Unstable Spreading of Ionic Liquids on an Aqueous Substrate

Abstract

The spontaneous spreading of thin liquid films over substrate surfaces is attracting much attention due to its broad applications. Under particular conditions, surfactants deposited on substrates exhibit unstable spreading. In spite of the large effects of the stability of the spreading on the accuracy and efficiency of industrial processes that use the spreading, understanding how the stability of the spreading process is governed by the physical and chemical properties of the system is still little known. Recently, ionic liquids have been characterized as a new kind of surfactant due to their special properties. Here, we investigate the stability of the spreading of deposited imidazolium-based ionic liquids on an aqueous substrate. We focus mainly on the effects that the water solubility of the ionic liquids has on the stability. Hydrophobic ionic liquids exhibit spreading that has a highly periodic and petal-like unstable spreading front, whereas hydrophilic ionic liquids spread without such a regular spreading front and their spreading area shrinks after reaching its maximum. We propose a model for the generation of unstable spreading of hydrophobic ionic liquids, i.e., the unstable spreading front is created by the penetration of oncoming water in front of the spreading tip into the more viscous spreading ionic liquid layer, like the viscous fingering that occurs in a Hele-Shaw cell. However, the direction of the penetration is the opposite of the direction that the interface moves (the spreading direction), which is contrary to that in viscous fingering.

Biomass delignification with green solvents towards lignin valorisation: ionic liquids vs deep eutectic solvents

“…Although a definition and general properties can be ascribed to ILs, there are still some exceptions. Some ILs can be volatile, flammable, unstable, and even toxic [14,15]. In this regard, a wise choice of IL must be always considered by having in mind the desired application.…”

Guanidinium Hydrophobic Magnetic Ionic Liquid-Based Dispersive Droplet Extraction for the Selective Extraction of DNA

“…and organic cations (phosphonium, quaternary ammonium, imidazolium, etc. ). − Compared with traditional solvents, ILs have the advantages of high heat resistance, wide variable viscosity range, low or even negligible vapor pressure, adjustable structure, low toxicity, and so forth. , Recent studies have shown that using a very small amount of ILs can achieve a high DNA extraction rate (97%) . Although ILs have high extraction efficiency, after DNA extraction, ILs are usually separated by extraction or distillation, which often leads to loss of ILs or incomplete separation.…”

“…and organic cations (phosphonium, quaternary ammonium, imidazolium, etc.). 11−13 Compared with traditional solvents, ILs have the advantages 14 of high heat resistance, wide variable viscosity range, low or even negligible vapor pressure, adjustable structure, low toxicity, and so forth. 15,16 Recent studies have shown that using a very small amount of ILs can achieve a high DNA extraction rate (97%).…”

Chemical Reaction-Driven Spreading of an Organic Extractant on the Gas–Water Interface: Insight into the Controllable Formation of a Gas Bubble-Supported Organic Extractant Liquid Membrane

“…Previous works indicated that the initial driving force for the wetting and spreading of an oil droplet on the air–water interface was dominated by the gravity force and balanced by the resistance from the viscous force. , With the progression of the spreading, the oil film became more and more thinner. The surface tension gradient replaced gravity gradually as the main spreading driving force, although the spreading resistance was still dominated by the viscous force. , Investigations on the spreading behavior of oil droplets driven by surface tension gradient have been conducted extensively. − It was demonstrated that the Marangoni convection induced along the air–water interface had a significant impact on the spreading characteristics of the oil droplet and the stability of the thin oil film. − The spreading stability of the oil film on the air–water interface depended closely on its rheological properties (viscosity and elasticity). − However, most of the works on the spreading behavior driven by the Marangoni effect focused on the interfacial flow characteristics of the oil film and the formation mechanism of Marangoni convection along the gas–water interface. , Investigations were scarce into the change in the interface viscosity and elasticity that resulted from the chemical reaction-driven Marangoni convection and its effect on the spreading behavior and the stability of the organic oil film.…”