Gorobets M. Effect of solvation and the nature of ion pairs on the conductivity of lithium salt solutions in dimethyl sulfoxide, propylene carbonate and dimethyl carbonate

The thesis deals with the study of speciation in lithium salts solutions in dimethyl sulfoxide (DMSO), propylene carbonate (PC) and dimethyl carbonate (DMC) in the concentration range of (0.05-0.25) mole fractions of a salt, searching for the criteria of the ion pair formation and understanding the nature of particles ensuring the transfer of charge. Phase diagrams and conductivity of lithium salt - solvent systems have been studied. The orders of anions for decreasing association of salts with DMSO and for increasing conductivity have been obtained. It is concluded that both phase diagrams and conductivity measurements are equally sensitive to all types of associations in the system. The enthalpy of association of liquid DMSO has been obtained as -11.7±0.9 kJ·mol-1. In Raman studies of cation and anion solvation, it has been found that in all solutions studied, solvation numbers of cations are constant and close to two. Solvation numbers of anions decrease if the salt content is growing and are close to two in concentrated solutions. The dependences of the amount of the solvated anions, the solvent separated ion pairs (SSIP) and the contact ion pair (CIP) on the salt concentrations have been determined to differ significantly from salt to salt and from one solvent to another. It has been found that solvated ions as well as all types of ion pairs are presented in lithium salts solutions in DMSO. No "free" ions exist for LiClO4 - PC and LiClO4 - DMC systems, and their conductance is solely ensured by SSIPs. Therefore, it has been shown for the first time that solvent separated ion pairs are able to serve as charge carriers in concentrated solutions.