Solvent contribution

A frequently used example of Oldroyd-type constitutive equations is the Oldroyd-B model. The Oldroyd-B model can be thought of as a description of the constitutive behaviour of a fluid made by the dissolution of a (UCM) fluid in a Newtonian solvent . Here, the parameter A, called the retardation time is de.fined as A = A (r s/(ri + s), where 7]s is the viscosity of the solvent. Hence the extra stress tensor in the Oldroyd-B model is made up of Maxwell and solvent contributions. The Oldroyd-B constitutive equation is written as... 

The energy of solvation can be further broken down into terms that are a function of the bulk solvent and terms that are specifically associated with the first solvation shell. The bulk solvent contribution is primarily the result of dielectric shielding of electrostatic charge interactions. In the simplest form, this can be included in electrostatic interactions by including a dielectric constant k, as in the following Coulombic interaction equation ... 

FIG. 9 Solvent contribution to the free energy of adsorption of I on Pt(lOO) at different temperatures as indicated. (From Ref. 164.)... 

An interesting phenomenon was observed when the CD of chiral molecules was measured in achiral solvents. The chiral solvent contributed as much as 10-20% to the CD intensity in some cases. Apparently, the chiral compound can induce a solvation structure that is chiral, even when the solvent molecules themselves are achiral. ... 

The solute solvent contribution to the free energy stabilizing the DNA poly ion can be calculated within the polymer RISM theory by a charging up process " ... 

FIGURE 35.5 Solvent contribution to the capacitance of the electrochemical double layer as obtained from a Monte Carlo simulation. (From Aloisi et ah, 1989, with permission from the American Institute of Physics.)... 

In order to simplify the expression for G, one has to employ a sufficiently simple model for the vibrational modes of the system. In the present case, the solvent contribution to the rate constant is expressed by a single parameter E, the solvent reorganization energy. In addition, frequency changes between the initial and final states are neglected and it is assumed that only a single internal mode with frequency co and with the displacement Ar is contributing to G. Thus the expression for G reduces to [124] ... 

Generally speaking, the influence of solvent on reaction rates (equilibria) is determined by the difference between the effects < n the stability of transition states (products) and reactants. According to what Leffler and Grunwald (1963) call the first approximation, the free energy of a solute molecule RX is given by the sum of internal and solvent contributions, as shown in (59). The... 

The experimental approach discussed in this article is, in contrast, particularly amenable to investigating solvent contributions to the interfacial properties 131. Species, which electrolyte solutions are composed of, are dosed in controlled amounts from the gas phase, in ultrahigh vacuum, onto clean metal substrates. Sticking is ensured, where necessary, by cooling the sample to sufficiently low temperature. Again surface-sensitive techniques can be used, to characterize microscopically the interaction of solvent molecules and ionic species with the solid surface. Even without further consideration such information is certainly most valuable. The ultimate goal in these studies, however, is to actually mimic structural elements of the interfacial region and to be able to assess the extent to which this may be achieved. 

If a liquid is placed into a sealed container, molecules will evaporate from the surface of the liquid and will eventually establish a gas phase over the liquid that is in equilibrium with the liquid phase. This is the vapor pressure of the liquid. This vapor pressure is temperature dependent, the higher the temperature the higher the vapor pressure. If a solution is prepared, then the solvent contribution to the vapor pressure of the solution depends upon the vapor pressure of the pure solvent, P°soivenb and the mole fraction of the solvent. We can find the contribution of solvent to the vapor pressure of the solution by the following relationship ... 

The QSAR technique, widely developed by Kamlet, Taft and coworkers38,98 for the prediction of specific solute-solvent interactions, has been used to predict the different solute-solvent contributions to property variations of compounds. The influence of solvent on the relative basicity of dipolar trimethylamines has been recently studied a descriptor was developed to describe a unique solute-solvent interaction involving dipolar amines99. 

Amokrane and Badiali proposed a semiempirical approach to the determination of the solvent contribution C, to the capacitance of the double layer in aqueous and nonaqueous " solutions. They used the relation C = Cf - C m, where Q is the experimentally determined capacity of the inner layer and Cm is the contribution of the metal. The plots ofC, vs. (Tm were presented for various solvents and correlated with their properties.However, the problem of the supporting electrolyte was entirely neglected in the quoted papers. It was shown recently that the height and position of the maximum on the C, vs. Gm plots depend on the type of the supporting electrolyte. Experimental differential capacity data obtained on the Hg electrode in methanol and ethanol containing various electrolytes with nonadsorbing anions (F , PFg, ClOi) indicate that the type as well as concentration of the electrolyte influences the position and the height of the maximum on the C, vs. plots (Fig. 13). 

This selective solvation of lithium ions by high-e solvent molecules would exclude the solvents of low-rj from the solvation sheath and leave the latter as free, noncoordinating solvent molecules. As a result, the media in which the solvated ions migrate are mainly composed of these free solvent molecules, which impart their low- to benefit the movement of the solvated ions. In this way, a synergistic participation from both high-e and low- solvents contributes to the optimization of ion conduction. 

It should also be remembered, as illustrated by the artifacts in the sucrose studies, that vacuum calculations could potentially be inadequate. Most carbohydrates are found in aqueous environments, and the influence of solvent upon conformation might be significant. Since physical properties are determined by free energies rather than mechanical energies, it may be necessary in some cases to compute (, ) maps of the potential of mean force from solution MD studies, which would include the solvent contribution. 

Production processes used in the pharmaceutical/fine chemical, cosmetic, textile, rubber, and other industries result in wastewaters containing significant levels of aliphatic solvents. It has been reported that of the 1000 tons per year of EC-defined toxic wastes generated in Ireland, organic solvents contribute 66% of the waste [27]. A survey of the constituents of pharmaceutical wastewater in Ireland has reported that aliphatic solvents contribute a significant proportion of the BOD/COD content of pharmaceutical effluents. Organic solvents are flammable, malodorous, and potentially toxic to aquatic organisms and thus require complete elimination by wastewater treatment systems. 

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