Multiphase composites

Thermoplastic elastomers are often multiphase compositions in which the phases are intimately dispersed. In many cases, the phases are chemically bonded by block or graft copolymerization. In others, a fine dispersion is apparentiy sufficient. In these multiphase systems, at least one phase consists of a material that is hard at room temperature but becomes fluid upon heating. Another phase consists of a softer material that is mbberlike at RT. A simple stmcture is an A—B—A block copolymer, where A is a hard phase and B an elastomer, eg, poly(styrene- -elastomer- -styrene). 

Numerous multiphase composite materials exhibit more than one characteristic of the various classes, fibrous, laminated, or particulate composite materials, just discussed. For example, reinforced concrete is both particulate (because the concrete is composed of gravel in a cement-paste binder) and fibrous (because of the steel reinforcement). 

Thermoplastic elastomers are multiphase composites, in which the phases are intimately depressed. In many cases, the phases are chemically bonded by block or graft copolymerization. At least one of the phases consists of a material that is hard at room temperature. ... 

It is important to mention that the structure/properties relationships which will be discussed in the following section are valid for many polymer classes and not only for one specific macromolecule. In addition, the properties of polymers are influenced by the morphology of the liquid or solid state. For example, they can be amorphous or crystalline and the crystalline shape can be varied. Multiphase compositions like block copolymers and polymer blends exhibit very often unusual meso- and nano-morphologies. But in contrast to the synthesis of a special chemical structure, the controlled modification of the morphology is mostly much more difficult and results and rules found with one polymer are often not transferable to a second polymer. 

Metallodielectrics and Other Multiphasic Composites Using Multiple Materials... 

The empirical equations are obtained by the intuitive suggestions with the use of experimental data. Here we cite an instance of two Lichtenecker equations [7-9] for two-phase and multiphase composites ... 

The primary objective in catalyst layer development is to obtain highest possible rates of desired reactions with a minimum amount of the expensive Pt (DOE target for 2010 0.2g Pt per kW). This requires a huge electroche-mically active catalyst area and small barriers to transport and reaction processes. At present, random multiphase composites comply best with these competing demands. Since a number of vital processes interact in a nonlinear way in these structures, they form inhospitable systems for systematic theoretical treatment. Not surprisingly then, most cell and stack models, in particular those employing computational fluid dynamics, treat catalyst layers as infinitesimally thin interfaces without structural resolution. 

We have developed such a multiphase composite using sol-gel processing which produces large size bulks of excellent optical quality (d). In this approach, we prepare highly porous monolith gel (in the present case silica) and thermally process it. The pores in the silica monolith under our processing conditions are in the nanoscale region ( 5 nm). This allows various molecules (such as fullerene) to be adsorbed in the pores by diffusion of a solution followed by evaporation of the solvent. Then the pores are filled with a polymerizable liquid such as methyl methacrylate (MMA) which is then... 

Figure 8.10. Morphologies in directed solidification. From V. S. Stubican, R. C. Bradt, F. L. Kennard, W. J. Minford, and C. C. Sorrel. Ceramic eutectic composites. In R. E. Tressler, G. L. Messing, C. G. Pantano, and R. E. Newnham (eds.). Tailoring Multiphase Composite Ceramics. Plenum, New York (1984). Morphologies from D. Michel, Y. Rouaux, and M. Perez y Yorba. J. Mater. Sci. 15,61 (1960). With kind permission of Kluwer Academic Publishers.

It is generally accepted that growth in plastics consumption and the development of new and specialized applications are related to advances in the field of multicomponent, multiphase polymer systems. These include composites, blends and alloys and foams. Fillers are essential components of multiphase composite structures they usually form the minor dispersed phase in a polymeric matrix. 

The dynamic flexibility of supramolecular polymers is exploited by Keizer et al. [34]. in polymerization-induced phase separation (PIPS) with hydrogen-bonded supramolecular polymers. In PIPS, a supramolecular polymer is dissolved in a reactive monomer, which is subsequently polymerized to cause phase separation resulting in two polymeric phases with certain morphology. PIPS is currently used to produce multiphase composite materials like high-impact polystyrene, avoiding the use of solvent and consequently resulting in the fast and clean production of polymeric materials. 

Conductive multiphase composites have been obtained by dilution of polyoxy-methylene/carbon black in the polyethylene-based phase (Lipatov et al. 1983). In this manner, the filler is localized at the interface between the polymeric components. Though a reinforcement agent was excluded to the interface of the polyoxymeth-ylene phase as it crystallized, a small percent remained dispersed in the component The conductive network at the polyethylene/polyoxymethylene interface enhanced the conductivity level at lower filler amounts. 

Multiphase composites formed of polymer substrates coated with thin metal films show special properties and are in great demand for various applications. The metal-polymer substrate interaction and the morphological structure at the interface influence the final properties of the composites of thin metal-polymer substrates. Thus, modifying the properties of the polymer substrate by wet (acid, alkali), dry (plasma), and radiation treatments (ultraviolet radiation and laser) appears as a significant step for increasing adhesion of thin film onto polymeric substrates. 

J. Aboudi, Micromechanical prediction of the effective coefficients of thermopiezoelectric multiphase composites. J. InteU. Mater. Syst. Struct. 9, 713-722... 

Both Voigt and Reuss models provide initial estimates of the upper and lower bounds of elasticity of multiphase composites with the only consideration of the inclusion volmne fraction but irrespective of inclusion shape/geometry, orientation and spatial arrangement. 

Duaii H L, Yi X, Huang Z P and Wang J (2007) A unified scheme for prediction of effective moduli of multiphase composites with interface effects. Part I Theoretical framework, Mech Mater 39 81-93. 

The physical properties of a composite can change by many orders of magnitude, depending on the way in which phase connections are made. As such, connectivity is a major feature in property development for multiphase composites. Each phase may be self-connected in zero, one. 

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