Cocontinuous Phase Morphology

A large number of homopolymer pairs exhibif partial miscibility when mixed together either in a melt-blending process or via precipitation from a single solution. Usually, the partial miscibility is revealed only upon thermal treatment to which is subjected the molecularly 

When the curve delimiting the homogeneous and the heterogeneous zones is convex, the mixture is identified as exhibiting lower critical solution temperature (LCST) behavior. If a miscible A/B blend having a composition slightly different from the diluted extreme cases is heated above any temperature, the LCST curve demixes into two distinct phases, A and B. 

In a mixed system (i.e., a 20/10 reactive/nonreactive polymer) the dimension can be reduced from 0.7 pm to 0.1 pm. 

2 Cocontinuous Morphologies in Melt-Mixed Polymer Blends 

Processing conditions or chemical reactions occurring in one or both phases of the blend can strongly affect the phase inversion. Of course, these two parameters have a direct effect on the viscosity ratio of the components. The same blend of polyamide/styrene-acrylonitrile copolymer developed phase morphology where PA6 is the matrix when processed using a single-screw extruder, whereas the inverse situahon occurred when the blend was mixed several times in a laboratory mixer. 

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Harrats C, Blacher S, Fayt R, Jerome R, Teyssie Ph. Molecular design of multicomponent polymer systems. XIX. Stability and cocontinuous phase morphologies in low density polyethylene/polystyrene blends emulsified by block copolymers. J Polymer Sci Part B Polym Phys 1995 33 801-811. 

There exist in polymer blends two or three major types of phase morphologies, depending on whether the encapsulated structures (composite droplets) are considered as a class apart. The most common is the droplet-in-matrix (as, for example, Figure 1.3), the (droplet-in-droplet)-in-matrix (as, for example. Figure 1.4), and the cocontinuous phase morphology where both phases are mutually interconnected throughout the whole volume of the blend (as, for example. Figures 1.5 and 1.6). 

Typical "thick" cocontinuous phase morphology in melt-blended binary blend. A scanning electron microscopy photomicrograph of a cryosmoothed and chloroform-etched 60 wt% polystyrene/40 wt% polypropylene melt-mixed blend. The etched phase is polystyrene. (From G. Lei, DeveUrpment of Three Phase Morphologies in Reactively Compatihilized Polyamide 6/Polypropylene/Polystyrene Ternary Blends, master s thesis, Katholieke Universiteit Leuven, Belgium, 2004.)... 

Cocontinuous phase morphology is developed in melt-mixed blends under a particular set of processing conditions, component characteristics, and blend compositions. As described above, melt-blended immiscible homopolymers A and B can exhibit a cocontinuous two-phase morphology at a specific condition involving mainly the following ... 

Many of the microscopic illustrations presented in this book deal with cocontinuous phase morphologies in melt-mixed blends. 

At the recent European Symposium on Polymer Blends [59] about half of the contributions dealt with thermodynamic effects on molecular architecture, on polymer morphology, and on processing and performance of polymer blend materials. Although some attention has been focused mainly on the interface (material) in heterogeneous blends, in general most thermodynamic studies of such heterogeneous blends deal with two- or more bulk phases. Essential morphological features such as droplet size, cocontinuous phases, micellar or... 

The detailed morphology of elastomer blends depends on (1) the mixing procedure, (2) the rheology of the blend components, and (3) the interfacial energy. As with other polymer blends, the elastomer of lower viscosity tends to be the continuous phase [26a-b]. Cocontinuous blend morphology is observed only for elastomers with similar viscosities. The viscoelastic forces developed during the formation of the compounded blend from two rheologi-... 

In a binary blend A/B, the phase morphology can be of an A-droplet-in-B-matrix when A is minor, a B-droplet-in-A-matrix when B is minor, and a third particular situation in between where the two phases A and B are cocontinuous. 

Illustrations of Phase Morphology Other Than Cocontinuous in Polymer Blends Including Thermoplastics/Thermoplastics, Thermosets/Thermoplastics... 

Percentage of cocontinuity as a function of PP content in the uncompatibiHzed PP/PCHMA blends showing the various composition windows where the phase morphology is dispersed, partially cocontinuous, or fully cocontinuous. (From C. Harrats, T. S. Omonov, G. Groeninckx, and P. Moldenaers, Polymer 45, 8115-8126, 2004. With permission.)... 

Provides microscopic photomicrographs of blend systems where the phase morphology is of the cocontinuous type... 

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