Dielectric Characterization

Dielectric characterization involves the measurement of dipole responses to an applied electric field. The simplest measurement of the dielectric constant and dielectric loss involves the separation of two conductive plates. When a voltage (V) is applied to one plate, a charge is produced (Q) and induces an opposite charge on the other plate with the capacitance defined by the expression (Q = CV). When a dielectric material is placed between the plates, a polarization change will result and the capacitance of the system will increase relative to 

The complex dielectric constant has been noted to be related to the refractive index (n) and the absorption index (K) by the following expressions [45]  

For non-polar polymers, the dielectric constant, e = n. Note that Eq. 5.21 is relevant at high frequency, where charge migration and dipolar polarization are negligible. 

Dielectric data typically obtained for characterization of polymeric materials involve e and e versus temperature or frequency. Generalized data for an imblended polymer or a single phase polymer blend are illustrated in Fig. 5.13. 

Experimental data showing single Tg behavior for chlorinated PVC blends with an ethy-lene/vinyl acetate (70 wt% VAc) copolymer are given in Fig. 5.14 for tan6 (e ft ) versus temperature [46]. 

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From a computational view point, chemical reactions in solution present a yet not solved challenge. On one hand, some of the solvent effects can be approximated as if the solute molecule would be in a continuum with a given dielectric characterization of the liquid, and this view point has been pioneered by Bom [1], later by Kirkwood [2] and Onsager [3] and even later by many computational quantum chemists [4-9], On the other hand, the continuum model fails totally when one is interested in the specific... 

Geyer, R. 1990. Dielectric Characterization and Reference Materials. NIST Technical Note 1338. National Institute of Standards and Technology, Boulder, CO. 

Kxanbuehl, D. E. Dynamic dielectric characterization of thermosets and thermoplastics using intrinsic cariables, p. 1251, Proc. 29th SAMPE Symp., 1984... 

R. J. Hunter, V. A. Hackley, and J. Texter, Handbook on Ultrasonic and Dielectric Characterization Techniques for Suspended Particles, American Chemical Society, Westerville, Ohio, 1998. 

In the continuum solvent distribution models, Vei is evaluated by resorting to the description of the solvent as a dielectric medium. This medium may be modeled in many different ways, being the continuous methods quite flexible. We shall consider the simplest model only, i.e. an infinite linear isotropic dielectric, characterized by a scalar dielectric constant e. The interested reader can refer to a recent review (Tomasi and Persico, 1994) for the literature regarding more detailed and more specialistic models. However, the basic model we are considering here is sufficient to treat almost all chemical reactions occurring in bulk homogeneous solutions. 

Dielectric Characterization of Water in Polyimide and Poly(amide—imide) Thin Films... 

Figure 8. Dielectric loss spectra of tetra-ethyleneglycol dimethacrylate between -114 and -86 °C, in steps of 2 °C, showing two secondary relaxation processes the high loss values on the low frequency side for the highest temperatures is due to the incoming of the main relaxation process associated with the glass transition (Tg= -83 C). Detailed dielectric characterization is given in [47].

Figure 10. Loss spectra of tetra-ethyleneglycol dimethacrylate (TeEGDMA) in the temperature range from -74 °C to -46 C, every 2 C. The high-frequency wing is due to the y secondary process (dielectric characterization in [45,47]).

Figure 15. 3D plot of loss spectra detected in neutralized chitosan (structure indicated where x=0.7 and y=0.3) in the temperature retnge from -120 to 150 C. The high temperature-low frequency range. The inset shows the Arrhenius-type dependence of relaxation times for the a process ( = 94 2 kJ mof ) (complete dielectric characterization in [149]). 

Shinoj, S., R. Visvanathan, and S. Panigrahi, Towards industrial utilization of oil palm fibre Physical and dielectric characterization of Hnear low density polyethylene composites and comparison with other fibre sources. Biosyst. Eng.106, 378-388 (2010). 

M. Stintz, F. Hinze, S. Ripptrtger, Partiele size characterization of inorganie eolloids by ultrasonic attenuation speetrometry, in Handbook on ultrasonic and dielectric characterization techniques for suspended particles, eds. by V.A. Hackley, J. Textirt (The Ameriean Ceramic Society, 1998), pp. 219-228. ISBN 1-57498-034-3... 

Katz, H. E., Schilling, M. L., and Washington, G. E., Solution-phase dielectric characterization of the 4-amino-4 -dicyanovinyl-azobenzene nonlinear-optical chromo-phore, J. Opt. Soc. Am. B, 7, 309-312 (1990). 

General references on dielectric characterization include N. G. McCrum, B. E. Read, and G. Wiliams, Anelastic and Dielectric Effects in Polymeric Solids, John Wiley Sons, Inc., New York, 1967 C. W. Reed, in F. E. Kraus, ed.. Dielectric Properties of Polymers, Plenum Press, New York, 1972 P. Hedvig, Dielectric Spectroscopy of Polymers, McGraw-Hill, New York, 1977 D. R. Day, in Ho-Ming Tong and Luu T. Nguyen, eds.. New Characterization Techniques for Thin Polymer Films, John Wiley Sons, Inc., New York, 1990. 

Potschke P, Abdel-Goad M, Alig I, Dudkin S and Bellinger D (2004) Rheological and dielectrical characterization of melt mixed polycarbonate-multiwalled carbon nanotube composites. Polymer 45 8863-8870. 

Moates, G. K., Noel, T. R., Parker, R., and Ring, S. G. (2000). Dynamic mechanical and dielectric characterization of amylose-glycerol films. Carbohydrate Polymers 44,247 253. 

Both poly(AN-itot-ATRIF) copolymer and poly(ATRIF) homopolymer were dielectrically characterized over a frequency range from 10 to 10 Hz, and covering a temperature range from 223 to 393 K [68]. 

These fluorocyanopolymers were dielectrically characterized in a wide range of frequencies and temperatures. The dominating relaxation process detected in these materials is the a-relaxation, associated with the dynamic glass transition. A VFTH temperature dependence of the relaxation times was found for these fluorocyanopolymers. The polarity-dielectric constant relationship has been established. Actually, the inclusion of CN group into fluorinated units enhances the dielectric increment and makes them potential candidates for film capacitors. 

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