Composite Droplet Phase Morphology

Fig. 3.71 Correlation between the fraction of POM droplets in POM/HaV blends with a composite-like phase morphology and the intensity of the homogeneous crystallization peak (Everaert et al. 2000)...

Figure 9-1 Schematic phase diagram of a binary fluid mixture of small molecules. The two-phase region lies under the binodal line, the apex of which defines the critical temperature Tc and critical composition Between the binodal and the spinodal lines, phase separation is by nucleation and growth (NG), while under the spinodal line it is by spinodal decomposition (SD). Within the region of spinodal decomposition, near the compositional symmetry line, there is a region where the morphology is initially bicontinu-ous. Outside of this region, one of the phases is a discontinuous droplet phase. Eventually,...

It is clear that this phenomenon is phase morphology-dependent. Only in those blends where the minor phase is dispersed into sufficiently fine droplets, this phase has the opportunity to exhibit fractirMiated crystallization. Hence, only at low blend compositions and/or good matching viscosities of both phases (where the capillary number C predicts droplet breakup being dominant above coalescence) the occurrence of coincident crystallization is possible. 

Scanning electron microscopy (SEM) is one of the very useful microscopic methods for the morphological and structural analysis of materials. Larena et al. classified nanopolymers into three groups (1) self-assembled nanostructures (lamellar, lamellar-within-spherical, lamellar-within-cylinder, lamellar-within-lamellar, cylinder within-lamellar, spherical-within-lamellar, and colloidal particles with block copolymers), (2) non-self-assembled nanostructures (dendrimers, hyperbranched polymers, polymer brushes, nanofibers, nanotubes, nanoparticles, nanospheres, nanocapsules, porous materials, and nano-objects), and (3) number of nanoscale dimensions [uD 1 nD (thin films), 2 nD (nanofibers, nanotubes, nanostructures on polymeric surfaces), and 3 nD (nanospheres, nanocapsules, dendrimers, hyperbranched polymers, self-assembled structures, porous materials, nano-objects)] [153]. Most of the polymer blends are immiscible, thermodynamically incompatible, and exhibit multiphase structures depending on the composition and viscosity ratio. They have two types of phase morphology sea-island structure (one phase are dispersed in the matrix in the form of isolated droplets, rods, or platelets) and co-continuous structure (usually formed in dual blends). 

Performance of immiscible blends depends on the composition, interphase and morphology. At equilibrium, for < ) < < > s 0.16 droplets are expected, while at higher concentrations fibers and lamellae are found [4]. Further increase of concentration leads to phase inversion at = 4>ii ... 

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). 

An illustration of a composite (encapsulated droplet-in-matrix) phase morphology in melt-blended ternary blend 70 wt% polyamide/15 wt% polystyrene/15 wt% polypropylene. The droplet is polypropylene, the encapsulating phase is polystyrene, and the matrix is polyamide. (From G. Lei, Development of Three Phase Morphologies in Reactively Compatihilized Polyamide 6/Polypropylene/Polystyrene Ternary Blends, master s thesis, Katholieke Universiteit Leuven, Belgium, 2004.)... 

SEM photomicrographs of blend 1 having HDPE as a matrix in which are dispersed the two minor phases (low-Mw polystyrene/low-Mw PMMA) at 2 min (A) and 15 min (B) of mixing time. PS is extracted by cyclohexane. A stable composite droplet morphology is obtained within 2 min of mixing. The white scale bar denotes 1 pm. (From J. Reignier, B. D. Favis, and M.-Cl. Heuzey, Polymer 44,49-59,2003. With permission.)... 

A droplet-in-matrix phase morphology developed in immiscible polymer blends depends on the viscoelastic properties and composition of the two components of the blend in the melt state. The rheological formalism used for the non-Newtonian phases as polymer melts follows, with adjustment of the... 

Contrary to the droplet-in-matrix, the mechanism and the control of the co-continuous phase morphology, where the two phases are continuous and interconnected throughout the whole volume of the blend, is still not well elucidated. The complexity arises mainly from the ambiguous effect of the viscoelastic characteristics of the components, their composition in the blends, and the magnitude of their interfacial tension. Several empirical expressions have been proposed so far to predict either the phase inversion or the conditions for which co-continuous morphology is generated. 

The formation of droplet-in-droplet morphology (or composite droplet morphology) has also been reported for immiscible systems (Fig. 10.14). For binary blends this type of morphology can be spontaneously generated when blending is carried out near the phase inversion region of the two polymer components. The formation of the inclusions is mainly controlled by the value of the interfacial tension. 

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