Morphology and Phase separation

Morphology and Phase Separation Studies in PER/PBNCO and PER/HTPB Biends... 

Silicon dioxide (Si02), also known as silica nanoparticles are widely used as nanofillers in different polymeric systems. The particular interest in SiOa is due to commercial availability of several types with different surface area and porosity, their thermal stability and the transparency of obtained nanocomposites [1], including polycarbonate and poly(methyl metacrylate) modified with nano-Si02 to mention just a few [2,3]. Another important aspect is arising from improved rheological and mechanical properties as well as control of the morphology and phase separation [4]. 

Mechanical properties of mbber-modifted epoxy resins depend on the extent of mbber-phase separation and on the morphological features of the mbber phase. Dissolved mbber causes plastic deformation and necking at low strains, but does not result in impact toughening. The presence of mbber particles is a necessary but not sufficient condition for achieving impact resistance. Optimum properties are obtained with materials comprising both dissolved and phase-separated mbber (305). 

Figure 13 shows the TEM micrograph of a star block containing 22% PpClSt. The morphology shows phase-separated domains of PpClSt and PIB. The PpClSt formed spherical domains with diffused interphase and are irregularly dispersed in the PIB matrix. The formation of irregular domains with diffused interphase is attributed to the presence of diblock and PpClSt contaminants. 

The initial mixture is homogeneous, and phase separation takes place during the cure of the thermoset. This second technique is called reaction-induced phase separation (Williams et al., 1997) and may lead to several types of morphologies a dispersion of modifier-rich particles in a thermoset matrix a dispersion of thermoset-rich particles in a modifier matrix (phase-inverted morphology), or two bicontinuous phases. 

Although such polymer/LC composite films are usually prepared by emulsification and phase separation techniques, the resulting composites have a variety of morphological characteristics arising from differences in conditions and compositions during sample preparation. The polymer/LC composite films are mainly classified into four types ... 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

Blend solutions. Solutions of blends comprising immiscible polymers Pj and P2 in a nonselective solvent have miscibility gaps as shown schematically in Fig. 14. When the polymer concentration increases by solvent evaporation the polymer coils start to interpenetrate above a certain concentration. As a consequence, interactions between the polymers become operative and phase separation must start above a critical polymer concentration p. The composition of the new phases will be situated on the branches of the coexistence curve. Finally, the unmixing process is arrested owing to enhanced viscosity. This simple scheme reveals the factors directing morphology evolution in blend solutions ... 

It was found that the nanocapsules are formed in a miniemulsion process by a variety of monomers in the presence of larger amounts of a hydrophobic oil. Hydrophobic oil and monomer form a common miniemulsion before polymerization, whereas the polymer is immiscible with the oil and phase-separates throughout polymerization to form particles with a morphology consisting of a hollow polymer structure surrounding the oil. The differences in the hydro-philicity of the oil and the polymer turned out to be the driving force for the formation of nano capsules. 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

The final morphology of a network system depends greatly on the flow properties and phase separation of the reactive components as seen in Fig. 5)16-18,29] Naturally, design of appropriate processes requires the ability to directly investigate the progress of reaction. This includes monitoring the chemistry of cure with spectroscopic techniques such as FTIR, NMR,... 

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