Segregative phase separation interfacial

Keywords Interpenetrating polymer networks Phase separation Interfacial region Segregation Heterogeneous structure... 

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. 

The rubber is segregated as big shapeless patches in a continuous nylon phase (the black domains in the micrograph). When the polymerization conditions are not optimum this can also occur in system 3. "Figure 2D" shows a polymer made according to this system where as a result of premature phase separation the polymer has segregated as big particles (about 3 p) and quite a few active groups have not reacted to form nylon blocks. The interfacial adhesion is very small and the mechanical properties of this polymer are equal to those of a polymer prepared according to system 1. 

Figure 9.17 Schematic illustrations of phase transition in (a) neat PS-b-PFMA and (b) the blended specimen. For neat PS-b-PFMA, homogeneous PFMA/CO2 phase separated to CO2 and PFMA/CO2 domains, resulting in the foaming structure. For the blend specimen, homoPS segregated toward the center of the polyst5trene domain, and a bicontinuous structure was formed by a change in the interfacial curvature.

There are situations where polymer blends may exhibit unique characteristics for utility in composite systems. One of these examples involves the segregation of conductive carbon black at the interface of phase separated polymer blends to yield a much lower concentration to reach the percolation threshold [ 1098,1099 ]. Another area of interest involves the addition of a polymer offering excellent adhesion to the filler as well as mechanical compatibility (or miscibility) with the matrix polymer. The polymeric interfacial agent can offer improved dispersion of this filler in addition to improved stress transfer across the interface between matrix and filler. The preferential concentration of filler particles in one phase is a situation... 

Phase separation can be either initiated by elevated temperature or by solvent extraction. Different reviews and articles have been focused on the phase separation initiated by elevated temperature [9,10] and a detailed description on interfacial phenomena of phase coexistence and/or segregation were... 

The immiscible blends of thermoplastic polymers are assumed to be compatible if the presence of a finely dispersed phase and the resistance to bulk phase separation/segregation result in satisfactory physical and mechanical properties. Compatibility is usually facilitated by copolymers, especially block or graft copolymers, with segments capable of specific interactions at the interface, thus resulting in a decrease of the interfacial tension and promoting mechanical interlocking by the interpenetration and entanglements between the blend components. 

It is seen that the segregation degree and fraction of the interfacial region depend concurrently on many factors, the conversion at the point of the onset of phase separation being the most important. The segregation degree a is determined by ... 

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