Viscosity, electrical conductivity, shear relaxation time and Raman spectra of aqueous and methanolic sodium thiocyanate solutions

Abstract

Measured viscosity, electrical conductivity, the shear relaxation time and the Raman spectra of aqueous and methanolic sodium thiocyanate solutions are reported as functions of concentration ( 0.0237≤m( mol kg −1)≤19.685) and temperature (273.15≤ T(K)≤323.15). The non-Arrhenius temperature dependence of viscosity, electrical conductivity and shear relaxation time was analysed by using the Vogel–Tammann–Fulcher (VTF) equation. Variation of the B Y parameter of the VTF equation with concentration evoked some kind of structural transition over a narrow concentration range. The concentration dependence of the viscosity and conductivity data was analysed by using the reported equations. In aqueous sodium thiocyanate solutions, the existence of the hydrated ions due to the ion–solvent interactions in the concentration range from dilute to 3.0 mol kg −1, the solvent-separated and(or) the solvent-shared ion-pairs due to the competition between the ion–solvent and the ion–ion interactions from 3.0 to 6.2 mol kg −1 and the contact ion-pairs due to the ion–ion interactions beyond 6.2 mol kg −1 govern the transport processes. In methanolic sodium thiocyanate solutions, from dilute to ∼3.9 mol kg −1, free and hydrogen bonded SCN − and beyond ∼3.9 mol kg −1, solvent-shared ion-pairs dominate in the solutions and govern the transport processes. The Raman spectra recorded for the ν C–N and ν C–S stretching frequencies shifted to higher frequency regions and reveal the existence of the complex adduct of SCN − with the solvent molecule.