Viscosity behavior solvent mixture

With the least polar solvent, 9 1 MIBK/MEOH, aggregation dominates the viscosity behavior. This solvent is of intermediate quality, between pure MeOH and the 1 1 mixture. Still, the viscosity is greatest using the 9 1 mix at all temperatures, by up to a factor of four. The effect of temperature on the aggregation in the 9 1 MIBK/MeOH solution is so large that the fmj versus 1/T curve becomes significantly nonlinear. An apparent E determined when... 

Another interesting contribution to the study of viscosity behavior in the helix-coil Jransition region is the one due to Hayashi et al. (22) on a PBLA sample (Mw = 23.2 x 104) in m-cresol and a mixture of chloroform and DCA (5.7 voL-% DCA). As mentioned in Chapter B, PBLA undergoes an inverse transition in the chloroform-DCA mixture, while it undergoes a normal transition in m-cresol. Furthermore, its cooperativity parameter is distinctly smaller in the former solvent than in the latter. Thus we may expect that, when compared at the same helical fraction and chain length, the PBLA molecule in the chloroform-DCA mixture assumes a more extended shape and hence a larger intrinsic viscosity than in m-cresol, provided these two solvents have comparable solvent powers for the polymer. The experimental results shown in Fig. 32 are taken to substantiate this prediction, because the approximate agreement of the data points atfN=0 indicates that the two solvents have nearly equal solvent powers for the solute. 

Variations in the temperature coefficient of viscosity with solvent, which have also been presented as evidence of association in concentrated solutions (135,143), could be similarly related to differences in Ta among the solutions. When free draining behavior is a possibility, the relative viscosities in different solvents should be compared at the same value of Co f°r the mixtures (that is, at constant free volume rather than at constant temperature). In any case, it is clear that a very well planned series of experiments is necessary in order to test for the existence of additional specific effects such as association. These comments are not meant to suggest that association can not occur at moderate concentrations. Indeed, the existence of association in various forms of polymethyl methacrylate seems well established (144). The purpose is rather to advocate that less specific causes be eliminated before association is inferred from viscosity measurements alone. 

In contrast to neutral polymer solutions, where reduced viscosity, 17sp/c, plotted against weight concentration (usually g/dL) shows a straight line (expressed by the Huggins equation) [32], the typical viscosity behavior of a polyelectrolyte solution is shown in Figure 4. This polyelectrolyte was made by quatemization of poly(styrene-co l-vinylpyridine) with n-butyl bromide [16]. The solvents used were a nitromethane/dioxane mixture. Figure 4... 

FIGURE 5.6 Variation of viscosity of solutions of partially chlorinated poly(l,4-phenylene-2,6-naphthalamide) dissolved in solvent mixture of hexamethylene phosphoramide and JV-methylpyrrolidone containing 2.9% Li Cl, as a function of solution concentration showing transition from isotropic to anisotropic behavior. (After Morgan, P. W. 1979. Chem. Tech., 316.)... 

Figure 12.1.6 shows two different behaviors for unassociated and associated block copolymers. The first type has a linear relationship between viscosity and concentration whereas with the second there is a rapid increase in viscosity as concentration increases. This is the best described as a power law function. Two polymers in combination have different reactions when dissolved in different solvents (Figure 12.1.7). In MEK, intrinsic viscosity increases as polymer concentration increases. In toluene, intrinsic viscosity decreases as polymer concentration increases. The polymer-solvent interaction term for MEK is very small (0.13) indicating a stable compatible system. The interaction term for toluene is much larger (0.58) which indicates a decreased compatibility of polymers in toluene andlowers viscosity of the mixture. Figure 12.1.8 explicitly shows that the behavior of...

Even binary solvent mixtures can show a very complex behavior of the viscosity depending on the mixing ratio, with minima, maxima and inflection points. The viscosity can also show values of more than double the viscosity of single components. A few examples are shown in Fig. 8.1. 

Several studies have been reported in the hterature about the viscosity behavior of methylimidazolium, pyridiniurn and pyrrolidinium as pure ILs or in binary mixture using water or organic solvents (IL + water or IL + organic solvent) at different temperatures and pressure values. [109]... 

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