Dependence of zero-shear viscosity

The rheological behavior of storage XGs was characterized by steady and dynamic shear rheometry [104,266]. Tamarind seed XG [266] showed a marked dependence of zero-shear viscosity on concentration in the semi-dilute region, which was similar to that of other stiff neutral polysaccharides, and ascribed to hyper-entanglements. In a later paper [292], the flow properties of XGs from different plant species, namely, suspension-cultured tobacco cells, apple pomace, and tamarind seed, were compared. The three XGs differed in composition and structural features (as mentioned in the former section) and... 

The motion of polymers in concentrated solution and bulk is of major theoretical and practical concern. For example, the strong dependence of zero-shear viscosity on molecular weight (approximately the 3.4 power) and the marked decrease of viscosity 1) with shear rate y not only bespeak some of the unusual properties of long-chain molecules but also are of essential importance in virtually every processing operation. Yet the reasons for these unusual behaviors have become clear only recently. The reptation con-... 

A more quantitative interpretation of the scattering data involves molecular models. As an example, we turned to the Rouse model [20] developed for solutions and extended to melts [21]. As this model is unable to account for the molecular weight dependence of zero-shear viscosity (t o M ) above the critical molecular weight (Mc 35 000 for PS), the analysis wall be extended as a next step to other models which are more realistic for entangled systems. A basic result of the Rouse model relates the monomeric friction coefiBcient Co and the zero-shear viscosity t o ... 

Figure 5.5 Illustration of the dependence of zero-shear viscosity t]o and equilibrium modulus Go on conversion p for a cross-linking system. (From Winter, Encyclopedia of Polymer Science and Engineering, Copyright 1989. Reprinted by permission of John Wiley Sons, Inc.)...

Figure 7.27. Concentration dependence of zero shear viscosity of polypropylene blends with two linear low density polyethylenes at 190°C. Points are experimental with error bars indicating the standard deviation [Dumoulin, 1988]. Lines are computed from Eq 7.125.

Figure 7.29 Concentration dependence of zero shear viscosity at 260, 280 and 300°C of polyethyleneterephthalate blended with polyamide-6,6. Points are experimental with the error bars indicating the error of measurements 2% ]Utracki et al, 1982].

Figure 7.31. Concentration dependence of zero shear viscosity at 200°C of PS/LDPE blends without (solid line) and with (broken line) 5 wt% SEE. Points — experimental error bars of measurement 3% [Austin et al., 1987].

An example is the molecular-weight dependence of zero-shear viscosity as shown in Fig. 4.7 for various nearly monodisperse polymers. As the molecular weight increases above a critical value Me, the viscosity increases much more rapidly than in the low-molecular-weight region below Me, exhibiting the well-known 3.4 power law. ... 

Dreval, V. E., Malkin, A. Y., and Botvinnik, G. O., Approach to generalization of concentration dependence of zero-shear viscosity in polymer solutions, J. Polym. Sci. Polym. Phys. Ed., 11,1055-1076(1973). 

Fig. 7.39 Concentration dependence of zero shear viscosity of PS/PMMA blends at 180 and 210 °C. Points are experimental (Valenza et al. 1991) solid lines are computed from Eq. 7.125...

Figure 26 Dependence of zero-shear viscosity and critical shear rate concentration on salt concentration for polyacrylamide aqueous solutions. (From KC Tam and C Tiu, Water-soluble polymers (rheological properties) in Polymeric Materials Encyclopedia, JC Salamone, ed. Boca Raton, FL CRC Press, 1996, p. 8655.)...

FIGURE 14.7 Temperature dependence of zero-shear viscosity. Zero-shear viscosities from modified Cross fits to the L-80 polyisohutylene data from Figure 14.6a [9] and plotted according to Equation 14.10. 

Solution. The temperature dependence of zero-shear viscosity is given by Equation 14.11. Therefore, between temperatures Tj and T2,... 

Equations 14.10 and 14.11 are two different ways of representing the temperature dependence of zero-shear viscosity. For a material that follows the WLF Equation 14.11, obtain an expression for the temperature-dependent activation energy E in Equation 14.10. 

Figure 4.1 The dependence of zero-shear viscosity /Jq on molecular weight for homopolymer melts (1) poly (dimethyl siloxane), (2) polyisobutylene,...

What is significant in these observations is that the molecular theory presented in the preceding section confirms the experimental observation that the composition dependence of zero-shear viscosities of miscible polymer blends depends on interaction parameter x, the extent of attractive segmental interactions. Without the molecular theory, we cannot explain the reason why the plots of log )ob versus blend composition show positive deviations from linearity for PMMA/PSAN blends and negative deviations from linearity for PMMA/PVDF blends. 

It should be clear that the disordered PS-Wocfe-PI chain does not possess the properties of a neat PS or neat PI chain, but it has new properties influenced by the chain connectivity. For instance, the friction coefficient of a disordered PS-fi/t)cA -PI chain would not be the same as the friction coefficient of neat PS chain or the friction coefficient of neat PI chain. It is reasonable to surmise that the friction coefficient of a disordered PS-h/ocfe-PI chain depends not only on its composition but also on chain connectivity (the junction effect) between the two chains. On the basis of the considerations presented above, we conclude that the stronger molecular weight dependence of zero-shear viscosity for disordered SI diblock copolymers a M for M > M ) displayed in Figure 8.34 is attributable to the presence of the styrene-isoprene (S-I) junction, which originates from the difference in the monomeric friction coefficients between PS and PI blocks. At present, however, we do not have theoretical guideline as to how the junction effect can be incorporated into the description of the dynamics of disordered block copolymers. 

In this contribution, a series of polydisperse polystyrene sanples with various eoncentrations were electrospim from THF solution. The concentrations for the onset of fiber formation as well as the complete fiber formation were determined by SEM analysis. The rheological properties of the aforementioned polystyrene-THF solutions were also studied. The dependence of zero-shear viscosity on the weight average molecular weight as well as the solution concentrations was determined. Results are compared with the monodisperse systems. The effects of molecular weight distribution were studied. 

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