Morphology of immiscible polymer blends

The effect of viscosity ratio on the morphology of immiscible polymer blends has been studied by several researchers. Studies with blends of LCPs and thermoplastics have shown indications that for good fibrillation to be achieved the viscosity of the dispersed LCP phase should be lower than that of the matrix [22,38-44]. 

Since the processing conditions and mixing equipment have a crucial effect on the morphology of immiscible polymer blends [45], experiments were carried out in four different types of extruders to find optimal conditions for blend preparation and fibrillation. Nevertheless, the morphologies of PP-LCP blends produced by... 

B. D. Favis, Factors Influencing the Morphology of Immiscible Polymer Blends in melt Processing, in Polymer Blends, Vol. I, D. R. Paul and C. B. Bucknall, Eds., Wiley-Interscience, New York, 1999. 

Meijer et al. [1988] and Elemans et al. [1988] investigated the potential of electron irradiation to stabilize the morphology of immiscible polymer blends. Their concept was that selective crosslinking of a dispersed phase in a matrix that remains unaffected, or degrades, should help fix the morphology of the blend. 

FIGURE 1.5 Variation of the first normal stress difference versus strain for (O) uncompati-bilized blends of polydimethylsiloxane (PDMS) in polyisoprene (PI) and for ( ) 10% com-patibilized blends of polydimethylsiloxane (PDMS) with polyisoprene (PI). (Adapted from Van Hemelrijck Ellen. Effect of physical compatibilization on the morphology of immiscible polymer blends. PhD thesis, K U Leuven, 2005.)... 

Van Hemelrijck Ellen. Effect of physical compatibilization on the morphology of immiscible polymer blends. PhD thesis, K U Leuven, 2005. 

It is well known that the mechanical properties of polymer blends are determined by their composition, domain size, and domain size distribution. The ability to monitor and control the morphology of immiscible polymer blends is very important. For example, Epstein and Carhart [56] used a Newtonian model for emulsions and derived relationships for the attenuation as a function of blend composition, domain size, R, and frequency,/ A longitudinal wave propagating in the matrix approaching an interface with a domain of the second fluid will give rise to reflected, transmitted shear and thermal waves, while excess attenuation can be determined as a linear function of the composition. A similar approach was also described elsewhere [57]. 

Effect of Flow Geometty on the Steady-State Shear Viscosity and Morphology of Immiscible Polymer Blends... 

Different monomers may be copolymerized to modify the properties of thermoplastics. For the same purpose, homo- and copolymers are frequently mixed with other substances, including other polymers, various fillers, and nanofillers. The presence of comonomers in macromolecules, as well as interactions between macromolecules in miscible blends, can affect both crystallization and morphology of the polymeric material. Interfaces and the confinement of polymer chains within a finite volume influence the solidification and morphology of immiscible polymer blends and polymer-based composites. They are also of special importance in ultra-thin polymer layers where the thickness is comparable to or smaller than the lamellar crystal thickness itself... 

INFLUENCE OF STAGGERING ANGLE OF KNEADING BLOCK ON PHASE MORPHOLOGY OF IMMISCIBLE POLYMER BLENDS IN... 

The properties of immiscible polymers blends are strongly dependent on the morphology of the blend, with optimal mechanical properties only being obtained at a critical particle size for the dispersed phase. As the size of the dispersed phase is directly proportional to the interfacial tension between the components of the blend, there is much interest in interfacial tension modification. Copolymers, either preformed or formed in situ, can localize at the interface and effectively modify the interfacial tension of polymer blends. The incorporation of PDMS phases is desirable as a method to improve properties such as impact resistance, toughness, tensile strength, elongation at break, thermal stability and lubrication. 

Several factors can be identified as being crucial for the foaming of immiscible polymer blends the blend morphology, the phase size of the blend constituents, the interfacial properties between the blend partners, and, last but not least, the properties of the respective blend phases such as the melt-rheological behavior, the glass transition temperature, the gas solubility, as well as the gas diffusion coefficient. Most of these factors also individually influence the melt-rheological behavior of two-phase blends. 

Rusu D (1997) In-situ study of immiscible polymer blends morphology under simple shear PhD thesis Ecole des Mines de Paris, Sophia Antipolis... 

The question might be addressed now to know whether phase morphology and properties of Immiscible polymer blends can be modified by a way different from the previously described emulsification. 

This chapter, related to the crystallization, morphological structure and melting of polymer blends has been divided into two main parts. The first part (section 3.1) deals with the crystallization kinetics, semicrystalline morphology and melting behavior of miscible polymer blends. The crystallization, morphological strucmre and melting properties of immiscible polymer blends are described in the second part of this chapter (section 3.4). 

Before discussing the rheological performance of polymer blends, it is important to recall the basic features of morphology in immiscible polymer blends. 

With the knowledge of the flow behavior of simpler systems, viz. suspensions, emulsions, block copolymers, as well as that of the mumal interactions between the rheology and thermodynamics near the phase separation, one may consider the flow of more complex systems where all these elements may play a role. Evidently, any constitutive equation that may attempt to describe flow of immiscible polymer blends should combine three elements the stress-induced effects on the concentration gradient an orientation function and the stress-strain description of the systems, including the flow-generated morphology. Such a comprehensive description stiU remains to be formulated. 

It should be noted that the Doi and Ohta theory predicts oifly an enhancement of viscosity, the so called emulsion-hke behavior that results in positive deviation from the log-additivity rule, PDB. However, the theory does not have a mechanism that may generate an opposite behavior that may result in a negative deviation from the log-additivity rule, NDB. The latter deviation has been reported for the viscosity vs. concentration dependencies of PET/PA-66 blends [Utracki et ah, 1982]. The NDB deviation was introduced into the viscosity-concentration dependence of immiscible polymer blends in the form of interlayer slip caused by steady-state shearing at large strains that modify the morphology [Utracki, 1991]. 

Because of the high interfacial tension, the morphology of the blends is not stable. Coalescence readily occurs in the molten state. As suggested by Macosko et al. (121), in melt mixing of immiscible polymer blends, the disperse phase is first stretched into threads and then breaks into droplets, which can coalesce together into larger droplets. The balance of these processes determines the final dispersed particle sizes. With increase of disperse phase fraction (usually more than 5 wt%), the coalescence speed increases and the dispersed phase sizes increase (121-123). 

Radioluminescence spectroscopy has been used to examine molecular motion, solubility, and morphology of heterogeneous polymer blends and block copolymers. The molecular processes involved in the origin of luminescence are described for simple blends and for complicated systems with interphases. A relatively miscible blend of polybutadiene (PBD) and poly(butadiene-co-styrene) and an immiscible blend of PBD and EPDM are examined. Selective tagging of one of the polymers with chromophores in combination with a spectral analysis of the light given off at the luminescence maxima gives quantitative information on the solubility of the blend components in each other. Finally, it is possible to substantiate the existence and to measure the volume contribution of an interphase in sty-rene-butadiene-styrene block copolymers. 

Elias, L., Fenouillot, R, Majeste, J. C., and Cassagnau, P. 2007. Morphology and rheology of immiscible polymer blends filled with silica nanoparticles. Polymer 48 6029-6040. 

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