Poly dielectric function

The effective dielectric function of poly electrolyte solutions remains as a mystery, demanding a better understanding of structure of solvent surrounding poly electrolyte molecules. 

FIG. 11.3 Complex dielectric functions of poly(vinyl acetate). (A) Dielectric loss s"[T) as a function of temperature for three frequencies. (B) Temperature dependence of the dielectric constant s (v) (top panel) and the dielectric loss s"(v) (bottom panel) of the complex dielectric function curves from right to left in the temperature range from 377 to 313 K with steps of 4 K and 312.5,311.5,310.5,310 K. (C) 3D plot of the dielectric loss s"[ ,T). The author is much indebted to Prof. M. Wubbenhorst (KU Leuven) for his illustrative measurements on PVAC, especially for the benefit of this book. 

Figure 3 Real and imaginary parts of the dielectric function for poly(di-n-hexylsilane) calculated from the reflectivity data shown in figure 2. The negative values for 62 just below the first UV transition are artifacts of the extrapolations used in the Kramers-Kronig analysis.

Figure 9 Composite plot of the dielectric function e = s -is" (top), the electric modulus M = IVf + iM" (middle), and the ionic conductivity a = a -I- ia" (bottom) shifted to a reference temperature (421.15 K) in the vicinity of the poly(4-chlorostyrene) ionic relaxation. The vertical dashed and short dashed lines give the locations of the ionic and segmental (a-) relaxations, respectively. Note that in all representations the crossing of the real and imaginary parts occurs at the same frequency which signifies the rate of the ion mobility.

The formation ofC—C bonds between aromatic rings is an important step in many organic syntheses and can be accomplished by chemical, photochemical, or electrochemical means. As was noted earlier, fundamental considerations of the parameters for a dielectric which must be dealt with in designing a thermally stable, low-dielectric-constant polymer naturally lead one to consider rigid-rod, nonconjugated aromatic polymers containing no lossy functional groups. A structure such as poly(naphthalene) is a likely candidate. 

Conformational energies as function of rotational angles over two consecutive skeletal bonds for both meso and racemic diads of poly(Af-vinyl-2-pyrrolidone) are computed. The results of these calculations are used to formulate a statistical model that was then employed to calculate the unperturbed dimensions of this polymer. The conformational energies are sensitive to the Coutombic interactions, which are governed by the dielectric constant of the solvent, and to the size of the solvent molecules. Consequently, the calculated values of the polymeric chain dimensions are strongly dependent on the nature of the solvent, as it was experimentally found before. 

The dielectric relaxation of bulk mixtures of poly(2jS-di-methylphenylene oxide) and atactic polystyrene has been measured as a function of sample composition, frequency, and temperature. The results are compared with earlier dynamic mechanical and (differential scanning) calorimetric studies of the same samples. It is concluded that the polymers are miscible but probably not at a segmental level. A detailed analysis suggests that the particular samples investigated may be considered in terms of a continuous phase-dispersed phase concept, in which the former is a PS-rich and the latter a PPO-rich material, except for the sample containing 75% PPO-25% PS in which the converse is postulated. 

Summary In this chapter, a discussion of the viscoelastic properties of selected polymeric materials is performed. The basic concepts of viscoelasticity, dealing with the fact that polymers above glass-transition temperature exhibit high entropic elasticity, are described at beginner level. The analysis of stress-strain for some polymeric materials is shortly described. Dielectric and dynamic mechanical behavior of aliphatic, cyclic saturated and aromatic substituted poly(methacrylate)s is well explained. An interesting approach of the relaxational processes is presented under the experience of the authors in these polymeric systems. The viscoelastic behavior of poly(itaconate)s with mono- and disubstitutions and the effect of the substituents and the functional groups is extensively discussed. The behavior of viscoelastic behavior of different poly(thiocarbonate)s is also analyzed. 

Puschnig, P. and Ambrosch-Draxel, C. (1999) Density-functional study of the oligomers of poly-para-phenylene Band structures and dielectric tensors. Physical Review. E, Condensed Matter, 60, 7891-8. 

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