Hydrophobic-like solvation in non-aqueous solutions: Positron annihilationin and compressibility of tert-butanol and tetramethylurea in ethylene glycol

The pioneer experimental results of positron annihilation experiments in no n-aqueous solutions of tetramethylurea and tert-butanol were compared to th ose of ultrasonic velocity. For tert-butanol, the positron annihilation res ults exclude existence of hydrophobic-like interactions and formation of we ak, labile crystalline-like solvates in solution. For tetramethylurea solut e the changes of annihilation parameters with concentration are minor and o nly limited conclusions can be drawn on this system, while they are stronge r for tert-butanol solute. However, all the above is consistent with an ass umption that the more hydrophobic solute (tert-butanol) should affect the o riginal glycol structure stronger than that interacting with glycol via hyd rogen bondings only. On the other hand, the ultrasonic data for the systems tested, although very precise, hardly confirm formation of any specific st ructure. It is possible, however, that the solvates do not differ in their compressibility from the pure liquids, and/or are formed only in very small amounts. Thus, usefulness of the positron annihilation method in investiga tion of liquid structure was proven.