Poly relaxed permittivity

Figures 2.31 and 2.32 show the dielectric permittivity and loss for poly(cyclobutyl methacrylate) (PCBuM) and poly(cyclobutylmethyl methacrylate) (see Scheme 2.5). In these figures the a relaxation is associated to the glass transition temperature and the p relaxation appear as a shoulder of the a relaxation.

At high temperatures and low frequencies conductivity contribution are important since the loss permittivity tends to increase continuously. Figure 2.41 show the Arrhenius plot for the determination of the activation energy for the 5 relaxation which is about 28 kJ mol-1. This is a value very close to those reported for similar structurally poly(methacrylate)s [28,29], Increasing the temperature, a y relaxation is observed. 

A frequency dependence of complex dielectric permittivity of polar polymer reveals two sets or two branches of relaxation processes (Adachi and Kotaka 1993), which correspond to the two branches of conformational relaxation, described in Section 4.2.4. The available empirical data on the molecular-weight dependencies are consistent with formulae (4.41) and (4.42). It was revealed for undiluted polyisoprene and poly(d, /-lactic acid) that the terminal (slow) dielectric relaxation time depends strongly on molecular weight of polymers (Adachi and Kotaka 1993 Ren et al. 2003). Two relaxation branches were discovered for i.s-polyisoprene melts in experiments by Imanishi et al. (1988) and Fodor and Hill (1994). The fast relaxation times do not depend on the length of the macromolecule, while the slow relaxation times do. For the latter, Imanishi et al. (1988) have found... 

Now, it has been shown for materials such as poly(propylene diol) (wherein both the absorption maximum for loss shear modulus and loss permittivity overlap near the frequency of IHz) that their normalized curves perfectly superimpose over their frequency band width. - As shown in Figure 9.15, the lower frequency loss shear modulus curves uniquely overlap with the loss permittivity data at higher frequency. As such the former is melded to calibrate the loss permittivity data to obtain a coarse estimate of the elastic modulus values. This provides an independent demonstration of the mechanic il resonance near 3 kHz and also allows reference to the 5 MHz dielectric relaxation as a mechanical resonance. Thus, as the folding and assembly of the elastic protein-based polymers proceed through the phase (inverse temperature) transition, the pentamers wrap up into a structurally repeating helical arrangement like that represented in Figure 9.17. 

For the case where the hxed charges are not uniformly distributed in the polyelectrolyte layer and that the relative permittivity in the poly electrolyte layer does not take the same value as that in the bulk solution phase, the above theory must be modihed as discussed by Ohshima and Kondo [52] and Hsu et al. [54]. Tseng et al. [55] considered the effects of charge regulation on the mobility in the polyelectrolyte layer. The case where the polyelectrolyte layer is not fully ion-penetrable is considered in Ref. [56]. Varoqui [57] considered the case where electrically neutral polymers are adsorbed with an exponential segment density distribution onto the particle surface with a charge density. Ohshima [58] extended Varoqui s theory [57] to the case where adsorbed polymers are charged. Saville [59] and Hill et al. [60] considered the relaxation effects of soft particles in electrophoresis. 

The real permittivity, at any temperature above of each polymer, as well as the intensity of the dielectric loss peaks observed for the main a-relaxation has been reported to be always greater for poly(AN-co-ATRIF) copolymer than for... 

Figures 20.21 (a, c) show that the permittivity below Tg is close to 3.0 and 3.2 for poly(MATRIF) homopolymer and poly(VCN-flZt-MATRIF) copolymer, respectively. Above Tg, the a relaxation phenomena occur with an important increasing of e for the poly(VCN-a/t-MATRIF) copolymer = 20 at 425 K) comparatively to poly(MATRlF) homopolymer (e = 4 at 370 K). This result arises from the increasing polarity of poly(MATRIF) by the incorporation of cyano groups (VCN).

Broadening of the distribution of relaxation times is also found to be caused by interactions between the mesogenic units. Haase et al and Parneix et al compared the dielectric properties of two poly acrylic scLCPs with slightly different mesogenic units PA/6/-/CN and PA/6/COO/CN. Both materials demonstrate a profound difference in the quasi-static dielectric permittivity and dielectric anisotropy gJ (PA/6/ -/CN) 12 versus 8 (PA/6/COO/CH) 19, and (a — i) 65 for the former versus 12 for the latter. Consequently, the strength of the... 

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