Blends dielectric relaxation

The first data on polymer systems were collected via (laser-) light-scattering techniques [1] and turbidity measurements, further developed by Derham et al. [2,3]. Techniques based on the glass-transition of the polymer-blend constituents were also tested, such as DSC, Dynamic Mechanical Spectroscopy, and Dielectric relaxation [4]. Films made from solutions of... 

Fig. 24 Similarity between the dielectric relaxation peak in PET ( ) and the mechanical peak in a polymer/additive blend containing 10% DMT additive ( ) at 1 Hz (from [13])...

The investigation of pure PET and PET/additive blends by combining dynamic mechanical analysis, dielectric relaxation and solid-state NMR techniques, leads to a clear attribution of the molecular processes involved in the ft relaxation of PET, as well as an understanding of the effect of an antiplasticiser additive ... 

Various experimental techniques (dielectric relaxation, dynamic mechanical analysis, 1H, 2H and 13C solid-state NMR) have been used for investigating the secondary transitions of BPA-PC, and the block copolymers of BPA and TMBPA carbonates as well as compatible blends of BPA-PC and TMBPA-PC. They have provided lots of information on the motions of methyl, phenyl ring and carbonate units in bulk BPA-PC. The effect of intermolecular packing has also been clearly evidenced. 

Later reports [49-51] provided further insight into the blend morphology for several of the cellulose/synthetic polymer blend systems fisted in Table 1. In particular, refining efforts were devoted to precise quantification of the scale of homogeneity in the blends. A dielectric relaxation... 

Dielectric relaxation measurement in similar to dynamic mechanical measurements, except that it exploits the dipole electrical properties of the blend. It is, therefore. 

When the blends were examined using dielectric relaxation measurements which probe the dipole relaxation spectrum, values of P were found to be much lower (0.1-0.22). This was interpreted as indicating the development of heterogeneity at the molecular level caused probably by the crystalhzation of the PEEK component. 

To reduce the cost, these elastomers have been diluted with some PBT homopolymer. Because of the chemical similarity between the hard segment of the copoly(ether-ester) elastomers and the PBT, they form fairly compatible blends. When the hard segment content in the copoly(ether-ester) is > 80 wt%, it was found to be completely miscible with PBT, showing a single T, amorphous phase and co-crystallization of the PBT segments of the elastomer with PBT homopolymer. As the hard segment content was lowered to < 60%, the blend exhibited incomplete miscibility, with two Tg s for two amorphous phases and also two separate crystalline phases. [Runt et al., 1989]. Nevertheless, a partial miscibility was indicated due to changes in the T observed in DSC and dielectric relaxation spectra. The partial miscibility and low interfacial tension between the phases makes the blend very compatible. 

The best proof of invalidity of the confinement scenario is provided by the DSC and dielectric relaxation data from Arrese-Igor et al. (2010) on the highly asymmetric blends of polyisoprene (PI) of molecular weight Af = 2700 with poly(tert-butylstyrene) (PtBS) of two different molecular weights M = 1300 and Mn = 2300. Their DSC measurements confirm the presence of two separate glass transition temperatures of the PI and the PtBS components for blends with less than 50% of PI. The components Tgf and Tgs of PI and PtBS in 35% and 20% PI blends from DSC are indicated by arrows in Figures 5.28 and 5.29, where the dielectric relaxation times data are presented in an Arrhenius plot. Like that discussed before in the PEO/PMMA blends, the detection of Tgf of the fast component by DSC, PI in the present case has basically ruled out the confinement scenario. This is because the relaxation time of order of 100 s obtained by DSC has to be that of the a-relaxation of the PI component. 

Thus, from both the DSC and the dielectric relaxation data cited earlier, the crossover of r y of PI in the HAPB of 35% and 20% PI with PtBS from VFT to Arrhenius dependences is not found at any temperature. This is the most direct proof that the confinement scenario is unreal. Arrese-lgor et al. (2010) admitted that the crossover predicted by the confinement scenario is not observed on Xaf of PI in the HAPB, but still maintained a vestige of confined dynamics by invoking the marked decrease of the intensity and increase of width as temperature decreases of the a-loss peak of PI in the 20% PI blend. 

Both cis-polyisoprene (PI) and poly(vinyl ethylene) (PVE) have the type-B dipoles perpendicular to the chain backbone, and PI also has the type-A dipoles parallel along the backbone (cf. Figure 3.2). The dielectric relaxation detects the fluctuation of these dipoles, as explained in Section 3.2.2. The fluctuation of the type-B dipoles is activated by the fast, local motion of the monomeric segments, which enables the dielectric investigation of this motion. In contrast, the slow dielectric relaxation of PI due to the type-A dipoles exclusively detects the fluctuation of the end-to-end-vector R (see Equation 3.23). These dielectric features of PI and PVE are clearly noted in Figure 3.11, where the e" data are shown for a PI/PVE blend with the component molecular weights Mp, = 1.2 x 1(P and Mpyp = 6 x 1(P and the PI content rvpi = 75 wt% (Hirose et al., 2003). The data measured at different temperatures are converted to the master curve after the time-temperature superposition with the reference temperature of T, = -20°C, as explained later in more detail. The three distinct dispersions seen at high, middle, and low... 

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