The characterization of aprotic polar liquids and percolation phenomena in DMSO/water mixtures.

In the previous papers of our research group it was shown, that the Clausius-Mossotti-Debye equation for the quasi-static dielectric constant (epsilonr) can be extended to liquids if the parameter Ei/E is introduced. Thus, it is possible to characterize polar liquids with the easily accessible parameter Ei/E. This property is also reflected by the fact that the parameter Ei/E can be directly related to the empirical ET(30) and the normalized ETN parameter to describe the polarity of liquids proposed by Reichardt (Chem. Rev. 94, 2319-2358) Ei corresponds to the local mean field due to close molecule-molecule interactions after the application of an external electric field E. In a recent work of our research group it was also demonstrated that the modified Clausius-Mossotti-Debye equation and the study of the relaxation time can be related to percolation phenomena in binary solvent mixtures leading to a valuable insight of the structure of polar liquids and to a better understanding of binary systems. In the present paper it is demonstrated that percolation phenomena for binary DMSO/water mixtures, become visible due to changes of parameters describing the dielectric spectrums. The interpretation of the percolation effects leads to the following conclusion: DMSO/water mixtures seem to have in the whole range of miscibility the same microscopic structure like water with a coordination number z approximately between 4 and 6 which could be the reason for the high permeability of DMSO through biological membranes.