varied,... 

In an analogous manner to DMA, dielectric thermal analysis (DETA) represents a technique to apply an alternating electric field across the tested sample, which contributes to a polarization of the material with consequent current flow. DETA enables measurement of dielectric properties, which can further be related to material properties and thermal transitions as described below. 

Differential scanning calorimetry (DSC) Modulated or stepwise DSC Dielectric thermal analysis (DETA)... 

The relaxation methods employed are Dynamic Mechanical Thermal Analysis (DMTA) and Dielectric Thermal Analysis (DETA). Generally in both cases a single excitation frequency is used and the temperature is varied, typically over a range between — 100 °C and +200 °C. Changes in molecular motion, and hence 7, are detected by both techniques, but in the case of DETA the process has to involve movement of dipoles or fully developed electrical charges on the polymer in order to be detected. Thus the two techniques can be used to complement each other, since transitions can be detected on DMTA and assigned as due to dipoles according to whether or not they also occur with DETA. 

Alternative approaches are based on (dc)conductivity measurements with dielectric thermal analysis (DETA) [51], the cessation of flow measured... 

Numerous techniques have been applied to the measurement of Tg [58-75] including DSC, [76] thermogravimetric analysis (TGA), DTA, DMA, TMA, dielectric thermal analysis (DETA) and NMR spectroscopy. Figure 3.1 shows a TMA curve of epoxy resin measured in nitrogen at a heating rate of 5 "C/min... 

Two techniques, dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA), have been used for the study of resin cure. Differential scanning calorimetry (DSC) has also been employed (for a discussion of the theory and instrumentation of DSC, see Chapter 9). The application of differential photocalorimetry to the measurement of cure rates of photocurable resins is discussed in Chapter 12. 

Dielectric thermal analysis (DETA) has been used in measnrement of Tg of neoprene, styrene-butadiene, polyisoprene, polybutadiene, polychloroprene, nitrile, ethylene-propylene-diene and butyl rubbers [4]. 

Electronic impedance spectroscopy (EIS) is used to measure the polymer dielectric properties and the changes in these properties with exposure time. This is based on the interaction of an external field with the electric dipole moment of the sample, often expressed by permittivity. Dielectric thermal analysis (DETA) measures the permittivity, capacitance and dielectric loss of a polymer sample under an oscillating electric field as a function of temperature. The dielectric properties of a blend system in general depend on structure, crystallinity, morphology and additives. " ... 

The dielectric thermal analysis (DETA) technique normally obtains data from thermal scans at a constant impressed frequency. The glass transition (Tg) at which molecular motions become faster than the impressed timescale are recorded as peaks in e " and tan 5. 

The principal techniques that have been used in resin cure studies are differential scanning calorimetry (DSC Chapter 7), photocalorimetry (Sections 11.3.1 and 11.3.2), dielectric thermal analysis (DETA Section 12.2.1) and dynamic mechanical thermal analysis (DMTA Section 8.3.2). Earlier differential photocalorimetry (DPC) instruments were based on a DSC instrument. However, these were only partially successful in the analysis of photocurable polymers. The failure to develop a completely adequate system has been the result of two factors. The first and most significant is the change in the intensity of the light with time of operation - as much as an 80% reduction in the first 100 hours of operation. The second reason for the limited success was the lack of data analysis software to convert raw data into easy-to-understand results that could be correlated with actual performance. 

Dielectric analysis (DEA) or dielectric thermal analysis (DETA) is another important thermoanalytical technique that is rapidly evolving. This technique measures two fundamental electrical characteristics of a material—capacitance and conductance—as a function of time. 

Polymer characterisation, stabilisation and degradation are very widely studied by Thermal Analysis (TA). Single techniques, such as thermogravimetric analysis (TG), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and dielectric thermal analysis (DETA) provide important information on the thermal behaviour of materials. However, to obtain a more complete profile of, say, polymer degradation gas analysis is required, particularly since all of the techniques listed give mainly physical information on the behaviour of materials. 

It should be noted that the sensitivity of the DMA technique is considerably greater than that of TMA or DSC in detecting transitions. The comparable techniques of dielectric thermal analysis (DETA, or DEA) produce similar results and cover a wider range of frequencies. 

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