Heterophase structure

Phase Structure of Block Polymers. Block polymers have heterophase structure in which the phases are highly interspersed. Two or more phases may be present, and each of these may be continuous or discrete depending on the relative amounts of the various polymeric species present and the conditions of preparation. The discrete phases may have various shapes usually referred to as "domains. Spheres, rods, and lamellae have been experimentally observed and theoretically justified. Molau (79) symbolizes the change in A-B-A structure as a function of A or B content, as shown in Figure 4. 

Influence of Structure on Properties. The characteristic behavior of block polymers may be thought of as a combination of properties arising from three distinct aspects of the phase structure individual phases, heterophase structure, and interfacial regions. 

Considering aU the above-discussed data, we conclude that the linear dependence in the coordinates of the BET equation does not yet imply that the general conclusions of the polymolecular adsorption theory can be applied to the description of sorption on hypercrosslinked polystyrenes. These cannot be regarded as rigid sorbents with a constant heterophase structure. Accordingly, calculation of the pore size distribution from the desorption branch of the isotherms for carbon dioxide using the Kelvin equation (Eq. [3.4], Chapter 3) results in the unrealistic pore dimensions of about 0.1 A. The isotherms for water produce more sensible data for pore diameters, 20—40 A, but one should not assume that the plots presented in Fig. 10.4 correspond correcdy to the real pore size distribution of the material. 

Thus, under some conditions, the composite models can be successfully applied to the description of the behaviour of amorphous and semi-crystalline polymers within the frameworks of the quasi-two-phase cluster model. In this case, an obvious possibility for obtaining quantitative correspondence between theory and experiment exists under the condition of heterophase structure of amorphous state and the accuracy of the cluster model [41]. 

The formation mechanism of structure of the crosslinked copolymer in the presence of solvents described on the basis of the Flory-Huggins theory of polymer solutions has been considered by Dusek [1,2]. In accordance with the proposed thermodynamic model [3], the main factors affecting phase separation in the course of heterophase crosslinking polymerization are the thermodynamic quality of the solvent determined by Huggins constant x for the polymer-solvent system and the quantity of the crosslinking agent introduced (polyvinyl comonomers). The theory makes it possible to determine the critical degree of copolymerization at which phase separation takes place. The study of this phenomenon is complex also because the comonomers act as diluents. 

As has already been emphasized in Fig. 1.1, there is the further problem of connecting the mesoscopic scale, where one considers length scales from the size of effective monomers to the scale of the whole coils, to still much larger scales, to describe structures formed by multichain heterophase systems. Examples of such problems are polymer blends, where droplets of the minority phase exist on the background of the majority matrix, etc. The treatment of... 

It is possible to explain the decrease of ZnCFO efficiency as component of various vulcanization systems for rubbers of general and special assignment in the earlier submitted line (fig. 10) also by character of formed morphology of compositions. So, at use of ZnCFO as the activator of sulfur vulcanization the structure of rubbers with the minimal value of parameter r is formed, and at transition from sulfur to peroxide vulcanization of elastomeric compositions the particles size of heterophase is increased (fig. 11 b). 

ZnCFO at the contents 5,0 phr promotes to formation of morphological structure of compositions with the minimal particles size of heterophase, that is realized in the improvement of physical-mechanical properties of rubbers. 

Filler surface chemistry is clearly important, although the effects vary widely according to the exact nature of the filler, polymer and surface modifier. Some of the factors that can influence toughness and are, at least in part, controlled by filler surface chemistry include the level of filler polymer interaction [40], the structure of heterophasic polymers [41], the amount of polymer degradation during compounding [42], filler dispersion [43] and polymer crystallinity arising from altered nucleation processes [44]. 

Figure B.6 (a) Singular heterophase interface between an f.c.c. and h.c.p. structures...

All sharp crystal/crystal homophase and heterophase interfaces can be classified as coherent, semicoherent, and incoherent. The structural features of these interfaces can be revealed by constructing them using a series of operations which always starts with a reference structure. 

Syntactic foamed materials are classified as foamed plastics because they are formally similar in structure to cellular gas-expanded plastics in that they are heterophase, gas-solid systems. In general, however, they differ from ordinary foamed plastics in that they are not binary but tertiary systems because the filler and binder are made usually from different materials 3 5). 

These findings suggest strongly that the composition of the elastomeric molecule and the nature of the functional groups affect its compatibility and rate of reaction with the epoxy resin, which in turn affect the molecular and morphological structure of the heterophase system. These data indicate the importance of the acrylonitrile comonomer and the carboxyl groups in controlling the polarity of the rubber, and subsequently its compatibility characteristics with the epoxy. We could also... 

For crystalline-crystalline interfaces we further discriminate between homophase and heterophase interfaces. At a homophase interface, composition and lattice type are identical on both sides, only the relative orientation of the lattices differ. At a heterophase interface two phases with different composition or/and Bravias lattice structure meet. Heterophase interfaces are further classified according to the degree of atomic matching. If the atomic lattice is continuous across the interface, we talk about a fully coherent interface. At a semicoherent interface, the lattices only partially fit. This is compensated for by periodic dislocations. At an incoherent interface there is no matching of lattice structure across the interface. 

Because of its heterophase nature, emulsion polymerization is generally more complicated than simple solution polymerization in which monomers and polymers are soluble in a suitably chosen solvent. In emulsion polymerization the different relative solubilities of monomers in water and in the polymer particles lead to different reaction locales and to different particle structures. Another complicating factor is the need to achieve and maintain colloidal stability throughout the polymerization and subsequent handling of the dispersions. Emulsion polymers can properly be called products by process since the process details exert such a powerful effect on the properties of the particles and resultant films. Consequently, an emulsion polymer is far more than a product defined by a simple polymer composition. 

With the advent of advanced characterization techniques such as multiple detector liquid exclusion chromatography and - C Fourier transform nuclear magnetic resonance spectroscopy, the study of structure/property relationships in polymers has become technically feasible (l -(5). Understanding the relationship between structure and properties alone does not always allow for the solution of problems encountered in commercial polymer synthesis. Certain processes, of which emulsion polymerization is one, are controlled by variables which exert a large influence on polymer infrastructure (sequence distribution, tacticity, branching, enchainment) and hence properties. In addition, because the emulsion polymerization takes place in an heterophase system and because the product is an aqueous dispersion, it is important to understand which performance characteristics are influended by the colloidal state, (i.e., particle size and size distribution) and which by the polymer infrastructure. 

An extension of the kinetic theory on cases when a mechanical pressure interacts with kinetic processes inside solid volume and on interfaces has wide application interests. The elastic deformations in solid are presented from influence of external forces and from presence of internal defects of crystal structure point defects (vacancy, intersite atoms, complexes of atoms, etc.), extended defects (dislocations and inner interfaces in polycrystals), and three-dimensional defects (heterophases crystals, polycrystals). 

The metal-insulator—semiconductor (MIS) structure is employed in the heterophase blocking where the thickness of the insulator used is the key factor in satisfying the blocking requirement. Differently from the solar cell with MIS structure, in which an insulating film tens of angstroms thick is used to avoid the back-diffusion of photoinduced carriers (Wronski et al., 1981), the photoreceptor of electrophotography has necessarily a rather thick insulating film to block carrier transport. 

Therefore, another idea is the synthesis of amphiphilic systems via radical polymerization using a two-phase or heterophase starting situation. In principle, these techniques allow the kinetic control of the copolymer structures or monomer sequence of the polymer chain. The final polymer chain is not only defined by the... 

Under defined conditions, the toughness is also driven by the content and spatial distribution of the -nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of the /1-phase in heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of -nucleated grades has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the /3-modification (towards the cross-hatched structure of the non-nucleated resin) which induce a higher mobility of both crystalline and amorphous phases. 

The terms incommensurate and semi-commensurate are analogous to incoherent and semi-coherent for interfaces - in grain boundaries, heterophase interfaces and epitaxial layers (cf. also Nabarro - with which layered misfit structures have much in common. In extreme cases noncommensurability may arise by mutual rotation (to varying degrees) of component layers with identical component lattices... 

Most food biopolymers have limited miscibility on a molecular level and form multicomponent, heterophase and nonequilibrium dispersed systems. A thermodynamic approach is applicable for studying structure-property relationships in formulated foods since their structures are based on nonspecific interactions between components and such thermodynamically based operations as mixing of components, changing temperature and/or pH, underlies processing conditions. 

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