Classical Salts Research Articles

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions.

Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PW12O403- (PW) and SiW12O404- (SiW) on the aqueous swelling and internal structure of nonionic poly(N-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and small-angle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations. The microgels thus become charged and swell at low POM concentration, surprisingly without strongly increasing the volume phase transition temperature, and deswell at higher POM concentration. The swelling arises because of the osmotic pressure of dissociated counterions of the POMs, while the deswelling is due to POMs acting as physical cross-links in the microgels under screened electrostatics in NaCl or excess POM solution. This swelling/deswelling transition is sharper for PW than for SiW related to the lower charge density, weaker hydration, and stronger binding of PW. The POMs elicit qualitatively and quantitatively different swelling effects from ionic surfactants and classical salts. Moreover, the network softness and topology govern the swelling response upon POM binding. The softer the microgel, the stronger is the swelling response, while, inside the microgel, regions of high polymer density swell/contract more upon electric charging/cross-linking than regions with low polymer density. POM binding thus enables fine-tuning of microgel properties and highlights the role of network topology in microgel swelling. Because POMs decompose at an alkaline pH, these POM/microgel systems also exhibit pH-responsive swelling in addition to the typical temperature responsiveness of pNiPAM microgels.

Hydrogen Bonds in Perovskite for Efficient and Stable Photovoltaic†

Comprehensive SummaryOwing to their distinctive optical and physical properties, organic‐inorganic hybrid perovskite materials have gained significant attention in the field of electronic devices, especially solar cells. The achievement of high‐performance solar cells hinges upon the utilization of top‐notch perovskite thin films. Nevertheless, the fabrication process involving solutions and the polycrystalline nature of perovskite result in the emergence of numerous defects within the perovskite films, consequently exerting a deleterious influence on the overall performance and stability of the devices. Improving the performance and stability of perovskite solar cells by additive engineering to suppress/passivate defects is a viable approach, which involves hydrogen bond interactions in these device engineering processes. This review explores the intrinsic hydrogen bonds in methylammonium and formamidium lead triiodide, while also considering cation rotations, phase transitions, and stability. Moreover, the review classifies additives into distinct categories, including organic small molecules, polymers, nanodots, classical salts, ionic liquids, and molten salts. The various forms and characterization techniques of hydrogen bonds are discussed, as well as their potential synergistic effects in conjunction with other chemical interactions. Furthermore, this review offers insights into the potential utilization of hydrogen bonds to further enhance the performance and stability of devices. Key ScientistsIn 2009, Tsutomu Miyasaka et al. prepared the first perovskite solar cell, which kicked off the research on perovskite light‐absorbing materials. However, the use of liquid electrolytes led to device instability. The transition to all‐solid‐state perovskite solar cells was realized by Nam‐Gyu Park's team in 2012, which was the beginning of high‐efficiency perovskite solar cells. Subsequently, a number of scientists have innovated the preparation ground process. Methods such as two‐step deposition by Michael Grätzel in 2013 and anti‐solvent extraction by Sang II Seok's team in 2014 were instrumental in advancing the development of perovskite. Liyuan Han's team then increased the cell's working area to 1 cm2 without compromising performance, making it possible to compare the performance metrics of perovskite solar cells with those of other types of solar cells on the same scale. Recently, You's team and Pan's team kept updating the world record by obtaining certified efficiencies of 25.6% and 25.8% in 2022 and 2023, respectively.

Superchaotropic Nano‐ion Binding as a Gelation Motif in Cellulose Ether Solutions

AbstractNanometer‐sized anions (nano‐ions) like polyoxometalates and boron clusters exhibit so‐called superchaotropic behavior, which describes their strong binding to hydrated non‐ionic matter in water. We show here that nano‐ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non‐ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel‐forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE‐chains upon nano‐ion binding. The attractive forces manifest themselves as aggregation of CE‐chains into a physically crosslinked polymer network (gel). In turn, the electrostatic repulsions hamper the viscosity increase and gelation. Superchaotropic nano‐ion binding emerges as a novel and general physical crosslinking motif for CE‐solutions and exceeds by far the conventional thickening effects of classical salts and ionic surfactants.

Superchaotropic Nano-ion Binding as a Gelation Motif in Cellulose Ether Solutions.

Nanometer-sized anions (nano-ions) like polyoxometalates and boron clusters exhibit so-called superchaotropic behavior, which describes their strong binding to hydrated non-ionic matter in water. We show here that nano-ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non-ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel-forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE-chains upon nano-ion binding. The attractive forces manifest themselves as aggregation of CE-chains into a physically crosslinked polymer network (gel). In turn, the electrostatic repulsions hamper the viscosity increase and gelation. Superchaotropic nano-ion binding emerges as a novel and general physical crosslinking motif for CE-solutions and exceeds by far the conventional thickening effects of classical salts and ionic surfactants.

Analysis of Entropy trajectories in very Heavy Fermions for Adiabatic Demagnetization Refrigeration at the T<1K range

Abstract With the aim to improve classical paramagnetic salts performances for adiabatic magnetization refrigeration processes, relevant thermodynamic parameters of recently discovered very heavy fermion Yb-based intermetallic compounds are investigated within the sub-Kelvin range of temperature. Focusing on fixed thermal points, required for e.g. photonic devices operating within the 100 mK range in orbital satellites, the nature of respective magnetic ground states are discussed together with the effect of an 'entropy bottleneck' imposed by the Nernst postulate the entropy S(T) trajectories. To gain insight into the main criteria for a proper choice of suitable materials for alternative applications, thermomagnetic S(T,B) trajectories and respective derivatives: δS/δT and δS/δB, are analyzed as key parameters for this magnetocaloric process and compared with those from the classical salt Cerium-Magnesium-Nitride (CMN).

ChemInform Abstract: The Zintl—Klemm Concept ‐ A Historical Survey

AbstractReview: 92 refs.

The Zintl‐Klemm Concept – A Historical Survey

AbstractThe Zintl‐Klemm concept (ZKC) is a combination of a valence electron counting rule and a set of structure‐chemical considerations which works well for a continuously growing class of compounds between classical salts and classical covalent compounds on the on hand, and intermetallic phases on the other. In this historical article the lines of development of the ZKC are reviewed. They originate from Eduard Zintl in Darmstadt and were carried on and extended by Wilhelm Klemm in Münster, early on. After World War II different schools developed their own points of view on the ZKC which converged in the 1990s, backed by blossoming quantum mechanical schemes of treating complex solids. The limits of applicability of the ZKC are subject of ongoing investigations, still, and it seems that the concept has reached a state of quite general acceptance in solid state sciences.

Metathesis of Ionic Liquids: Continuous Ion Exchange by Donnan Dialysis

AbstractIonic liquids (IL) are salts that have extraordinary low melting points below 100 °C. While only a very limited number of possible IL can be synthesized directly, the vast majority is prepared via the synthesis of a precursor IL with the desired cation and a subsequent anion exchange. This paper presents the continuous anion exchange by Donnan dialysis in aqueous solution with anion exchange membranes. The retention of the anion exchange membranes used in this work for inorganic and IL cations was found to be R > 99 %. The average integral transport coefficients were determined for the exchange of chloride/acetate, chloride/hydroxide and bromide/hydroxide for various IL and classical salts. The values of the integral average transport coefficients were found to be independent of the investigated counterions. Process modeling was applied to optimize the flow conditions to reach an anion exchange > 98 %. Ultrapure hydroxide solutions and acetates of common classes of IL cations were prepared with a conversion of the reactant anions of > 99 % and cationic impurity contents of < 1 %.

Contrasting Behavior of Classical Salts versus Ionic Liquids toward Aqueous Phase J-Aggregate Dissociation of a Cyanine Dye

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.

From Molten Salts to Ionic Liquids: A “Nano” Journey

Ionic liquids (ILs), a special group of classical molten salts, are widely used in various fields of science. Historically, researchers have tested ILs out of curiosity or to improve a specific property in a particular system in many areas of chemistry or materials science. However, today, ILs are far from being simple chemical curiosities and sit at the center of various green industrial innovation processes, where they play important roles in materials extraction, reactive catalytic supports, spatial devices, and biotransformations. In this Account, we describe a journey into a nanostructured universe to better understand the unique properties of ionic liquids and their modern applications. Because molten salts have been known for centuries and have found limited uses, we try to explain why modern nonaqueous ILs deserve increased interest and curiosity. We discuss the characteristics that distinguish modern nonaqueous ILs and compare them with classical molten salts. One of the main differences between room temperature ILs, especially those based on imidazolium cations, and simple molten salts, is the molecular asymmetry built into at least one of the ions. This asymmetry in modern, nonaqueous ILs opposes the strong charge ordering due to ionic interactions that normally would cause the system to crystallize. In addition, the presence of a cooperative network of hydrogen bonds between the cations and anions induces structural directionality (the entropic effect). Therefore, modern ILs form preorganized structures, mainly through hydrogen bonding, that induce structural directionality. In contrast, classical salts form aggregates only through ionic bonds. In other words, weak interactions order the structures in modern ILs while charges order the structure within classical salts. ILs cannot be regarded as merely homogeneous solvents. In fact, ILs form extended hydrogen-bond networks with polar and nonpolar nano domains and therefore are by definition "supramolecular" fluids. Thus, ILs are better described as hydrogen-bonded polymeric supramolecules of the type [(DAI)(m)(X)(m_n))](n+)[(DAI)(m_n)(X)(x))](n-). This structural pattern is a general trend for both the solid and the liquid phase and is apparently maintained to a large extent even in the gas phase. This structural organization of ILs can be used as entropic drivers (the "IL effect") for the preparation of well-defined nanoscale structures with extended order, either in the bulk phase or at the gas/vacuum interface.

Precipitation of Nickel Hydroxides from Nickel Dodecylsulphate

Classical precipitation techniques applied to a nickel di-dodecylsulphate Ni(DS)2 precursor were developed. In the range of concentrations studied this precursor forms direct micelles in water. In pH-controlled double jet precipitation with soda at 60°C, the pure a, poorly crystallised bbc and well crystallised b phases are successively obtained by pH shifts from 8 to 11, whereas the platelet morphology remains similar. In the same conditions, classical salts never lead to a phase and the particle size and morphology is pH dependent. Hydroxide precipitation by ammonia decomplexation, via heating at 60°C, Ni(DS)2 leads to well-calibrated stacks of b- Ni(OH)2 nanopancakes (300 nm in diameter and 200 nm stacking length) whereas classical salts lead to micrometric particles characterised by thin interconnected walls.

Mucosal adjuvants and delivery systems for oral and nasal vaccination

Muscosal vaccination offers the advantages of blocking pathogens at the portal of entry, improving patient compliance, facilitating vaccine delivery and decreasing the risk of unwanted spread of infeptious agents via contaminated syringes. During the last several decades, an enomous expansion in the knowledge of mucosal immunity, cellular immunology and molecular biology has led to new perspectives for creating mucosal vaccines with the ability to induce a balanced systemic and secretory immune response. Better understanding of the mechanisms of action has resulted in an explosion of technologies. In addition to classical aluminium salts, components of microbial origin (DNA motifs, lipid A, bacterial toxins), emulsions and particles (immunostimulating complexes, liposomes. PLGA and saponins), as well as synthetic analogues and cytokines, are examples of adjuvants and delivery systems in use or under preclinical or clinical development.