Apparent Non-Newtonian Behavior of Ionic Liquids

Area of Science:

• Rheology
• Materials Science
• Physical Chemistry

Background:

• Ionic liquids and Newtonian liquids show viscosity variations with shear rate above a critical threshold.
• Observed viscosity changes are often attributed to non-Newtonian behavior.
• Discrepancies exist between experimental critical shear rates and simulation predictions.

Purpose of the Study:

• To investigate the discrepancy in critical shear rates observed in rheometry experiments.
• To elucidate the underlying mechanisms causing viscosity variations in ionic and Newtonian liquids.
• To differentiate between non-Newtonian behavior and other physical phenomena.

Main Methods:

• Conducting rheometry experiments on both ionic liquids and Newtonian liquids.
• Varying rheometer geometry and zero-shear viscosity.
• Analyzing viscosity changes in relation to shear rate and temperature.

Main Results:

• Both viscosity decrease and increase were observed for all tested liquids.
• Viscosity decrease is attributed to viscous heating, influenced by temperature-dependent viscosity.
• Viscosity increase is linked to the development of instabilities at high shear rates.

Conclusions:

• Observed viscosity variations are not exclusively indicative of non-Newtonian behavior.
• Viscous heating and flow instabilities are key factors influencing viscosity changes.
• Experimental conditions significantly impact the observed rheological response.