Interphase miscibility

CuCl, PEG6000-(TEMPO)2, and oxygen are essential for the oxidation of benzyl alcohol into benzaldehyde. The presence of C02 improves the reaction, presumably being ascribed to high miscibility of 02 into compressed C02, thus eliminating interphase transport limitation, and expandable effect of PEG in compressed C02 [63, 64],... 

Figure 9.4c and 9.4d represent intermediate cases, 9.4c indicates partial miscibility we see a two-phase system of AB blends with different A/B ratios. This might be the result of segregation into the binodals. Figure 9.4d is called an interphase or a multiphase blend. The system is quasi-homogeneous, but it contains all A/B ratios between cpi = 0 and concentration gradients as a result of non-completed diffusion in a combination of well-compatible polymers. 

In the graphical example shown in Fig. 2, interphase equilibria are shown by dashed tie-lines connecting the raffinate and extract compositions. As the mass fraction of C is increased, the tie-lines become shorter until the limit of miscibility is reached at the point P on Fig. 2. 

The basic issue confronting the designer of polymer blend systems is how to guarantee good stress transfer between the components of the multicomponent system. Only in this way can the component s physical properties be efficiently used to give blends with the desired properties. One approach is to find blend systems that form miscible amorphous phases. In polyblends of this type, the various components have the thermodynamic potential for being mixed at the molecular level and the interactions between unlike components are quite strong. Since these systems form only one miscible amorphous phase, interphase stress transfer is not an issue and the physical properties of miscible blends approach and frequently exceed those expected for a random copolymer comprised of the same chemical constituents. 

Obtaining good stress transfer is possible in systems where the mixture forms a miscible amorphous phase (where interphase stress transfer is not an issue) ... 

The concentration dependence of rig conqjuted from Equation 20 Is shown In Fig. 30, where the solid points represent the experimental data and the open points their values corrected for the effects of PP degradation. For System-1 there Is strong negative deviation (NDB) from the log additivity rule, viz. Equation 1, but for System-2 NDB Is visible at low PP content, converting to positive deviation (PDB) at high. It Is worth recalling that ng was computed from corrected for the yield stress values of n. The NDB behavior. Indicative of Interlayer slip, reflects poor miscibility In System-1 and that at low concentration of PP In System-2. The emulslon-llke behavior of Syetem-2 at high PP content reflects a better Interphase Interaction. 

In the cases of the SPM series of polymers, only a single transition was observed at around 225 °C, which is marginally lower than that of pure BACY. It appears that the two phases are miscible, as otherwise a second transition due to pure BACY should have appeared at higher temperature. The uniform dispersion of the high-Tg polymer and strong matrix/reinfor cement interphase aided... 

Morphological study, together with DMTA and DSC results, confirms the expectation of miscibility of the diblock copolymer with each component of the blend. This miscibility occurs at the interphases between the components of blends, allowing enhanced interphase interactions and better stress transfer in the blend system. This is probably due to the anchoring of each sequence of the block with its corresponding component of the blend, which is in good... 

Enhanced interphase interactions, deduced from thermal and dynamic mechanical properties and morphology observed by SEM, demonstrate the efficient compatibilizing effect of iPS-fo-iPP copolymer on iPS-iPP blends. Each sequence of the iPS-fc-iPP diblock copolymer can probably penetrate or easily anchor its homopolymer phase and provide important entanglements, improving the miscibility and interaction between the iPS and iPP phases. This is in good agreement with what is inferred from the mechanical properties of the iPS-fo-iPP-iPS-iPP polyblends. 

The density profile across the interface follows an exponential decay (see Figure 1.1). The intercepts of the steepest tangential line with the horizontal lines defining the volume fraction of either one of the two polymeric ingredients, (p = 0 and 1, define the thickness of the interphase, Al [Helfand and Tagami, 1971, 1972]. Experimentally Al varies from 2 to 60 run [Kressler et al., 1993 Yukioka and Inoue, 1993, 1994]. Measurements of Al have been recently used to map the miscibility region of PC/SAN blends when varying the AN-content and temperamre [Li et al, 1999]. 

For example, the effects of AN content on miscibility of SAN with PMMA was studied by measuring the thickness of the interphase [Higashida et al., 1995]. The effects of concentration, compatibilization and annealing for PA with either PS or PE (compatibUized by addition of 5 wt% of PP-MA or SMA) were studied by SEM [Chen et al., 1988]. Compatibilization reduced the diameter of dispersed phase by a factor of ten... 

Some polymers have been found miscible with many other resins, or in other words there are many immiscible blends whose components are miscible with the same polymer. Addition of this polymer can be used to partially homogenize the system, i.e., to compatibilize the blend. The added polymer is a co-solvent. Of particular interest are systems in which presence of a co-solvent makes it possible for the two immiscible components to form three-body interactions. In this case, the blend is indeed compatibilized, with the co-solvent being located in the interphase. For the thermodynamic reasons, mostiy copolymers belong to this type of co-solvents. In the left hand side column of Table 4.1 there are polymers that may be used as co-solvents for pairs of resins listed in the other column. Some of the latter resins may show local miscibihty (e.g., PS with styrenic copolymers), but the vast majority is immiscible. 

Two types of coalescence must be recognized, the hrst being determined by equilibrium thermodynamics e.g., liquid-liquid miscibility, interfacial tension coefficient, rheological conditions of the interphase, etc.), the second, dynamic one, being also affected by the rheology. In the following text, only the second type will be discussed. 

Blending two immiscible polymers always creates the third phase — the inteiphase. In binary blends, thickness of this third phase, AZ, is inversely proportional to the interfacial tension coefficient, When the blend approaches miscibility, approaches zero and AZ goes to infinity. Thus the interphase, with its own set of characteristic parameters e.g., viscoelasticity) may dominate the behavior of nearly miscible systems, as well as that of compatibilized blends. For further details on this topic see Chapter 4. Interphase and Compatibilization of Polymer Blends. 

It has been found in the study of PVME and SBS triblock copolymer that solubility of PVME in PS block copolymer domains is larger than in PS homopolymer. This may indicate that the mixing enthalpy has an effect on the blend miscibility [Xie et al., 1993]. The behavior has been attributed to the effect of PB segments in SBS. The phase equilibria and miscibility in polymer blends containing random or block copolymer was reviewed [Roe and Rigby, 1987]. More recent data are presented in Chapter 4 Interphase and Compatibilization by Addition of a Compatibilizer in this Handbook. 

For proper understanding of the immiscible polymer blends it is important to take into account the interphase. In binary blends, the interphase thickness, is inversely proportional to the interfacial tension coefficient, thus, poorer the miscibility, larger the interfacial tension coefficient and smaller the interphase thickness. Owing to the thermodynamic forces the polymeric chain-ends concentrate at the interface and the low molecular weight components difiuse to it as well. Thus,... 

The interphase thickness depends on the miscibility of the polymeric component as well as on the compatibilization. For uncompatibilized binary, strongly immiscible systems, the interphase thickness Al - 2 nm. The thickest interphase has been observed for reactively compatibilized polymer alloys Al = 65 nm. For most blends, the interphase thickness is in between these two limits. The importance on the interphase can be appreciated noting that its volume will be the same as that of the dispersed phase when the drop diameter (without interphase) is about 500 nm. It is noteworthy that in most commercial polymer alloys the drop diameter is about five times smaller, making the importance of the interphase much greater. 

PP-g-SBH copolymers cocrystallize completely with bulk iPP, which increases PP crystaUinity degree part of the SBH component (SBH grafts of PP-g-SBH copolymers and bulk SBH) enters the mutual amorphous phase of the blends, leading to a decrease of the intensity of the SBH peak. That means each part of the compatibilizer is miscible with the corresponding bulk phase of the blend. The compatibilized iPP/LCP blends display improved crystallization kinetics, enhanced degree of crystallinity, and improved interphase adhesion (37,38). Consequently, an improvement of the mechanical characteristics should be expected for these blends. In fact, the investigation of the Vickers microhardness of uncompatibilized and... 

It is worth mentioning that interphase interactions in blends proceed only within mesophases whose thickness for incompatible polymers is between 2 and 50 nm depending on the thermodynamic interactions of the phases, temperature, regimes of mixing, and some other factors (7,11,29,30). The mesophase thickness depends on the miscibility of the components and in first approximation (7) is where xi2... 

Liquid phase aromatic mononitration under normal industrial conditions is an example of mass transfer with simultcuieous chemical reaction. The problem of determining the magnitude cind nature of the resistance to interphase transfer has been avoided in much research on nitration kinetics by the simple expedient of working in a solvent with vdiich all reactcints are miscible. 

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. 

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