Dielectric constant of organic solvent

Non-Aqueous Colloidal Metal Solutions. It has been difficult to prepare colloidal gold in non-aqueous media due to limitations in preparative methods (low salt solubilities, solvent reactivity, etc.), and the fact that the low dielectric constant of organic solvents has hindered stabilization of the particles. In aqueous solution the gold particles are stabilized by adsorption of innocent ions, such as chloride, and thus stabilized toward flocculation by the formation of a charged double layer, which is dependent on a solvent of high dielectric constant. Thus, it seemed that such electronic stabilization would be poor in organic media. 

The low dielectric constant of organic solvent will expand the size of the Coulomb cage, which may also lower the probability of successful escape. 

Nonaqueous capillary electrophoresis (NACE) involves the separation of analytes in a medium composed of organic solvents. The viscosity and dielectric constants of organic solvents affect both sample ion mobility and the level of EOF. The changes in separation selectivity in nonaqueous conditions contribute to a better separation of some substances that have very small charge-to-mass differences in aqueous phases (linear alkylbenzene sulfonates, or triazines). Further adsorption on the capillary wall and/or ion interactions, which cause solute precipitation (e.g., anionic surfactants with cations), can be avoided using NACE. 

Fig. 6.3 The relationship between rate constants of Eu(ni) complexes and dielectric constants of organic solvent, a The radiative and b nonradiative constant ( Eu(hfa)3(rBu-xantpo) 8-TDH, O Eu(hfa)2(xantpo)2 8-SAP, 1 toluene, 2 chloroform, 3 acetone, 4 DMF)...

Aryl and, more so, chlorine substituents on silicon enhance thermal stability of silacyclobutanes. The rate of the first-order thermal decomposition of silacyclobutanes varies inversely with the dielectric constant of the solvent used. Radical initiators have no effect on the thermal decomposition and a polar mechanism was suggested. Thermal polymerization of cyclo-[Ph2SiCH212 has been reported to occur at 180-200°C. The product was a crystalline white powder which was insoluble in benzene and other common organic solvents [19]. 

In addition to optimization of molecular structures, small variations in the assay operation conditions can also induce similar effects for improved polymer-sensitized dye emission [40], For instance, introduction of organic solvent into buffer can discourage PET owing to decreased dielectric constant of the solvent... 

The hydrogen ion probably falls, for a corresponding concentration, between Li+ and Ba++, and the ions of metals such as Ag, Cu, Zn, Pb, and Hi, or the rare earths, have a much stronger catalytic effect (6 ) which is further increased if the dielectric constant of the solvent is decreased by adding organic liquids such as acetone or dioxane 323). The degrees of dissociation (Table XII) and the exchange constants (Table XV) of the cations are also related to their catalytic activity (cf. Section IV,E,/,d). 

Grafting reactions were also carried out in organic solvents. Fig. 4 shows the polymerization of methyl methacrylate in the fifteen species of organic solvents having various dielectric constants and water systems without cellulose. The numbers in the figure express the dielectric constants of the solvent in the order. As the organic solvent (No. 1-6) with the dielectric constants around 2 was added, the conversion became 0-11% and the value of dioxane (No. 2), which is soluble in water, was the highest. As the solvents with dielectric constants above 8 were used, the conversion increased, except cyclohexane (No. 11). 

One would expect the organic phase of other amine extraction systems in which more than one metal anion can be formed to exhibit similar equilibria. It is fortunate that in this system not only is the solvent not present in the coordination sphere of either complex but also the equilibrium constant between the two is of an order of magnitude which allows concentration of both to be measured readily by spectrophoto-metric methods. This allows the effect of the dielectric constant of the solvent on the ratio of the species to be studied easily without the perturbing effect of specific interactions caused by differences in the tendency of the solvents to enter the coordination sphere. 

Equation 3.15 predicts the effect of electrolyte on the CMC of ionic surfactants, indicating that the log of the CMC will decrease linearly with log C which is in accordance with experimental findings (equation 3.3). It also indicates that the CMC of ionic surfactants will decrease with increase in the extent of binding of the counterion to the micelle since that decreases the charge density on the micellar surface. Organic additives that decrease the dielectric constant of the solvent will increase the CMC of the surfactant, both of which are consistent with the experimental results discussed previously. The effect of temperature on the CMC of ionic surfactants is difficult to predict from equation 3.15. An increase in the temperature should cause a direct decrease in the CMC, but since an increase in temperature causes a decrease in the dielectric constant er of the solvent and may also affect a, the overall effect of an increase in temperature is not readily determinable from the equation alone. 

The dissociation constant in aprotic organic solvents can be derived from fundamental principles (Brandstorm, 1977), based on Bjerrum s theory for ion pairs, as a function of the dielectric constant of the solvent, temperature, and the distance between the ions in the ion pair. However, in most organic media, the dissociation constant of ion pairs is very small (on the order of 10 4-10 5), and hence, the free ion concentration is negligibly low. 

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