Viscosity Aqueous solutions, pure

In aqueous solution at room temperature the coefficient B is positive for the majority of electrolytes. For some, however, it is negative in such a case the viscosity at moderate concentrations, where the B term is predominant, is less than that of pure water, while at lower concentrations, where the A s/c term becomes predominant, the value of the viscosity rises above that of pure water. An example of this is shown in Fig. 51, where abcissas are /c. The straight line is a plot of A s/c with A = +0.0052, while the lower curve is a plot of Be with B = —0.033. On adding the ordinates of these two curves the middle curve is obtained, which reproduces, within the experimental error, the values of 17/770 obtained for KC1 in aqueous solution at 18°C. 

Correlation between Ionic Entropy and Viscosity. In Chapter 9, when we noticed that certain ions in aqueous solution cause a decrease in viscosity, and asked how this should be explained, it seemed natural to interpret the effect in terms of order and disorder. In pure water at room temperature there is a considerable degree of short-range order ... 

Transition Region Considerations. The conductance of a binary system can be approached from the values of conductivity of the pure electrolyte one follows the variation of conductance as one adds water or other second component to the pure electrolyte. The same approach is useful for other electrochemical properties as well the e.m. f. and the anodic behaviour of light, active metals, for instance. The structure of water in this "transition region" (TR), and therefore its reactions, can be expected to be quite different from its structure and reactions, in dilute aqueous solutions. (The same is true in relation to other non-conducting solvents.) The molecular structure of any liquid can be assumed to be close to that of the crystals from which it is derived. The narrower is the temperature gap between the liquid and the solidus curve, the closer are the structures of liquid and solid. In the composition regions between the pure water and a eutectic point the structure of the liquid is basically like that of water between eutectic and the pure salt or its hydrates the structure is basically that of these compounds. At the eutectic point, the conductance-isotherm runs through a maximum and the viscosity-isotherm breaks. Examples are shown in (125). 

Kxtemivc work has been done on measuring liquid viscosities of the pure Penh. indthcu aqueous solutions Fig-uie 24-9 is a plm of ilw pure ncid viscosities up to I50T. Figures 24-U> 24-11. and 24 12 present aqueous solution data from the Iniwiuttonul CrUiait rj/tfri. ... 

In several previous papers, the possible existence of thermal anomalies was suggested on the basis of such properties as the density of water, specific heat, viscosity, dielectric constant, transverse proton spin relaxation time, index of refraction, infrared absorption, and others. Furthermore, based on other published data, we have suggested the existence of kinks in the properties of many aqueous solutions of both electrolytes and nonelectrolytes. Thus, solubility anomalies have been demonstrated repeatedly as have anomalies in such diverse properties as partial molal volumes of the alkali halides, in specific optical rotation for a number of reducing sugars, and in some kinetic data. Anomalies have also been demonstrated in a surface and interfacial properties of aqueous systems ranging from the surface tension of pure water to interfacial tensions (such as between n-hexane or n-decane and water) and in the surface tension and surface potentials of aqueous solutions. Further, anomalies have been observed in solid-water interface properties, such as the zeta potential and other interfacial parameters. 

Condensation via Terephthalic Acid. The salt from the acid and the diamine is formed easily in the aqueous phase (8). Crystallization is effected by isopropyl alcohol addition. Recrystallization is unnecessary when pure starting components are used. The aqueous solution of the salt is heated under pressure, the solution water is distilled off, the condensation begins, the temperature is increased, and the pressure is lowered. The reaction is complete when the desired viscosity is reached. 

Experiments are performed in a 0.395 m high and 23 mm internal diameter stainless steel reactor, packed with various particles (Table 1). a is measured via C02 fast absorption into 1.5 kmol/m3 DEA aqueous solutions of varying viscosity through addition of ethylene-glycol (ETG). k,a is measured via C02 slow absorption into 0.05 kmol/m3 DEA in ETG. All the experiments are carried out at 298 K. The gas mixture is obtained by mixing 5% vol. COz in pure N2. C02 conversion is determined by gas phase chromatography analysis. Physicochemical properties of the liquids tested are shown in Table 1. 

Arrhenius 6 investigated the effects of addition of non-electrolytes, or very weak electrolytes, small amounts of which (e.g. acetic acid) markedly increase the viscosity of a salt solution, although the pure substance may have a smaller viscosity than water, and the viscosity often reaches a maximum, which becomes flatter with rising temperature. This seems to be confined to aqueous solutions. 

Fig.4 shows the concentration dependence of the t/t water and q/Hwater i various electrolytic aqueous solutions, where the t water is the relaxation time of pure water, and the t] and Tlwater mean the viscosity of the aqueous solution and pure water, respectivelyThe parameter P of the electrolytic aqueous solution changes from /3 - 0.9 to 0.7 for monovalent ions (LiCl, NaCl, KCl, RbCl) and from P -0.9 to 0.5 for divalent ions (Mga2, CaCl2) with increasing concentration. Solid lines represent the concentration dependence of the viscosity ratio of various electrolyte solutions. 

The viscosity of aqueous solutions of povidone depends on their average molecular weight. This can therefore be calculated from the viscosity, giving the viscosity-average molecular weight (see Section 2.2.6). Fig. 7 shows the very considerable differences in viscosity between solutions of the different povidones in water, as a function of their concentration. A 20% aqueous solution of povidone K 12 shows hardly any visible difference to pure water, while a 20% solution of povidone K 90 in water gives high viscosities until 5000 mPa-s. 

The viscosity of concentrated solutions can be quite different from that of the pure solvent. Many models have been proposed to calculate the viscosity of liquid mixtures from the viscosity of the pure components. These models rely on interpolation. As is often the case, mixtures of components that can exhibit intermolecular hydrogen bonding and especially aqueous solutions must be considered separately. 

Table 5.2 also gives examples of the viscosity of some aqueous solutions. It is seen that most solutes increase the viscosity, although the increase is quite small for KC1. A 20% aqueous ethanol solution is seen to have a distinctly higher viscosity than each of the pure liquids this must be related to the contraction—hence a decrease in free volume—occurring upon mixing of the two liquids. Also for solutions it is useful to have a look at the effects of dispersed particles (or molecules). 

Viscosity studies of ionic polysoaps in pure aqueous solution usually suffer from the polyelectrolyte behaviour experienced at low concentrations [46, 49, 52, 75, 78, 98, 99, 126, 130,193, 219, 229, 338]. Indeed, as the dissociation of the ionic groups varies with the concentration, meaningful concentration dependent studies become difficult. The problem was frequently overcome by addition of salt (Fig. 19). But ternary systems are created, making the systems even more complex, and many ionic polysoaps tend to precipitate in brine [50, 54, 299], These problems can be avoided by zwitterionic polysoaps, facilitating the interpretation of concentration dependence [78]. 

The diminished viscosity of a polyelectrolyte in aqueous solution is a complex function of polymer concentration and ionic strength. This is shown schematically in Fig. 4. Curve 1 represents a polyelectrol3rte in pure water ionization increases with increasing dilution, and the mutual repulsion of the charged groups causes the macromolecule to expand. According to the theory of Fuoss, there is a monotonic increase in the value of /,p/c with increasing dilution (solid fine) Rosen, Kamath, and Eirich, ... 

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