Compositional Dependence of Viscosity

The compositional dependence of the viscosity of glass forming melts is closely related to the connectivity of the structure. In general, changes in composition which reduce connectivity reduce the viscosity, while those which increase connectivity increase the viscosity. These changes are accompanied by changes in fragility which may or may not follow the trend in viscosity, but which are very important in discussion of the temperature dependence of viscosity. 

Viscosity data are usually presented in one of two forms. The first form of presentation, which is termed the isothermal viscosity, reports the viscosity at specified temperatures. The second form of presentation reports the temperature at which specified viscosities occur, e.g., the values of the Littleton softening temperature or the glass transformation temperature. In general, temperatures referring to a specified viscosity are termed isokom temperatures for that viscosity. If a series of curves showing the isokom temperatures are presented on a figure, the individual curves are termed isokoms (lines of constant viscosity). 

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COMPOSITIONAL DEPENDENCE OF VISCOSITY OF BITUMENS AND HEAVY OILS... 

Numerous studies on the effect of temperature on bitumen viscosity have been conducted by various researchers in recent years and a number of viscosity correlations have been proposed. However, due to the complexities involved in determining the extent of asphaltene aggregation, not much attention has been paid to the compositional dependence of viscosity of bitumens and heavy oils. 

Concentrated, Binary Mixtures of Nonelectrolytes Several correlations that predict the composition dependence of Dab. re summarized in Table 5-19. Most are based on known values of D°g and Dba- In fact, a rule of thumb states that, for many binary systems, D°g and Dba bound the Dab vs. Xa cuiwe. CuUinan s equation predicts dif-fusivities even in hen of values at infinite dilution, but requires accurate density, viscosity, and activity coefficient data. 

Kandyrin, L. B. and Kuleznev, V. N. The Dependence of Viscosity on the Composition of Concentrated Dispersions and the Free Volume Concept of Disperse Systems. Vol. 103, pp. 103-148. 

Composition Dependence of Alloy Viscosity. Attempts have been made to calcnlate the viscosity of a dilnte liquid alloy from a theoretical standpoint, but with little success. This is primarily due to the fact that little is known about the interaction of dissimilar atoms in the liquid state. Empirical relationships for the viscosity of dilute liquid alloys have been developed, but these are generally limited to specific alloy systems—for example, mercury alloys with less than 1% impurities. The viscosities of binary liquid alloys have been empirically described using a quantity called the excess viscosity, (not to be confused with the excess chemical potential), which is defined as the difference between the viscosity of the binary mixture (alloy), pa, and the weighted contributions of each component, xipi and X2P2-... 

Real examples illustrating different types of time dependences of viscosity, can be found elsewhere.52 It is worth mentioning that the rheokinetics of polymerization, even for a specific type of polymer (for example, polyurethane) depends on the composition, which determines both the kinetics of the process and the structure of the newly formed polymer. Clearly, the important factor is whether a linear or three-dimensional polymer is formed. In the first case, the viscosity increases... 

The dependence of viscosity at 30 °C on composition is studied for the liquid complex fertilizer consisting of diammonium phosphate, potash and water (NH4)2HP04, K2C03, H20. For the investigation, the region of unsaturated solutions for both salts at 30 °C is selected (Fig. 3.28), the side of the concentration triangle being m=0.5. 

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