Solvents, mixed aqueous refractive index

These points arc illustrated by the elegant studies of Nelson and Hummel (1962) on the kinetics of denaturation of ribonuclease by urea. As is shown in Fig. 16, the difference spectrum generated with ribonuclease using 7 M urea versus aqueous reference solvent is markedly time-dependent. Difference spectra taken shortly after mixing protein and urea solvent reflect the refractive index red-shift of urea on the tyrosyl and phenylalanyl groups of the protein in its native conformation. As the urea denaturation... 

Swelling of Aqueous La-Phases by Matching the Refractive Index of the BUayers with that of the Mixed Solvent... 

Micellar stmctures from surfactants have a higher refractive index than water. For this reason, micellar solutions scatter light. The differences between the refractive index of micellar stmctures and the solvent water can be eliminated by adding hydrophilic co-solvents such as glycerol to the aqueous phase. The change of the refractive index of the mixed solvent has also consequences on the interaction between the micelles. With the matching of the refractive index between solvent and micellar stmctures, the attractive forces between the stmctures disappear because the Hamaker constant in the DLVO theory decreases towards zero. The consequence of this is that L -phases in two-phase Li/ La-systems swell until the La-phase takes up the whole volume of the sample. 

We present in this work all pubhshed data on density, refractive index, viscosity, electrical conductivity and surface tension for all systems IL + water and + ethanol covering a broad range of concentrations. For density, refractive index and viscosity the data for mixtures with water or ethanol are very similar, and also their behaviour with concentration is not really dependent of the IL mixed with any solvent (except for its value). Density and refractive index can be deduced one from another using Newton s model, which demonstrates the close relationship between both magnitudes. For electrical conductivity and surface tension, the solvent nature determines the data behaviour obtained. Thus, the electrical conductivity value of the pntre IL for aqueous systems increases up to 10 times, while that increase is halved for ethanol systems. In the case of surface tension the behaviour is completely different depending on the solvent and IL studied. For alkyl-methyl-imidazolium tetrafluoroborate the IL acts like a surfactant in water, and the surface tension value decreases sharply from that of water to that of the pure IL for small concentrations of this last, effect that does not appear for halogenated imidazohum ILs. If we change the water for ethanol, that surfactant like effect disappear, and the surface tension value of the only four ILs measured decreases linearly with the ethanol content down to a common value at about equimolar mixture, and then all data has the same value. 

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