Viscosity of solvents

Solvents which are kinetically stable with lithium show either high viscosity and high permittivity, or low viscosity and low permittivity. The diminution of high viscosity of solvents such as PC or EC is accom-... 

Exciplexes are complexes of the excited fluorophore molecule (which can be electron donor or acceptor) with the solvent molecule. Like many bimolecular processes, the formation of excimers and exciplexes are diffusion controlled processes. The fluorescence of these complexes is detected at relatively high concentrations of excited species, so a sufficient number of contacts should occur during the excited state lifetime and, hence, the characteristics of the dual emission depend strongly on the temperature and viscosity of solvents. A well-known example of exciplex is an excited state complex of anthracene and /V,/V-diethylaniline resulting from the transfer of an electron from an amine molecule to an excited anthracene. Molecules of anthracene in toluene fluoresce at 400 nm with contour having vibronic structure. An addition to the same solution of diethylaniline reveals quenching of anthracene accompanied by appearance of a broad, structureless fluorescence band of the exciplex near 500 nm (Fig. 2 )... 

Since most of our observations on the reacting systems were made by means of conductivity measurements it is necessary to remember that in these systems the only factor which increases conductivity is an increase in the concentration of ions, but that a decrease of conductivity could be due to any or all of the following effects increase of size of cation by polymerisation, increase of viscosity of solvent due to polymer, occlusion of ions in precipitated polymer, trapping of polymer between the electrodes. A similar list was given by Matyska in one of the earliest applications of conductivity measurements to a cationic polymerisation, that of isoprene by aluminium bromide in toluene solvent [19]. 

Volume hold-up - organic phase Volume hold-up - aqueous phase Dynamic viscosity of solvent [cP]... 

Much of the recent impetus for temperature control has focused on exploiting the effects of elevated temperature on viscosity and diffusion coefficients [2], These lead to faster separations and also allow smaller particle diameters to be employed with conventional HPLC hardware. As the viscosity of solvents decreases, the column pressure drops. This can be exploited by using faster flow rates and smaller particle diameters. All of this leads to faster separations. In one experiment in this laboratory, a separation which required 8 min at room temperature was reduced to 2 min at 50°C without changing the column. Speed enhancements of as much as 50-I00-fold have been reported [13] as shown in Figure 9.1. 

The Influence of the Viscosity of Solvents on the Quantum Yields of Photorearrangement Products. The Photolysis of 4-Methylphenyl Acetate (55)33... 

Note, further, that this leveling off occurs at progressively lower potentials as the concentration of electrolyte increases. Increasing both the potential and the electrolyte concentration tends to increase the field in the double layer (see Table 12.1), which in turn increases the viscosity of solvent in the double layer. As the effective viscosity of the medium increases, the surface of shear occurs progressively further from the surface. This accounts for the fact that hs falls behind J/0 as [/0 increases. These conclusions are consistent with the experimental observation that HS for Agl becomes independent of the concentration of the potentialdetermining Ag + and I ions once the concentrations of these ions are well removed from the conditions at which the particles are uncharged. 

Table 3.1—Eluotropic force and viscosity of solvents used as mobile phases. The eluant strength of the mobile phase can be adjusted by mixing different solvents together.

The Stokes-Einstein relationship was used to express the diffusion coefficient through the viscosity of solvent D[cm2/s] = 0.894 x 10 5/r [cP]. All other parameters that change with viscosity, including Pekar s factor y, were borrowed or calculated from the same data sources [148]. They are listed in Table I. 

DIFFUSIVITY OF SOLUTE, cm jl VISCOSITY OF SOLVENT, cP t = FUNCTION OF SOLVENT... 

The conditions that most favored mass transfer of anthracene (250 and 300 rpm and presence of Triton X-100) were evaluated in terms of enzyme inactivation as well as all viscosities of silicone oil. Inactivation coefficients, kd, were calculated according to first-order kinetics (Fig. 10.14). The increase of the agitation rate to 300 rpm did not have a remarkable effect on the inactivation in presence of Triton, whereas in aqueous medium inactivation coefficients slightly increased. The viscosity of solvent does not seem to affect inactivation, except for 10 cSt, which led to the highest values. 

The temperature effect on the viscosity of solvents can be described by Andrade s equation... 

Photochromic transformations from the para- to ana-quinone structure of these compounds occur through intermediate photoproducts in the triplet state.51 The experimental evidence of the influence of oxygen in solution and the viscosity of solvents on the lifetime of these photoproducts supports this statement. It was found that both initial and photoinduced forms have lower triplet levels of the mi -type. 

Here Vi is the molar volume of the solute / incm3/(mol) at its normal boiling point (for some values of Vu see Tables 2.9a and b), p the viscosity of solvent in pP, i//. an association parameter for solvent, and T the absolute temperature in K. Recommended values of the association parameters are 2.6 for water, 1.9 for methanol, 1.5 for ethanol, and l.Ofor benzene, ether, heptane, and other unassociated solvents. Equation (2.82) should be used only for dilute nondissociating solutions. 

When polymers are used as steric stabilizers or binders in a ceramic suspensions, they have two effects (1) to increase the viscosity of solvent and (2) to increase the effective volume of the particle due to specific adsorption. The increase in solvent viscosity is accounted for by the Einstein equation... 

From Wilke-Chang correlation, D°AB=7.4xlO 8(tMB) TAlBVA - , where D°AB/cm l is mutual diffusion coefficient of solute A in solvent B, Mb /g-mok is molecular weight of solvent B, tib /cp is viscosity of solvent B, Va /cm3-mol is molar volume of solute A at its nomial boiling temperature, and is association factor of solvent B. 

Here the subscript i refers to the solvent, whereas the superscript (A or B) refers to the component homopolymer. For example, ai is the thermal diffusion coefficient of a homopolymer consisting of component B in solvent 1. Parameters [rj]i and Xi are the intrinsic viscosity and retention parameter measured on the copolymer in solvent i T g in equation 9c is the temperature at the center of gravity of the retained polymer zone in solvent i, while rjo is the viscosity of solvent i at Teg- Equations 7 through 9 are applicable to copolymers with only two components similar equations could be derived for n-component copolymers, in which case My and Xa are determined from retention and viscosity data in n separate solvents. 

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