Blend phase segregation

The two generic terms found in the blend literature are compatibility and miscibility. Components that resist gross phase segregation and/or give desirable blend properties are frequently said to have a degree of compatibility even though in a thermodynamic sense they are not miscible. In the case of immiscible systems, the overall physicomechanical behavior depends critically... 

In this chapter we have discussed the thermodynamic formation of blends and their behavior. Both miscible and immiscible blends can be created to provide a balance of physical properties based on the individual polymers. The appropriate choice of the blend components can create polymeric materials with excellent properties. On the down side, their manufacture can be rather tricky due to rheological and thermodynamic considerations. In addition, they can experience issues with stability after manufacture due to phase segregation and phase growth. Despite these complications, they offer polymer engineers and material scientists a broad array of materials to meet many demanding application needs. 

The only real sources of difference between the additive and comonomer systems would be the potential lack of homogeneity of the polymer blends, which may result either through incomplete blending or segregation by phase separation. Since such nonhomogeneity could lead to irreproducibility in the burning trials, this would be detected by the flammability testing. 

A mixture of a BMI (Compimide 796) with 4,4 -bis(orf/zo-propenylphe-noxy)benzophenone (TM 23) was blended in solution with Udel 700 (polysul-fone from Union Carbide), Ultem 100 (General Electric polyether imide), and PH 10 (Bayer polyhydantoin) (Fig. 35). The thermoplastics were introduced at various concentrations up to 33%. A phase segregation did not appear with PH 10, but two phases were observed with Ultem. With both semi-IPNs the observed Glc were found to be four- to fivefold the Glc of the neat BMI [113]. 

The role of the miscibility of semi-IPN components on the mechanical properties has been discussed. The linear bisnadimide was a benzhydrol bisnadimide (Fig. 33). Three polyimides prepared from the same diamine and three different dianhydrides (Fig. 37) were used as linear components. The blends were cured up to 300 °C in a similar fashion to the bisnadimide alone. The results for the blend containing 20% by weight of linear polymers are summarized in Table 9. The non-miscible character of the components gives a phase segregation leading to the best toughness [121]. 

Furthermore, the friction forces acting in the flow field can induce phase segregation at the mould surface [189]. As pointed out by Cakmak and Cronin [191], in PP/EP blends with a high content of EP particles even shear amplification phenomena may occur due to the presence of the small rubber particles. The shear amplification results from considerable shear fields occurring in small gaps between rubber particles which in turn are subjected to the macroscopic shear field extended over the whole width of the sample. 

Kinetics of Phase Segregation in Thermotropic Liquid-Crystalline Copolyester and Polyether Imide Blends... 

Fig. 3.59 AFM topographic images (top) and cross-sectional profiles (bottom) of PS/PBMA blend (with 20 wt%PS) thin film before and after being washed by cyclohexane (inset Scheme of phase segregation on PS/PBMA blend (with 20 wt % PS) surface). Reprinted with permission from [133]. Copyright 2002. American Chemical Society...

Structural instability due to phase segregation in donor-acceptor blends over time is a function of materials and temperature. At moderate temperatures of 50-80 C, the problem is more severe in MDMO-PPV PCBM than P3HT PCBM blend films. This... 

In another study Arias et al. showed that a vertical phase segregation could be induced in thin films spin cast from F8BT PFB blends by interfacial modification of the PEDOT PSS layer with SAMs [241]. To introduce the SAM, the PEDOT PSS layer was first modified by oxygen plasma treatment leading to... 

At the time of this writing, the most immediate application for the surfaces discussed in this section is to provide models for viscous isotropic phase liquid crystals and certain phase-segregated polymer blends and block copolymers. In this subsection, we show how to calculate diffraction peak intensities from a class of model structures based on these surfaces. The method applies to scattering-density profiles (electron densities for x-ray scattering) determined by ... 

The crystallization in PEO/PMMA blends is influenced by the nature of the casting solvent. Phase segregation in the blend and PEO crystal growth inhibition by PMMA in certain directions have been observed in these miscible blends [Radhakrishnan and Venkatachalapati, 1996]. In PET/PC blend (Makroblend 4T 1018), the chemical and solvent influences are improved, compared to constituent polymers. The chemical resistance of this blend is shown in Table 12.17 [Mark et al., 1988]. 

In order to investigate the cocrystallization and phase segregation behaviors of the above-mentioned PE blend samples, we performed the experiments for both the isothermal and nonisothermal crystallizations. In the nonisothermal crystallization, the temperature is changed gradually and the WAXD, SAXS, or infrared spectra are collected as a function of temperature. In the isothermal crystallization, the... 

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