Phase morphologies

The rate G has a maximum between the glass transition (Tg) and the equilibrium melting temperature (T°), whereas the diffusion rate increases continuously with temperature. In regime I (Fd G), generally observed at low crystallization temperatures, the noncrystalUzing component, which separates upon crystallization, remains 

Examples of crystallizable systems with full melt miscibility over the whole composition range have been pointedoutforpoly(ethyleneterephthalate)/poly(butylene terephthalate) (PET/PBT), poly (hydroxy butyrate)/ poly (ethylene oxide) (PHB/PEO), and polycarbonate/ poly(e-caprolactone) (PC/PCL) blends [29]. 

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Nevertheless, possibiUties for confusion abound. From the definitions of microemulsions and macroemulsions and from Figure 1, it immediately follows that in many macroemulsions one of the two or three phases is a microemulsion. Until recentiy (49), it was thought that all nonmultiple emulsions were either oil-in-water (O/W) or water-in-oil (W/O). However, the phase diagram of Figure 1 makes clear that there are six nonmultiple, two-phase morphologies, of which four contain a microemulsion phase. These six two-phase morphologies are oleic-in-aqueous (OL/AQ, or O/W) and aqueous-in-oleic (AQ/OL, or W/O), but also, oleic-in-microemulsion (OL/MI), microemulsion-in-oleic (MI/OL), aqueous-in-microemulsion (AQ/MI), and microemulsion-in-aqueous (MI/AQ) (49). 

Fig. 8. Emulsion morphology diagram, illustrating where the microemulsion in various macroemulsion morphologies is a continuous phase or dispersed phase. Morphology boundaries (—), aqueous, continuous (--------------), oleic, continuous (--), microemulsion, continuous.

Unlike incompatible heterogeneous blends of elastomer-elastomer, elastomer-plastic, and plastic-plastic, the reactively processed heterogeneous blends are expected to develop a variable extent of chemical interaction. For this reason the material properties, interfacial properties, and phase morphology of reactively processed blends would differ significantly from heterogeneous mixtures. 

The SEM investigation shows that the particle size of the dispersed domain size decreased from 3.3 to 1.1 fxm with the incorporation of 6 wt%, EMA, and this indicates the increased surface area of the dispersed phase morphology. The increase in surface area led to effective compatibilization and is responsible for the increased adhesion strength and tensile impact strength of compatibilized blends. 

M. Liu, T.R. Finlayson, and T.F. Smith, Thermal expansion of VaSi with controlled martensite-phase morphology, Phys. Rev. 852 530 (1995). 

The two-phase morphologic structure has also been observed in the electron micrographs of polyethylene films and fibers obtained by orientational crystallization16 in which the amount of ECC was approximately 15 to 20% (the fraction of ECC in Porter s samples47 was 17 to 25%). 

More recently, St. Clair and co-workers176) reported the use of aromatic amine terminated polydimethylsiloxane oligomers of varying molecular weights in an effort to optimize the properties of LARC-13 polyimides. They observed the formation of two phase morphologies with low (—119 to —113 °C) and high (293 to 318 °C) temperature Tg s due to siloxane and polyimide phases respectively. The copolymers were reported to have improved adhesive strengths and better thermal stabilities due to the incorporation of siloxanes. 

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

Tough, transparent, heat and flame resistant, multiblock (bisphenol fluorenone carbonate) (BPF)-dimethylsiloxane copolymers have been synthesized by interfacial polycondensation of phosgene with various mixtures of BPF end-capped siloxane oligomers and free BPF or its monosodium salt 232). Siloxane content of the copolymers were varied between 7 and 27%. Presence of two Tg s, one below —100 °C and the other as high as 275 °C, showed the formation of two-phase morphologies. 

Preparation and thermal crosslinking reactions of oc, -vinylbenzyl terminated polysulfone-b-polydimethylsiloxane, ABA type block copolymers have been discussed 282,313) However, relatively little characterization was reported. Molecular weights of polysulfone and PDMS segments in the copolymers were varied between 800-8,000 and 500-11,000 g/mole, respectively. After thermal curing, the networks obtained showed two phase morphologies as indicated by the detection of two glass transition temperatures (—123 °C and +200 °C) corresponding to PDMS and polysulfone phases, respectively. No mechanical characterization data were provided. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Other reports on the morphology and mechanical behavior of organosiloxane containing copolymeric systems include polyurethanes 201 202), aliphatic 185, 86) and aromatic117,195> polyesters, polycarbonates 233 236>, polyhydroxyethers69,311, siloxane zwitterionomers 294 295) and epoxy networks 115>. All of these systems display two phase morphologies and composition dependent mechanical properties, as expected. 

Since the syrup solids increase generally stepwise while proceeding from one compartment to the next, and the contents of each compartment are boiling under constant pressure, the temperature in each succeeding compartment increases. It is claimed that the linear flow behavior provided by the reactor staging results in more favorable rubber phase morphology than would be the case if the second reactor were operated as a single CSTR. 

The results of the mechanical properties can be explained on the basis of morphology. The scanning electron micrographs (SEM) of fractured samples of biocomposites at 40 phr loading are shown in figure. 3. It can be seen that all the bionanofillers are well dispersed into polymer matrix without much agglomeration. This is due to the better compatibility between the modified polysaccharides nanoparticles and the NR matrix (Fig. 4A and B). While in case of unmodified polysaccharides nanoparticles the reduction in size compensates for the hydrophilic nature (Fig. 3C and D). In case of CB composites (Fig. 3E) relatively coarse, two-phase morphology is seen. 

FIGURE 2.14 Tapping mode phase morphology of the nanocomposites (a) poly[styrene-(ethylene-co-butylene)-styrene] (SFBS)-Cloisite 20A and (b) its 3D image. (From Ganguly, A., Sarkar, M.D., and Bhowmick, A.K., J. Polym. ScL, Part B Polym. Phys., 45, 52, 2006. Courtesy of Wiley InterScience.)... 

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