Phase Separation Reaction Research Articles

Thickness regulation of electric double layer via electronegative separator to realize High-Performance Lithium-Metal batteries

Lithium metal anode is considered as a promising electrode material for next-generation energy storage systems due to their high theoretical capacity and a low redox potential. However, the uncontrollable growth of Li dendrites severely hindered its practical application. Separators, a vital component in batteries, offer a promising solution to this issue, which can regulate the transport of lithium ions (Li+) and guide the homogenous deposition of Li+. In this study, a three-dimensional porous structure coating layer is constructed on the surface of the commercial polyethylene separator by polymer-induced phase separation (PIPS) and UV-induced cross-linking reactions. The incorporation of synthetized sulfonated SiO2 particles (S-SiO2) enable the successful construction of a negatively charged separator (PE@S-SiO2) based on negatively charged moieties on the surface, which compresses the thickness of the electric double layer (EDL) to optimize the Li+ transport dynamics and suppress dendritic growth. The resulting PE@S-SiO2 separator displays superior electrolyte wettability, much higher thermal resistance, high lithium transference number (0.86), and ionic conductivity (1.15 mS/cm). Consequently, when assembled into lithium metal batteries, the negatively charged separator endows stable cycling over 800 h at a current density of 1 mA cm−2.

Construction of a durable, halogen-free, and phosphorus-free flame retardant cotton fabric system with hydrophobic properties by phase separation and interface polymerization

Inspired by the synthesis of polyurethane, a multifunctional fabric with hydrophobic and long-lasting flame retardancy was prepared through the phase separation and interfacial reaction process between PEI (polyethyleneimine)/BX (borax) aqueous solution and isocyanate terminated polydimethylsiloxane (PDMS-NCO) in tetrahydrofuran solution. The limit oxygen index of the treated fabric increased from 18.0 % to 33.7 %, and the total heat release decreased by 34.2 %. The enhancement of flame retardant performance and thermal stability is attributed to the enhanced char-forming capacity. After 50 cycles of water washing, the cotton fabric can still pass the vertical flammability test because of the curing effect of PDMS-NCO on functional additives. Furthermore, SEM analysis revealed that the formation of nano-rough structures on the fibers was promoted by phase separation, thus leading an increased water contact angle of sample to 139°. The materials utilized in this modified process do not contain elements such as F, Cl, Br, and P, indicating its potential as an environmentally friendly methodology for fabric functionalization.

Multiple potential phase-separation paths in multi-principal element alloys

It is now well established that multi-principal element alloys (MPEAs) offer ample opportunities for exploring new compositions beyond those accessed previously by conventional alloys. However, there is one more realm of possibility presented by MPEAs that has not been touch upon thus far. Here we show that, different from conventional alloys based on a single host element, a given starting MPEA solid solution on its way towards equilibrium can take a rich variety of potential decomposition pathways via multi-stage phase separation, offering a wide range of composition destinations. If/when some of them are reached, assuming kinetically allowed, the multiple phase separation reactions one after another would lead to domains that are compositionally complex and spatially localized. This hypothetical scenario is demonstrated in this paper using a model that mimics Cr-Co-Ni MPEA, showing a preponderance of multiplicity even when assuming only fcc-based phases can form. The complex chemical heterogeneities created as such are expected to be an additional knob to turn for tuning spatially variable composition and chemical order and therefore mechanical properties. Our results thus advocate multiple phase separation possibilities with many potential paths and terminal chemical heterogeneities as yet another important characteristic that distinguishes MPEAs from conventional alloys.

Solidification paths of Al-Cu-Sn alloys: Comparison of thermodynamic analyses and solidification experiments using in situ X-radiography

The increasing importance of Al-Cu-Sn alloys as materials for producing self-lubricating bearing materials in automotive industries requires the development of uniform microstructures with improved performance, which could be achieved by a precise control of solidification processes. Adding Sn to Al-Cu binary alloy could dramatically alters the solidification path, generating liquid phase separation and monotectic reaction. In this paper, Al-10 wt% Cu-X wt% Sn (with X = 0; 5; 10 and 20) alloys have their solidification paths investigated by three different complementary approaches. Firstly, the solidification paths were calculated by using the CALPHAD method through Thermo-Calc software revealing the sequence of transformations that could occur during the solidification of these alloys, from the formation of the initial α-Al dendrites to the final eutectic reaction. Secondly, experimental thermal analysis was carried out by DSC (Differential Scanning Calorimetry), which reveals the successive events that occur during the controlled melting and cooling of these alloys. Thirdly, directional solidification was performed on all alloys, with in situ and real-time observations achieved through the utilization of X-radiography. The comparison between the various approaches showed a suitable correspondence between the history of the alloy solidifications computed by Thermo-Calc and those obtained experimentally (DSC and directional solidification experiments). Additional information about the dynamics of each reaction was obtained during the directional solidification experiments in terms of microstructures, segregation, and the genesis of the liquid phase separation that occurred for high Sn-content alloys.

Discontinuous phase separation, interstitial ordering and recrystallization during nitriding of FeNiCo medium entropy alloy

The sequence of phase transformations triggered as a consequence of inward diffusion of interstitial N during nitriding of FeNiCo medium entropy alloy was investigated. Recrystallized and cold rolled specimens of FeNiCo alloy were nitrided at 580 °C in a flowing ammonia gas atmosphere. Detailed microstructural characterization was carried out using scanning and transmission electron microscopies, X-ray and electron back scattered diffraction and atom probe tomography. Firstly, N supersaturation of about 2 at.% was observed to be established without any nanoscale chemical heterogeneities. Further increase in N-content triggered the occurrence of a discontinuous phase separation reaction, resulting in the formation of alternating Fe+N enriched and Co+Ni enriched phases with a characteristic lamellar morphology and cube-on-cube orientation relationship. The Fe+N enriched lamellae then undergo rapid interstitial N ordering, forming a γ′- Fe4N type nitride phase. The compositional partitioning however is only transient and is followed by a recrystallization of the lamellar microstructure into a compositionally homogeneous γ′-(FeCoNi)4N type matrix. Thermodynamic calculations show that this discontinuous phase separation reaction and subsequent composition homogenization via recrystallization results from isothermally forcing the alloy composition to first enter the metastable miscibility gap in the FeNiCo-N FCC solid solution (at N-supersaturation close to 2 at.%) and then moving out of the miscibility gap at high N contents, beyond 20 at.%. Role of volume misfits, the chemical partitioning and homogenization on the sequential occurrence of different transformations is discussed.

Dip Coating of Water‐Resistant PEDOT:PSS Films Based on Physical Crosslinking

AbstractWater‐resistant poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are valuable in biomedical applications; however, they typically require crosslinkers to stabilize the films, which can introduce undesired aggregation or phase separation reactions. Herein, a dipping‐based process to prepare PEDOT:PSS films on nonplanar surfaces without crosslinker is developed. Sequential soaking of a dip‐coated PEDOT:PSS film in ethanol and water imparts water resistance to the film. Microscopic and spectroscopic techniques are used to monitor the process and confirm that the ethanol soaking elutes the excess PSS from the film bulk, which stabilizes the film prior to the water‐soaking process. The obtained films act as conductors and semiconductors on curved surfaces, including 3D‐printed objects. A film deposited on a curved surface is successfully applied as the channel layer in a neuromorphic organic electrochemical transistor. This approach can enable integrated bioelectronic and neuromorphic applications that can be readily deployed for facile prototyping.

Front Cover: A Thermodynamic Model for the Insertion Electrochemistry of Battery Cathodes (ChemElectroChem 7/2023)

The Front Cover illustrates a crystal layer of nickel hydroxide that undergoes phase separation during electrochemical ion deinsertion (oxidation) and its corresponding cyclic voltammogram (CV). This phase separation phenomenon is revealed by a thermodynamic modelling of solid-solution and phase-separation reaction modes in battery cathodes. Furthermore, according to this model, the hysteresis observed during charge-discharge in the CV curves results from this phase separation which itself is a consequence of large radius changes in the crystal's central metal ion. More information can be found in the Research Article by K. Malaie, F. Scholz and U. Schröder.

Energy and Matter Supply for Active Droplets

AbstractChemically active droplets provide simple models for cell‐like systems that can grow and divide. Such active droplet systems are driven away from thermodynamic equilibrium and turn over chemically, which corresponds to a simple metabolism. Two scenarios of nonequilibrium driving are considered. First, droplets are driven via the system boundaries by external reservoirs that supply nutrient and remove waste (boundary‐driven). Second, droplets are driven by a chemical energy provided by a fuel in the bulk (bulk‐driven). For both scenarios, the conservation of energy and matter as well as the balance of entropy are discussed. Conserved and nonconserved fields are used to analyse the nonequilibrium steady states of active droplets. Using an effective droplet model, droplet stability and instabilities leading to droplet division are explored. This work reveals that droplet division occurs quite generally in active droplet systems. The results suggest that life‐like processes such as metabolism and division can emerge in simple nonequilibrium systems that combine the physics of phase separation and chemical reactions.

Iodine Electrochemistry Dictates Voltage‐Induced Halide Segregation Thresholds in Mixed‐Halide Perovskite Devices

AbstractOwing to straightforward stoichiometry–bandgap tunability, mixed‐halide perovskites are ideal for many optoelectronic devices. However, unwanted halide segregation under operational conditions, including light illumination and voltage bias, restricts practical use. Additionally, the origin of voltage‐induced halide segregation is still unclear. Herein, a systematic voltage threshold study in mixed bromide/iodide perovskite devices is performed and leads to observation of three distinct voltage thresholds corresponding to the doping of the hole transport material (0.7 ± 0.1 V), halide segregation (0.95 ± 0.05 V), and degradation (1.15 ± 0.05 V) for an optically stable mixed‐halide perovskite composition with a low bromide content (10%). These empirical threshold voltages are minimally affected by composition until very Br‐rich compositions, which reveals the dominant role of iodide/triiodide/iodine electrochemistry in voltage‐induced Br/I phase separation and transport layer doping reactions in halide perovskite devices.

Synchronous Engineering for Biomimetic Murray Porous Membranes Using Isocyanate.

Highly permselective and durable membranes are desirable for massive separation applications. However, currently most membranes prepared using nonsolvent-induced phase separation (NIPS) suffer from low permeability and a high fouling tendency due to the great challenges in a rational design and also practical approach for membrane optimization. Inspired by the natural Murray network from vascular plants, we developed a hierarchical membrane via a straightforward yet robust strategy, using isocyanate as a multifunctional additive. Thanks to the integrated functions of a phase separation regulator, blowing agent, cross-linker, and functionalization anchor of isocyanate, our strategy is featured as a perfect combination of a phase separation and chemical reaction, and it enables synchronous engineering of the membrane hierarchy on porosity and components. The representative membrane exhibits superior water permeance (334 L/m2·h·bar), protein retention (>98%), and antifouling ability (flux recover ratio ∼ 98%). This work highlights a versatile path for pursuing a highly enhanced performance of NIPS-made membranes, from the fancy perspective of Murray bionics.

Self-controlled wave solutions to the Tzitzeica-type nonlinear models in mathematical physics

Quantum field theory and solid-state physics phenomena are interpreted using the Tzitzeica-Dodd-Bullough model and nonlinear optics and electromagnetic waves are studied through the Dodd-Bullough-Mikhailov equation. The nonlinear Cahn-Allen model is important for describing the evolution of non-conserved order fields during anti-period sphere coarsening and the phase separation reaction–diffusion processes in multicomponent alloy structures. In this article, we have assessed the advanced and broad-spectrum solitary wave solutions to the stated models and studied the effects of wave speed as well as physical coordinates on the wave profiles and affirmed that waveform varies with the change of the free parameters associated to them. The soliton solutions are extracted by balancing the exponents of the highest-order linear and nonlinear terms. To thoroughly analyze the wave characteristic of the closed-form solutions, different standard wave profiles including kink, bell-shaped soliton, anti-peakon, periodic, quasi-periodic, complex singular, and several general solitons are depicted. Both Painlevé and traveling wave transformation play important roles in converting the equations into nonlinear differential equations. The solutions formulated in this probe are further generic, wide-spectral and some are distinctive which have not been established in the former studies.

Structural analysis of light-colored separated lignin (lignocresol) and its antioxidant properties

The use of lignin is limited by its heterogeneity and complexity. This study was processed using different methods to obtain spruce milled wood lignin (SMWL), spruce kraft lignin (SKL), and spruce lignocresol (SLC) for comparative analysis of the structure and antioxidant activity. SMWL has a complete softwood lignin side-chains structure and lignin carbohydrate complexes. SKL contains fewer ether bonds, while more conjugate structures and condensed structures contribute to the color. However, the α-position of the lignin side chain eliminates most of the hydroxyl and ether bonds (β-O-4/α-OH, phenylcoumaran, and dibenzodioxocine structure) and effectively grafts p-cresol in the phase separation reaction. It not only inhibits the self-condensation of lignin, but also forms the 1,1-diarylpropane unit while protecting β-O-4 linkages from not breaking. Importantly, SLC has few conjugate structures that result in the lightest color among all lignin isolated. Besides, SLC has a high yield and contains trace carbohydrates, indicating that the phase separation method can achieve great amounts of purity separated lignin. The antioxidant activity of lignin was evaluated, results show that 85% of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals were scavenged at the end of 60 min. Owing to its unique color, structural properties, and continuous antioxidant activity, SLC has the potential to manufacture antioxidant cosmetics.

Density Functional Theory for Polymer Phase Separations Induced by Coupling of Chemical Reaction and Elastic Stress

AbstractA density functional theory is applied to phase separation dynamics influenced by crosslinking reactions in dense polymer solutions. The crosslinking reaction is modeled by a change from non‐crosslinked polymers comprising transient network (TN) to crosslinked polymers participating in the percolated permanent network (PN). Deformed TN polymers are considered to relax to the isotropic equilibrium state according to the Maxwellian linear viscoelastic constitutive equation, which is used in the modeling of viscoelastic phase separations. The PN is modeled by a linear elastic constitutive model. When TN polymers are taken into the PN by crosslinking reaction, the instantaneous deformation of the TN polymers are frozen, and such frozen deformations are accumulated as time goes on. A series of simulations is performed using this model, so that two specific features of the viscoelastic and reactive phase separation are obtained, i.e., 1) two‐stage phase separation process that leads to a domain structure with two different characteristic length scales, and 2) fixing the phase‐separated structure before reaching the macrophase separation.

Analysis of phenolation potential of spruce kraft lignin and construction of its molecular structure model

The structure of kraft lignin is heterogeneous and the reaction activity is low due to the complicated and somewhat uncertain chemical reactions under the strong alkali and high temperature conditions of kraft pulping chemistry. At present, people still lack understanding of its structure, so it is difficult to be used as high quality industrial raw material for many years despite its huge output. In this paper, the phenolation potential of industrial Spruce Kraft Lignin (SKL) in phase separation system was explored. Compared with previous studies on phase separation reaction, due to the direct use of lignin as feedstock, sulfuric acid would only act as a phenolation catalyst, and is no longer used for swelling cell walls and hydrolyzing carbohydrates, so a modest reduction of acid concentration is feasible. In the phase separation system, the benzyl position of lignin was activated to selectively graft the p-cresol groups. Due to the protection of organic phase on lignin, the breakage of the β linkages and the condensation reaction of lignin were effectively prevented, so the original structure of lignin was well preserved. In order to capture the detailed structural changes of lignin after phenolation in phase separation system, FT-IR, GPC and quantitative NMR techniques (1H-NMR, 31P-NMR and 2D-NMR) were used to analyze the changes of main functional groups, linkages and substructures of industrial lignin samples before and after phenolation. The results showed that the industrial spruce kraft lignin still have many active sites which can be modified by phenolation. And through p-cresol treatment, a kind of high activity industrial lignin with more phenolic hydroxyl groups, more uniform molecular size and higher purity was obtained. Then the molecular structure models of spruce kraft lignin before and after phenolation is proposed respectively based on the molecular weights, quantitative analysis of functional groups, linkages, substructures and introduced p-cresols. This will be helpful to understand the structural changes of industrial spruce kraft lignin during phenolation in phase separation system, and provide guidance for the high value utilization of this high activity industrial lignin in the future.

A novel ceramifiable epoxy composite with enhanced fire resistance and flame retardance

A novel epoxy composite with flame retardance and fire resistance was prepared by adding silicate glass frit (SGF) and ammonium polyphosphate (APP) into the epoxy resin. In the combustion test, epoxy composites displayed obvious flame retardance feature, showing much lower heat release rate, total heat release and total smoke production than epoxy resin. The composite residue formed at 900 °C had a flexural strength of 19.05 MPa. In addition, possible mechanisms for the phase separation and crystallization reactions at high temperatures were also investigated in detail through thermogravimetric analyzer, X-ray diffraction, X-ray photoelectron spectrometer, and scanning electron microscopy. It was suggested that phosphorus element tends to migrate to the surface of the composite residue during firing process, and sodium element from SGF is selectively combined with the phosphorus element to obtain crystalline phases. With this unique phase separation and crystallization reactions, the fire resistance of the epoxy composite was significantly improved.

Non-equilibrium phase separation with reactions: a canonical model and its behaviour

Materials undergoing both phase separation and chemical reactions (defined here as all processes that change particle type or number) form an important class of non-equilibrium systems. Examples range from suspensions of self-propelled bacteria with birth–death dynamics, to bio-molecular condensates, or ‘membraneless organelles’, within cells. In contrast to their passive counterparts, such systems have conserved and non-conserved dynamics that do not, in general, derive from a shared free energy. This mismatch breaks time-reversal symmetry and leads to new types of dynamical competition that are absent in or near equilibrium. We construct a canonical scalar field theory to describe such systems, with conserved and non-conserved dynamics obeying model B and model A, respectively (in the Hohenberg–Halperin classification), chosen such that the two free energies involved are incompatible. The resulting minimal model is shown to capture the various phenomenologies reported previously for more complicated models with the same physical ingredients, including microphase separation, limit cycles and droplet splitting. We find a low-dimensional subspace of parameters for which time-reversal symmetry is accidentally recovered, and show that here the dynamics of the order parameter field (but not its conserved current) is exactly the same as an equilibrium system in which microphase separation is caused by long-range attractive interactions.

PH-Controlled Coacervate-Membrane Interactions within Liposomes.

Membraneless organelles formed by liquid–liquid phase separation are dynamic structures that are employed by cells to spatiotemporally regulate their interior. Indeed, complex coacervation-based phase separation is involved in a multitude of biological tasks ranging from photosynthesis to cell division to chromatin organization, and more. Here, we use an on-chip microfluidic method to control and study the formation of membraneless organelles within liposomes, using pH as the main control parameter. We show that a transmembrane proton flux that is created by a stepwise change in the external pH can readily bring about the coacervation of encapsulated components in a controlled manner. We employ this strategy to induce and study electrostatic as well as hydrophobic interactions between the coacervate and the lipid membrane. Electrostatic interactions using charged lipids efficiently recruit coacervates to the membrane and restrict their movement along the inner leaflet. Hydrophobic interactions via cholesterol-tagged RNA molecules provide even stronger interactions, causing coacervates to wet the membrane and affect the local lipid-membrane structure, reminiscent of coacervate–membrane interactions in cells. The presented technique of pH-triggered coacervation within cell-sized liposomes may find applications in synthetic cells and in studying biologically relevant phase separation reactions in a bottom-up manner.

Mechanism of gold precipitation in the Gezigou gold deposit, Xinjiang, NW China: Evidence from fluid inclusions and thermodynamic modeling

The Gezigou gold deposit, which is located in west Junggar (Xinjiang, China), is mainly hosted in graphite-bearing siltstone. These ore bodies, which consist of gold-bearing hydrothermal veins and mineralized siltstone with disseminated sulfides, formed in three stages: quartz-sulfides-native gold (I), arsenopyrite-calcite-native gold (II), and quartz-calcite (III) stages. The microthermometric and laser Raman spectroscopic analysis of the fluid inclusions in stage I-quartz demonstrate that the ore-forming fluid was moderate temperature (353–392 °C), low-salinity (2.9–5.3 wt% NaCl equiv.), and H2O-CH4-dominant. The thermodynamic modeling of the Au-Cu-As-Fe-S system performed using the SUPCRT92 software package with the updated database of slop16.dat indicates that a decrease in H2S activity (aH2S) and oxygen fugacity (fO2) were responsible for reducing the solubilities of As and Au, which might be responsible for the coexistence of arsenopyrite and native gold. The decreases in aH2S and fO2 caused by phase separation and fluid-rock reactions induced the precipitation of native gold in the quartz-sulfides-native gold stage. Graphite-bearing siltstone, which may lower the fO2 of ore-forming fluids, is thus an important indicator of prospective gold deposits.

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.

Slight Symmetry Reduction in Thermoelectrics

Thermoelectric research on germanium telluride (GeTe) has been mainly focused on the enhancement of its performance in the high-temperature cubic phase since the 1960s. Recently in Joule, Pei and co-workers achieved an unprecedented thermoelectric figure of merit in rhombohedral-phase GeTe by exploiting slight symmetry breaking in the structure, which simultaneously improved the electronic properties and reduced the lattice thermal conductivity.