Amorphous loss tangent

The dielectric constant is generally different in the crystalline and amorphous phases. In this case, Xc in Eq. (95) does not mean the volume fraction of the crystalline phase itself. Furthermore, the amorphous phase exhibits dielectric relaxation in the region where the mechanical relaxation occurs. Considering this effect, Xc should be taken as a complex quantity with a negative imaginary part. However, the inequality (100) is valid in so far as the dielectric loss tangent is smaller than the mechanical one. The inequality (101) holds more generally because the effect of dielectric relaxation enhances the positive value of d"jd. ... 

The electical properties of amorphous poly-DSP are characterized by a small temperature dependence of the dielectric constant measured between room temperature and 100 °C. The dielectric loss tangent is small and, in addition, the dc conductivity is extremely low. 

At low temperatures the storage modulus is almost the same Crystalline as well as amorphous regions behave stiff. At the common glass transition temperature at about 0 °C there is a small peak in the loss tangent and a decrease in the storage modulus due to the... 

Storage Modulus and Loss Tangent of an Amorphous Polymer... 

Fig. 31. Diagram of master curves for modulus and loss tangent for a t5T>ical amorphous poljmier showing five characteristic physical states (73).

Figure 123 shows the temperature dependence of storage (Young s) modulus ( )> ioss modulus (E") and loss tangent (tan 6) of the amorphous Las5Al25Ni2o all[Pg.197]

Figure 5.2. Illustration of loss tangent (damping) and storage modulus characteristics for a linear amorphous polymer illustrating various distinct physical states that the polymer assumes with varying temperature or frequency (Collins et al. 1973). Reprinted with permission of John Wiley and Sons, Inc.

The mechanical loss tangents are nearly equal at very low temperatures For amorphous polymers, tan 5m(4.2 K) 10 (this asymptotic, peakless behavior may be attributed to tunneling processes which exhibit a smooth distribution of relaxations at very low temperatures). For partially crystalline polymers, tan Sm(4.2 K) 4-8 X 10 (depending on crystallinity). Somewhat higher values were found for polymers having loss peaks at low temperatures, eg, poly(ethyl methacrylate), PS. 

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