Viscous medium

It is now thought that the holes present in the melts are decisive for the conduction in melts. When an electric field is applied, the ion nearest a hole (in the direction of migration) will jump into the hole and leave a hole in its own former place, and thus the next ion can jump into this hole, and so on. Ionic migration thus is not a smooth motion in a viscous medium but, rather, a sequence of ion-hole transitions. 

Ionic (electrolytic) conduction of electric current is exhibited by electrolyte solutions, melts, solid electrolytes, colloidal systems and ionized gases. Their conductivity is small compared to that of metal conductors and increases with increasing temperature, as the resistance of a viscous medium acts against ion movement and decreases with increasing temperature. 

The velocity of motion of the particles depends on their dimensions and shape, on the interaction (e.g. association) between the solvent molecules and finally on the interaction between particles of the dissolved substance and solvent molecules. Consider the simplest case, where the molecule of the dissolved substance is much larger than the solvent molecule, is spherical and the interaction between the solute molecules and the solvent is negligible. Then the motion of the particles of the solute can be considered as the motion of spherical particles with radius rf through a viscous medium with viscosity coefficient rj. The velocity v is then described by the Stokes law ... 

Now suppose that the harmonic oscillator represented in Fig. 1 is immersed in a viscous medium. Equation (32) will then be modified to include a damping force which is usually assumed to be proportional to the velocity, -hx. Thus,... 

Debye [6] suggested that a spherical or nearly spherical molecule can be treated as a sphere (radius r) rotating in a continuous viscous medium with the viscosity, rj, of the bulk liquid. The relaxation time is given by Eq. (12) ... 

The ions are regarded as rigid balls moving in a liquid bath. It is assumed that the macroscopic laws of motion in a viscous medium hold, and that the electrostatic interaction is determined by the theory of continuous dielectrics. This assumption implies that the moving particles are large compared to the molecular structure of the liquid. The most successful results of continuous theories can be found in any textbook of physical chemistry Stokes , law for viscous motion, Einstein s derivation of the dependence of viscosity on the concentration... 

HEISS, J. F. and Coull, J. Chem. Eng. Prog. 48 (1952) 133. The effect of orientation and shape on the settling velocity of non-isometric particles in a viscous medium. 

A variety of results obtained in studies of dipolar relaxation in the environment of the fluorescence probe 2,6-TNS are illustrated in Figure 2.10. In the model viscous medium (glycerol at 1 °C), the fluorescence spectra exhibit a marked dependence on the excitation wavelength. When 2 varies from 360 to 400 nm, the shift of the fluorescence spectrum maximum is 10 nm with a certain decrease of the half-width. In media with low viscosity, for instance, in ethanol (Figure 2.10a), this effect is never observed. 

An additional length, intermediate in size between /0 and Zk, which often arises in formulations of equations for average quantities in turbulent flows is the Taylor length (A), which is representative of the dimension over which strain occurs in a particular viscous medium. The strain can be written as (U /l0). As before, the length that can be constructed between the strain and the viscous forces is... 

For calculating the time-dependent properties of biopolymers, the equations of motion of the molecule in a viscous medium (i.e., water) under the influence of thermal motion must be solved. This can be done numerically by the method of Brownian dynamics (BD) [83]. Allison and co-workers [61,62,84] and later others [85-88] have employed BD calculations to simulate the dynamics of linear and superhelical DNA BD models for the chromatin chain will be discussed below. 

Recall that the diffusion coefficient of a molecule will decrease with increasing viscosity of the solvent. Thus, the rate of encounter complex formation will decrease in a viscous medium. Since viscosity is itself temperature dependent, such encounters in solution will have their own activation energy. 

The dry raw herbs are ground into powder and are mixed either with water or with a viscous medium and shaped into pills. These may be of different sizes, depending on the practitioner s specification. 

Lozenges are taper-shaped pills. They are made from herbal powders with the addition of a viscous medium. 

There is another possible mechanism for delayed fluorescence in rigid medium. Some media at 77°K. may not be entirely rigid. Since many triplet lifetimes are very long at 77°K., sufficient diffusion may take place, even in a viscous medium, to produce an appreciable intensity of P-type delayed fluorescence, particularly if solute concentrations are high and intensities of exciting light large. Thus, if the triplet lifetime is increased from 0.001 to 3.2 sec., the viscosity would have to increase by a factor of 107 to maintain the efficiency of P-type delayed fluorescence at the same value (see eq. 70). However the delayed fluorescence of acriflavine observed by Lim and Swenson does not appear to have been produced by such a mechanism because the decay of its intensity was non-exponential. 

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