Shear relaxation times of some binary liquid systems and electrolyte solutions

Abstract

Ultrasonic velocities (u), densities (p) and viscosities (Tl) of LiCIO₄. NaCIO₄, Mg(CIO₄)2 and AI(CIO₄)₃ have been measured in water in the concentration range 0.02 to 4.0 mol kg^-I at 298 K. The isentropic compressibilities (K_s) of various salts have been calculated and used to evaluate shear relaxation times (τ_s). Shear relaxation times of CuClO₄and NaClO₄ in cyanobenzene, cyanomethane and pyridine at 298, 308 and 318 K as well as of a large number of binary liquid systems at 298 K have also been calculated by using ultrasonic velocity and viscosity data from our previous studies. In binary liquid mixtures the relaxation time shows a .strong dependence on solvent composition and in electrolyte solutions on salt concentration. For AI(ClO₄)₃. Mg(ClO₄)₂ and LiClO₄, the relaxation time increases significantly while for NaCIO₄ it decreases slightly with the increase in salt concentration. At a given concentration, the relaxation time varies in the order: Al(ClO₄)₃> Mg(CIO₄)₂> LiClO₄. > NaCIO₄. Both for CUClO₄ and NaClO₄ in cyanobenzene, cyanomethane and pyridine. the shear relaxation time also increases significantly with the increase in salt concentration. With the exception ofCuClO₄ in cyanomethane, the relaxation time decreases with the increase in the temperature. The relaxation times for both these salts are in the order: cyanobenzene > pyridine> cyanomethane.