Composite two-phase

Mechanical Properties. Although wool has a compHcated hierarchical stmcture (see Fig. 1), the mechanical properties of the fiber are largely understood in terms of a two-phase composite model (27—29). In these models, water-impenetrable crystalline regions (generally associated with the intermediate filaments) oriented parallel to the fiber axis are embedded in a water-sensitive matrix to form a semicrystalline biopolymer. The parallel arrangement of these filaments produces a fiber that is highly anisotropic. Whereas the longitudinal modulus of the fiber decreases by a factor of 3 from dry to wet, the torsional modulus, a measure of the matrix stiffness, decreases by a factor of 10 (30). 

Immiscible Blends. When two polymers are blended, the most common result is a two-phase composite. The most interesting blends have good adhesion between the phases, either naturally or with the help of an additive. The barrier properties of an immiscible blend depend on the permeabihties of the polymers, the volume fraction of each, phase continuity, and the aspect ratio of the discontinuous phase. Phase continuity refers to which phase is continuous in the composite. Continuous for barrier appHcations means that a phase connects the two surfaces of the composite. Typically, only one of the two polymer phases is continuous, with the other polymer phase existing as islands. It is possible to have both polymers be continuous. 

The selection of a suitable matrix for a composite material involves many factors, and is especially important because the matrix is usually the weak and flexible link in all properties of a two-phase composite material. The matrix selection factors include ability of the matrix to wet the fiber (which affects the fiber-matrix interface strength), ease of processing, resulting laminate quality, and the temperature limit to which the matrix can be subjected. Other performance-related factors include strain-to-failure, environmental resistance, density, and cost. 

Upon substitution into either one of the equations of stability [Eq. (98) or (99)], we can then determine whether the gas mixture exists in one or two stable phases. If two phases exist at some temperature and pressure, we can calculate the two phase compositions by utilizing the two equilibrium relations... 

Some experimental results for the helium-xenon system are shown in Fig. 25. (The critical temperature of xenon is 16.6°C.) At temperatures several degrees above the critical of xenon, the two phase-compositions are significantly different even at pressures as low as 200 atm. However, to obtain the same degree of separation at higher temperatures, much higher pressures are required. 

The mechanical behaviour of a two-phase composite system depends partly on the filler characteristics, such as the geometry of inclusions, their size, the size distribution, the orientation of inclusions, the filler volume-fraction, the relative positions between the inclusions, the physical state of the filler, etc. and partly on the matrix characteristics, which are related to the physico-chemical state of the matrix, the degree of its polymerization, the crystallinity, the degree of cross-linking, etc. 

Polymer composites of mbber-hydrogel are permeable for water-soluble low-molecular weight compounds in a swollen state. Therefore, it is suitable for dmg delivery carrier. Many papers have researched the basic role of composite morphology in low-molecular weight component transport through two-phase composites where only one phase played the main role. 

MIEC with an additional ionically conductive phase, such as GDC or SDC, typically extends the electrochemically active region still further due to the higher ionic conductivity of GDC and SDC compared to that of the perovskites. The optimal composition of a two-phase composite depends in part on the operation temperature, due to the larger dependence of ionic conductivity on temperature compared to electronic conductivity. A two-phase composite of LSCF-GDC therefore has an increasingly large optimal GDC content as the operating temperature is reduced [14], A minimum cathode Rp for temperatures above approximately 650°C has been found for 70-30 wt% LSCF-GDC composite cathodes, while at lower temperatures, a 50-50 wt% LSCF-SDC composite cathode was found to have a lower Rp [15]. 

Figure 2. Common strategies for SOFC cathodes (a) porous single-phase electronically conductive oxide such as (La,Sr)Mn03 (LSM) (b) porous single-phase mixed conductor (c) porous two-phase composite. The SEM micrograph of LSM on YSZ in a is adapted from ref 84. (Adapted with permission from ref 84. Copyright 1997 Swiss Federal Institute of Technology.)...

Finally, collagen can form a variety of collagen composites with other water-soluble materials. Ions, peptides, proteins, and polysaccharides can all be uniformly incorporated into a collagen matrix. The methods of composite formation include ionic and covalent bonding, entrapment, entanglement, and co-precipitation. A two-phase composite can be formed between collagen, ceramics, and synthetic polymers for specific biomedical applications. 

In a two-phase composite material of isolated spherical particles embedded in a matrix, there is a driving force to transport material from particles enclosed by isotropic surfaces of larger constant mean curvature to particles of smaller constant mean curvature. This coarsening process and the motion of internal interfaces due to curvature are treated in Chapter 15. 

Gray and McCrum735 used the Hashin-Shtrikman theory to explain the origin of the y relaxation in PE and PTFE, Maeda et al.745 have given exact analyses of several two phase models for semi-crystalline polymers and Buckley755 represented a biaxially oriented sheet of linear polyethylene by a two phase composite model. 

Fig. 6a-c. Graphic representation of syntactic foam structures 85) a Random dispersion of spheres, two-phase composite b Hexagonal closed-packed structure of uniform-sized spheres, two-phase composite c Three-phase composite containing packed microspheres, dispersed voids, and binding resin... 

The principle of composition of three-phase syntactic foams can be represented by a ternary phase diagram (Fig. 7). Point A on the diagram denotes a composite of the following volume fractions resin 0.15, microspheres 0.60, voids 0.2586>. The pure void free syntactic foam has a two-phase composition which falls along the... 

The two-phase composite of microspheres and voids only (i.e. packed spheres without any binding resin) has also a minimum limit. Cubic packing (volume fraction 0.53) is the lower limit, below which the structure is not selfsupporting any more, and some resin is required to fill in between the spheres. S). 

Another two-phase composite is chemically or physically blown foam, composed of polymer and voids only (i.e. conventional foamed or cellular polymer). Its compositions lie along the polymer-void border of Fig. 7, and it, too, is limited by the maximum volume fraction of voids allowed, while still maintaining the definition of a foam. The limits mentioned define the allowed compositions for syntactic foams and determine the area within the diagram where they are located. One limiting case is point B which represents the composition of microspheres (0.74), polymer (0.11), and voids (0.15). The microspheres, in this case, are arranged in a hexagonal close packing 85). 

The concept of connectivity is discussed in Section 2.7.4 and in [4]. There are 10 different ways of connecting the phases in a two-phase composite, each described by two numbers, the first defining (in the present context) how the active ceramic phase is connected and the second how the passive polymer phase... 

Surface of separation. Where volume fraction of the dispersed phase is high so that the area of contact between contiguous particles of the second phase is unnegllgible the extent of the surface of separation between the second phase and the matrix has to be considered in measuring the degree of dispersion. For a two-phase composite the degree of separation dp is defined as ... 

As pointed out above, the semicrystalline polymer can be considered as a two-phase composite of amorphous regions sandwiched between hard crystalline lamellae (Fig. 4.2(a)). Crystal lamellae ( c) are normally 10-25 nm thick and have transverse dimensions of 0.1-1 pm while the amorphous layer thickness, a, is 5-10 nm. As mentioned in the previous section, melt-crystallized polymers generally exhibit a spherulitic morphology in which ribbon-like lamellae are arranged radially in the polycrystalline aggregate (Bassett, 1981). Since the indentation process involves plastic yielding under the stress field of the indenter, microhardness is correlated to the modes of deformation of the semicrystalline polymers (see Chapter 2). These... 

This cross-axis CPC provides the universal application of protein samples with a dextran-PEG polymer-phase system. Using a prototype of the L cross-axis CPC with a 130-mL column capacity, profilin-actin complex was purified directly from a crude extract otAcanthamoeba with the same solvent system as used for the serum protein separation earlier. The sample solution was prepared by adding proper amounts of PEG 8000 and dex-tran T500 to 2.5 g of the Acanthamoeba crude extract to adjust the two-phase composition similar to that of the solvent system used for the separation. The experiment was performed by eluting the upper phase at 0.5 mL/min under a high revolution rate of 1000 rpm. The profihn-actin complex was eluted between 60 mL and 84 mL fractions and well separated from other compounds. The retention of the stationary phase was 69.0% of the total column capacity. 

Another alternative that would help to raise catalyst utilization would be to make CLs of extremely thin two-phase composites. Electroactive Pt (eventually deposited on a substrate) should form the electronically conductive phase. The remaining volume should be filled with liquid water. Since the layer is only a two-phase composite, not impregnated with ionomer, the problem of the protonic contact resistance at the PEM CL interface could be mitigated, making the CCL insensitive to the type of PEM. Using Pois-son-Nemst-Planck theory, it could be shown that close to 100% of the catalyst would be utilized, since transport of oxygen and protons would be unproblematic for such thicknesses ( 100 nm) [129],... 

The term tungsten heavy metal or heavy metal is used for a group of two-phase composites, based on W-Ni-Fe and W-Ni-Cu. They are characterized by a high density and a novel (unique) combination of strength and ductility. 

Physically, the relationship between catalytic activity and Z f can be understood from a study of single phase bismuth cerium molybdate solid solutions. The results show that maximum activity is achieved when there exists a maximum number and optimal distribution of all the key catalytic components bismuth, molybdenum and cerium in the solid. Therefore, it reasonably follows that the low catalytic activity observed for the two phase compositions where Af Af(min) results from the presence of interfacial regions in the catalysts where the compositional uniformity deviates significantly from the equilibrium distribution of bismuth and cerium cations present in the solid solutions. These compositions may contain areas in the interfacial region which are more bismuth-rich or cerium-rich than the saturated solid solutions. Conversely, at Af(min), the catalyst is similar to an ideal mixture of the two optimal solid solutions. The compositional homogeneity of the interfacial region approaches that of the saturated solid solutions. Therefore, the catalytic behavior of compositions at Af(min) is similar to that of the saturated solid solutions. 

Let s consider first a defect-free grain of one phase in a two-phase composite. The state of this crystal can be described by the equation of motion of elastic media [11] ... 

To model the microstructure and evaluate the thermoelectric properties, we used following simple equivalent electric circuit model shown in Figure 2. We considered the two phase composite as a cluster pararrel network circuit. Setting for each cluster the characteristic single phase physical property, and settle the material composition to the cluster number ratio, we can simulate the total thermopower of the system by Millman s theorem of d.c. circuit. 

A filled rubber may be regarded at once as a two-phase composite material and as a polymeric network containing giant multifunctional cross-links. Neither concept alone leads to very useful generalizations. The physical properties of a filled vulcanizate do not appear capable of close description in terms of the component filler and rubber properties. On the other hand no degree of cross-linking per se produces effects identical to filler reinforcement. 

Consequently, at fixed temperature the two phase compositions and the pressure are fixed. Varying the average mole fraction would change the mass distribution between the two phases, but would not change the composition of either phase or the total pressure. That is, when two liquid phases and a vapor phase exist in a binary mixture, the equilibrium pressure depends only on temperature and not on average composition. 

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