Viscosity, Electrical Conductivity, Density and Surface Tension of Methyltriphenylphosphonium Carboxylate Ionic Liquids

Abstract

Abstract In this paper, three new kinds of phosphonium-based room temperature ionic liquids (ILs) [Ph3PCH3][CH3(CH2)8COO] (MTPP-D), [Ph3PCH3][CH3(CH2)10COO] (MTPP-L), and [Ph3PCH3][CH3(CH2)12COO] (MTPP-M) were synthesized using triphenylphosphine, dimethyl carbonate and carboxylic acids as raw materials. The viscosity, electrical conductivity, density and surface tension of the synthesized ILs were measured in the temperature range from 298.15 K to 333.15 K under ambient pressure. Meanwhile, the effects of temperature and alkyl chain length on their viscosity, electrical conductivity, density and surface tension were also investigated. The molecular volume, standard entropy, lattice energy and isobaric expansivity of the three ILs were calculated at 298.15 K. Experimental results indicate that the viscosity, density and surface tension of the three ILs decrease significantly with the increase of temperature, while the electrical conductivity shows an opposite trend. The longer the alkyl chain, the higher the viscosity, the lower the electrical conductivity, density and surface tension of the ILs. The experimental dynamic viscosity can be well correlated by the Vogel-Fulcher-Tammann (VFT) equation and simple linear equation. The temperature dependence of electrical conductivity can be well fitted by Arrhenius equation and VFT equation. The molecular volume, standard entropy and isobaric expansivity increase with increasing alkyl chain length, while the lattice energy decreases.