Thermodynamic and computational study of isomerism effect at micellization of imidazolium based surface-active ionic liquids: Counterion structure

The correlation between the micelle morphology of surface-active ionic liquids with self-assembly and thermodynamic characteristics: coarse-grained MD simulation and experiment

Surface-active ionic liquids (SAILs) show great promise as novel green solvents due to their low vapor pressure, high thermal stability, high electrical conductivity, and bio-friendly nature to replace traditional volatile organic solvents in industrial processes. In the present work, the combination of coarse-grained (CG) molecular dynamics (MD) simulations with conductivity measurements was employed to explain the correlation between the micelle morphology and physicochemical and thermodynamic properties of self-assembly. A homologous series of SAIL molecules, 1-n-alkyl-3-methylimidazolium bromide [Cnmim][Br] (n = 4, 6, 8, 10, and 12), were chosen at various concentrations to shed light on this issue. Simultaneously two factors of concentration and alkyl chain length affected the morphology to control the physical and thermodynamic features. Moreover, the nature of the headgroup for two SAILs with the longest alkyl chain was assessed by shifting from imidazolium into ammonium. First, the critical micelle concentration (CMC), the degree of counterion dissociation of micelles, and the standard Gibbs energy of micellization of SAILs were determined using conductivity data. The micelle morphology such as the aggregation number, micelle radius, and moment of inertia was computed before, around, and after the CMC by MD simulation. Simulated results in accordance with the experimental measurements provide a quantitative understanding of the micellar properties. Increasing the alkyl chain length was associated with a non-spherical bigger micelle while the ammonium-based surfactant with a lower repulsion between neighboring monomers in micelles induced bigger and more spherical aggregates. Raising the SAIL concentration did not considerably influence the sphericity of the micelle except for the SAIL with the longest tail. The umbrella sampling method calculated the potential of mean force (PMF) for pulling a monomer of SAIL from a pre-assembled micelle into the solution. The dissociation energy of a SAIL monomer from a micelle increased with the tail length or with shifting into the ammonium head group and was substantially influenced by micelle morphology. Comparison between a sphere micelle with an oval one demonstrated that the dissociation of a SAIL monomer from a non-spherical shape needed a higher amount of energy. An improved understanding of how the shape of the SAIL micelles controls the physicochemical properties and stability helps to extend their application to different chemical processes.

In Search for an Ionic Liquid with the Best Performance during 210Pb/210Bi Cherenkov Counting in Waters on an LS Counter

The research presented in this paper aims to investigate the performance of several newly synthesized ionic liquids during ²¹⁰Pb/²¹⁰Bi detection in water on a liquid scintillation spectrometer Quantulus 1220 via Cherenkov counting. These experiments have been triggered by the recent reports that certain ionic liquids can act as wavelength shifters, thus significantly increasing the detection efficiency of Cherenkov radiation. The benefit of ionic liquid's addition to the analysed samples is reflected in the detection limit's decrement during ²¹⁰Pb quantification, which is pertinent considering naturally low levels of ²¹⁰Pb in aqueous samples. Firstly, it was discovered that ionic liquid, 1-butyl-3-methylimidazolium salicylate, is more efficient than the previously explored 2-hydroxypropylammonium salicylate. Consequently, the impact of a few other ionic liquids on Cherenkov counting efficiency with the same cation group (1-butyl-3-methylimidazolium benzoate, 1-butyl-3-methylimidazolium 3-hydroxybenzoate and 1-butyl-3-methylimidazolium 4-hydroxybenzoate) was also explored to test their potential influence. Molecular simulations have been carried out to reveal which structures of ionic liquids assure wavelength-shifting behavior. The obtained results confirmed that, among the investigated ones, only ionic liquids with the salicylate anion exhibited a wavelength shifting effect.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

The desire of improving various processes like enhanced oil recovery (EOR), water treatment technologies, biomass extraction, organic synthesis, carbon capture etc. in which conventional surfactants have been traditionally utilized; prompted various researchers to explore the self-assembly and aggregation behavior of different kinds of surface-active molecules. Ionic liquids (ILs) with long alkyl chain present in their structure constitute the advantageous properties of surfactant and ILs, hence termed as surface-active ionic liquids (SAILs). The addition of ILs and SAILs significantly influence the surface-activity and aggregation behavior of industrially useful conventional surfactants. After a brief review of ILs, SAILs and surfactants, the prime focus is made on analyzing the self-assembly of SAILs and the mixed micellization behavior of conventional surfactants with different ILs.

Interplay between aggregation number, micelle charge and hydration of catanionic surfactants

Catanionic mixtures are commonly used in applications due to synergetic properties of both cationic and anionic surfactants. To better understand the mechanism of the micellization process of salt-free catanionic surfactants, alkyltrimethylammonium alkanecarboxylates, [CxMe3N]+[Cy]-, with medium to long alkyl chains on both cation and anion (x,y = 6-10), were investigated in aqueous solution by density and zeta potential measurements, isothermal titration calorimetry (ITC), and dielectric relaxation spectroscopy (DRS). The obtained ITC data was analysed with the help of a two-step model equation, yielding the thermodynamic parameters, micelle charge and aggregation numbers. Comparison with the "parent" decyltrimethylammonium chloride and sodium decanoate reveals that combined dehydration of both alkyl chains increases entropy upon micellization. In the first step neutral smaller micelles with partly dehydrated alkyl chains are formed, while in the second step larger charged micelles with fully dehydrated alkyl chains are equally favourable. At low temperature both formations are thermodynamically equivalent, while with increasing temperature neutral micelles become more entropically favourable and charged micelles more enthalpically favourable. The resulting average micelle charge and average aggregation number are decreasing with temperature. From the DRS spectra, effective hydration numbers of the free monomers and micelles were deduced and are comparable to the "parent" cationic surfactant micelles.