Microstructure interpenetrating

Copolymers (graft or block) made of immiscible sequences give rise to biphasic morphologies depending on the ratio of immiscible sequences (or of their lengths). Such possible microstructures are reported in Figure 33. A minor phase can be dispersed as nodules (spheres) or filaments (cylinders) while, when concentrations of both phases get similar, lamellar (interpenetrated) structures can appear. It should be noted that rather similar morphologies could also be found in (compatibilised) polymer blends. 

Hydrated Acidic Polymers. Hydrated acidic polymers are, by far, the most commonly used separator materials for low-temperature fuel cells. Their typical nanoseparation (also see Section 1) leads to the formation of interpenetrating hydrophobic and hydrophilic domains the hydrophobic domain gives the membrane its morphological stability, whereas the hydrated hydrophilic domain facilitates the conduction of protons. Over the past few years, the understanding of the microstructure of these materials has been continuously growing, and this has been crucial for the improved understanding of the mechanism of proton conduction and the observed dependence of the conductivity on solvent (water and methanol) content and temperature. 

Figure 48. Kenjo s ID macrohomogeneous model for polarization and ohmic losses in a composite electrode, (a) Sketch of the composite microstructure, (b) Description of ionic conduction in the ionic subphase and reaction at the TPB s in terms of interpenetrating thin films following the approach of ref 302. (c) Predicted overpotential profile in the electrode near the electrode/electrolyte interface, (d) Predicted admittance as a function of the electrode thickness as used to fit the data in Figure 47. (Reprinted with permission from refs 300 and 301. Copyright 1991 and 1992 Electrochemical Society, Inc. and Elsevier, reepectively.)...

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25... 

The theoretical and experimental investigations of rupture and permeability of amphiphile bilayers are valuable also for the understanding of some microstructural effects in interfacial layers and phases of small volumes. The interpenetration of macroscopically measured quantities, e.g. r and W, by means of molecular statistical models seems to be most interesting and useful. As first attempts in this respect, a molecular statistical lattice model of such bilayers has been proposed [427] and a lattice model of such bilayers has been studied by means of Monte Carlo simulation by Chowdhury and Stauffer [429]. The results obtained have been compared with some experimental data presented in this Section. Clearly, the combination of macro and micro considerations is a promising way to obtain a deeper insight into the properties of matter and, especially, of interfacial layers and phases of small volumes. 

On the experimental side, tills size exclusion has been observed in tlie case for diblock copolymers [308] in which nanoparticles of different size but same nanoparticle ligand chains assume distinct locations within tlie microstructure (Fig. 25) and for particle interpenetration into polymer brushes [309]. 

Blending of polyacetylene with polybutadiene provides an avenue for property enhancement as well as new approaches to structural studies. As the composition of the polyacetylene component is increased, an interpenetrating network of the polymer in the polybutadiene matrix evolves from a particulate distribution. The mechanical and electrical properties of these blends are very sensitive to the composition and the nature of the microstructure. The microstructure and the resulting electrical properties can be further influenced by stress induced ordering subsequent to doping. This effect is most dramatic for blends of intermediate composition. The properties of the blend both prior and subsequent to stretching are explained in terms of a proposed structural model. Direct evidence for this model has been provided in this paper based upon scanning and transmission electron microscopy. 

Several kinds of ceramics prepared from metallorganic polymers have been described. By controlling the precursor and conversion process, polymer precursor ceramics have the possibility to form novel types of structure, such as an interpenetrated microstructure, that is different from that of earlier ceramics. 

Williamson SL, Armentrout RS, Porter RS, McCormick CL (1998) Microstructural examination of semi-interpenetrating networks of poly(N, N-dimethylacrylamide) with cellulose or chitin synthesized in lithium chloride N, N-dimethylacetamide. Macromolecules 31 8134-8141... 

GLASS-CONTAINING COMPOSITES WITH INTERPENETRATING MICROSTRUCTURES... 

To fabricate glass-containing composites with interpenetrating microstructures either a glass slurry or molten glass is infiltrated into the porous preform or a metallic or polymer... 

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