Shear-induced phase transition in the aqueous solution of an imidazolium-based ionic liquid

Abstract

An ionic liquid (IL) is a salt that consists of a cation and an anion, one of which possesses an organic component. Because of the non-volatile property, these solvents have a high recovery, and hence they are considered as environment-friendly green solvents. It is necessary to study the detailed physicochemical properties of these liquids for designing and processing techniques and find suitable operating conditions for IL-based systems. In the present work, the flow behavior of aqueous solutions of an imidazolium-based IL, 1-methyl-3-octylimidazolium chloride ([OMIM][Cl]), is investigated where the dynamic viscosity measurements indicate a non-Newtonian shear thickening behavior in the solutions. Polarizing optical microscopy shows the pristine samples to be isotropic that transforms into anisotropic after shear. This shear thickened liquid crystalline samples change into an isotropic phase upon heating which is quantified by the differential scanning calorimetry. The small angle X-ray scattering study revealed the pristine isotropic cubic phase of spherical micelles to distort into a non-spherical micelles. This has provided the detailed structural evolution of mesoscopic aggregates of the IL in an aqueous solution and the corresponding viscoelastic property of the solution.

Temperature-dependent anomalous viscosity of aqueous solutions of imidazolium-based ionic liquids

“…In a recent study, Sharma et al have reported the mesoscopic structure of the OMIM Cl aggregates in aqueous solution 31 measured at room temperature. Above the CMC, these molecules form spherical micelles, which finally correlate at higher concentrations to create a body-centered cubic liquid crystalline phase.…”

“…Therefore, at a given temperature, the viscosity value is higher for the aqueous solution of DMIM Cl compared to OMIM Cl. In a recent paper by Sharma et al, 31 the concentrated aqueous solution of OMIM Cl (2.5 M-7.5 M) shows a shear thickening at a high shear rate (42000 s À1 ), while no changes were observed at a lower shear rate. 2.5 M concentration used by the authors closely corresponds to the concentrations used in the present study.…”

“…Self-assembly of ILs in an aqueous solution into different morphologies has been studied by various experimental methods 28–31 and molecular dynamics simulations. 32,33 These self-assembled structures have dynamic heterogeneity, 34 leading to the uniqueness of each structure.…”

“…Analyzing the rheological behaviour of the aqueous solution of these ILs is fundamental in various commercial applications. 26,27 Self-assembly of ILs in an aqueous solution into different morphologies has been studied by various experimental methods [28][29][30][31] and molecular dynamics simulations. 32,33 These self-assembled structures have dynamic heterogeneity, 34 leading to the uniqueness of each structure.…”

Ionic Liquid-Induced Assembly of DNA at Air–Water Interface

“…The class of salts known as ILs is made up of cations and anions and is distinguished by its distinct physicochemical properties, typically possessing a melting point at or below 100 °C. − These flexible and environmentally friendly molecules offer a wide range of potential applications in IL-based technologies owing to their nonvolatility, high recovery rates, and diverse range of advantageous characteristics. ,,− The interaction between DNA and ILs has recently seen a significant increase in research activity due to the wide range of potential applications in areas like drug delivery, gene therapy, and biosensors. − Jumbri et al demonstrated the binding mode of imidazolium-based ILs ([C n bmim]Br where n = 2,4,6) with calf thymus DNA using molecular docking and fluorescence experiments . Chandran et al shed light on the atomistic mechanisms underlying the exceptional stability displayed by DNA in ILs in a separate study.…”