Viscosity of Aqueous Solutions of Tetramethyl-, Tetraethyl-, Tetra-n-propyl-, Tetra-n-butyl-, and Tetra-n-pentylammonium Cyclohexylsulfamates from 293.15 K to 323.15 K

Cveto Klofutar,¹ Jaka Horvat,² Marija Bešter-Rogač³ and Darja Rudan-Tasič^1,*

¹ Biotechnical Faculty, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
² Acies Bio d. o. o., Tehnološki park 21, SI-1000 Ljubljana, Slovenia.
³ Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
* Corresponding author: E-mail: darja.rudan.tasic@bf.uni-lj.si

Abstract
The viscosities of aqueous solutions of tetramethyl-, tetraethyl-, tetra-n-propyl-, tetra-n-butyl-, and tetra-n-pentylammonium cyclohexylsulfamate were determined at 293.15, 298.15, 303.15, 313.15 and 323.15 K. The relative viscosity was analysed and interpreted in terms of the Kaminsky equation, η_r= 1 + Ac^1/2 + Bc + Dc². The viscosity A-coefficient was calculated from Falkenhagen-Dole theory and its temperature coefficient estimated. The viscosity B-coefficients of the solutes are positive and relatively large, while their temperature coefficients are negative and decrease with increasing molecular weight of the solutes. The viscosity D-coefficient was discussed in terms of higher terms of the long-range Coulombic forces and hydrodynamic effects, as well as structural solute-solute interactions. The limiting thermodynamic functions of activation for viscous flow of solute, i. e. the Gibbs free energy, enthalpy and entropy, were evaluated using the theoretical approach given by Feakins et al. From the limiting partial molar functions of activation of the solute the contribution to the activation functions of solvent molecules were calculated using the corresponding limiting functions of activation for charge transport of solute ions.

Keywords: Viscosity data, viscosity A-, B- and D-coefficients, activation parameters, cyclohexylsulfamates, aqueous solutions