Relaxation measurements, polymer blends

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described eadier, it can be operated as a forced-vibration instmment. It is fully computerized and automatically determines G, and tan 5 as a function of temperature at low frequencies (10 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstmctures of polymer blends (285) and latex films (286). 

A more complex but faster and more sensitive approach is polarization modulation (PM) IRLD. For such experiments, a photoelastic modulator is used to modulate the polarization state of the incident radiation at about 100 kHz. The detected signal is the sum of the low-frequency intensity modulation with a high-frequency modulation that depends on the orientation of the sample. After appropriate signal filtering, demodulation, and calibration [41], a dichroic difference spectrum can be directly obtained in a single scan. This improves the time resolution to 400 ms, prevents artifacts due to relaxation between measurements, and improves sensitivity for weakly oriented samples. However, structural information can be lost since individual polarized spectra are not recorded. Pezolet and coworkers have used this approach to study the deformation and relaxation in various homopolymers, copolymers, and polymer blends [15,42,43]. For instance, Figure 7 shows the relaxation curves determined in situ for miscible blends of PS and PVME [42]. The (P2) values were determined... 

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... 

Carbon-13 rotating-frame relaxation rate measurements are used to elucidate the mechanism of gas transport in glassy polymers. The nmr relaxation measurements show that antiplasticization-plasticization of a glassy polymer by a low molecular weight additive effects the cooperative main-chain motions of the polymer. The correlation of the diffusion coefficients of gases with the main-chain motions in the polymer-additive blends shows that the diffusion of gases in polymers is controlled by the cooperative motions, thus providing experimental verification of the molecular theory of diffusion. Carbon-13 nmr relaxation... 

In this section 10.2, we review the various solid-state NMR methods used to investigate interpolymer interactions, molecular motion and the spatial structure of a polymer blend. An interaction between component polymers affects the chemical shifts and lineshapes (see Section 10.2.2.1) and the molecular motions of the component polymers (see Section 10.2.2.2). In Section 10.2.3.1, microheterogeneity from 2 to 50 nm is studied by measuring spin diffusion indirectly from its effects on H spin-lattice relaxation. The spin-diffusion processes can also be monitored by several methods based on the Goldman-Shen experiment [8] (see Section 10.2.3.2). Homonuclear and heteronuclear two-dimensional correlation experiments reveal how and to what extent component polymers interact with each other (see Section... 

The spinning drop tensiometer method is particularly suitable for measuring the interfacial tension of melted polymers and is generally used in polymer compatibility, blend and composites research. In this case, a spinning polymer drop (smaller density) is rotated inside another immiscible polymer (higher density). Measurement of drop diameter versus time allows the determination of relaxational and extensional properties of polymeric systems. 

The linear viscoelastic properties in the melt state of highly grafted polymers on spherical silica nanoparticles are probed using linear dynamic oscillatory measurements and linear stress relaxation measurements. While the pure silica tethered polymer nanocomposite exhibits solid-like response, the addition of a matched molecular weight free matrix homopolymer chains to this hybrid material, initially lowers the modulus and later changes the viscoelastic response to that of a liquid. These results are consistent with the breakdown of the ordered mesoscale structure, characteristic of the pure hybrid and the high hybrid concentration blends, by the addition of homopolymers with matched molecular weights. 

The possibilities arising from the advent of MTDSC will now be discussed Complex thermal histories affect the ease with which it is possible to make determinations of the increment of heat capacity, ACp, at Tg because of structure relaxation. If a thermal analysis apparatus that can separate the structure relaxation part from the total heat flow signal can be developed ACp could be determined accurately. It is well known that ACp is related to the weight fraction of each component in a heterogeneous system such as a polymer blend. In multi-phase polymeric materials, each phase has its own characteristic glass transition temperature and ACp. Thus, important information may be obtained from ACp and glass transition measurements, allowing such materials to be analysed quantitatively. 

Enthalpy relaxation studies have also been used to assess the aging of polyether ether ketone blends with polyetherimide, PEEK/PEI = 50/50 (Hay 1992). The preparation of the blend produced an amorphous system with Tg 215 °C, but crystallization of the PEEK occurred after raising the temperature above Tg. Data could only be collected in the temperature range Tg to Tg — 50) and no aging could be detected at temperatures below 150 °C (Table 13.7). The enthalpic relaxation data were analyzed using the C-E model and fits )delded values of p = 0.4, intermediate between those of the pure polymers. It was noted that values of p were higher than those obtained from dielectric relaxation measurements (0.1-0.22). This technique probes the dipole relaxation spectmm, and the lower... 

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