Dynamic viscosity versus probe-reported microviscosity of aqueous mixtures of poly(ethylene glycol)

[Display omitted] ► Aqueous polymer mixtures, non-toxic media of huge industrial importance, are investigated. ► Bulk viscosity of aqueous. PEG mixtures is shown to vary widely with composition & temperature. ► T-dependent viscosity follows Arrhenius behavior suggesting aqueous PEGs to be Newtonian fluids. ► Microviscosity sensed by a fluorescence ratiometric probe is estimated and correlated with viscosity. ► Microviscosity correlates well with bulk viscosity at higher PEG concentrations. Correlation between the dynamic viscosity ( η) and the microviscosity of a hybrid green medium constituted of water and poly(ethylene glycol) (PEG) of average molar mass (200, 400, and 600) g · mol −1, respectively, is explored over the temperatures range (10 to 90) °C across the complete composition regime. The microviscosity is obtained using a fluorescence probe 1,3- bis-(1-pyrenyl)propane (BPP), which is manifested through the ratio of the monomer-to-intramolecular excimer intensities ( I M/ I E). Aqueous PEG mixtures are observed to behave similar to Newtonian fluids as the temperature dependence of dynamic viscosity follows Arrhenius-type behavior. Surprisingly, a simple and convenient linear dependence of ln η with wt% PEG of the mixture is established. The BPP I M/ I E is observed, in general, to increase with the bulk dynamic viscosity of the mixture having >10 wt% PEG suggesting a good correlation between the bulk dynamic viscosity and BPP-reported microviscosity when the viscosity of the aqueous PEG mixture is relatively high.