Experimental techniques viscosity measurements

Some 30 years ago, transport properties of molten salts were reviewed by Janz and Reeves, who described classical experimental techniques for measuring density, electrical conductance, viscosity, transport number, and self-diffusion coefficient. 

The coefficient of viscosity was introduced in Chapter 2, Section 2.3a, but this parameter is elusive enough to warrant further comment. In this section we examine the definition of the coefficient of viscosity—the viscosity, for short —of a fluid. This definition leads directly to a discussion of some experimental techniques for measuring viscosity these are discussed in the following sections. 

The material in this chapter is organized broadly in two segments. The topics on monolayers (e.g., basic definitions, experimental techniques for measurement of surface tension and sur-face-pressure-versus-area isotherms, phase equilibria and morphology of the monolayers, formulation of equation of state, interfacial viscosity, and some standard applications of mono-layers) are presented first in Sections 7.2-7.6. This is followed by the theories and experimental aspects of adsorption (adsorption from solution and Gibbs equation for the relation between... 

Concentration/separation of sample solutes is one of most important functions in micro- and nanofluidic systems. TGF has proved to be a promising technique that can achieve concentration and separation in microfiuidic devices. However, so far very limited experimental and theoretical investigations have been reported. Experimentally, it is highly desirable to develop various microfiuidic structures that can be utilized by the TGF technique to cmicentrate different samples. Furthermore, more experiments should be carried out to characterize the thermoelectrical properties of buffers and samples so as to obtain the temperature-dependent electroosmotic mobility and electrophoretic mobility, as well as buffer conductivity, viscosity, and dielectric permittivity for each individual sample and buffer solution. In addition, the development of reliable, accurate, high-resolution, experimental techniques for measuring fiow, temperature, and sample solute concentration fields in microfiuidic channels is needed. Theoretically, the model development of TGF is still in its infancy. The models presented in this study assume the dilute solute sample and linear mass flux-driving forces correlations. However, when the concentrations of the sample solute and the buffer solution are comparable, the aforementioned assumptions break down. Moreover, the channel wall zeta potential in this situation may become nonconstant. More comprehensive models should be developed to incorporate the solute-buffer and solute-channel wall... 

Contemporary applications of liquid crystals [1,2] exploit the unique properties of these materials arising from their anisotropic response to external fields and forces. For example, the anisotropy in the dielectric properties makes it possible to construct electro-optical displays, and the characteristic response time of such devices is determined by the anisotropic viscoelastic properties of the liquid crystal [3]. In turn, these viscoelastic properties are related to various kinds of flows and deformations of the material in question. The exact number and nature of viscoelastic constants required to characterise fully the properties of the phase are determined by careful consideration of both static and dynamic behaviour [4]. The specific focus of this Datareview is the description of experimental techniques for measuring the various types of viscosity coefficients allowed in nmiatic phases. 

The experimental techniques to measure viscosity are falling ball, capillary tube or the two cylinder Stabinger method. We think this last is the ideal to measure IL mixtures, where the viscosity value changes some orders of magnitude with the concentration of solvent, because there is not necessary vary the measurement cell with the viscosity value, as it happens in the two first techniques. 

Shear viscosity is a measure of the ahihty of one layer of molecules to move over an adjacent layer. Bulk viscosity will be mentioned in Section V.2. Since viscosity usually refers to shear viscosity, the term will he used in this way unless otherwise stated. Recommended techniques for measuring the viscosity of high-temperature melt are given below. Experimental data are available from the database mentioned in Section 1.2. Data on viscosities of slags (7 single component systems, 35 two-component... 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

Frequency dependent complex impedance measurements made over many decades of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics [1-4]. They are of particular importance for quality control monitoring of cure in complex resin systems because the measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, It is one of the few experimental techniques available for studying the poljfmerization process of going from a monomeric liquid of varying viscosity to a crosslinked. Insoluble, high temperature solid. 

A solution viscosity measurement is a hydrodynamic-thermodynamic technique, and the extent to which a polymer molecule increases the viscosity of a solvent depends on the nature of its interactions with that solvent (as well as on its own molecular weight). These interactions are characterized by the quantity a that appears in equation (3). The calibration of the method, using samples, of the same polymer having known molecular weights, in essence determines its value. The disadvantage of this calibration requirement is offset by the simplicity of the experimental measurements. 

Adamson [15] and Miller et al. [410] illustrate some techniques for measuring surface shear viscosity. Further details on the principles, measurement and applications to foam stability of interfacial viscosity are reviewed by Wasan et al. [301,412], It should be noted that most experimental studies deal with the bulk and surface viscosities of bulk solution rather than the rheology of films themselves. 

Experimental techniques such as those used to measure specific values of viscosity (e.g. softening point) are still in common use, but are not as powerful as those in which a range of viscosities can be measured. Hence, only the Margules (1 to 106 Pa-s), parallel plate (103 to 108), and beam bending viscometers (107 to 1014 Pa-s) will be discussed here. These devices are manufactured and marketed by Theta Industries. 

A number of experimental techniques have been developed for measuring the viscosity and the first (and second) normal stress coefficient. In Table 15.2 a survey of these methods has already been given. 

The chain reaction process can be used as a diagnostic aid to determine whether free radicals are generated from a drug when irradiated. Acrylamide is an acrylic monomer, which is widely used in gel electrophoresis, as a polymer formed in situ by peroxide or UV-initiated polymerization. This monomer is a water soluble solid, more easily handled than most other vinyl monomers, and the progress of its polymerization can be readily followed by measuring its contraction in volume utilizing dilatometry, or its increase in viscosity in a viscometer. Details of this experimental technique can be found in Moore and Burt (18). 

A variety of experimental techniques are available to investigate the structure of microemulsions small angle scattering, specific heat, viscosity and electrical conductivity measurements. In the DDAB systems, conductivity measurements eidiibit a dramatic decrease (typically eight orders of magnitude) as water is added to the mixture. Such changes occur over just a few percent variation in water content, apparently difficult to reconcile with the fact that the oil is (relative to water) non-conducting. It implies that the... 

The viscoelasticity in polymer solutions has been investigated for some time but the experimental techniques which enabled measurements at high dilutions have been developed since around 1948 (24). When a polymer solution is subject to a sinusoidally varying shearing stress its response can be expressed in terms of a complex intrinsic viscosity [j ], the imaginary part of which is the rigidity ... 

M[tj] where [tj] is the intrinsic viscosity. sY and R are two different parameters. sY is an equilibrium parameter R is a dynamic parameter and depends on the method by which it is obtained. Rh becomes the Stokes radius R, in diffusion measurements and the Einstein radius R in viscosity measurements. Because SEC fractionation depends on R, the method is not appropriate for a direct measure of sY - Convenient experimental methods to measure sY are scattering techniques. 

To understand this discrepancy, we need to remember that there is a second source of error in any experiment systematic error that causes a shift in the measured values from the true value and reduces the accuracy of the result. By making more measurements, we can reduce the uncertainty due to random errors and improve the precision of our result however, if systematic errors are present, the average value will continue to deviate from the true value. Such systematic errors may result from a miscalibration of the experimental apparatus or from a fundamental inadequacy in the technique for measuring a property. In the case of Millikan s experiment, the then-accepted value for the viscosity of air (used in calculating the charge e) was subsequently found to be wrong. This caused his results to be systematically too high. 

Structural studies in fused salts by means of careful and thorough high-temperature measurements of electrical conductivity, density, viscosity, and laser- Raman spectroscopy have been reviewed. Four problem areas are discussed (1) melting mechanisms of ionic compounds with large polyatomic cations, (2) salts as ultra-concentrated electrolyte solutions, (3) structural aspects and Raman spectroscopy, and (4) electrolysis of molten carbonates. The results in these areas are summarized and significant contributions to new experimental techniques for molten-salt studies are discussed.275 The physical properties and structure of molten salts have also been reviewed in terms of operational (hole, free volume, partly disordered crystal) and a priori (intermolecular potential) models.276 Electrochemistry... 

The compression or decompression of bovine serum albumin monolayers spread on an aqueous substrate at a pH near the isoelectric point can effect surface tension. The surface pressure changes depend on the distance between the position of the surface pressure measuring device and the compression barrier. This effect is minimal at a pH above or below the isoelectric point and undetected for small molecules (myristic acid and eicosyl sodium sulfate) even when the substrate contains substituted alkyl amines. A theory is proposed which attributes the above observation to surface drag viscosity or the dragging of a substantial amount of substrate with the BSA monolayer. This assertion has been experimentally confirmed by measuring the amount of water dragged per monolayer using the technique of surface distillation. 

We have been searching for experimental methods that can measure surface viscosities as low as 10 10 g/sec or measure the collisional dynamics that should correspond to the Mann-Cooper model. To qualify, the experimental method must respond to dilute monolayers having densities less than 1014 mojecules/cm2. From our experience with the ESR spin label technique for measuring bulk viscosity effects in ultrathin films (8),... 

Whorlow (15) and others (16,17) described very useful experimental techniques. Very often, measurements are made with a suspension sample placed in the annulus between two concentric cylinders. The shear stress is calculated from the measured torque required to maintain a given rotational velocity of one cylinder with respect to the other. Knowing the geometry, the effective shear rate can be calculated from the rotational velocity. Less useful are the various kinds of simplified measuring devices found in many industrial plants and even in their technical support laboratories. Such devices may not be capable of determining shear stresses for known shear rates or may not be capable of operation at shear rates that are appropriate to the process under consideration. Instruments that are capable of absolute viscosity measurements provide much more useful information. 

Viscosity Measurements. Although it is not intended to give a complete review on the rheometry, some problems and related remarks on the pertinent experimental techniques are given for suspensions. The viscosity measurements are intended for relatively dilute suspensions where the shear rate can be defined. For a more complete listing of experimental techniques on rheometry, one is referred to Van Wazer... 

The experimental technique involved with phase equilibria is of necessity, elaborate. For this reason, as with viscosity measurement, the method is unlikely to be adopted as a method for the assessment of slagging potential. 

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