A comprehensive review on the rheological behavior of imidazolium based ionic liquids and natural deep eutectic solvents

Abstract

The rheological behavior of a fluid is an important property that has a distinct impact on its flow conduct, which influence viscosity dependent phenomena and applications such as pumping, mass transfer rates, and hydrodynamics. As a result, the necessity of studying the different rheograms and the viscoelastic properties of fluids is essential. In this review, a vast number of novel imidazolium-based combinations of ionic liquids (IL) and natural deep eutectic solvents (NADES) in terms of different hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA) having different molar ratios of HBA:HBD were classified. The rheological behaviors of these combinations at ambient temperature conditions and higher temperatures are critically evaluated. The influence of different parameters such as the effect of adding different polymers, metal oxides, and water on the rheological behaviors and eventually on the flow assurance of these solvents are investigated. Moreover, an intensive overview of all the key research papers, mainly highlighting the initial apparent viscosity and steady-state viscosity for both IL & NADES solvents with different scenarios was conducted by collecting the different trends in rheograms using different measuring devices from several experimental efforts. Also, the relatively few studies on the oscillatory measurement was also highlighted, as it has shown to be a useful analysis method to determine the elastic properties. In addition, oscillatory mode measurements were best to describe and enhance studies on IL and NADES with high viscosities, which can aid their potential uses in challenging applications such as in pumping of liquid material in many industrial processes, through the study of their elasticity behaviors under the effect of several field operation conditions. Furthermore, eight different rheological regression models from different polynomial degrees were used to describe and physically interpret the viscous and viscoelastic behaviors of the studied solvents.