Interfacial morphologies

Kaelble has developed a model137) to relate mechanical properties of SBS and SIS copolymers to their interfacial morphology. The adsorption-interdiffusion model for the interfacial phase defines the size, shape, and connectivity of microdomains. Kaelble has applied his model to the interfacial morphology in order to explain the initial tensile yielding, cold drawing, and subsequent hysteresis in recovery of Kraton 101138,139). 

Chen K, Fan A, Reif R. Interfacial morphologies and possible mechanisms of copper wafer bonding. J Mater Sci 2002 37 3441-3446. 

Y. Mi, X. Chen, Q. Guo, Bamboo fiber-reinforced polypropylene composites crystallization and interfacial morphology. J. Appl. Polym. Sci. 64(7), 1267-1273 (1997)... 

It is imperative to mention that component polymer surfaces and interfaces play a major role in the properties and applications of blends such as in biocompatibility, switching, or adaptive properties. Whether it is an everyday plastic part or parts in automotives or in an airplane, not only the development of interfacial morphology but also the analyses of blends interfaces are equally important. The compatibilizing effect is primarily due to the interfacial activity of the constituent partners. This in turn raises the question of what are the effects of the molecular weight, concentration, temperature, and molecular architecture of the... 

The choice of the polymer and fillers is very important to develop advanced hybrid membranes for a particular separation process, but the major challenge is to prepare a defect-free interface between the organic and inorganic phase. Indeed, the interfacial morphology plays a crucial role for the determination of the transport properties of the hybrid matrix, and a departure from ideal conditions can lead to a severe worsening of the separation performance. In Fig. 7.6 the possible conditions at the interface are shown. 

Figure 7.7 Effects of interfacial morphology on the separation performance of hybrid membranes.

It has been indicated how interfacial morphology plays a crucial role in the transport properties of hybrid membranes, and conditions as close as possible to the ideal case must be achieved to ensure advanced separation performances. For this reason, several fabrication techniques have been developed to reduce as much as possible the influence of a nonideal interfacial morphology on the transport characteristics of the hybrid membranes. Among the most frequently used procedures there are solution blending, the sol-gel procedure, surface modification, and interfacial polymerization. In some cases a combination of these techniques is required to reach the best dispersion of the filler within the matrix. 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

The morphology characterization of hybrid membranes is very important to identify the possible interfacial morphology and particle dispersion in the final membrane matrix. Electron microscopy is typically used to investigate the filler dispersion and the hybrid membrane morphology. Scanning electron microscopy is the most frequently used technique, and it allows the characterization of the sample surface. The sample s cross-sections can be examined to analyze the inner morphology. Transmission electron microscopy is also a very useful technique because it allows a direct evaluation of the inner morphology of the sample. 

Another possible approach to indirectly characterize the membrane morphology is based on the investigation of the free volume within the matrix. Density measurements [119,120] and positron annihilation lifetime spectroscopy evaluation [47] are common methods. Typically, the comparison between the theoretical density or free volume (calculated by simple additivity rules) and the experimental one can reveal the presence of a good interfacial morphology or the presence of interface voids or clustering formation. Fig. 7.13 shows the influence of filler content on the morphology of poly(trimethylsilyl propyne) (PTMSP)/Ti02 NCMs in terms of the volumetric fraction of interface voids as calculated from a comparison of the expected and measured membrane density [119],... 

Since the stress required for the onset of cavitation in the whisker reinforced material is roughly one half that required for the non-reinforced material, it appears that the degradition in tensile creep behavior can be traced to the interfacial morphological and chemical cVianges associated with the presence of the wliiskers which results in enhanced cavity nucleation and growth. 

Varga, J. and Karger-Kocsis, J. (1995) Interfacial morphologies in carbon fibre-reinforced polypropylene microcomposites. Polymer, 36, 4877-4881. 

Karger-Kocsis J and Varga J (1999) Interfacial morphology and its effects in poljrpropylene composites, in Polypropylene An A-Z Reference (Ed. Karger-Kocsis J) Kluwer, Dordrecht, Netherlands,... 

Sun X, Li H, Zhang X, Wang J, Wang D and Yan S (2006) Effect of fiber molecular weight on the interfacial morphology of iPP fiber/matrix single polymer composites. Macromolecules 39 1087-1092. 

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