Characterization of ionic conductivity, viscosity, density, and self-diffusion coefficient for binary mixtures of polyethyleneglycol (or polyethyleneimine) organic solvent with room temperature ionic liquid BMIBF₄ (or BMIPF₆)

A mixture of polyethyleneglycol (PEG, M_w = 200, 300, 400) and polyethyleneimine (PEI, M_w = 423) with ionic liquids 1-butyl-3-methylimidazole tetrafluoroborate (BMIBF₄) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) is used to investigate physical properties such as viscosity, density, and conductivity. Nuclear magnetic resonance is used to investigate the effects of solvent content (X = 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) and temperature (303-338 K) on the self-diffusion coefficient, diffusion radius, dissociation and association degree, and transport number of IL cations and anions in the mixture. When the addition of PEG increases, the viscosity and conductivity of the ionic liquid/solvent mixture decrease significantly. The cluster formation decreases the number of conductive free ions; hence, the conductivity of the mixture decreases. The hydrodynamic radius and the aggregation become larger, and the transport number of BMI⁺ becomes smaller when PEG is mixed with BMIBF₄ and BMIPF₆. BMIBF₄/PEG system possesses higher association degree, lower cationic transport number than that of BMIPF₆/PEG system.