Discrete phase domain

The relaxation data for the poly(vinyl chloride)/poly(butadiene-co-acrylonitrile), PVC/NBR, system shown in Figure 2.9, on the other hand, appear essentially as a series of parallel lines (Manabe et a/., 1969). The broad spectrum of relaxation times observed also suggests a lack of discrete phase domains. 

The morphologies of the miscible, immiscible, and partially miscible polymer blends are distinct from each other. In an immiscible blend, two phases are present the discrete phase (domain), which is lower in concentration, and the continuous phase, which is higher in concentration. The miscible polymer blends exhibit singlephase morphology. Partially miscible polymer blends may form completely miscible blends at a different composition. The two phases may not have a well-dehned boundary. Each component of the blend penetrates the other phase at a molecular level. The molecular mixing that occurs at the interface of a partially miscible two-phase blend can stabilize the domains and improve the interfacial adhesion. A compatible blend that has commercial possibilities may be immiscible, and a miscible polymer blend may lack commercial applications due to other factors such as cost, source of raw materials, safety, and environmental issues such as recyclability. 

Though both miscible and immiscible blends are composite materials, their properties are very different. A miscible blend will exhibit a single glass transition temperature that is intermediate between those of the individual polymers. In addition, the physical properties of the blends will also exhibit this intermediate behavior. Immiscible blends, on the other hand, still contain discrete phases of both polymers. This means that they have two glass transition temperatures and that each represents one of the two components of the blend. (A caveat must be added here in that two materials that are immiscible with very small domain sizes will also show a single, intermediate value for Tg.) In addition, the physical properties... 

Woo et al. (1994) studied a DGEBA/DDS system with both polysul-fone and CTBN. The thermoplastic/rubber-modified epoxy showed a complex phase-in-phase morphology, with a continuous epoxy phase surrounding a discrete thermoplastic/epoxy phase domain. These discrete domains exhibited a phase-inverted morphology, consisting of a continuous thermoplastic and dispersed epoxy particles. The reactive rubber seemed to enhance the interfacial adhesive bonding between the thermoplastic and thermosetting domains. With 5 phr CTBN in addition to 20 phr polysul-fone, Glc of the ternary system showed a 300% improvement (700 Jm-2 compared with 230 J m 2 for the neat matrix). 

Styrenic block copolymers derive their useful properties from their ability to form distinct styrene (hard phase) and diene (rubber phase) domains, with well defined morphologies. To achieve this requires an unusual degree of control over the polymerization. The polymerization must yield discrete blocks of a uniform and controlled size, and the interface between the blocks must be sharp. This is best achieved by so-called living polymerization. For a polymerization to be classified as truly living, it is generally accepted that it must meet several criteria [3] ... 

A structural model, based on a complex process of stretch induced ordering in the polyacetylene domains, was proposed to account for these observations. Support for this model was obtained using electron microscopic techniques. Low polyacetylene content blends (<20% PA) were found to consist of discrete polyacetylene domains dispersed in a continuous polybutadiene matrix. In the high polyacetylene content blends (>70% PA), both phases were simultaneously continuous, forming an interpenetrating network structure. Blends with intermediate compositions consist of both continuous and isolated domains of polyacetylene distributed throughout the polybutadiene matrix. 

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. 

Under partial acetylation, the size of Valonia cellulose crystals diminished in diameter such decrease is not homogeneous and corresponds to the loss of discrete fragments. At the beginning of the acetylation, the la phase is more susceptible to acetylation than the ip phase the latter appears more resistant. The missing fragments correspond to la domains, which are solubilized initially. These domains, which are more susceptible to acetylation, are acetylated first leaving behind exposed surfaces somewhat depleted in the la phase (Fig. 39). This confirms that in Valonia cellulose the la and Ip phases occur as discrete phases within the same microfibril. 

The majority of textile fibers have a morphology that can be described by the classical two-phase model for semicrystalline polymers [105]. In this model, discrete crystalline domains on... 

The following strategy has been utilized in numerical simulations. First, the flow fields of drying air were simulated without the discrete phase until a converged solution was obtained. At the next step, spray droplets were injected into the domain and two-way coupled calculations were performed until a converged steady solution was achieved. 

It is energetically favourable for the SS and HS not to mix. Thus during cooling from above a critical order-disorder temperature, spontaneous segregation of SS and HS into separate soft (SS-rich) and hard (HS-rich) phases occurs by the process of spinodal decomposition. To achieve elastomeric performance, the SS must be the majority constituent by mass, and the phase structure then takes the form of discrete hard domains dispersed within a soft matrix. Such a phase structure impacts on mechanical properties, and a further structural parameter of importance, therefore, is the degree of phase separation. 

Percolation phenomena deal with the effect of clustering and coimectivity of microscopic elements in a disordered medium [129], Percolation theory represents a random composite material as a network or lattice structure of two or more distinct types of microscopic elements or phase domains, the so-called percolation sites. These elements represent mutually exclusive physical properties, e.g., electrically conducting vs. isolating phase domains, pore space vs. solid matrix, atoms with spin up vs. spin down states. Here, we will refer to black and white elements for definiteness. The network onto which black and white elements of the composite medium are distributed could be continuous (continuum percolation) or discrete (discrete or lattice percolation) it could be a disordered or regular network. With a probability p a randomly chosen percolation site will be... 

The lattice Boltzmann method is a mesoscopic simulation method for complex fluid systems. The fluid is modeled as flctitious particles as they propagate and collide over a discrete lattice domain at discrete time steps. Macroscopic continuum equations can be obtained from this propagation-collision dynamics through a mathematical analysis. The nature of particulates and local dynamics also provide advantages for complex boundaries, multi-phase/multicomponent flows, and parallel computation. 

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