Dielectric thermal analysis applications

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. 

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. 

DETA (dielectric thermal analysis) Electrical equivalent of DMTA but less generally applicable. Characterises motional processes involving dipole reorientation. Mobile-phase content (hence crystallinity). Measurement of conducting polymers over complete working range. Definition of electrical quantities—dielectric permittivity and loss. 

Keating, M., Evaluation of Moisture Effects on the Dielectric Properties of Polymer Films, Thermal Analysis Application Brief Number TA-124, TA Instmments... 

The application of dielectric constant techniques to thermophysical measurement of solids has been used for a number of years (114, 115). The early uses of the technique involved isothermal measurements employing bridge methods. Recently, techniques have been developed that permit the measurement of the dielectric constant of a solid as a function of temperature, in a manner similar to other TA techniques. Chiu (116) used the term dynamic electrothermal analysis (ETA) to describe the measurement of both the capacitance and the dissipation factor of polymeric samples. Nottenburget al (117) developed an automated technique that permitted the rapid determination of the dielectric properties of a substance over a wide range of temperature and frequencies. This technique, which was called dynamic dielectric analysis (DDA), was modified to measure concurrently the DTA curve of the sample as well (117, 118). This new technique was called dynamic dielectric analysis-differential thermal analysis, DDA-DTA,... 

Thermal analysis (TA) consists of a family of analytical techniques in which a property of the sample is monitored against time or temperature while the temperature of the sample is programmed. The properties include weight, dimension, energy take-up, differential temperature, dielectric constant, mechanical modulus, evolved gases, and other, less common attributes. The application of thermal analysis is widespread within the polymer and elastomer industries. Thermal analyzers are used to qualify a material for fitness of use and to troubleshoot processing problems. Thermal analysis consists of three primary techniques that may be used individually or in combination ... 

For the identification of space effects on polymers, numerous standard tests must be used, namely spectroscopy, thermal analysis, dielectric and conductivity measurements, mechanical and viscoelastic property determination, etc. In the late 1990s NASA decided to substitute polyurethane coatings (having carcinogenic) with another one. The 18 alternative candidates were subjected to 34 standard test procedures (Table 3.7). In the following report the number of candidates fell to eight, from which the best with the lowest cost-to-performance ratio will have to be selected. This procedure illustrates how involved the polymeric testing for space application is, even if the test procedures are quite standard. 

Because of the improved thermal stability for PADS containing polyimides vis a vis other available siloxane polyimides, a screening program to correlate properties such as Tg, solubility, thermal stability, adhesion properties, and water absorption characteristics to structure was undertaken. Several copolymers were prepared from diamines and co-dianhydrides. An ODAN/ ODA copolymer in which 30 mole % PADS was substituted for ODAN, was prepared and TGA analysis at 450°C indicated that the material was the first siloxane containing polyimide identified that exceeded the established thermal stability criteria for interlevel dielectric applications. Stability and solubility of these materials as a function of PADS concentration is illustrated in Table VI. 

The mechanical, thermal, and dielectric properties of sisal fiber have been studied in detail. X-ray diffraction, Infrared Spectroscopy, Thermal Gravimetric Analysis, Scanning Electron Microscopy, Differential Scanning Calorimetry, Dynamic Mechanical Analysis etc., have been used to determine the characteristics of sisal fiber and provide theoretical support for processing and application of the fiber. 

BordaUo HN, Zakharov BA, Boldyreva EV, Johnson MR, Koza MM, Seydel T, Fischer J (2012) Application of incoherent inelastic neutron scattering in pharmaceutical analysis relaxation dynamics in phenacetin. Mol Pharm 9 2434-2441 Bptker JP, Karmwar P, Strachan CJ, Cornett C, Tian F, Zujovic Z, Rantanen J, Rades T (2011) Assessment of crystalline disorder in cryo-milled samples of indomethacin using atomic pairwise distribution functions. Int J Pharm 417 112-119 Boutonnet-Fagegaltier N, Menegotto J, Lamure A, Duplaa H, Caron A, Lacabanne C, Bauer M (2002) Molecular mobihty study of amorphous and crystalline phases of a pharmaceutical product by thermally stimulated current spectrometry. J Pharm Sci 91 1548-1560 Bras AR, Noronha JP, Antunes AMM, Cardoso MM, Schdnhals A, Affouard Fdr, Dionfsio M, Correia NIT (2008) Molecular motions in amorphous ibuprofen as studied by broadband dielectric spectroscopy. J Phys Chem B 112 11087-11099... 

The sum is taken over all atompairs which do not interact via covalent bonds is the distance between such a pair Afj and B j are coefficients depending on the type of the atoms i and j the Z s are the (partial) charges of the atoms, and D is the dielectric constant. Reasonable estimates of the parameters in Equation (2) are known from analysis of the structures and heats of sublimation of crystals of small molecules [10-13], and these are applicable to folded macromolecules when slightly modified to account for differences in thermal motion and hence thermal expansion [14]. 

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