Tan 8 peak

Glass transition temperature (Tg) for pure NR is —63.43°C, while for the nanocomposite it increases to —61.92°C. NR-rectorite nanocomposite shows a higher glass transition temperature, lower tan 8 peak, and slightly broader glass transition region compared to pure NR. 

The tan 8 peak of a dmta thermogram provides a second measure of... 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

Fig. 13 Dielectric tan 8 peaks in PET associated with the p relaxation process observed at 10kHz ( ), 1 kHz ( ), 100Hz ( ), 10Hz (O) and 1 Hz (A) (from [13])...

From the behaviour of the BXT copolymers, the authors concluded that j3 blocks of seven to nine units are required for a BPA-PC-like j3 transition. Such a conclusion can be questioned since the tan 8 curves for B3T and B5T copolymers show a clear shoulder in the - 100 °C region, suggesting that in these copolymers the motions involved in the ft transition of BPA-PC can occur within the B blocks. The larger tan 8 peak around - 25 to 0 °C reflects the motions encountered in the alternate BT copolymer. However, it is worth noting that a deeper analysis of the whole set of results would require consideration of the dynamic mechanical loss compliance, /", as done in Sects. 6, 7 and 8. 

As regards the BT series (Fig. 31), a shift of the tan 8 peak maximum from 0 to 25 °C is observed between BTi and BT3, but it does not change further when increasing the T y block. 

Figure 5. Location of tan 8 peak as a function of composition for BR-IR homopolymers and diblocks Rheovibron,...

In addition, it was found that the area integration under the tan 8 curve (Figure 9.10) for microcellular specimens was less than that of their solid counterparts, indicating less damping in the microcellular components. For solid samples, the area under the Tan-8 peak decreased slightly with the addition of MWCNTs, as shown in the Figure 9.10. Also, the addition of MWCNTs had shifted the peak... 

Fig. 10. The quantities and tan 8 peak when the natural frequency of chain motion equals the external vibrational frequency. At the peak, the relaxation time, Tj, approximately equals the time of the experiment (or the inverse of the frequency).

Figure 5-4 gives the temperature dependence of E and tan 8 for polyvinyl chloride at various frequencies. The shift of the tan 8 peak maximum to higher temperatures with increasing frequency occurs in accordance with the WLF equation and is again an illustration of the rate dependence of the glass transition phenomenon. 

Table 3.4 Effect of thermal spiking and moisture conditioning at 96% RH and 50°C on the primary (T.i) and secondary (t 2) tan 8 peaks for advanced epoxy resin systems [22]... 

Energies required for main-chain and side-group motions can be obtained by determining the effect of frequency on the maximum temperatures of the loss or tan 8 peaks. The temperature at the peak maxima, Tmax, increases with increasing frequency and the activation energy, of the relaxational process may be determined from the slope of a semilog plot of frequency (/) versus reciprocal peak-temperature (l/Tmax) as... 

Figure 6.18 shows the temperature dependence of tan 5 of neat NR and NR composites. The position of the tan 8 peak in the tan 5-temperature curve can... 

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