Single Fusion Events at Polarized Liquid–Liquid Interfaces

A new electrochemical framework for tracking individual soft particles in solution and monitoring their fusion with polarized liquid–liquid interfaces is reported. The physicochemical principle lies in the interfacial transfer of an ionic probe confined in the particles dispersed in solution and that is released upon their collision and fusion with the fluid interface. As a proof-of-concept, spike-like transients of a stochastic nature are reported in the current–time response of 1,2-dichloroethane(DCE)|water(W) submilli-interfaces after injection of DCE-in-W emulsions. The sign and potential dependence of the spikes reflect the charge and lipophilicity of the ionic load of the droplets. A comparison with dynamic light scattering measurements indicates that each spike is associated with the collision of a single sub-picoliter droplet. This opens a new framework for the study of single fusion events at the micro- and nanoscale and of ion transport across biomimetic soft interfaces.     

Chemistry Design Towards a Stable Sulfide‐Based Superionic Conductor Li4Cu8Ge3S12

Sulfide‐based superionic conductors with high ionic conductivity have been explored as candidates for solid‐state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide‐based superionic conductor Li₄Cu₈Ge₃S₁₂ with superior stability was developed based on the hard/soft acid–base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10^?4 S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu‐Ge‐S open framework that increases its stability. Meanwhile, the weak bonding between Li⁺ and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid‐state electrolytes.     

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)‐surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod‐like cellulose nanocrystal (CNC)‐based NP‐surfactants, termed CNC‐surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau–Rayleigh (PR) instabilities of a free‐falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end‐functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC‐surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three‐dimensional (3D) printing, of all‐liquid constructs.     

Manipulation of Biomolecule‐Modified Liquid‐Metal Blobs

Soft and deformable liquid metals (LMs) are building components in various systems related to uncertain and dynamic task environments. Herein we describe the development of a biomolecule‐triggered external‐manipulation method involving LM conjugates for the construction of future innovative soft robotics operating in physiological environments. Functional soft hybrids composed of a liquid‐metal droplet, a thiolated ligand, and proteins were synthesized for the expression of diverse macroscopic commands, such as attachment to cells, binary fusion, and self‐propelled movement through molecular recognition and enzymatic reactions. Our technology could be used to create new state‐of‐the‐art soft robots for chemical and biomedical engineering applications.     

ZrO2 Nanoparticles Synthesized using Ionic Liquid Microemulsion

The water‐in‐ionic liquid (W/IL) microemulsion has been used to prepare the tetragonal ZrO₂ nanoparticles. A number of anomalous spherical dispersed particles have been obtained. However, the ZrO₂ nanoparticles synthesized using traditional water‐in‐xylene (W/O) microemulsion show an obvious fusion trace, indicating that the congregation takes place when the precursor was calcined. High thermostable ionic liquid may act as a protector to prevent the congregation of product. The samples are further characterized by XRD, SEM, TEM, and UV‐Vis spectroscopy. The results suggest that the obtained product has high degree of crystallinity and a narrow size distribution (15–40 nm). The XRD pattern has indicated a typical tetragonal crystal structure of ZrO₂. Moreover, the UV‐Vis absorption of the samples also shows the otential advantage in an application of screening ultraviolet radiation.     

Impact of an ionic surfactant on the ion transfer behaviors at meso-liquid/liquid interface arrays

The influence of ionic surfactants,cetyltrimethylammonium bromide(CTAB),self-assembled within silica-nanochannels of a hybrid mesoporous silica membrane(HMSM) on simple ion transfer(IT)behaviors at the meso-water/1,2-dichloroethane(W/DCE) interface arrays supported by such a HMSM was investigated by voltammetry for the first time.Significantly,it is found that the CTAB in HMSM can dramatically enhance the peak-current responses corresponding to ITs of some anions and even lower their Gibbs transfer energies from W to DCE,which could be ascribed to an anion-exchange process between anions and the bromide of CTAB associated with partial ion-dehydration induced by the CTAB.This work will provide a new strategy to study anion transfer processes and improve the electroanalytical performance for anion detection at the liquid/liquid interface.     

Superionic Conduction over a Wide Temperature Range in a Metal–Organic Framework Impregnated with Ionic Liquids

Most molecules in confined spaces show markedly different behaviors from those in the bulk. Large pores are composed of two regions: an interface region in which liquids interact with the pore surface, and a core region in which liquids behave as bulk. The realization of a highly mobile ionic liquid (IL) in a mesoporous metal–organic framework (MOF) is now reported. The hybrid shows a high room‐temperature conductivity (4.4×10^?3 S cm^?1) and low activation energy (0.20 eV); both not only are among the best values reported for IL‐incorporated MOFs but also are classified as a superionic conductor. The conductivity reaches over 10^?2 S cm^?1 above 343 K and follows the Vogel–Fulcher–Tammann equation up to ca. 400 K. In particular, the hybrid is advantageous at low temperatures (<263 K), where the ionic conduction is superior to that of bulk IL, making it useful as solid‐state electrolytes for electrochemical devices operating over a wide temperature range.     

Impact experiments at the Interface between Two Immiscible Electrolyte Solutions (ITIES)

Within the field of single-entity electrochemistry through so-called impact experiments, the use of soft interfaces can be a valuable and advantageous complement to conventional solid microelectrodes, as recently demonstrated for both hard and soft micro- and nanoparticles. Additionally, this approach can offer a new platform for fundamental studies of key aspects of electronic and ionic transfers across liquid–liquid interfaces, with applications in relevant biological, technological and industrial systems. Experimental results with Interfaces between Two Immiscible Electrolyte Solutions (ITIES) are reviewed and discussed under the light of theoretical treatments are here revisited or developed.     

Apparent First‐Order Liquid–Liquid Transition with Pre‐transition Density Anomaly,in Water‐Rich Ideal Solutions

The striking increases in response functions observed during supercooling of pure water have been the source of much interest and controversy. Imminent divergences of compressibility etc. unfortunately cannot be confirmed due to pre‐emption by ice crystallization. Crystallization can be repressed by addition of second components, but these usually destroy the anomalies of interest. Here we study systems in which protic ionic liquid second components dissolve ideally in water, and ice formation is avoided without destroying the anomalies. We observe a major heat capacity spike during cooling, which is reversed during heating, and is apparently of first order. It occurs just before the glassy state is reached and is preceded by water‐like density anomalies. We propose that it is the much‐discussed liquid–liquid transition previously hidden by crystallization. Fast cooling should allow the important fluctuations/structures to be preserved in the glassy state for leisurely investigation.     

Nucleation and Growth of Amino Acid and Peptide Supramolecular Polymers through Liquid–Liquid Phase Separation

The transition of peptides and proteins from the solution phase into fibrillar structures is a general phenomenon encountered in functional and aberrant biology and is increasingly exploited in soft materials science. However, the fundamental molecular events underpinning the early stages of their assembly and subsequent growth have remained challenging to elucidate. Here, we show that liquid–liquid phase separation into solute‐rich and solute‐poor phases is a fundamental step leading to the nucleation of supramolecular nanofibrils from molecular building blocks, including peptides and even amphiphilic amino acids. The solute‐rich liquid droplets act as nucleation sites, allowing the formation of thermodynamically favorable nanofibrils following Ostwald's step rule. The transition from solution to liquid droplets is entropy driven while the transition from liquid droplets to nanofibrils is mediated by enthalpic interactions and characterized by structural reorganization. These findings shed light on how the nucleation barrier toward the formation of solid phases can be lowered through a kinetic mechanism which proceeds through a metastable liquid phase.     

Host–Guest Hydrogen Bonding Varies the Charge‐State Behavior of Magnetic Sponges

The electron‐donor(D) and ‐acceptor(A)‐assembled D₂A‐layer framework [{Ru₂(m‐FPhCO₂)₄}₂TCNQ(OMe)₂]?nDCE ( 1‐nDCE ; m‐FPhCO₂^?=m‐fluorobenzoate; TCNQ(OMe)₂=2,5‐dimethoxyl‐7,7,8,8‐tetracyanoquinodimethane; DCE=1,2‐dichloroethane) undergoes drastic charge‐ordered state variations via three distinct states that are a two‐electron‐transferred state (2e‐I), a charge‐disproportionated state (1.5e‐I), and a one‐electron‐transferred state (1e‐I), depending on the degree of solvation by nDCE. The pristine form 1‐4DCE has a paramagnetic 2e‐I state, which eventually produces the solvent‐free form 1 in 1.5e‐I via an intermediate state 1‐nDCE (n≤1) in 1e‐I. Resolvation of 1 stabilizes 1‐DCE , allowing it to switch between 1.5e‐I and 1e‐I, and to become ferrimagnetic with a T_c of 30 K (1.5e‐I) and 88 K (1e‐I). The stabilization of the 1e‐I state of 1‐DCE is due to the presence of host–guest hydrogen bonding that enables to suppress the electron‐donation ability of D even in an identical framework with 1 .     

Water Purification and Microplastics Removal Using Magnetic Polyoxometalate‐Supported Ionic Liquid Phases (magPOM‐SILPs)

Filtration is an established water‐purification technology. However, due to low flow rates, the filtration of large volumes of water is often not practical. Herein, we report an alternative purification approach in which a magnetic nanoparticle composite is used to remove organic, inorganic, microbial, and microplastics pollutants from water. The composite is based on a polyoxometalate ionic liquid (POM‐IL) adsorbed onto magnetic microporous core–shell Fe₂O₃/SiO₂ particles, giving a magnetic POM‐supported ionic liquid phase (magPOM‐SILP). Efficient, often quantitative removal of several typical surface water pollutants is reported together with facile removal of the particles using a permanent magnet. Tuning of the composite components could lead to new materials for centralized and decentralized water purification systems.     

Insights into Tris‐(2‐Hydroxylethyl)methylammonium Methylsulfate Aqueous Solutions

We report herein a combined experimental–computational study on tris‐(2‐hydroxylethyl)methylammonium methylsulfate in water solutions, as a representative ionic liquid of the aqueous‐solution behavior of hydroxylammonium‐based ionic liquids. Relevant thermophysical properties were measured as a function of mixture composition and temperature. Classical molecular dynamics simulations were performed to infer microscopic structural features. The reported results for ionic liquid in water‐rich solutions show that it behaves as isolated non‐interacting ions solvated by water molecules, through well‐defined solvation shells, exerting a disrupting effect on the water hydrogen bonding network. Nevertheless, as ionic liquid concentration increase, interionic association increases, even for diluted water solutions, evolving from the typical behavior of strong electrolytes in solution toward large interacting structures. For ionic‐liquid‐rich mixtures, water exerts a minor disrupting effect on the fluid’s structuring because it occupies regions around each ion (developing water–ion hydrogen bonds) but without significantly weakening anion–cation interactions.     

Particle self-assembly at ionic liquid-based interfaces

This review presents an overview of the nature of ionic liquid (IL)-based interfaces and self-assembled particle morphologies of IL-in-water, oil- and water-in-IL, and novel IL-in-IL Pickering emulsions with emphasis on their unique phenomena, by means of experimental and computational studies. In IL-in-water Pickering emulsions, particles formed monolayers at ionic liquid–water interfaces and were close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. Interestingly, other than equilibrating at the ionic liquid–water interfaces, microparticles with certain surface chemistries were extracted into the ionic liquid phase with a high efficiency. These experimental findings were supported by potential of mean force calculations, which showed large energy drops as hydrophobic particles crossed the interface into the IL phase. In the oil- and water-in-IL Pickering emulsions, microparticles with acidic surface chemistries formed monolayer bridges between the internal phase droplets rather than residing at the oil/water–ionic liquid interfaces, a significant deviation from traditional Pickering emulsion morphology. Molecular dynamics simulations revealed aspects of the mechanism behind this bridging phenomenon, including the role of the droplet phase, surface chemistry, and inter-particle film. Novel IL-in-IL Pickering emulsions exhibited an array of self-assembled morphologies including the previously observed particle absorption and bridging phenomena. The appearance of these morphologies depended on the particle surface chemistry as well as the ILs used. The incorporation of particle self-assembly with ionic liquid science allows for new applications at the intersection of these two fields, and have the potential to be numerous due to the tunability of the ionic liquids and particles incorporated, as well as the particle morphology by combining certain groups of particle surface chemistry, IL type (protic or aprotic), and whether oil or water is incorporated.     

Particle self-assembly in ionic liquid-in-water Pickering emulsions

We report the self-assembly of a single species or a binary mixture of microparticles in ionic liquid-in-water Pickering emulsions, with emphases on the interfacial self-assembled particle structure and the partitioning preference of free particles in the dispersed and continuous phases. The particles form monolayers at ionic liquid-water interfaces and are close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. In contrast to those at oil-water interfaces, no long-range-ordered colloidal lattices are observed. Interestingly, other than equilibrating at the ionic liquid-water interfaces, the microparticles also exhibit a partitioning preference in the dispersed and continuous phases: the sulfate-treated polystyrene (S-PS) and aldehyde-sulfate-treated polystyrene (AS-PS) microparticles are extracted to the ionic liquid phase with a high extraction efficiency, whereas the amine-treated polystyrene (A-PS) microparticles remain in the water phase.     

Superfluorinated Ionic Liquid Crystals Based on Supramolecular,Halogen‐Bonded Anions

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen‐bonded supramolecular anions [C_nF_{2 n+1}‐I⋅⋅⋅I⋅⋅⋅I‐C_nF_{2 n+1}]⁻ are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen‐bonded liquid crystals, and 2) imidazolium‐based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation.     

Melanin‐Containing Films: Growth from Dopamine Solutions versus Layer‐by‐Layer Deposition

Films formed by oxidation of dopamine are of interest for functionalisation of solid–liquid interfaces owing to their versatility. However, the ability to modulate the properties of such films, for example, permeability to ionic species and the absorption coefficient, is urgently needed. Indeed, melanin films produced by oxidation of dopamine absorb strongly over the whole UV/Vis part of the electromagnetic spectrum and are impermeable to anions even for a film thickness as low as a few nanometers. Herein we combine oxidation of dopamine to produce a solution containing dopamine–melanin particles and their alternating deposition with poly(diallyldimethylammonium chloride) to produce films which have nearly the same morphology as pure dopamine–melanin films but are less compact, more transparent and more permeable to ferrocyanide anions.     

Cu Nanoparticles Electrodeposited at Liquid–Liquid Interfaces: A Highly Efficient Catalyst for the Hydrogen Evolution Reaction

The electrochemical deposition of Cu nanoparticles with an average diameter of approximately 25–35 nm has been reported at liquid–liquid interfaces by using the organic‐phase electron‐donor decamethylferrocene (DMFc). The electrodeposited Cu nanoparticles display excellent catalytic activity for the hydrogen evolution reaction (HER); this is the first reported catalytic effect of Cu nanoparticles at liquid–liquid interfaces.     

Dendronized supramolecular polymers self‐assembled from dendritic ionic liquids

The synthesis, structural, and retrostructural analysis of a library of self‐assembling dendrons containing triethyl and tripropyl ammonium, pyridinium and 3‐methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate at their apex are reported. These dendritic ionic liquids self‐assemble into supramolecular columns or spheres which self‐organize into 2D hexagonal or rectangular and 3D cubic or tetragonal liquid crystalline and crystalline lattices. Structural analysis by X‐ray diffraction experiments demonstrated the self‐assembly of supramolecular dendrimers containing columnar and spherical nanoscale ionic liquid reactors segregated in their core. Both in the supramolecular columns and spheres the noncovalent interactions mediated by the ionic liquid provide a supramolecular polymer and therefore, these assemblies represent a new class of dendronized supramolecular polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4165–4193, 2009