Discrete phase

Impact polystyrene contains polybutadiene added to reduce brittleness. The polybutadiene is usually dispersed as a discrete phase in a continuous polystyrene matrix. Polystyrene can be grafted onto rubber particles, which assures good adhesion between the phases. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Early ia the development of chemical reaction engineering, reactants and products were treated as existing ia single homogeneous phases or several discrete phases. The technology has evolved iato viewing reactants and products as residing ia interdependent environments, a most important factor for multiphase reactors which are the most common types encountered. 

There are a large number of processes in the chemical industries that handle a variety of suspensions of solid particles in liquids. The application of filtration techniques for the separation of these heterogeneous systems is sometimes very costly. If, however, the discrete phase of the suspension largely contains settleable particles, the separation can be effected by the operation of sedimentation. The process of sedimentation involves the removal of suspended solid particles from a liquid stream by gravitational settling. This unit operation is divided into thickening,... 

A completely discrete phase space (i.e. discrete values of lattice-site positions, particle velocities and time, so that particles move from site-to-site and collisions taken within discrete time steps). 

The eukaryotic somatic cell cycle is defined by a sequential order of tasks a dividing cell has to complete it must replicate its DNA, segregate its chromosomes, grow, and divide. The cell cycle can be divided into four discrete phases. DNA replication is restricted to S phase (DNA synthesis phase), which is preceded by a gap phase called G1 and followed by a gap phase called G2. During mitosis (M phase) the sister chromatids are segregated into two new daughter nuclei and mitosis is completed by the division of the cytoplasm termed cytokinesis (Fig. 1). 

In each of the studies described above, the reader is encouraged to watch the development of the two phases from the original homogeneous mixture. Note that there is significant clustering of like molecules well before two discrete phases form. Another observation is the ragged nature of the interface. It is not a smooth discrete separation in this molecular system level model. 

In the cements of this type a number of phases are known to be present. For example, in the zinc oxychloride cement two discrete phases, corresponding to the composition ZnO. ZnCl. H O in the ratios 4 1 5 and 1 1 2 respectively, are known to occur (Sorrell, 1977). Similarly, in the magnesium oxychloride cement, phases corresponding to Mg(OH)a. MgClj. HjO in the ratios 5 1 8 and 3 1 8 have been shown to exist and have been studied by X-ray diffractometry (Sorrell Armstrong, 1976). 

Sorrell showed that the two discrete phases could be readily and reversibly interconverted. For example, the 1 1 2 phase was found to react... 

This regime is characterized by the presence of one continuous fluid phase and one discrete fluid phase in tubular systems. The existence of the discrete phase generates a large interfacial area per unit tube volume for all flow configurations included in this regime. For that reason, Regime IV is of pragmatic interest when interphase heat and mass transfer are of key importance. 

It is assumed that the discrete phase exists as drops (or bubbles) that can be characterized by an average velocity, an average size, and an average enthalpy at each axial position. A steady-state balance on the number of drops (or bubbles) present at each axial position is given by... 

In this section subscript I refers to the discrete phase and subscript II to the continuous phase. 

Figure 10,5 Schematic diagram of various discrete phase morphologies a) rods, b) platelets and c) spheres...

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... 

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form... 

The scattering patterns from any materials that are made from a finite number of discrete phases conform to Porod s law. In most of the practical applications it is sufficient to consider the most simple case of a two-phase system. In-depth considerations concerning the interpretation of scattering data from multiphase systems have been published by JAnosi [138],... 

Fe(II) is the immediate reduced product, possibly bound to organic ligands ( Fe(II)-LFe(n) ), and eventually released to a larger pool of Fe(II), including Fe(II)aq. In terms of quantities that may be measured for their Fe isotope compositions, these would include the ferric substrate, Fe(II)aq, and likely Fe(II)-LFe(n) (although not a discrete phase) if this exists in the aqueous solution component. We assume that the Fe(III)-LFe(ni) component is not represented in a sample of the ambient aqueous solution, but instead is closely bound to or associated with the cells. 

Figure 7.3 The cell cycle Is Illustrated In this figure. Cell division proceeds through discrete phases Gj during which the cell grows and prepares for division the S phase where the DNA content and chromosomes double where the cell develops the structures needed for cell division and the M phase where the nucleus splits Into two and the cell divides Into two daughter cells.

Krahenbuhl, J. L. (1980). Effects of activated macrophages on tumor target cells in discrete phases of the cell cycle. Cancer Res. 40, 4622-4627. 

Title Degradable Polymeric Implantable Medical Devices with a Continuous Phase and Discrete Phase... 

At present, we believe that the jump transitions observed in many of the gels studied here represent first order phase transitions. If this is the case, then the gels studied here are among the first found so far in which a first order phase transition occurs near room temperature in pure aqueous solvent with substantial added salt. Early studies by Tanaka s group with poly(acrylamide) based gels required that hydrophobic solvents such as acetone be added for a discontinuous phase transition to be observed near room temperature [6-10]. The more recently studied gels based on poly(n-isopropylacrylamide) [11, 12] and other lower critical solution temperature polymers show discrete phase transitions in water with no salt [11], but the swelling transitions become continuous when moderate amounts of salt are added [12],... 

Our discussion of RNA synthesis begins with a comparison between transcription and DNA replication (Chapter 25). Transcription resembles replication in its fundamental chemical mechanism, its polarity (direction of synthesis), and its use of a template. And like replication, transcription has initiation, elongation, and termination phases—though in the literature on transcription, initiation is further divided into discrete phases of DNA binding and initiation of RNA synthesis. Transcription differs from replication in that it does not require a primer and, generally, involves only limited segments of a DNA molecule. Additionally, within transcribed segments only one DNA strand serves as a template. 

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