Interface, interfacial compatibilization

In this paper, Monte Carlo simulation studies will be discussed which provide insight into the underlying factors that affect the ability of a copolymer to strengthen and interface and compatibilize a polymer blend. The interpretation ofthese results will then be correlated to the experimental evidence that currently exists in the literature. It is expected that the results of this work will provide important fundamental information on the underlying physics that govern the interfacial behavior of copolymers. In turn, this information can be utilized to develop processing schemes by which materials can be efficiently created from polymer mixtures with optimized and tunable properties. 

In the PS/EPR blends, Radonjic and co-workers (179) found the S-B-S triblock copolymer with Mn of the PS blocks of 7,000, to be localized at the PS/EPR interface. The compatibilization efficiency of this block copolymer was further confirmed by finer dispersion in the resulting PS/EPR/S-B-S blends, as well as by improved PS/EPR adhesion. This short triblock copolymer appears to be a good compatibilizer also in iPP/aPS blends. According to mit and Radonjic (180), S-B-S forms an interfacial layer between dispersed honeycomb-like PS/S-B-S particles and PP matrix and influences also crystallization in iPP. 

Often, even immiscible and/or incompatible polymers are also made compatible by addition of a compatibilizer. Compatibilizers are believed to primarily reside at the polymer/polymer interfaces. The compatibilizer can be presynthesized or formed by in situ polymerization. Often the product engineer can make a judicious choice of compatibilizer resulting in improvement of mechanical properties, sometimes with synergistic effects. The compatibilizer is believed to stitch itself across the polymer/polymer interfaces. The addition of a compatibilizer lowers the interfacial tension between the two immiscible phases. The compatibilizer may sometimes be made of block copolymer composed of two different components. One of the block components may be miscible with polymer A, and the block component may be miscible with polymer B. Even if a polymer A and polymer B are immiscible, such a block copolymer would compatibilize the blend of A and B. 

Keywords Polymer interfaces Interfacial tension Compatibilizers Interfacial partitioning Emulsifying agents... 

Compatibility and various other properties such as morphology, crystalline behavior, structure, mechanical properties of natural rubber-polyethylene blends were investigated by Qin et al. [39]. Polyethylene-b-polyiso-prene acts as a successful compatibilizer here. Mechanical properties of the blends were improved upon the addition of the block copolymer (Table 12). The copolymer locates at the interface, and, thus, reduces the interfacial tension that is reflected in the mechanical properties. As the amount of graft copolymer increases, tensile strength and elongation at break increase and reach a leveling off. 

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

In a blend of immiscible homopolymers, macrophase separation is favoured on decreasing the temperature in a blend with an upper critical solution temperature (UCST) or on increasing the temperature in a blend with a lower critical solution temperature (LCST). Addition of a block copolymer leads to competition between this macrophase separation and microphase separation of the copolymer. From a practical viewpoint, addition of a block copolymer can be used to suppress phase separation or to compatibilize the homopolymers. Indeed, this is one of the main applications of block copolymers. The compatibilization results from the reduction of interfacial tension that accompanies the segregation of block copolymers to the interface. From a more fundamental viewpoint, the competing effects of macrophase and microphase separation lead to a rich critical phenomenology. In addition to the ordinary critical points of macrophase separation, tricritical points exist where critical lines for the ternary system meet. A Lifshitz point is defined along the line of critical transitions, at the crossover between regimes of macrophase separation and microphase separation. This critical behaviour is discussed in more depth in Chapter 6. 

One of the most important applications of block copolymers is as compatibi-lizers of otherwise immiscible homopolymers. This compatibilization results from the reduction of interfacial tension due to segregation of copolymer to the interface between homopolymers. Experiments and theory concerned with the understanding of the thermodynamics of these ternary blends are discussed in this chapter. 

Polymer brush theory was applied to the compatibilization of homopolymers A and B by an AB diblock by Leibler (1988). The reduction in interfacial tension due to the segregation of copolymers to the interface was calculated. Considering a film of block copolymers at the homopolymer-homopolymer interface, the free energy was found to be... 

SBM) as a compatibilizer. As a result of the particular thermodynamic interaction between the relevant blocks and the blend components, a discontinuous and nanoscale distribution of the elastomer at the interface, the so-called raspberry morphology, is observed (Fig. 15). Similar morphologies have also been observed when using triblock terpolymers with hydrogenated middle blocks (polystyrene-W<9ck-poly(ethylene-C0-butylene)-Wock-poly(methyl methacrylate), SEBM). It is this discontinuous interfacial coverage by the elastomer as compared to a continuous layer which allows one to minimize the loss in modulus and to ensure toughening of the PPE/SAN blend [69],... 

The solubility of carbon dioxide at the selected saturation conditions of 5 MPa and 40°C, is shown in Table 1. Both the uncompatibilized and the compatibilized PPE/SAN blends absorb similarly high amounts of carbon dioxide in the range of 100, mgg-1. However, in contrast to one-phase systems, the solubility data of the overall multiphase blend is not sufficient to describe the system, but the content of carbon dioxide in each blend phases needs to be considered. In the case of PPE/SAN blends compatibilized by the SBM triblock terpolymers, one can distinguish three distinct phases, when neglecting interfacial concentration gradients (idealized case) (1) the PPE phase intimately mixed with the PS block, (2) the SAN phase mixed with the PMMA block, and (3) the PB phase located at the interface between PPE/PS and SAN/PMMA. 

It appears that both compatibilization and the nanostructure formation at the interface play a key role for nucleation. The supposed heterogeneous nucleation activity will therefore be discussed in more detail. Heterogeneous nucleation in general is strongly affected by the particle size and the interfacial properties [79, 80], As the particle size of the PPE phase is well above the critical radius of nucleation of several nanometers [80], the interface demands closer examination. 

The interfacial properties of an amphiphilic block copolymer have also attracted much attention for potential functions as polymer compatibilizers, adhesives, colloid stabilizers, and so on. However, only a few studies have dealt with the monolayers o well - defined amphiphilic block copolymers formed at the air - water interface. Ikada et al. [124] have studied monolayers of poly(vinyl alcohol)- polystyrene graft and block copolymers at the air - water interface. Bringuier et al. [125] have studied a block copolymer of poly (methyl methacrylate) and poly (vinyl-4-pyridinium bromide) in order to demonstrate the charge effect on the surface monolayer- forming properties. Niwa et al. [126] and Yoshikawa et al. [127] have reported that the poly (styrene-co-oxyethylene) diblock copolymer forms a monolayer at the air - water... 

The incorporation of SWCNTs induces a remarkable increase in the storage modulus of the matrix at temperatures below the glass transition, which becomes worthless at higher temperatures. The increase in E is more pronounced for the compatibilized samples, attributed to their improved CNT dispersion and interfacial adhesion between the filler and matrix interfaces. 

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