Melt-like regions

At the comparison of concentration dependencies of the characteristic quantities (6.61) with experimental determinations, one has to remember that effect of excluded volume was not taken into account in equations (6.61), which allow us to say only about qualitative correspondence. The behaviour of the initial viscosity is the most widely studied (Poh and Ong 1984, Takahashi et al. 1985). The concentration dependence of the viscosity coefficient in the melt-like region can be represented by a power law (Phillies 1995). The index can be found to be approximately 25 + 1, in accordance with (6.61). There are some differences in the behaviour of polymer solutions, which are connected with different behaviour of macromolecular coils at dilution. 

The content of liquid-like region (aa) is obtained by deconvoluting the intensity in the twisting region into a narrow band centered at 1,295 cm-1 and a melt-like broader component centered at 1,303 cm-1. Thus,... 

Figure 3.28 Each of the two images contains superimposed configurations of a chain at many different instants in time in a molecular-dynamics simulation of a melt of such chains in a box. Over the time scale simulated, each chain appears to be confined to a tube-like region of space, except at the chain ends. (From Kremer and Grest, reprinted with permission from J. Chem. Phys. 92 5057, Copyright 1990 American Institute of Physics.)...

Polyester BB1 was run twice in steady mode at 290°C (Figure 10), and shows that the orientational effect of the first run has a drastic effect on steady shear viscosity. In the first run the log viscosity vs. log shear rate had a slope of -0.92 (solid like behaviour, yield stress), but in the second run a pseudo-Newtonian plateau was reached from approx. 1 sec 1. Capillary viscosity values corresponded reasonably well with the second run steady shear data. The slope at high shear rates was close to -0.91 which corresponds nicely to the first-run steady shear run. All this could suggest, that this system is not completely melted, but still has some solid like regions incorporated. At 300°C capillary viscosity data showed an almost pseudo-Newtonian plateau. This corresponds quite well to the fact that fiber spinning as mentioned earlier was difficult and almost impossible below 290°C, but easy at 300°C. At an apparent shear rate of 100 sec 1, a die-swell was found to be approximately 0.95. 

Fig. 2 Left . Simulated monomer density profile (distribution of intrastar density around the center of mass) for a melt of stars of varying arm number f (from left star to right open square . 2 (linear chain), 4, 8, 16, 24, 36, 48, 64) [41]. The low intrastar density at low functionalities indicates penetrability by other stars (to satisfy incompressibility condition), whereas at high functionality the star core is formed with constant density. Inset . Cartoon illustration of a multiarm star with the three areas in different colors melt-like inner black core, theta-like intermediate blue unswollen and excluded-volume outer red swollen region. Right . The predicted Daoud-Cotton [28] monomer density distribution. The horizontal dashed line indicates the average solution concentration...

The spatial aggregation of topological defects evident in Figs, 5a- la is directly related to the other prominent feature of the dense WCA liquid extensive solid-like regions, which appear as rafts of nearly hexagonal Voronoi cells. As we will show, this dramatic spatial inhomogeneity is a consequence of the defect condensation transition that produces the liquid phase. Thus, it is the key qualitative feature of liquid structure that is required to understand 2D melting. 

In contrast to its minor role in TATA-directed assembly of TFIIIB, the TBlIB-like region of Brfl plays a major role in Pol III recruitment and promoter melting (Hahn and Roberts, 2000 Kassavetis et al., 1998, 2001). The TFIIB-core region of Brfl is sufficient for a binary interaction with two Pol Ill-specific subunits, Rpcl7 and Rpc34 (Ferri et al., 2000 Khoo et al.,... 

In the previous chapter, we discussed the dynamics of a polymer in a fixed network. We shall now discuss the polymer dynamics in concentrated solutions and melts. In these systems, though aU polymers are moving simultaneously it can be argu that the reptation picture will also hold. Consider the motion of a certain test polymer arbitrarily chosen in melts. If the test polymer moves perpendicularly to its own contour, it drags many other chains surrounother hand the movement of the test polymer along its contour will be much easier. It will be thus plausible to assume that the polymer is confined in a tube-like region, and the major mode of the dynamics is reptation. 

Much of the interesting physics in semicrystaUine materials is hidden in the transition region between the crystalline domain and the melt-like domain. In particular in polymeric systems with a certain degree of stiffness of the backbone, the chain connectivity between both phases results in a rather wide transition region. In the following, we focus on the characterization of the crystal-melt interface by invoking the Gibbs construction of a sharp... 

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