Entanglement other forms

To understand this viscosity enhancement, it is easier to start with the theory for linear polymers. The behavior of linear polymers can be described by the reptation model.For a linear polymer of high molecular weight in the melt, chains can be modeled as a confined tube where the diffusion of the chain is restricted along the tube contour. Entanglements are formed between chains where the reptation of a chain along its contour becomes the dominant mode of movement. The addition of a branch point prevents reptation and other forms of movement must occur for the chain to change its configuration. In the case... 

Other more complex morphologies also arise for A-B mixtures. In particular, domains A and B may enclose each other, forming entangled networks, separated by a hyperbolic interface. Those cases include mesh , bicontinuous microemulsions, bicontinuous cubic phases and their disordered counterparts, sponge phases, which are discussed below. In these cases too, the sign (convex/concave) of the interfacial mean curvature sets the Type . A representation of the disordered mesostructure in a Type 2 bicontinuous microemulsion is shown in Figure 16.3. A hyperbolic interface may be equally concave and convex (a minimal surface, e.g. see Figure 16.2(c)) so that the mesophase is neither Type 1 nor Type 2. Lamellar mesophases ( smectics or neat phases) are the simplest examples. Bicontinuous balanced microemulsions, with equal polar and apolar volume fractions are further examples. 

The coverage of the surface of a filler with a polymer layer which is capable of interdiffusion with the matrix proved to be very effective both in stress transfer and in forming a thick, diffuse interphase with acceptable deformability. In this treatment the filler is usually covered by a functionalized polymer, preferably by the same polymer as the matrix, which is attached to the surface by secondary, hydrogen, ionic or sometimes even by covalent bonds. The polymer layer inter-diffuses with the matrix, entanglements are formed and, thus strong adhesion is created. Because of its increased polarity, in some cases reactivity, usually maleic anhydride or acrylic acid modified polymers are used, which adsorb to the surface of most polar fillers even from the melt. This treatment is frequently used in polyolefin composites, since other treatments often fail in them, on the one hand, and functionalization of these polymers is relatively easy, on the other. Often a very small amount of modified polymer is sufficient to achieve significant improvement in stress transfer [126, 127]. 

The plastic endblocks phase regions, called domains , are shown in sphere-like form. Other forms are discussed later. These domains act as crosslinks between the ends of the rubber chains, serving to lock the rubber chains and their inherent entanglements in place. The system acts like a conventionally vulcanized rubber that contains dispersed reactive filler particles. 

In this chapter, we will look at a few selected examples to illustrate the different ways networks can interpenetrate, as well as other forms of entanglement related to... 

There are a number of other forms of entanglement besides interpenetration (and self-penetration), which have received considerable interest in recent times. One such class of materials is the polyrotaxane or poly-threaded structures. These entanglements show great variety, partly because there are a number of different types of entanglement which can fall under this banner. 

An analogy to sHp dislocation is the movement of a caterpillar where a hump started at one end moves toward the other end until the entire caterpillar moves forward. Another analogy is the displacement of a mg by forming a hump at one end and moving it toward the other end. Strain hardening occurs because the dislocation density increases from about 10 dislocations/cm to as high as 10 /cm. This makes dislocation motion more difficult because dislocations interact with each other and become entangled. SHp tends to occur on more closely packed planes in close-packed directions. 

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