Loss-tangent, definition

Note that VTD-variance of Loss Tangent, and that SDTD is the standard deviation of Loss Tangent with similar definitions for GSP (G or real modulus) and GDP (G or loss modulus). 

It should be taken into account that the general definition of the tan 8 is related to the ratio of loss energy and reactive energy (per periode), i. e. all measurements of the loss tangent also include possible contributions of conductivity a of a non-ideal dielectric given by tan 8 = a/uie. ... 

In many investigations dynamic-mechanical properties have been determined not so much to correlate mechanical properties as to study the influence of polymer structure on thermo-mechanical behaviour. For this purpose, complex moduli are determined as a function of temperature at a constant frequency. In every transition region (see Chap. 2) there is a certain fall of the moduli, in many cases accompanied by a definite peak of the loss tangent (Fig. 13.22). These phenomena are called dynamic transitions. The spectrum of these damping peaks is a characteristic fingerprint of a polymer. Fig. 13.23 shows this for a series of polymers. 

The data show that there is a significant oxidation effect on both the dielectric constant and the loss tangent of residual carbon content in the composites. However, for the Nextel 312 (BN) system, heat treatment at temperatures above 450°C is definitely not recommended, because of degradation of the boron nitride interface at those temperatures. 

As we know, the dielectric constant and the dielectric loss are not independent, and the dielectric loss originally results from the slow polarization, i.e, the interfacial polarization in this case. For an ER suspension of a large dielectric loss tangent it probably means that the proportion of gj to e is large. Obviously, the dispersed particle of a large dielectric loss may definitely result in a large dielectric loss of the whole suspension, then a large interfacial polarization. So the interfacial polarization physically stems from the dielectric loss of dispersed particles. There should be no obvious interfacial polarization if the particulate material does not have an appreciable dielectric loss. 

Figure 5 shows a typical mass loss in a decomposition experiment. The obvious definition would seem to be where the mass loss is steepest, which corresponds to the peak temperature T in the DTG plot. However, this is merely the point where reaction is fastest and does not represent the start of reaction, e.g. where bonds in the compound begin to break. The position of T will depend upon the sample size, packing, and heat flow properties. The point Tjis the initial temperature or onset temperature, but is not easy to identify and depends on the sensitivity of the balance and the amount of drift or noise seen. There may be traces of impurities, which decompose or promote some decomposition ahead of the main reaction. A better definition of start of reaction is the extrapolated onset temperature T. This requires drawing of tangents to the curve at the horizontal baseline and the steepest part of the curve and marking their intersection. For a reaction that starts very slowly and only speeds up later, T and Tj will be very different and a more satisfactory point would be shown as temperature where the fraction reacted a is equal to 0.05, i.e. Tq.05- Another definition of reaction temperature, important in kinetic studies, is when the reaction is half over, that is, when the fraction reacted... 

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