Viscosity and conductivity measurements

By the time COlL-2 took place in 2007, the nanostructured nature of the ionic liquids had been postulated using molecular simulation [50] and evidenced by indirect experimental data [54, 85] or by direct X-ray or neutron diffraction studies [56]. This microscopic vision of these fluids changed the way their physico-chemical properties could be explained. The concept of ionicity was supported by this microscopic vision, and indirect experimental evidence came from viscosity and conductivity measurements, as presented by Watanabe et al. [54, 86]. This molecular approach pointed towards alternative ways to probe the structure of ionic liquids, not by considering only the structure of the conponent ions but also by using external probes (e.g. neutral molecular species). Solubility experiments with selected solute molecules proved to be the most obvious experimental route different molecular solutes, according to their polarity or tendency to form associative interactions, would not only interact selectively with certain parts of the individual ions but might also be solvated in distinct local environments in the ionic liquid. 

F. M. Jager and B. Kampa measured the mol. conductivity, /x, of potassium iodide at 6 between 691 5° and 814° to be /x=85 41 +0T564(d—700). P. Walden studied the relation between the viscosity and conductivity of soln. of potassium and sodium iodides. F. Kohlrausch has also measured the sp. gr. and specific conductivities of soln. of potassium iodide of various cone., and computed the degree of ionization, a. 

Measurements of dielectric properties have been used to monitor chemical reactions in organic materials for more than fifty years. In 1934, Kienle and Race 11 reported the use of dielectric measurements to study polyesterification reactions. Remarkably, many of the major issues that are the subject of this review were identified in that early paper the fact that ionic conductivity often dominates the observed dielectric properties the equivalence between the conductivity measured with both DC and AC methods the correlation between viscosity and conductivity early in cure the fact that conductivity does not show an abrupt change at gelation the possible contribution of orientable dipoles and sample heterogeneities to measured dielectric properties and the importance of electrode polarization at low frequencies. 

We return now to an important result that measurable values in AHb in DP+-PSS and CP+-PSS solutions are observed at total surfactant concentration around 1 X 10 5 mol dm 3 in accordance with potentiometric measurements (compare Figure 7 with Figures 9 and 10). Other properties, like changes in viscosity of the polyion, volume changes which accompany polyelectrolyte-induced micellization, and conductivity measurements are in agreement with the above findings. 

Once the sampling protocol has been decided, the next step is analysis of the sample(s). Of course, sampling and analysis may also be integrated. In the past 50 years, the type of assays that were done in-process exploited the nonselective properties of the process stream, such as density, viscosity and conductivity. This monitoring has been achieved by both automatic and automated instruments. Selective properties of the process stream, such as chemical composition, were usually measured by taking grab samples and examining them in a laboratory by off-line techniques as they are more difficult to adapt for process stream analysis. 

Accurate density, viscosity, and dielectric-constant measurements for hexamethylphosphortriamide are reported, and conductance measurements show that the solvent is a strongly differentiating medium for the donor... 

In this chapter we will firstly present a literature survey on vapour pressure, viscosity and conductivity properties of phosphoric acid with an emphasis on the temperature and composition range relevant for fuel cell applications. In a second part we want to elucidate the physico-chemical interactions of a protic electrolyte like phosphoric acid as a doping agent with polybenzimidazole-type polymer membranes. Literature data on m-PBI and AB-PBI as well as own measurements on Fumapem AM-55, a commercial PBI derivative, will be cOTisidered. On the basis of the observed doping behaviour a model describing the thermodynamics of the adsorption process is presented. 

Fig. 3. The relative speed of sound, viscosity and conductivity as a function of added hexanol at 303.2 K and 0.1 MPa. The NaDDS molality was 0.2 m. (The temperature for the conductivity measurements was 298.2 K)...

In this reference viscosity and conductivity seem to have been measured at 50°C. This is strange considering the melting point of MA is 53°C (Table 1.2). 

Viscosity experiments, conductivity measurements [62, 63] and NMR data [71] can be interpreted with the rod-like model but these techniques do not actually confirm its validity. 

Another approach was considered to verify the behaviour of vanadium (111) sulphate in the sulphuric acid solution. In this approach, the density, viscosity and conductivity of several glycerol-sulphuric acid solutions in 2.0 M sulphuric acid were measured at 25°C as shown in Table 10.10. The variation of the conductivity values of these solutions with the increase in their viscosity was compared to that of vanadium (111) sulphate solutions in 2.0 M sulphuric acid at 25°C. The measured conductivity values for each of the solutions in the two sets were plotted against the corresponding viscosity values as shown in Figure 10.17. 

Table 10.13 shows the measured density, viscosity and conductivity values for the 2.0 M vanadium (II) sulphate solution. These results show that while the density and viscosity values are less than those of vanadium (III) solutions, conductivity values are significantly higher. The difference between the properties of these solutions reflects the difference in the behaviour of vanadium (II) and vanadium (III) ions in sulphuric acid solutions. 

The density of vanadium (II) sulphate solutions increases with the increase in the vanadium concentration. The extent of the increase is less than that observed for vanadium (III) sulphate solutions. Nevertheless, it should be noted that the difference between the density of vanadium (II) and vanadium (III) sulphate solutions is not significant compared to the differences in the viscosity and conductivity values. This reflects the insensitivity of the density measurements to the changes in the chemical compositions of the solutions compared to the other two methods. 

The measured values of each of the physical properties (density, viscosity and conductivity) were fitted to an empirical formula that describes the property as a function of the vanadium (III) sulphate concentration, sulphiuic acid concentration and temperature. The three properties showed good agreement between the measured and calculated values, indicating successful fitting. 

Before we are in a position to discuss the viscosity of polymer melts, we must first give a quantitative definition of what is meant by viscosity and then say something about how this property is measured. This will not be our only exposure to experimental viscosity in this volume—other methods for determining bulk viscosity will be taken up in the next chapter and the viscosity of solutions will be discussed in Chap. 9—so the discussion of viscometry will only be introductory. Throughout we shall be concerned with constant temperature experiments conducted under nonturbulent flow conditions. 

Effect of Uncertainties in Thermal Design Parameters. The parameters that are used ia the basic siting calculations of a heat exchanger iaclude heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used ia the basic siting calculations. In reaUty, there are uncertainties ia these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes caimot be produced ia precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exactiy, a dding to the uncertainty ia the design and performance calculations. 

Following the general trend of looldng for a molecular description of the properties of matter, self-diffusion in liquids has become a key quantity for interpretation and modeling of transport in liquids [5]. Self-diffusion coefficients can be combined with other data, such as viscosities, electrical conductivities, densities, etc., in order to evaluate and improve solvodynamic models such as the Stokes-Einstein type [6-9]. From temperature-dependent measurements, activation energies can be calculated by the Arrhenius or the Vogel-Tamman-Fulcher equation (VTF), in order to evaluate models that treat the diffusion process similarly to diffusion in the solid state with jump or hole models [1, 2, 7]. 

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