The ability of ionic liquids (ILs) to support amphiphile self-assembly into a range of mesophase structures has been established as a widespread phenomenon. From the ILs evaluated as self-assembly ...media, the vast majority have supported some lyotropic liquid crystal phase formation. Many neat ionic liquids have been shown to segregate into polar and non-polar domains to form a nanostructured liquid. A very strong correlation between the nanostructure of the ionic liquid and its characteristics as an amphiphile self-assembly solvent has been found. In this review we discuss ionic liquids as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liquids are likely to have good promotion properties as self-assembly media. In particular these trends focus on the nanostructure of neat ionic liquids, their solvent cohesive energy density, and the related solvophobic effect. We forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.
Solvent nanostructure within ionic liquids strongly influences the solvophobic effect and amphiphile self-assembly.
he key properties that distinguish protic ionic liquids (PIL) from other ionic liquids (IL) is the proton transfer from the acid to the base, leading to the presence of proton-donor and -acceptor ...sites, which can be used to build up a hydrogen-bonded network. PILs have a number of unique properties compared to other ILs, with the exception of some Bronsted acidic ILs.
In recent years, the number of non-aqueous solvents which mediate hydrocarbon-solvent interactions and promote the self-assembly of amphiphiles has been markedly increased by the reporting of over 30 ...ionic liquids which possess this previously unusual solvent characteristic. This new situation allows a different exploration of the molecular "solvophobic effect" and tests the current understanding of amphiphile self-assembly. Interestingly, both protic and aprotic ionic liquids support amphiphile self-assembly, indicating that it is not required for the solvents to be able to form a hydrogen bonded network. Here, the use of ionic liquids as amphiphile self-assembly media is reviewed, including micelle and liquid crystalline mesophase formation, their use as a solvent phase in microemulsions and emulsions, and the emerging field of nanostructured inorganic materials synthesis. Surfactants, lipids and block co-polymers are the focus amphiphile classes in this critical review (174 references).
Water is a unique solvent that is ubiquitous in biology and present in a variety of solutions, mixtures, and materials settings. It therefore forms the basis for all molecular dynamics simulations of ...biological phenomena, as well as for many chemical, industrial, and materials investigations. Over the years, many water models have been developed, and it remains a challenge to find a single water model that accurately reproduces all experimental properties of water simultaneously. Here, we report a comprehensive comparison of structural and dynamic properties of 30 commonly used 3-point, 4-point, 5-point, and polarizable water models simulated using consistent settings and analysis methods. For the properties of density, coordination number, surface tension, dielectric constant, self-diffusion coefficient, and solvation free energy of methane, models published within the past two decades consistently show better agreement with experimental values compared to models published earlier, albeit with some notable exceptions. However, no single model reproduced all experimental values exactly, highlighting the need to carefully choose a water model for a particular study, depending on the phenomena of interest. Finally, machine learning algorithms quantified the relationship between the water model force field parameters and the resulting bulk properties, providing insight into the parameter–property relationship and illustrating the challenges of developing a water model that can accurately reproduce all properties of water simultaneously.
Ionic liquids (ILs) are highly tailorable solvents with many potential applications. Knowledge about their solvation properties is highly beneficial in the utilization of ILs for specific tasks, ...though for many ILs this is currently unknown. In this study, we have investigated the solvation properties of 12 protic ionic liquids (PILs) and 9 molecular solvents based on the Kamlet-Abboud-Taft′ (KAT) multi-parameter solvation scales. The KAT parameters, which are dipolarity/polarizability (π*), HBD acidity (
α
), HBA basicity (
β
), and the electronic transition energy (
E
T
) were first obtained for the molecular solvents with an extensive set of 11 solvatochromic probe dye molecules. Based on these results the dyes which exhibited the highest sensitivities to polarity changes, and had the greatest chemical stability, were used to determine the KAT parameters of 12 PILs which contained alkyl-, dialkyl-, alkanol-, or dialkanolammonium cations paired with nitrate, formate or acetate anions. Solvation parameters were also obtained for the PILs using the three fluorescent probes pyrene, Coumarin 153 and Nile red for comparison. The PILs containing nitrate anions showed the greatest polarity, polarizability and HBD acidity followed by those containing formates and acetates. Almost all the PILs were found to have solvation properties comparable to water and single short chain alcohols like methanol and ethanol. The relative order of the IL polarities was similar for the solvatochromic and fluorescent probes. Through this study, in addition to the well-known distinct solvent properties of alkylammonium cation PILs, the high solvation capability of these PILs has been explicitly shown, which makes this class of ILs desirable for solvent-sensitive applications which require high polarity and H bonding ability.
Ionic liquids (ILs) are highly tailorable solvents with many potential applications. Knowledge about their solvation properties is highly beneficial in the utilization of ILs for specific tasks, though for many ILs this is currently unknown.
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Deep eutectic solvents (DESs) are a tailorable class of solvents that are rapidly gaining scientific and industrial interest. This is because they are distinct from conventional ...molecular solvents, inherently tuneable via careful selection of constituents, and possess many attractive properties for applications, including catalysis, chemical extraction, reaction media, novel lubricants, materials chemistry, and electrochemistry. DESs are a class of solvents composed solely of hydrogen bond donors and acceptors with a melting point lower than the individual components and are often fluidic at room temperature. A unique feature of DESs is that they possess distinct bulk liquid and interfacial nanostructure, which results from intra- and inter-molecular interactions, including coulomb forces, hydrogen bonding, van der Waals interactions, electrostatics, dispersion forces, and apolar-polar segregation. This nanostructure manifests as preferential spatial arrangements of the different species, and exists over several length scales, from molecular- to nano- and meso-scales. The physicochemical properties of DESs are dictated by structure–property relationships; however, there is a significant gap in our understanding of the underlying factors which govern their solvent properties. This is a major limitation of DES-based technologies, as nanostructure can significantly influence physical properties and thus potential applications. This perspective provides an overview of the current state of knowledge of DES nanostructure, both in the bulk liquid and at solid interfaces. We provide definitions which clearly distinguish DESs as a unique solvent class, rather than a subset of ILs. An appraisal of recent work provides hints towards trends in structure–property relationships, while also highlighting inconsistencies within the literature suggesting new research directions for the field. It is hoped that this review will provide insight into DES nanostructure, their potential applications, and development of a robust framework for systematic investigation moving forward.
The nanostructure of a series of 20 protic ionic liquids (PILs) has been investigated using small- and wide-angle X-ray scattering (SAXS and WAXS). The PILs contained alkylammonium, dialkylammonium, ...trialkylammonium, and cyclic ammonium cations combined with organic or inorganic anions. The presence of hydroxyl and methoxy substituents on the alkyl chains of the cations was also explored. Many of the PILs showed a nanostructure resulting from segregation of the polar and nonpolar components of the ionic liquid. It was found that this segregation was enhanced for longer alkyl chains, with a corresponding increase in the length scale, whereas the presence of hydroxyl groups on the alkyl chains led to much less ordered liquids. The broad range of protic ionic liquids studied allowed several structure−property relationships to be established. The solvophobic effect was shown to be dependent on the nanostructure of the PILs. These PILs support amphiphile self-assembly, and it was shown that the less structured PILs had more “water-like” behavior in the diversity of lyotropic liquid-crystal phases supported, and the thermal stability ranges for these phases.
Lipids form complicated self-assemblies in polar non-aqueous solvents such as deep eutectic solvents and ionic liquids. Created with Biorender.com.
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Self-assembled structures have ...numerous applications including drug delivery, solubilization, and food science. However, to date investigations into self-assembled structures have been largely limited to water, with some additives. This limits the types of assemblies that can form, as well as the accessible temperature range. Non-aqueous, polar solvents such as ionic liquids and deep eutectic solvents offer alternative self-assembly media that can overcome many of these challenges. These novel solvents can be designed to support specific types of assemblies or to remain stable under more extreme conditions.
This review highlights recent advances in the field of self-assembly in polar non-aqueous solvents. Here we quantify the contribution of certain solvent properties such as nanostructure and solvent cohesion to lipid self-assembly. While this field is still relatively new, preliminary design rules are emerging, such as increasing hydrophobic regions leading to decreasing solvent cohesion, with a consequent reduction in lipid phase diversity.
Ultimately, this review demonstrates the capacity for solvent control of lipid assemblies while also drawing attention to areas that need further work. With more systematic studies, solvents could be explicitly designed to achieve specific lipid assemblies for use in target applications, such as cargo delivery to particular cell types (e.g. cancerous), or triggered release under desired conditions (e.g. pH for release on wound infection).
The melting point of a deep eutectic solvent formed from a ternary mixture of ethylammonium bromide (EABr), butylammonium bromide (BABr) and urea is 10 °C, which is almost 40 °C lower than the ...melting points of binary DESs formed from either EABr:urea or BABr:urea mixtures. This reveals a new route to prepare room temperature DESs via mixing different cations.
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