Phase separation blends

Conducting Polymer Blends, Composites, and Colloids. Incorporation of conducting polymers into multicomponent systems allows the preparation of materials that are electroactive and also possess specific properties contributed by the other components. Dispersion of a conducting polymer into an insulating matrix can be accompHshed as either a miscible or phase-separated blend, a heterogeneous composite, or a coUoidaHy dispersed latex. When the conductor is present in sufftcientiy high composition, electron transport is possible. 

Porous membranes have been prepared by leaching an additive from films and tubes of PCL (64,72). The procedure involves extrusion or casting blends of PCL and Pluronic F68, the latter being an FDA-approved oxyethylene-co-oxypropylene triblock copolymer. Treatment of the phase-separated blend with aqueous acetone or aqueous alcohols causes both swelling of the polymer and extraction of the Pluronic F68. The induced pore size and void volume may be controlled by the time, temperature, and solvent composition. 

Phase-separated blends consisting of poly(4-phenylene sulfide) and poly(ethylene-co-propylene) or poly(cthylene-co-l-butylene) were prepared by Matsuoka et al. (3) and are discussed. 

Paints, adhesives and lubricants are typically multicomponent polymer systems. The behavior of phase-separated blends in the bulk after quenching into the unstable region of the phase diagram is variable. In the bulk, the concentration fluctuations... 

The animation video clip for the surface of the phase-separated blend samples and another of the inner cavity of the blend sample can analyse the branch structure for all of the inner cavities. The scale width increases as the thermal treatment time increases. The micrometre-scale phase-separated structure of the PS-Br/PMMA blends is shown in Figure 23. It is seen that phase separation advances with the thermal treatment time. The distribution of the branch structure for a bicontinuous structure obtained from 3D NMR images is shown in Figure 23, where the thermal treatment times for the samples are 6 h for A, 8 h for B and 10 h for C at 180 °C. As seen from this figure, the fraction that the bicontinuous structure takes of the three branches, at each junction point, is more than 50%. The average distribution of the branching number at the junction points is almost independent of the thermal treatment time in the present experiments. 

To examine the effect of phase separation on the loss modulus, a sample of a 50/50 chemical blend was phase separated by annealing at 130 C and then evaluated by DMS, Figure 8. Note that the unannealed 50/50 blend shows a broad transition similar to that obtained by DSC and by Hourston and Hughes (24). As compared to the unannealed blend, the annealed PVME/PS blend shows a broader transition. Similarly, the IPN has a still broader transition than the blend. However, the LA s for the three samples are relatively constant, 5%, agreeing also with theory. Table II. Note that overall experimental error is 10%. Also, it was observed that the phase separated blend has a milky white appearance whereas the IPN is slightly hazy. This indicates that the size of the phase separated domains in the IPN are smaller. 

Pulsed force mode scans on the thin film of the phase separated blend of P2VP and PtBMA show pronounced contrast in two imaging modes, i.e., height and adhesion, while the stiffness suffers to some extent from artefacts. In a new mode called combined dynamic X mode SFM, these problems are overcome [30]. 

We can exploit mixtures of per-deuterated and per-hydrogenated polymers in small-angle neutron scattering measurements to reveal information on the configuration of individual chains as well as assemblies of chains in the case of phase separating blends, block copolymers, and other inhomo-... 

For a non-phase-separated blend of P H B/ P LA, the visual image of the elongated polymer appears homogeneous and has a uniform thickness [53]. This observation is also reflected in the images derived from the PHB- and PLA-specific absorption bands. Furthermore, the orientation function of the PHB and PLA absorption bands is, over the whole area, negative and positive, respectively. 

Zumbulyadis et al. [133-135] showed that proton to deuterium CP transfer is also useful to investigate miscibility. For a completely deuterated PMMA (d8-PMMA) homopolymer, a very weak deuterium FID signal, which was created by CP between a small amount of residual protons ( 2%), was detected (Fig. 10.17(a)) [134], For miscible d8-PMMA/PVPh = 18.8/81.2, an appreciable enhancement was observed (Fig. 10.17(c)). However, for the phase-separated blend, the signal enhancement was small as compared to that for the miscible one (Fig. 10.17(b)). They concluded that the signal enhancement in the phase-separated blend comes from interfacial regions (see Section 10.3). 

Fig. 10.17. Time-domain CP/MAS NMR spectra of pure deuterated-PMMA and deuterat-ed-PMMA/PVPh = 18.8/81.2 (a) Only a very weak signal due to CP from residual H is observed for deuterated-PMMA (b) time-domain signal of a partially phase-separated blend cast from tetrahydrofuran and (c) time-domain signal of a homogeneous blend cast from methylethylketone. (Reprinted with permission from Ref. [134]. 1993 American Chemical Society, Washington, DC.)...

Note that we assume fast spin diffusion within each phase in the phase-separated blend (Model D in Fig. 10.18), i.e., each phase is homogeneously mixed from the spin-diffusion point of view. In other words, one Tip or Ti value is associated with one phase. As shown in Section 10.3.1, such heterogeneity of a blend manifests itself as multiexponential relaxation decay curves. For Model D, we expect a double-exponential decay for the respective spins of polymers A and B. For spin-locking Tip experiment, the two double-exponential decay curves are given for the two component polymers as... 

For type 2 phase separation (blends from 12.8 to 19.0 wt% TP), the viscoelastic behavior shows that the (3-phase is continuous because at this moment which is before the gelation of the resin, it is the only phase that can be... 

Highly efficient LED operation is only achieved through efficient exciton EL (Section 2.2), and exciton retrapping has hence to be reduced. In blend LEDs, this could be achieved via large phases and sharp phase interfaces to provide uninterrupted escape paths for the excitons. On the other hand, this morphology potentially promotes large leakage currents, which is detrimental to efficient operation. Bilayer or vertically phase-separated blends could provide a solution to circumvent this trade-off. 

An alternative, and interesting, possibility is to introduce a phase-separating blend as the fluid component (a schematic of this system is shown in Fig. 11). The phase-separating A-B polymer blend will evolve, and phase separate, at its own length- and timescales. However, to minimize the interface between the A and B domains of the polymer blend it may be desirable for the length-scale of phase separation to conform to the wavelength of undulation growth found in... 

Even in the phase separated blends, where some degree of partial miscibility or compatibility exists between the components, simple melt blending in an intensive shear mixer is adequate for making a well dispersed, reasonably stable blend product with useful combination of properties, such as polypropylene/ethylene-propyl-ene rubber blend, ABS/polycarbonate blend, etc. The self-compatibUizing nature of these blends stems from partial miscibility and the mutual interpenetration of polymer chains at the interface. Slight modifications of the polymer backbone are often employed, particularly in the case of styrenic and ABS resins to induce partial miscibility with other resins. 

Because of their highly polar and hydrogen bonded structure of the backbone, as a general rule polyamides are immiscible with most of the commercially known polymer systems. In addition, the high degree of interfacial tension [Wu, 1989] between polyamides and other classes of polymers leads to highly phase separated blends with poor delamination resistance. Hence simple blends of PA with other commercial polymers generally do not have any practical value. 

The binary blends of polycarbonate with polybutylene terephthalate (PBT/PC) or polyethylene terephthalate (PET/PC) are now known to be essentially phase separated blend systems exhibiting two glass transition temperatures in each case, one for the polycarbonate-rich phase, and another for the polyester-rich phase. [Murff et ah, 1984 Huang and Wang, 1986 Wahrmund et ah, 1978]. The evaluation of the amorphous phase miscibility... 

While miscible blends have attracted considerable interest due to the thermodynamic implications and commercial relevance, phase separated blends have had a prominent role in polymer blend technology. While mechanical compatibility is assured in miscible blends, phase separated blends can often achieve property advantages not capable with single phase blends. (Mechanical... 

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