Blends orientation effects

R. Schledjewski and K, Friedrich, Orientation Effects on the Thermal, Mechanical and Tribological Performance of Neat, Reinforced and Blended LCP, in Oriented Polymer Materials (ed. E Sokyo), Hiittig Wepf Verlag, Zug, 1996, Chap. 17. 

Recently, Mg and Be compounds have been used in alloys with ZnSe to make blue and green semiconductor lasers. Bulk growth by zone melting and molecular beam epitaxy (MBE) ° has been used. In these cases, good semiconductor material has been obtained dilution with group IIB compounds may be responsible. However, growth of pure MgS in very thin films on ZnSe has been achieved the epitaxial orientation effect of the substrate results in a tetrahedral cubic (sphalerite or zinc-blende) structure. It is likely that improvements in these materials will take place at a rapid rate, driven in part by applications and in part by newer, cleaner synthetic methods. 

SMA copolymers appear to nucleate crystallisation of PCL from the melt. For blends containing >20 wt % SMA copolymer the high nucleation density prevented the determination of spherulite growth rates and thin films could not be studied by low-angle-laser-light-scattering because of orientation effects [148]. 

While thin polymer films may be very smooth and homogeneous, the chain conformation may be largely distorted due to the influence of the interfaces. Since the size of the polymer molecules is comparable to the film thickness those effects may play a significant role with ultra-thin polymer films. Several recent theoretical treatments are available [136-144,127,128] based on Monte Carlo [137-141,127, 128], molecular dynamics [142], variable density [143], cooperative motion [144], and bond fluctuation [136] model calculations. The distortion of the chain conformation near the interface, the segment orientation distribution, end distribution etc. are calculated as a function of film thickness and distance from the surface. In the limit of two-dimensional systems chains segregate and specific power laws are predicted [136, 137]. In 2D-blends of polymers a particular microdomain morphology may be expected [139]. Experiments on polymers in this area are presently, however, not available on a molecular level. Indications of order on an... 

Epitaxial effects are not limited to single-crystalline substrates. The possibility for substrate-induced epitaxial development in the difficult case of ZnSe (cf. conventional electrodeposition) has been established also by using strongly textured, albeit polycrystalline, zinc blende (111) CdSe electrolytic films to sustain monolithic growth of ZnSe in typical acidic selenite baths [16]. Investigation of the structural relations in this all-electrodeposited ZnSe/CdSe bilayer revealed that more than 30-fold intensification of the (111) ZnSe XRD orientation can be obtained on the textured (111) CdSe films, compared to polycrystalline metal substrates (Fig. 4.2). The inherent problems of deposition from the Se(IV) bath, i.e., formation of... 

In a classic series of articles, Monnerie and coworkers have used IRLD to study the effect of deformation on the orientation of a series of polymers and polymer blends [22,23]. For example, Figure 5 shows the p- and s-polarized... 

However, a PS-fo-PI/PI blend shows direct L G transitions without appearance of the PL phase. The L microdomain is more favourable than the PL phase since the volume fraction of the PI block component and the symmetry of microdomains is increased by the addition of PI homopolymer. Hence, the PL phase may not be formed as an intermediate structure if relatively high molecular weight PI homopolymer is added. The latter is not able to effectively fill the corners of the Wigner-Seitz cells in consequence packing frustration cannot be released and the PL phase is not favoured [152]. In contrast, the addition of low molecular weight PI homopolymer to the minor component of the PL phase reduces the packing frustration imposed on the block copolymers and stabilizes it [153]. Hence, transition from the PL to the G phase indicates an epitaxial relationship between the two structures, while the direct transition between L and G yields a polydomain structure indicative of epitaxial mismatches in domain orientations [152]. 

The use of an electric field is not the only effective way to influence the LC polymer structure, magnetic fields displays a closely similar effect167 168). It is interesting as a method allowing to orient LC polymers, as well as from the viewpoint of determining some parameters, such as the order parameter, values of magnetic susceptibility, rotational viscosity and others. Some relationships established for LC polymer 1 (Table 15), its blends with low-molecular liquid crystals and partially deuterated polyacrylate (polymer 4, Table 15) specially synthesized for NMR studies can be summarized as follows ... 

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