Poly dielectric relaxation spectra

Comparison of the dielectric and viscoelastic relaxation times, which, according to the above speculations, obey a simple relation rn = 3r, has attracted special attention of scholars (Watanabe et al. 1996 Ren et al. 2003). According to Watanabe et al. (1996), the ratio of the two longest relaxation times from alternative measurements is 2-3 for dilute solutions of polyisobu-tilene, while it is close to unity for undiluted (M 10Me) solutions. For undiluted polyisoprene and poly(d,/-lactic acid), it was found (Ren et al. 2003) that the relaxation time for the dielectric normal mode coincides approximately with the terminal viscoelastic relaxation time. This evidence is consistent with the above speculations and confirms that both dielectric and stress relaxation are closely related to motion of separate Kuhn s segments. However, there is a need in a more detailed theory experiment shows the existence of many relaxation times for both dielectric and viscoelastic relaxation, while the relaxation spectrum for the latter is much broader that for the former. 

Extraneous molecules in solid phase polymer systems are not limited to plasticizer molecules or even exclusive to substances deliberately added. Impurities wdien present often affect the dielectric behaviour of pol mers and water in particular often has very significant effects on the dielectric spectrum. Poly(niethyl methacrylate) poly(oxymethylene) , and nylons to mention a few are influenced by moisture in this way. The influence of moisture on dielectric relaxation can be the result of interfacial polarization as well as dipolar mechanism. Further, this complication is not restricted to additives such as water but may occur whenever a combination of phase boundary and bulk or sur ce conductivity to or over the botmdaiy can take place. The proof that a relaxaticu is the result of interfacial polarization is not easy to establish, but there is evidence that mie of the relaxations in nylons and pol3 urethanes) are of this type. As expected, conductive fillers will introduce interfacial polarization and this effect has been well documented, especially in carbon filled rubbers . Indeed, as we shall disci later, electronic conductance when localized by interfacial boundaries does result in a form of interfacial polarization. Here, because of its large magnitude the phenomenon has been termed hyperelectronic polarization. 

The dielectric loss relaxation spectrum e"( )/ was shown to be uniformly accurately described by EQxp(—aa> ) at smaller frequencies and ea> at larger frequencies. For a small 38 kDa poly(D,L-lactic) acid, the scaling parameters are substantially independent of c with a larger 119 kDa poly(D,L-lactic) acid, a increases with increasing c. The parameter S is often but not always equal to unity when 5 = 1, a is a true time. At elevated polymer concentration, the exponent x is smaller correspondingly, dielectric loss relaxation spectra become broader. 

A few hyperbranched poly(ester amide)s have been prepared using a similar A2 + BBV approach, in which phthalic anhydride or maleic anhydride as an A2 monomer and diethanol amine as a BB 2 monomer were used. The polycondensation polymerisation technique is used to prepare the polymers. These poly(ester amide)s are modified by long alkyl chain (fatty acids) end groups. The dielectric properties of the modified polymers were investigated over a range of frequencies and temperatures. No relaxation peak was noticed in the dielectric spectrum at different temperatures. Castor oil and Mesua ferrea L. seed oil-based hyperbranched poly(ester amide)s are prepared using diethanol fatty amide of the oils with different types of anhydrides and dibasic acids with or without diethanolamine. 

In addition to the well-established molecular relaxations, the TSC spectrum shows a weak / relaxation, ascribed to rotation of trace amounts of absorbed water, and a weak [3 relaxation, a dielectric signal that may correspond to translational mobility of charges, hindered sidechain motions, or even structural relaxation effects [see, e.g., Muzeau et al. (1995) Kalogeras (2004). The a relaxation has a peak at = 110 °C, near the DSC Tg (Kalogeras and Neagu 2004). The intrachain effect of the stiffness of individual chain segments is—at least in the case of PMMA and some other poly(n-alkyl metharylate)s— more important than the interchain effect of the cohesive (attractive) forces... 

---