Interfaces in polymer blends

X represents the distance from the interface in the perpendicular direction, while h is the segmental length which is assumed to be the same for both polymers. 

Additionally, the interfacial tension F12 can be estimated as a function of the interaction parameter and segmental length according to Eq. (3.24), where po is the density (assumed equal for both polymers)  

From the above equations it is clear that, with decreasing interaction parameter Xui the density profile becomes flatter and the interfacial thickness increases with the square-root of Xi2- When Xu approaches zero, AI goes to infinit) that is, the interface can no longer be distinguished and a single-phase system is formed. The basic Helfand-Tagami model was then extended by Broseta et al. [44] for the interface of polymers with defined chain lengths  

Comparing Eqs (3.23) and (3.25), it can be shown that the interface becomes broader in systems with low-molecular-weight components [45]. The experimentally estimated interfacial thicknesses [45-48] were found to be in reasonable agreement with the Helfand-Tagami and Broseta predictions. The distribution of the chain segments for systems containing at the interface a block copolymer as a compatibilizer, was derived by Noolandi [49]. Typical values of the interfacial thickness in different polymer blends are summarized in Table 3.1. 

The addition of a block copolymer acting as a compatibilizer represents another possibility of inducing linkages between the bulk phases. In the simplest case, it is assumed that the block copolymer is anchored in both phases, and that its blocks are miscible with the main components of the blend. If the molecular weight of 

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H. R. Brown, Strengthening Polymer-Polymer Interfaces, in Polymer Blends Volume 2 Performance, D. R. Paul and G. B. Bueknall, Eds., Wiley, New York, 2000, Chapter 23. 

Within this context, this chapter discusses the possibilities to produce surface patterns by surface segregation of an additive towards the interface in polymer blends. Surface segregation is the result of the preferential migration of one blend component to the interface thereby inducing selective enrichment at the nearsurface level. As will be discussed below in detail, this effect is directed by the surface thermodynamics that favors the presence at the interface of the component of a mixture lowering the surface tension. As a consequence, this phenomenon is the cause of having large differences between the surface and the bulk composition. 

Most engineered plastics mix with more than two polymers. It is hard to achieve flame retardant formulations because the microstructures of polymer blends are continuously changing during heating, which can result in phase separation. Even though the functionalized clays can be exfoliated and/or intercalated in homopolymers, it is necessary to consider the interfaces in polymer blends. Recently, Si et al. [5] showed that when Cloisite clays... 

Preparing conductive polymer blends with selected localization of CB has attracted considerable research interested with a near continuous stream of publications whose detailed review is outside of the scope of the present book. The thermodynamic and kinetic factors that govern the localization of CB particles at interfaces in polymer blends are rather complex since systems far from equilibrium state are obtained, as recently considered by several authors. ... 

Thus, for the investigation of buried polymer interfaces, several techniques with molecular resolution are also available. Recently NMR spin diffusion experiments [92] have also been applied to the analysis of a transition zone in polymer blends or crystals and even the diffusion and mobility of chains within this layer may be analyzed. There are still several other techniques used, such as radioactive tracer detection, forced Rayleigh scattering or fluorescence quenching, which also yield valuable information on specific aspects of buried interfaces. They all depend very critically on sample preparation and quality, and we will discuss this important aspect in the next section. 

Usually polymeric substances of appropriate chemical structure and morphology which promote the miscibility of incompatible materials. Block copolymers are especially useful surfactants at the polymer/polymer interface because the two blocks can be made up from molecules of the individual polymers to be mixed. Typical compatibilisers in polymer blends are LDPE-g-PS in PE/PS CPE in PE/PVC acrylic- -PE, -PP, -EPDM in polyolefin/PA and maleic-g-PE, -PP, -EPDM, -SEBS in polyolefin/polyesters. 

Electron microscopy, 16 464, 487-495 history of, 16 487-488 in polymer blend morphology determination, 20 339-340 of PVC particles, 25 658-659 of silica, 22 371-372 in surface and interface imaging, 24 75-80... 

Junctions that are formed at the interface of polymer blends and those in materials that reveal nano-scale phase separation. 

H T2 experiments have also been used to see whether they are suitable for analysing interfaces between different phases in polymer blends, such as SBS block copolymers [158] and (methylmethacrylate)-Z -(n-butylacrylatc) block copolymers [159]. 

There are now available a number of theoretical treatments (1-11) dealing with the problem of polymer compatibility and the polymer-polymer interfaces either in polymer blends or in block copolymers. 

Altstadt V (1997) Fatigue crack propagation in homopolymers and blends with high and low interphase strength. In European Conference on Macromolecular Physics -Surfaces and Interfaces in Polymers and Composites, Lausanne, Switzerland... 

M. Muller, K. Binder, and W. Oed (1995) Structural and thermodynamic properties of interfaces between coexisting phases in polymer blends - a monte-carlo simulation. J. Chem. Soc. Faraday Trans. 91, pp. 2369-2379... 

FAYT ETAL. Interface Modification in Polymer Blends... 

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