Interfacial modifier

The integrated DLS device provides an example of a measurement tool tailored to nano-scale structure determination in fluids, e.g., polymers induced to form specific assemblies in selective solvents. There is, however, a critical need to understand the behavior of polymers and other interfacial modifiers at the interface of immiscible fluids, such as surfactants in oil-water mixtures. Typical measurement methods used to determine the interfacial tension in such mixtures tend to be time-consuming and had been described as a major barrier to systematic surveys of variable space in libraries of interfacial modifiers. Critical information relating to the behavior of such mixtures, for example, in the effective removal of soil from clothing, would be available simply by measuring interfacial tension (ILT ) for immiscible solutions with different droplet sizes, a variable not accessible by drop-volume or pendant drop techniques [107]. 

Plasma polymerized organosilanes as interfacial modifiers in polymer-metal systems... 

The use of borane-containing monomers clearly presents an effective and general approach in the functionalisation of polyolefins, which has the following advantages stability of the borane moiety to coordination catalysts, solubility of borane compounds in hydrocarbon solvents (such as hexane and toluene) used as the polymerisation medium, and versatility of borane groups, which can be transformed to a remarkable variety of functionalities as well as to free radicals for graft-form polymerisations. The functionalised polymers are very effective interfacial modifiers in improving the adhesion between polyolefin and substrates and the compatibility in polyolefin blends and composites [518],... 

Special methods of incorporation filler and interfacial modifier were premixed before extrusion " ... 

Some most impressive computer simulations have been made in efforts to model the structure of liquid water. Yet, because these calculations usually are based on pair additivity of the potentials for the H-bonded water molecules, the possibility exists that subtle effects may escape the theoretician, as no means are provided to incorporate the possibility of extensive cooperativity—an aspect that Henry Frank (1972) has so eloquently stressed. Very likely, this is the crux of the problem of interfacially modified water if nothing else, the thermal anomalies (discussed below) in the properties of vicinal water strongly implicate cooperativity on a large scale—a collective behavior of water molecules that no existing potential function is able to reproduce. The cooperativity reflects nonpair additivity, and it does not seem plausible that effective potential energy functions can be devised that will remedy the specific lack of a detailed understanding of many-body interactions in water. Attempts to allow for cooperativity have been made by Finney, Barnes, and co-workers, notably Quinn and Nicholas (see Barnes et al., 1979). 

Liang H, Favis BD, Yu YS, Eisenberg A. Correlation between the interfacial tension and dispersed phase morphology in interfacially modified blends of LLDPE and PVC. Macromolecules 1999 32 1637-1642. 

EMAA ionomer (0-30 parts) dispersed phase particle size vs. interfacial modifier concentration / emulsification curves / effects of mixing protocol / also blends containing PP in place of HDPE Favis, 1988... 

Favis [1994] and Willis andFavis [1988] prepared compatibilized PA blends with PP and carboxylic acid-functionalized EMAA ionomer. Blends containing 90-10 parts PA-6, 0-30 parts EMAA ionomer, and 10-90 parts PP were combined in an internal mixer at 250°C and characterized by torque rheometry and SEM. Dispersed phase particle size vs. interfacial modifier concentration was determined. Emulsification curves were constructed. Effects of mixing protocol on blend properties were studied. Blends were also prepared containing HOPE in place of PP. 

To improve the compatibility in the ternary blends based on iPP and polyamides, different polymers grafted with maleic anhydride were added to the blend as interfacial modifier (20-24). Generally, the addition of the compatibihzer led to finer dispersion of the particles of the minor component and an upgrading of the mechanical properties of the blend. 

The Role of the Interfacial Modifiers from the Matrix Side... 

From above discussion, it becomes obvious that interfacial modifications may be driven either by the dispersed phase or from the matrix perspective, or even both. But driving forces in both cases must be well balanced to achieve the desired performance of the material at the macroscopic scale. Nevertheless, because of their affinity with the matrix, an increase in the flow across the interphase due to the presence of the interfacial modifiers from the matrix side is always observed. 

Besides, a decrease in the critical particle size for the polymer/polymer systems could also be obtained due to the decrease in the Weber number values, caused by an increase in the interfacial area available. A saturation level at the interaction plane across the interphase and in the concentration of the interfacial modifiers also emerges from the finite dimensions of the interphase. Above a critical concentration, the interfacial modifier could form its own phase, and then a nth phase ought to be considered in the studies rather than a model based on modified interfaces. Following sections show some examples of the role of the interfacial modifiers from the matrix side for both rigid and nondeformable dispersed phase polypropylene/mineral reinforcement system and polymer/polymer binary system based on polypropylene and polyamide 6. 

Figure 13.4 shows the variations between the tensile test parameters for the PP/interfacial modifier/talc composites as a function of either the grafted group, succinic anhydride (SA) or succinyl-fluorescein (SF) attached to an atactic polypropylene, as well as the differences on tensile strength and strain levels at yield or at break points, depending on the amorphous or semicrystalline nature of the interfacial modifier as it was fully discussed elsewhere (29,31). 

Figure 13.5 compares the differences between the evolution of the elastic modulus and tan 8 from the DMA tests with both the kind of attached group at the atactic polypropylene and the level of grafting of the interfacial modifier present in the composites. The different effect of each interfacial agent is clearly concluded as discussed elsewhere (33,56). 

The capability of the succinyl-fluorescein grafted polypropylene used as interfacial modifier in the PP/talc composites to saturate the interfacial area available at the interphase is well observed on the left-hand plots of Fig. 13.6 where it can be seen how the amount of molten material during the second heating cycle in dynamical tests by DSC, compared to that previously ordered during the cooling step, evolves as a min-max curve in a very similar way that strength at break does (34,35). 

Right-hand plots in the same Fig. 13.6 allows to conclude the well-optimized material performance from the macroscopic up to the mesoscales by the correspondence between the elastic modulus component obtained from the tensile tests and the elastic component of complex modulus from the DMA measurements performed at room temperature and which ratio results to be independent of the grafting level in the interfacial modifier (32,55). 

Figure 13.4 Macroscopic responses by changes at the interfacial level. Variations on tensile test parameters with the amount and the structure of the interfacial modifiers for the PP/talc system. (From Reference 29 with permission of Elsevier.)...

Both from an applied and from an academic point of view, the polypropylene/ polyamide 6 system is indeed one of the most studied polymer/polymer binary systems, together with the interfacial modification possibilities induced in the morphology of the blend either by mixing during the processing steps or by the presence of interfacial modifiers. 

Figure 13.5 Mechanical and dynamic mechanical responses on PP/mica system. Changes with the grafting level and the structure of the interfacial modifier. (From References 33, 56 with permission of John Wiley Sons, Inc.).

Figure 13.6 Examples of correlation between responses from different scales when the interfacial modifier is changed Left, tensile strength at break point (up) and relative crystalline variation for the polypropylene matrix (down) versus the grafting level in the interfacial modifier right, elastic moduli (tensile/DMA) ratio (up) and components of the complex modulus from DMA tests (down) versus the grafting level in the interfacial modifier. (From References 32 and 55 with permission of John Wiley Sons, Inc. and Elsevier, respectively.)...

Optical microscopy on phase contrast mode allows observation of the different morphologies obtained for each PP/interfacial modifier/PA6 blend. By image analysis techniques, it is possible to carry out statistical field measurements not only of the mean number of particles on the dispersed phase but also of their preferential geometry, mean size, and size distribution. 

Moreover, the correspondence with the solid-state behavior of these blends can be observed in Figs. 13.8 and 13.9. The latter showing the differences between both a-PP-SA and a-PP-SF as interfacial modifiers for the PP/PA6 system at, respectively, the macroscopic mechanical response level, Fig. 13.8, and at the... 

The different roles played by each interfacial modifier when located at the interphase are evident when we observe the two opposite effects caused by the a-PP-SF/SA in the 85/15 and the 15/85 PP/PA6 modified blends. For the former, where the polypropylene is the matrix, the presence of the lowest amount of a-PP-SF/SA is enough to increase the tensile strength values with respect to the unmodified blend, while both strength at yield and at break decrease if the a-PP-SF/SA amount continues to increase. 

As it has been demonstrated in the previous sections and also in numerous works available in the literature, the efficiency of the succinic anhydride grafted groups onto polypropylene backbone as interfacial modifiers on blends and composites based on polypropylene is indeed proved. 

Due to the importance of the presence of a biphasic interface on the macroscopic properties of a polymer blend, substantial work has been completed towards understanding and improving the interface and thus the macroscopic properties of the mixture. In particular, the effect of adding a copolymer to act as an interfacial modifier has received abundant attention. Much of this work has centered on the ability of a copolymer to strengthen the biphasic interface, lower interfacial tension (to create a finer dispersion), and inhibit coalescence during processing. Each of these mechanisms apparently contributes to the improvement of macroscopic properties of biphasic polymer blends upon addition of a copolymer and the importance of each has been the subject of some debate in the literature. 

Much of the work on copolymers as interfacial modifiers has utilized block copolymers as additives. The role of copolymer molecular weight, composition, and other molecular parameters on the ability of a block copolymer to improve the properties of a biphasic blend is well understood. However, block copolymers are expensive and difficult to synthesize. Therefore, their use as interfacial modifiers in commercial applications has been limited. Other copolymer stmctures, including random copolymers, may also act as compatibilizers. However, there exist conflicting results regarding the utility of random copolymers as interfacial modifiers."- w - 5.25... 

Thus, from this data, it appears that both the alternating and diblock copolymers are the most efficient at compatibilizing polymer blends. Unfortunately, these two copolymers are also the most difficult to realize and therefore, this is of little use from a commercial standpoint. It is interesting that the alternating copolymer may rival the diblock copolymer as a compatibilizer and this possibility is currently under investigation in our laboratory. Within the random copolymers (Px = 0.5, 1.0, and 1.5), these results suggest that the blocky structure is much better at interacting with the homopolymers than the alt-ran structure, and thus should be a more effective interfacial modifier. 

The change in volume of the copolymer as the system goes from a miscible to an immiscible state has been utilized as a qualitative measure of its ability to compatibilize a biphasic blend. This can be quantified by using the difference between the volume of the copolymer in the miscible system and the volume of the copolymer in the phase separated system at its deepest quench as a measure of the effectiveness of the copolymer as a compatibilizer. This value is plotted vs. the sequence distribution, Px in Figure 2. This data quantifies the trend that is described above the alternating and diblock copolymers are the best compatibilizers, however within the random structures, the more blocky structures is a more effective interfacial modifier than the statistically random copolymer which is more effective than an alternating-random structure. 

However, for a copolymer of styrene and 2-vinyl pyridine, similar experiments show a slightly different pattern. 25Using ADCB, Kramer and coworkers have found that a diblock copolymer (50/50 composition, Mw = 170,000) creates an interface with strength of 70 J/m2, whereas a random copolymer (50/50 composition, Mw = 700,000) was able to produce an interface with strength of 140 J/m. Thus, for this system, the random copolymer is a better interfacial modifier than the diblock copolymer. 

Fowlks, A.C., Narayan, R. The effect of maleated polylactic acid (PLA) as an interfacial modifier in PLA-talc composites. J. Appl. Polym. Sci. 118, 2810-2820 (2010)... 

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