Domain-matrix interface

In contrast, Li and Shimizu [103] ascribed the toughening behavior of the PLA-based blends to debonding at the rubber/matrix interface during deformation, which released the hydrostatic stress and facilitated the occurrence of shear yielding. When the hydrostatic stress is released within a PLA/polyurethane elastomer (PU) blend, debonding is easily induced at the interface between the (PU) domains and PLA matrix. This results in voids around the rubber, which allows shear yielding and improved the toughness of the materials, as shown by... 

A key factor in the NIA theory is the constant value of the interfadal layer thickness at the domain-matrix boundary. There has been mudt discusaon on the existence and magnitude of an interfadal region where partial mixing of the two components takes place. Its existence has been established by positron annihalation studies whilst its magnitude is still a source of interest. Williams has proposed that this interface is unsymmetric and of considerable extent, in terms of volume fraction, whilst Krause concludes that the interphase volume fraction is very small. Mechanical and dynamical mechanical properties have been discussed , in greater or lesser detail, in terms of the interphase volume fraction and Williams has successfully... 

The microstructure of the homopolymers should be examined for comparison with the multiphase polymer. Scanning electron microscopy of an Izod fracture surface of a POM/PP copolymer is shown in Fig. 5.78. The two phases are incompatible (i.e., they are present as two distinct phases). The dispersed phase particles range from less than 0.5 to 2 /im in diameter. The sample fracture path follows the particle matrix interface and holes remain where particles have pulled out of the matrix, showing there is little adhesion between the phases. The shape of dispersed phase particles is determined by the flow field and heat gradients that affect polymer orientation. For instance, the microstructure of copolymers of PE and PP is similar to the skin-core textures described for PE [362]. The orientation of the dispersed phase can affect the mechanical properties of the system. Spherical domains are more commonly formed in systems where phase separation occurs while the polymers are liquid. The SEM image appears to reveal spherical... 

Morphology of the anionically synthesized triblock copolymers of polyfp-methyl-styrene) and PDMS and their derivatives obtained by the selective chlorination of the hard segments were investigated by TEM 146). Samples with low PDMS content (12%) showed spherical domains of PDMS in a poly(p-methylstyrene) matrix. Samples with nearly equimolar composition showed a continuous lamellar morphology. In both cases the domain structure was very fine, indicating sharp interfaces. Domain sizes were estimated to be of the order of 50-300 A. 

One of the key issues of mechanical behavior of multicomponent materials such as TPV is the stmcture and properties of the interface regions. The phase image in Figure 20.1 Id shows a part of TPV sample with few mbber domains surrounded by iPP matrix. An extended rectangle area outlined with a white dotted box includes several interfaces between mbber domains and the plastic matrix. Examination of the interfaces is a challenging task and one possible approach is AFM-based... 

FIGURE 20.12 (a) Top part shows variations of elastic modulus profile measured in different locations of the polypropylene (PP)-ethylene-propylene-diene terpolymer (EPDM) blend. The locations are shown by white dots in the blend phase image placed at the bottom. Vertical white dashed lines show the components borders and the elastic modulus value for this location. Vertical black dotted lines indicate the locations where elastic modulus E gradually changes between PP (E ) and EPDM (E )- These values are indicated with black arrows on the E axis, (b) LvP curves for PP-matrix, EPDM-domains, and one of interface locations. The approach curves are seen as solid black lines and the retract curves as gray lines. 

Interfacial behavior of different silicones was extensively studied, as indicated in Section 3.12.4.6. To add a few more examples, solution behavior of water-soluble polysiloxanes carrying different pendant hydrophilic groups, thus differing in hydrophobicity, was reported.584 A study of the aggregation phenomena of POSS in the presence of amphiphilic PDMS at the air/water interface was conducted in an attempt to elucidate nanofiller-aggregation mechanisms.585 An interesting phenomenon of the spontaneous formation of stable microtopographical surface domains, composed primarily of PDMS surrounded by polyurethane matrix, was observed in the synthesis of a cross-linked PDMS-polyurethane films.586... 

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