Dynamic viscosity experimental techniques

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. 

Squires, Venier, and Aida (1983) describe an experimental technique they use to study the effect of solvent viscosity on the cisitrans ratio of stilbene irradiated in supercritical CO2. They use a dynamic flow technique similar to that described in chapter 4. In their system trau5-stilbene is coated onto glass beads, which are then packed into a high-pressure column. Supercritical CO2 flows through the column and solubilizes some of the trans-stilbene. The C02-stilbene phase is continuously irradiated with ultraviolet light as it flows through a quartz photoreactor at a fixed temperature and pressure. As the solvent viscosity increases, the photoisomerization of the cis isomer is inhibited while that of the trans isomer is facilitated. We should expect to see the cisitrans ratio of stilbene vary as the density of CO2 varies. This viscosity effect is clearly shown in figure 11.11. While there is a small effect of pressure on the... 

To make the significance of the NMR technique as an experimental tool in surfactant science more apparent, it is important to compare the strengths and the weaknesses of the NMR relaxation technique in relation to other experimental techniques. In comparison with other experimental techniques to study, for example, microemulsion droplet size, the NMR relaxation technique has two major advantages, both of which are associated with the fact that it is reorientational motions that are measured. One is that the relaxation rate, i.e., R2, is sensitive to small variations in micellar size. For example, in the case of a sphere, the rotational correlation time is proportional to the cube of the radius. This can be compared with the translational self-diffusion coefficient, which varies linearly with the radius. The second, and perhaps the most important, advantage is the fact that the rotational diffusion of particles in solution is essentially independent of interparticle interactions (electrostatic and hydrodynamic). This is in contrast to most other techniques available to study surfactant systems or colloidal systems in general, such as viscosity, collective and self-diffusion, and scattered light intensity. A weakness of the NMR relaxation approach to aggregate size determinations, compared with form factor determinations, would be the difficulties in absolute calibration, since the transformation from information on dynamics to information on structure must be performed by means of a motional model. 

Mefliods of study and data interpretation still require further work and refinement. Several experimental techniques are used, including microscopy (TEM, SEM) dynamic light scattering " using laser sources, goniometers, and digital correlators spectroscopic methods (UV, CD, fluorescence) fractionation solubility and viscosity measurements and acid-base interaction. "... 

A further aspect regarding the viscometric properties of liquid real systems which must be carefully considered when investigating this property—and in particular when one would expect reliable information on specific interactions between components—is represented by the choice of experimental measurement technique because it is possible to obtain two different quantities, such as kinematic viscosity (v/cSt, IcSt = Kk V) or dynamic viscosity (v/cP, IcP = lmPa s). These properties can be interconverted by the fundamental relation... 

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. 

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. 

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),... 

The Marangoni elasticity can be determined experimentally from dynamic surface tension measurements that involve known surface area changes. One such technique is the maximum bubble-pressure method (MBPM), which has been used to determine elasticities in this manner (24, 26). In the MBPM, the rates of bubble formation at submerged capillaries are varied. This amounts to changing A/A because approximately equal bubble areas are produced at the maximum bubble pressure condition at all rates. Although such measurements include some contribution from surface dilational viscosity (23, 27), the result will be referred to simply as surface elasticity in this work. 

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