Cluster Ions Research Articles

The behaviour of charged particles (ions) during new particle formation events in urban Leipzig, Germany

Abstract. Air ions are electrically charged particles in air. They are ubiquitous in the natural environment and affect the Earth's radiation budget by accelerating the formation and growth of new aerosol particles. Despite this, few datasets exist exploring these effects in the urban environment. A neutral cluster and air ion spectrometer was deployed in Leipzig, Germany, to measure the number size distribution of charged particles from 0.8 to 42 nm, between 27 July and 25 August 2022. Following previous analyses, charged particles were classified into small (0.8–1.6 nm), intermediate (1.6–7.5 nm), and large (7.5–22 nm) fractions by mass diameter, and their mean concentrations (sum of positive and negative polarities) during the campaign were 405, 71.6, and 415 cm−3, respectively. The largest peaks in intermediate and large ions were explained by new particle formation (NPF), with intermediate ions correlating well with sulfuric acid dimer. Smaller morning and evening peaks were coincident with black carbon concentrations and attributed to primary emissions. NPF events, observed on 30 % of days, coincided with intense solar radiation and elevated sulfuric acid dimer. Small charged particles were primarily associated with radioactive decay and highest during the early hours, and they are unrelated to primary emissions or NPF. The apparent contributions of charged particles to 3 and 7.5 nm particle formation rates were 5.7 % and 12.7 %, respectively, with mean growth rates of 4.0 nm h−1 between 3–7.5 nm and 5.2 nm h−1 between 7.5 and 22 nm. The ratio of charged to total particle formation rates at 3 nm suggests a minor role for charged particles in NPF. We conclude that NPF is a primary source of > 3 nm ions in our data, with primary emissions being the major source in the absence of NPF.

Thermodynamic origin of the affinity, selectivity, and domain specificity of metallothionein for essential and toxic metal ions.

The small Cys-rich protein metallothionein (MT) binds several metal ions in clusters within two domains. While the affinity of MT for both toxic and essential metals has been well studied, the thermodynamics of this binding has not. We have used isothermal titration calorimetry measurements to quantify the change in enthalpy (ΔH) and change in entropy (ΔS) when metal ions bind to the two ubiquitous isoforms of MT. The seven Zn2+ that bind sequentially at pH 7.4 do so in two populations with different coordination thermodynamics, an initial four that bind randomly with individual tetra-thiolate coordination and a subsequent three that bind with bridging thiolate coordination to assemble the metal clusters. The high affinity of MT for both populations is due to a very favourable binding entropy that far outweighs an unfavourable binding enthalpy. This originates from a net enthalpic penalty for Zn2+ displacement of protons from the Cys thiols and a favourable entropic contribution from the displaced protons. The thermodynamics of other metal ions binding to MT were determined by their displacement of Zn2+ from Zn7MT and subtraction of the Zn2+-binding thermodynamics. Toxic Cd2+, Pb2+, and Ag+, and essential Cu+, also bind to MT with a very favourable binding entropy but a net binding enthalpy that becomes increasingly favourable as the metal ion becomes a softer Lewis acid. These thermodynamics are the origin of the high affinity, selectivity, and domain specificity of MT for these metal ions and the molecular basis for their in vivo binding competition.

Reactive Gas Cluster Ion Beams for Enhanced Drug Analysis by Secondary Ion Mass Spectrometry.

In this study, we investigate the formation and composition of Gas Cluster Ion Beams (GCIBs) and their application in Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis. We focus on altering the carrier gas composition, leading to the formation of (Ar/CO2)n or (H2O)n GCIBs. Our results demonstrate that the addition of a reactive species (CO2) to water GCIBs significantly enhances the secondary ion yield of small pharmaceutical compounds in the positive ion mode. In negative ion mode, the addition of CO2 resulted in either a positive enhancement or no effect, depending on the sample. However, an excess of CO2 in the carrier gas leads to the formation of carbon dioxide clusters, resulting in reduced yields compared to that of water cluster beams. Cluster size also plays a crucial role in overall yields. In a simple two-drug system, CO2-doped water clusters prove effective in mitigating matrix effects in positive ion mode compared to pure water cluster, while in negative ion mode, this effect is limited. These clusters are also applied to the analysis of drugs in a biological matrix, leading to more quantitative measurements as shown by a better fitting calibration curve. Overall, the doping of water clusters with small amounts of a reactive gas demonstrates promising benefits for higher sensitivity, higher resolution molecular analysis, and imaging using ToF-SIMS. The effectiveness of these reactive cluster beams varies depending on the experimental parameters and sample type.

Overcoming strength-ductility and functional period-degradability tradeoffs: Multifunctional biodegradable polyesters with ionic cluster skeleton and PDMS skin

To overcome the strength-ductility and functional period-degradability tradeoffs of biodegradable polyesters, we proposed a nanophase structure design strategy to construct a soft-hard dual phase in poly(butylene succinate) (PBS) copolymers by simultaneously introducing polydimethylsiloxane (PDMS) and isophthalate-5-sulfonate (SIPM) on PBS macromolecular chains to improve the stiffness, toughness, and multifunctionality. The high-resolution transmission electron microscope (HR-TEM) and energy dispersive X-Ray spectroscopy (EDX) tests indicated that PBS copolymers possessed continuous “ionic cluster skeleton” and “PDMS skin”. The hybrid liquid state theory and self-consistent field approach for copolymers further demonstrated the mechanism of microphase separation for PDMS blocks and SIPM segments. The copolymers showed excellent yield strength of 52 MPa, great impact strength of 171 J/m, large extensibility of 491 %, and long functional period in the acidic environment. The novel stereo nanostructure endowed the materials with advanced multifunctions that can be applied in various applications, such as the biomedical field and flexible electronic devices. Compared with PBS, copolymers possessed excellent in vitro attachment and proliferation of MC3T3-E1 cells. Furthermore, the synergistic effect of the ionic skeleton and PDMS skin improved the ionic conductivity of the materials. The copolymer film was innovatively employed as anion-exchanging separators of supercapacitors with acid-organized electrolytes. It has been testified that this newly designed strategy of a novel stereo nanophase structure was efficient in endowing the biodegradable polyesters with excellent combined properties and multifunctions.

Orientation Control of Perfluorosulfonic Acid Films via Addition of 1,2,4-Triazole during Casting.

Perfluorosulfonic acid (PFSA) polymers are used as electrolyte membranes in polymer electrolyte fuel cells. To investigate the effect on proton conductivity through structural orientation control, we added 1,2,4-triazole to PFSA films during casting to impart anisotropy to the ion-cluster structure of the films. The proton conductivities of the films were found to be high in the film-surface direction and low in the film-thickness direction. Structural analysis using small-angle X-ray scattering suggested that the anisotropy in proton conductivity was due to anisotropy in the ion-cluster structure, which in turn was attributed to the formation of a phase-separated structure via strong bonding between sulfonic acid groups and 1,2,4-triazole during cast film formation and the surface segregation of fluorine. We expect the findings of this study to aid in the fabrication of PFSA films with controlled ion clusters.

Analysis of sulfur in soil and plant digests using methane as a reaction gas for ICP-MS

Quantitation of sulfur (S) is vitally important for analysis of agricultural soil and plant samples due to the requirement of S in living organisms. Although inductively coupled plasma mass spectrometry (ICP-MS) is a commonly used and robust instrument for multi-elemental detection, S is usually analysed by ICP-optical emission spectroscopy (OES) since S quantitation poses a particular challenge for ICP-MS due to interferences on all S isotopes. The requirement for analysis by two instruments increases time and cost for sample analysis, hence analysis by one instrument is desirable. The use of reaction gases in ICP-MS can improve the performance by shifting S to a mass for detection where no interference is present. This work explored the potential of methane as a reaction gas for analysis of S in soil and plant samples to give users an alternative option to oxygen. The product ion clusters CH2SH+ were monitored (m/z 47 and 49 on ICP-MS and with mass shift of +15 from Q1 → Q2 using 32 → 47 and 34 → 49 on triple quadrupole ICP-MS). As expected, triple quadrupole ICP-MS performed better than single quadrupole ICP-MS containing a reaction cell due to the ability to preselect the m/z of choice and remove ions that may react with methane in the reaction cell. The method detection limit (MDL) was 150 mg kg−1 S for plants and 53 mg kg−1 S for soils which is fit for requirements. This is the first-time methane has been reported as a reaction gas for analysis of S and shows promising results for agricultural samples when using a triple quadrupole ICP-MS. Results compared well to those obtained via the more commonly used ICP-optical emission spectroscopy (OES) method with results <20 % for all samples. Interlaboratory comparison samples were within 2 Z-scores of the consensus mean. In the absence of ICP-MS/MS, Q-ICP-MS with detection of cluster m/z 47 was deemed to be suitable for detection of S in plant samples, with acceptable MDL (250 mg kg−1 S), acceptable precision (<20 % RSD) and <20 % variation to the reported ICP-OES result.

Generation of seed electrons in guided ionization waves in He–O2 mixtures: The effect of negative ion cluster formation

The kinetics of electrons and negative ions was numerically studied under the conditions, which are typical for multi-pulsed guided ionization waves in He flows ejected into ambient air. It was shown that, in He with a small admixture of O2 or air, O2− ions formed due to three-body electron attachment in the discharge afterglow are rapidly converted to O4− cluster ions in pulse off time. We suggested that seed electrons are generated at the leading edge of a pulse in two steps, and these steps are dissociation of O4− ions to form O2− ions followed by electron detachment from the O2− ions. The rate of O4− dissociation was calculated in He–O2 mixtures for various reduced electric fields on the basis of a Monte Carlo simulation. This rate, as well as the rate of electron detachment from O2− ions calculated previously, was used to simulate seed electron generation in a high-voltage nanosecond pulse in He–O2 mixtures for different gas pressures. It was shown that the formation of O4− ions drastically hinders the generation of seed electrons in multi-pulsed guided ionization waves in He–O2 and He–air mixtures.

Density functional theory study of physisorption of ionic liquid pairs on hydroxylated and oxygen terminated α-SiO2 (001) surfaces

In this work, we investigate the ion pair tetramethylphosphonium cation, [P1,1,1,1]+, and bis(oxalato)borate anion, [BOB]−, as a model system for the study of ionic liquids interacting with both hydroxylated and oxygen terminated α-SiO2 (001) surfaces, using first-principles electronic structure theory. We use a single ionic pair and clusters of ion pairs, in order to have exclusively neutral supercell slab models. We use dispersion-corrected density functional theory (DFT) to ascertain that both the strong physical binding between the ions, dominated by ionic binding, and the weaker physical binding of ions to the different surfaces are correctly described. We have found that the binding of ion pairs is stronger to the hydroxylated α-SiO2 (001) surface compared to the oxygen terminated surface, which is attributed to the formation of H-binding with the oxygen atom(s) of the [BOB]− anion. Through rotation of ionic pair(s), we estimate the surface-ions energy barrier for translational movement and, thus, the strength of H-binding of the ions. At the surface of hydroxylated α-SiO2 (001), we have studied how water molecules form a network of H-binding with the OH groups of the surface and the [BOB]− anion, which offers an explanation for the reduction in the friction of ionic liquids on the inclusion of water. We suggest modeling protocols for simulation of ion pairs on surfaces, which can open up the possibility to use DFT to aid in designing and understanding the physicochemical mechanism of interactions of ionic materials (including ionic liquids) in various technological applications.

Clustering of biphenyl oxamide ions by chiral recognition.

Gels created by self-assembly of small organic molecules are dynamic soft materials that have unique properties and demanding characterization. Four chiral gelators, with two valinol- or leucinoloxamido arms attached to the 2,2'-positions of the proatropisomeric biphenyl group were chosen to show that the electrospray ionization mass spectrometry (ESI-MS) could be used to differentiate the gelation feature of the chiral compounds 1-4 and also to shed light on the gelation processes. By inspecting the gelation of several solvents, we showed that 1 (R, R) proved to be the most efficient gelator, forming the largest observable assemblies in the gas phase. The strong intermolecular H-bonds hold single-charged assemblies consisting of up to five monomer units detectable by ESI MS. Enantiomer 1 (R, R) is a good gelator due to favorable intramolecular interactions that remain preserved in the gas phase. Compound 3 (meso) does not have gelator properties and detected signals of larger assemblies in the gas phase. So, the detected signals correlate with the conformations of the studied compounds. MS could be used to elucidate the preferential type of noncovalent interaction due to the chiral recognition. The study paves a novel way to investigate the influence of chirality on the molecular assembly and consequently macroscopic properties and functions of materials.

One-Pot In Situ Construction of a Highly Stable Acylhydrazone-Derived Dy9 Cluster with Photodynamic Sterilization Property.

The extremely low stability of lanthanide clusters with precise structures and nanometer dimensions in aqueous solutions limits their application in the field of photodynamic sterilization. In this study, an hourglass-shaped nine-nucleated Dy9 cluster (1) with excellent light-driven reactive oxygen species (ROS) generation ability and photodynamic sterilization property was constructed using acylhydrazone multidentate chelating ligands obtained via an in situ reaction. The eight chelating ligands were distributed outside cluster 1, tightly wrapping the cluster core, thus preventing solvent molecules from attacking the cluster nucleus and ensuring the stability of cluster 1 in solution, which was demonstrated via X-ray diffraction and high-resolution electrospray ionization mass spectrometry (HRESI-MS). Time-dependent HRESI-MS monitoring of the self-assembly process of cluster 1 allowed two possible self-assembly mechanisms. The heavy atom effect of multiple Dy(III) ions in the Dy9 cluster enhanced the ISC pathway through spin-orbit coupling, promoting energy transfer from the excited singlet state (S1) to the triplet state (T1), which was stabilized, inducing the generation of more ROS. Cluster 1 showed a remarkable sterilization effect due to the generation of abundant ROS under light irradiation conditions. To our knowledge, this is a rare instance of lanthanide clusters with photodynamic sterilization, providing new horizons for the construction of fast and efficient sterilizers.

PCA, PC-CVA, and Random Forest of GCIB-SIMS Data for the Elucidation of Bacterial Envelope Differences in Antibiotic Resistance Research.

Antibiotic resistance can rapidly spread through bacterial populations via bacterial conjugation. The bacterial membrane has an important role in facilitating conjugation, thus investigating the effects on the bacterial membrane caused by conjugative plasmids, antibiotic resistance, and genes involved in conjugation is of interest. Analysis of bacterial membranes was conducted using gas cluster ion beam-secondary ion mass spectrometry (GCIB-SIMS). The complexity of the data means that data analysis is important for the identification of changes in the membrane composition. Preprocessing of data and several analytical methods for identification of changes in bacterial membranes have been investigated. GCIB-SIMS data from Escherichia coli samples were subjected to principal components analysis (PCA), principal components-canonical variate analysis (PC-CVA), and Random Forests (RF) data analysis with the aim of extracting the maximum biological information. The influence of increasing replicate data was assessed, and the effect of diminishing biological variation was studied. Optimized m/z region-specific scaling provided improved clustering, with an increase in biologically significant peaks contributing to the loadings. PC-CVA improved clustering, provided clearer loadings, and benefited from larger data sets collected over several months. RF required larger sample numbers and while showing overlap with the PC-CVA, produced additional peaks of interest. The combination of PC-CVA and RF allowed very subtle differences between bacterial strains and growth conditions to be elucidated for the first time. Specifically, comparative analysis of an E. coli strain with and without the F-plasmid revealed changes in cyclopropanation of fatty acids, where the addition of the F-plasmid led to a reduction in cyclopropanation.

Towards a better understanding of the surface smoothing effect in gas cluster ion beam processing with molecular dynamics simulation and experiment

In recent years, the application of gas cluster ion beam (GCIB) technology has made great progress. Due to the similar essence of a monoatomic ion beam, the GCIB also shows flashes of brilliance in material processing. It has been reported that smoothness can be greatly improved after the rough surface is bombarded by the GCIB. This indicates that the GCIB processing has great potential in optical fabrication. Although the surface smoothing effect has been investigated, there is still a lack of dynamic micro-analysis for GCIB processing, which is limited for better understanding the mechanism of smoothing effect. In this paper, the surface smoothing effect in GCIB processing is explicitly investigated with molecular dynamics (MD) simulation and experiment. The principle of GCIB processing is compared with the traditional monoatomic ion-beam based processing, and details of the MD simulation procedure are introduced. Based on this, the dynamic micro-analysis of GCIB processing is conducted under different processing conditions. The simulations reveal the phenomena of atomic removal and migration in GCIB processing, which plays an important role in explaining the mechanism of surface smoothing effect. The experiment was performed on the silicon substrate with the in-house GCIB processing machine. The results indicate that the initial rough surface with dense protrusions can be greatly smoothed, and the root mean square (RMS) value is reduced from 0.586 nm to 0.191 nm. Both simulation and experiment can provide a better understanding of smoothing effect mechanism in GCIB processing.

Formation of ions under the action of cosmic rays in humid air

The processes of ion formation in humid tropospheric air under the action of cosmic rays are considered. In this case, positive and negative cluster ions appear. For this analysis, a kinetic model was developed that includes 55 components and 161 reactions. The calculation was carried out using the KINET software package. It is shown that the ionization of air by cosmic rays at altitudes of 5–35 km leads to the formation of plasma consisting mainly of NH4+⋅NH3⋅H2O, H+⋅(H2O)4 and O2−⋅(H2O)2 ions. The maximum concentrations of ions under conditions of minimum magnetic rigidity are observed at altitudes from 10 to 18 km. These results differ sharply from the calculation results obtained for the dry air model.

Reactions of Aluminum Oxide Cluster Cations with Ethane: A Mass-Spectrometric and Vibrational Spectroscopy Study.

The pathways for the reactions of aluminum oxide cluster ions with ethane have been measured. For selected ions (Al2O+, Al3O2+, Al3O4+, Al4O7+) the structure of the collisionally-stabilized reaction intermediates were explored by measuring the photodissociation vibrational spectra from 2600 cm-1 to 3100 cm-1. Density functional theory was used to calculate features of the potential energy surfaces for the reactions and the vibrational spectra of intermediates. Generally, more than one isomer contributes to the observed spectrum. The oxygen-deficient clusters Al2O+ and Al3O2+ have large C-H activation barriers, so only the entrance channel complexes in which intact C2H6 binds to aluminum are observed. This interaction leads to a substantial (~200 cm-1) red shift of the C-H symmetric stretch in ethane, indicating significant weakening of the proximal C-H bonds. In Al3O4+, the complex formed by interactions with three C2H6 is investigated and, in addition to entrance channel complexes, the C-H activation intermediate Al3O4H+(C2H5)(C2H6)2 is observed. For oxygen-rich Al4O7+, the C2H6 is favored to bind at an aluminum site far from the reactive superoxide group, reducing the reactivity. As expected, oxygen-rich species and open-shell cluster ions have smaller barriers for C-H bond activation, except for Al3O4+ which is predicted and observed to be reactive.

High-Strength MOF-Based Polymer Electrolytes with Uniform Ionic Flow for Lithium Dendrite Suppression.

The uneven formation of lithium dendrites during electroplating/stripping leads to a decrease in the utilization of active lithium, resulting in poor cycling stability and posing safety hazards to the battery. Herein, introducing a 3D continuously interconnected zirconium-based metal-organic framework (MOF808) network into a polyethylene oxide polymer matrix establishes a synergistic mechanism for lithium dendrite inhibition. The 3D MOF808 network maintains its large pore structure, facilitating increased lithium salt accommodation, and expands anion adsorption at unsaturated metal sites through its diverse large-space cage structure, thereby promoting the flow of Li+. Infrared-Raman and synchrotron small-angle X-ray scattering results demonstrate that the transport behavior of lithium salt ion clusters at the MOF/polymer interface verifies the increased local Li+ flux concentration, thereby raising the mobility number of Li+ to 0.42 and ensuring uniform Li+ flux distribution, leading to dendrite-free and homogeneous Li+ deposition. Furthermore, nanoindentation tests reveal that the high modulus and elastic recovery of MOF-based polymer electrolytes contribute to forming a robust, dendrite-resistant interface. Consequently, in symmetric battery systems, the system exhibits minimal overpotential, merely 35mV, while maintaining stable cycling for over 1800 h, achieving low-overpotential lithium deposition. Moreover, it retains redox stability under high voltages up to 5.3V.

(Invited) Solid/Electrolyte Interface Under Confinement in Divalent Water-in-Salt Electrolytes

Concentrated aqueous electrolytes (water-in-salt electrolytes, WiSEs) have gained increasing attention in the last few years because they display much wider electrochemical stability windows (upwards of 3V) than the thermodynamic limit of water (1.23V), making them exciting candidates for a variety of electrochemical systems including aqueous batteries. Importantly, it is the ions directly at the electrode/electrolyte interface that are key to explaining this unexpected reactivity. The electrode/electrolyte interface is classically thought of as the electrical double layer (EDL), or the ion arrangement at an interface that builds up to neutralize the surface potential. WiSEs present very different EDL structures than do classical dilute electrolytes. However, most work has focused on monovalent WiSEs, primarily motivated by Li-battery applications using lithium bis(trifluoromethylsulphonyl)imide (LiTFSI).In this work, we aim to understand how divalent ions within the WiSE regime alter both the short-range and long-range signatures of the EDL under confinement. For most of the above applications, reactions occur within the pore-space of a porous electrode, which exhibit confined, overlapping EDLs. Therefore, we use confinement as a tool to probe both the short-range layering structure (<10 nm) and electrostatic decay length (~10-100 nm) away from a charged interface with Surface Forces Apparatus (SFA) measurements.Using WiSEs comprising LiTFSI, Zn(TFSI)2, and mixtures of the two salts, we first establish the bulk structure of these electrolytes using Wide Angle X-Ray Scattering and Raman Spectroscopy, which reveal that the anion and cation are closely associated in all electrolytes, regardless of cation valency. Additionally, clusters of ions are formed in all electrolytes, however, the clusters are suppressed with increasing divalent ion fraction. Under confinement, SFA results demonstrate that the thickness of the adsorbed layer of ions at a solid/electrolyte interface grows with increasing divalent ion fraction. Multiple interfacial layers are formed following this adlayer, and these layers seem dependent on anion size, rather than cation. Importantly, all electrolytes exhibit very long electrostatic decay lengths that are insensitive to valency. This work contributes significant fundamental understanding regarding the structure and charge-neutralization mechanism in this class of electrolytes both in the bulk and under confinement at an interface.

Evolution of 2D Nanostructures on Charged Surfaces through the Precipitation of Hydrolyzable Ions

The significance of surface charge at solid-liquid interfaces extends to crucial roles in diverse chemical processes, including crystallization, self-assembly, fuel cell reactions, and heterogeneous catalysis. Building upon the classical mean field description derived from the Gouy–Chapman model, the electrostatic attraction between a charged interface and counterions in solutions prompts oppositely charged ions from the solution to accumulate at the interface, forming an electric double layer (EDL), with distinct properties from those observed in bulk solutions. While the model accounts for the distribution of ions based on their spatial average perpendicular to the surface, the discussion regarding the lateral structure at the interface, particularly the local molecular-level details, is relatively limited.In this study, we explored the interfacial structure of mica, a mineral with an atomically flat surface and intrinsic negative charge, in electrolytes containing different multi-valent cations, utilizing in-situ liquid phase atomic force microscopy (LP-AFM). We find that, as the solution pH is gradually raised, cations precipitate and form a monolayer hydroxide film on mica surface. Divalent ions such as Mg2+, Ni2+, and Co2+, form large continuous monolayers in a manner that aligns with expectations based on classical nucleation theory. For trivalent ions like Al3+, Fe3+, and Cr3+, hydrolyzed species adsorb in increasing amounts as pH is increased. Instead of exhibiting a random distribution, these ions reveal intricate lateral ordering and eventually evolve into an ordered ion network. Upon further pH increase, the ion network undergoes a transition to a discontinuous film with a persistent network of gaps. The links between the surface nanostructure and local surface charge were investigated using three-dimensional fast force mapping (3D FFM) and complementary streaming potential apparatus (SPA) measurements. As films form, an inversion from negative to positive zeta potential on mica is observed through SPA and is accompanied by the appearance of a long-range tip-sample forces through 3D FFM. These findings suggest that electrostatic interactions between positively charged ions/films and a negatively charged substrate stabilize the surface nanostructure. Furthermore, films created by trivalent ions are more strongly charged compared to those formed by divalent ions.The lateral structure at mica-electrolyte interfaces was simulated using a charge-frustrated lattice gas model, where the ions experience competing interactions between short-range chemical bonding and long-range electrostatic forces. For weak charge effects, the film undergoes a first-order transition from sparse adsorbates to large continuous sheets, aligning with the behavior observed with divalent ions. When the charge effect is sufficiently strong, the surface forms various states, including ordered patterns of ions, ion clusters, and microphase-separated partial films, corresponding to the behavior observed with trivalent ions. This study provides molecular-level understanding of how electric fields control the spontaneous formation of interfacial nanostructures, and offers valuable insights into using electric fields to control crystallization processes for the development of functional materials.

Computational Analysis of Ion Clustering Statistics in Liquid Battery Electrolytes

The transport properties of liquid battery electrolytes critically depend on molecular-level solvation structures of ions. In contrast to the dilute regime where the majority of counterions are sufficiently separated spatially, in global or localized high-concentrated electrolytes (HCEs) counterions tend to form superstructures such as contact-ion pairs (CIPs) or aggregates (AGGs). The presence and relative population of such superstructures can drastically change the ionic transport behavior in liquid electrolytes. We have developed a computer program [1] that can efficiently perform analysis of ion clustering statistics from molecular dynamics simulations, complementary to experimental measurements. We have successfully applied our method to various systems, including (1) a prototypical concentrated liquid electrolyte (Li:EC:DEC) [2], and (2) a series of newly developed high-entropy liquid electrolytes [3]. In both cases, we find consistent agreements between our prediction and experimentally measured nanostructures and solvation strengths. We envision that our method would be widely applicable to generic structurally disordered systems.[1] Cohen et al., Journal of Open Source Software 8, 84 (2023)[2] Xie and Wang et al., Science Advances 9, eadc9721 (2023)[3] Kim and Wang et al. Nature Energy 8, 814–826 (2023)

Cluster Formation Induced by Local Dielectric Saturation in Restricted Primitive Model Electrolytes.

Experiments using the Surface Force Apparatus (SFA) have found anomalously long-ranged charge-charge underscreening in concentrated salt solutions. Meanwhile, theory and simulations have suggested ion clustering to be a possible origin of this behavior. The popular Restricted Primitive Model of electrolyte solutions, in which the solvent is represented by a uniform relative dielectric constant, εr, is unable to resolve the anomalous underscreening seen in experiments. In this work, we modify the Restricted Primitive Model to account for local dielectric saturation within the ion hydration shell. The dielectric "constant" in our model locally decreases from the bulk value to a lower saturated value at the ionic surface. The parameters for the model are deduced so that typical salt solubilities are obtained. Our simulations for both bulk and slit geometries show that our model displays strong cluster formation and these give rise to long-ranged density correlations between charged surfaces, at distances similar to what has been observed in SFA measurements. An electrolyte model wherein the dielectric constant remains uniform does not display similar clusters, even with εr equal to the low saturated value at ion contact. Hence, the observed behaviors are not simply due to an enhanced Coulomb interaction. In the latter case, cluster growth is counteracted by long-ranged repulsions between like-charged ions within clusters; this is an effect that is considerably reduced when the dielectric response drop is local. Our results imply that long-ranged interactions in these systems are mainly due to cluster-cluster correlations, rather than large electrostatic screening lengths.

Effect of one- and two-dimensional nanomaterials on polysulfone-based anion exchange membranes for fuel cells

To investigate nanoparticle morphology's impact on the performance of composite anion exchange membrane (AEM), one-dimensional quaternized branched polyethyleneimine @multi-walled carbon nanotubes (QBPEI@MWCNTs) and two-dimensional quaternized branched polyethyleneimine @graphene oxide sheets (QBPEI@GO) were prepared and incorporated into quaternized polysulfone (QPSF) matrices to form QQ-x-MWCNTs and QQ-x-GO AEMs. These AEMs exhibited superior mechanical properties due to the flexible QBPEI cross-linking and nanoparticle reinforcement. Moreover, QBPEI facilitated microphase separation and ion cluster formation along the surface of nanoparticles, enhancing OH− transport. As a result, QQ-1.0%-MWCNTs and QQ-0.7%-GO AEMs both showed high ionic conductivity (83.19 mS/cm and 76.14 mS/cm at 80 °C). QQ-x-MWCNTs AEMs displayed higher conductivity than QQ-x-GO AEMs over the entire temperature range (20–80 °C) at the same level of ion exchange capacity. QQ-0.7%-MWCNTs AEM excelled, achieving a peak power density of 102.44 mW/cm2 in an H2/O2 fuel cell (80 °C, 40 % RH), surpassing QQ-0.5%-GO AEM (86.50 mW/cm2). Evidently, one-dimensional MWCNTs are effective for establishing long-range interconnected ion transport channels, making them excellent AEM fillers.