Shear- and Temperature-Dependent Viscosity Behavior of Two Phosphonium-Based Ionic Liquids and Surfactant Triton X-100 and Their Biocidal Activities

The viscosity of ionic liquids triisobutyl(methyl)phosphonium tosylate (IL-1) and trihexyl(tetradecyl)phosphonium bis-2,4,4-(trimethylpentyl)phosphinate (IL-2) were studied along with the surfactant p-tert-octylphenoxypolyoxyethylene(9.5)ether (Triton X-100 or TX-100). These fluids are non-Newtonian and witnessed mostly shear thinning and thickening behavior studied over a wide range of shear rate ((0.12 to 5.63) s(-1)) in the temperature range of (293 to 333) K. The activation parameters Delta H* (enthalpy of activation), Delta G* (free energy of activation), Delta S* (entropy of activation), and Delta C-p* (change in heat capacity) values for their viscous flow were evaluated and presented. The magnitudes of the parameters were fairly large. The values of Delta G* increased with temperature, whereas the rest decreased. The values of Delta H* and Delta S* nicely compensated each other. Microbiological activities of IL-1, IL-2, and TX-100 were examined against two bacterial strains Bacillus subtilis (gram positive) and Escherichia coli (gram negative) by measuring the diameter of the inhibition zone ("diz"); both the ILs exhibited greater antimicrobial activity than that of TX-100.