PANI-PMMA blend, temperature dependence

The earlier theimopower data for PAni/PVC blends [80] are similar to that for the blends in Figure 11.56, except for negative values at very low temperatures. In the only other data on PAni blends, the theimopower of PAni-CSA/PMMA blends measured by Yoon el al [102] is very close to that of the PAni/PMMA blends investigated here, in magnitude as well as temperature dependence (except for small negative values seen at very low temperatures). These data further emphasise the similarity of PAni blend thermopowers. The theimopower of the pure PAni does appear to be significantly smaller than that of the blends small thermopowers (of either sign) have been seen for some PAni samples by other authors [93,94,95]. 

All samples show a nearly temperature-independent magnetic susceptibility down to 50 K. Below 50 K, a temperature-dependent Curie-like susceptibility is observed. Figure 1.16 shows the y vs. 1/T plots for unblended PAni and PAni-PMMA blends. The temperature-independent Pauli susceptibility is calculated from the above plot, and the density of the states at the Fermi energy is calculated. 

Figure 23.24 Temperature dependence of peak-to-peak EPR linewidth for unblended PANI (open circles) and PANI-PMMA blend (solid circles), Upper panel, unannealed...

The conductivity of the unblended polyaniline (PAni), PAni-poly(methyimethacrylate) (PMMA) blends and the PAni extracted from blend was measured from room temperature down to millikelvin temperatures at various fields. For PAni (33%)-PMMA (67%), PAni (40%)-PMMA (60%) blends, the reduced activation energy, W = dln(cr)/dln( T), decreases on decreasing the temperature below 1 K and the systems are found to be on the metallic side of the MI transition [25a]. In the case of PAni extracted from the blend, the slope change of Woccurs at 70 K. For unblended PAni, W increases as temperature decreases (Figure 1.43). The temperature dependence of the conductivity is given by... 

The temperature dependence of the resistivity for PAN I-CSA/PMMA blends is shown in Fig. 2.56 for 0.(K)2 < f 1 [175]. As a metallic system near the boundary of the metal-insulator transition, p(T) in PANI-CSA is characterized by a positive temperature coefficient [34,35]. Although the positive temperature coefficient is restricted to higher temperatures upon dilution of PAN 1-CSA in PMMA, it is remarkable that this distinctly metallic feature is observed even in samples containing volume fractions of PANI-CSA as low as 0.3%, indicating that even at such dilution the PANI-CSA within the phase-separated network is comparable in quality to that of pure PANI-CSA. 

Again, the subtle variations in the temperature dependence can be most clearly observed from W vs. T plots, as shown in Fig. 2.57. The temperature dependence of the resistivity of PANI-CSA/PMMA blends can be classified into three categories ... 

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