Spontaneous Segregation Research Articles

Self-stratification and phase separation in drying binary colloidal films

HypothesisFilms that develop compositional heterogeneity during drying offer a promising approach for achieving tailored functionalities. These functionalities can be realized by strategically directing different components during the drying process. One approach to achieve this is through spontaneous size segregation of colloidal particles. Two variants thereof have previously been observed in binary suspensions: layer formation (self-stratification) due to kinetically driven concentration gradients, and micro-domain formation (phase separation) due to thermodynamic depletion interactions between the small and large species. Surprisingly, in the context of binary colloidal films, these phenomena have never been investigated concurrently during evaporation. ExperimentsWe show how we can achieve both self-stratification and domain formation in a single step. Using real-time 3D confocal fluorescence microscopy, we quantitatively unravel the effects of various parameters on the emergence of compositional heterogeneity. FindingsWe reveal that beyond a certain size ratio, micro-phase separation becomes a prominent mechanism dictating the final morphology. The initial volume fraction minimally affects the final domain size but significantly impacts self-stratification. Reducing the evaporation rate increases the domain size while minimizing stratification. Finally, reducing the colloidal electrostatic interaction by a small increase in salt concentration enhances phase separation yet reverses stratification. These findings unveil a strategy for harnessing two distinct size segregation mechanisms in a single film, forming a foundation for customizable self-partitioning coatings.

Development of a new Mg–25Al–5Zn filler metal containing trace Y for brazing AZ91D magnesium alloy

In this work, the investigation focused on the effects of trace Y on the microstructure and characteristics of the Mg–25Al–5Zn filler metal, and then the optimal Mg–25Al–5Zn-0.5Y was used to braze the AZ91D magnesium alloy. Five kinds of filler metals showed good wettability on AZ91D magnesium alloy. Compared with Mg–25Al–5Zn filler metal, the wetting area of Mg–25Al–5Zn-0.5Y filler metal was increased by 134 % and the wetting angle was decreased by 58 %. This was mainly due to the spontaneous segregation of the active element Y at the interface. Thus, the surface tension was reduced and the wettability of the solder was improved. Different from the precipitation of α-Mg near the interface at different brazing temperatures, the distribution of α-Mg in brazing seam was more homogenous as the holding time increased. The microhardness of the brazing seam gradually increased from AZ91D side to the center of the brazing seam due to a lot of β-Mg17Al12 with high microhardness in joint. However, with the increase of brazing temperature and holding time, a large number of α-Mg solid solutions with low microhardness were precipitated in the brazing seam. As a result, the microhardness of the brazed joint gradually decreased. The shear strength of the brazed joint reached the maximum value (42 MPa) at 520 °C for 60 s. After calculation, the contribution of grain boundary strengthening and solid solution strengthening to shear strength was 67.98 % and 28.96 %, respectively.

Self-formation of dual-phase nanocomposite Zr–Cu–N coatings based on nanocrystalline ZrN and glassy ZrCu

A novel type of nanocomposite Zr–Cu–N material based on hard nanocrystalline ZrN and amorphous glassy ZrCu was prepared by atom-by-atom deposition using reactive magnetron co-sputtering. The elemental composition of the coatings was systematically controlled over a wide range, so that the stoichiometry of both phases was the same in all coatings and only phase fractions varied. Experimental results obtained using X-ray diffraction and electron microscopies were complemented by thirteen ab-initio simulations for the same coating compositions. We found that the structure of the as-deposited Zr–Cu–N coatings undergoes a gradual transition from an amorphous to nanograined and finally to nanocolumnar structure. When ZrN fraction exceeds 20 mol.%, both phases exhibit the tendency for spontaneous segregation even without heating, forming a heterogenous dual-phase nanocomposite structure. At approximately 50 mol.% ZrN, the ZrN nanocrystals enveloped by a relatively thin amorphous ZrCu phase reach an optimum size (3–5 nm), resulting in a maximum enhancement of hardness by 38 % compared to the rule of mixture. For ZrN fractions > 80 mol.%, hardness and plastic work fraction follow the trend proposed by the rule of mixture and the coatings with a lower hardness but a higher plasticity compared to the ZrN coating are prepared.

Enhanced crack propagation resistance after healing treatment by addition of boron in FeNi-base superalloy

The objective of the present study was to investigate whether the crack propagation resistance of boron-containing FeNi-based superalloy could be enhanced by healing treatment. The healing treatment was performed by pre-straining and subsequent heat treatment, resulting in a pronounced boron segregation zone at the interface. Formation of boron segregation zone reinforced the crack propagation path, thereby effectively enhancing the mechanical properties of FeNi-based superalloy. The tested alloys were prepared by hot-rolling followed by aging treatment, resulting in precipitation of γ′-Ni3Ti and γ''-Ni3Nb embedded in the γ matrix. After pre-straining and healing heat treatment, η-Ni3Ti phase formed at the grain boundary, leading to the formation of a boron segregation zone at the interface between the η-Ni3Ti phase and γ matrix. Both strength and ductility were improved with increasing boron content from 0 at% to 0.2 at% after healing treatment. The spontaneous segregation of boron at the precipitate-matrix interface played a role in enhancing both strength and ductility by interface strengthening. Moreover, it was revealed that a critical amount of boron segregation is required for interface strengthening. Dislocation density analysis revealed that the recovery effect was weaker in alloys with boron than in those without it, leading to a more pronounced work-hardening effect.

Self-Organized States from Solutions of Active Ring Polymers in Bulk and under Confinement.

In the present work, we study, by means of numerical simulations, the structural and dynamical behavior of a suspension of active ring polymers in bulk and under lateral confinement. At high activity, when changing the distance between the confining planes and the polymers' density, we identify the emergence of a self-organized dynamical state, characterized by the coexistence of slowly diffusing clusters of rotating disks and faster rings moving in between them. We further assess that self-organization is robust in a range of polymer sizes, and we identify a critical value of the activity, necessary to trigger cluster formation. This system has distinctive features resembling at the same time polymers, liquid crystals, and active systems, where the interplay between activity, topology, and confinement leads to a spontaneous segregation in an initially one-component solution.

Revisiting a Cu-rich layer on the aluminum surface after twin-jet electropolishing

Twin-jet electropolishing (TJE) is a well-known method to prepare Cu-containing Al alloys for transmission electron microscopy (TEM) observation. Previous studies have reported a Cu-rich layer usually formed between Al matrix and outermost alumina layer at the electropolished Al surface. However, characteristics and formation mechanisms of the Cu-rich layer remain largely unexplored. Herein, configurations, formation process and property of the Cu-rich layer formed during TJE of Al alloys are revealed detailly employing aberration-corrected scanning TEM (STEM), STEM image simulations and first-principles calculations. The results reveal a new orientation relationship between the Cu-rich layer (θ’-Al2Cu) and Al matrix, which produces a low interfacial Al strain field. Formations of ∼2-nm-thick θ’ layer and its beneath ∼6-nm-thick Cu diffusion zone at the electropolished Cu-containing Al surface are mainly associated with traces of Cu in the electrolyte and anodization. Selective oxidation of elements, Cu-emitting alumina layer and spontaneous solute Cu segregation at the Al surface are also responsible for formations of the θ’ layer and Cu diffusion zone. Further study reveals that the θ’ layer behaves a strong self-healing ability after damaged by high-energy electron beam. The obtained results provide a potential insight into the surface modification of metals and alloys using electrochemical method.

Widening the temperature range and improving the linearity of CaCu3Ti4O12 ceramics for high-temperature NTC thermistor application through entropy engineering strategy

The entropy engineering strategy has been used for the first time to improve the grain boundary (GB) barrier of CaCu3Ti4O12 (CCTO) ceramics, in order to solve its nonlinear problem at around 300 ℃ and expand its application in the field of high-temperature thermistors. To achieve this goal, we prepared (CaBaEuZnSr)0.2Cu3Ti4O12 (CBEZSCT) high-entropy ceramics, and the GB spontaneous segregation properties were exploited to improve the GB resistance of CBEZSCT ceramics. The results show that the GB activation energy of CBEZSCT high-entropy ceramics (0.87 eV) is higher than that of CCTO ceramics (0.7 eV), which linearizes the resistance temperature curve and extends the application temperature limit from 300° to 750 °C. The proposed method of using a high entropy strategy to tune the GB resistance of CCTO to optimize its performance is highly effective, thus providing a new way of thinking about studying high-performance CCTO materials.

Phase Transition and Phase Separation in Realistic Thylakoid Lipid Membrane of Marine Algae in All-Atom Simulations.

Thylakoid membranes are specialized membranes predominantly composed of uncommon galacto- and sulfolipids, having distinct roles in photosynthesis. Large acyl chain variety and richness in polyunsaturated fatty acid (PUFA) content of thylakoid lipids further add to the compositional complexity. The function of these membrane systems is intimately dependent on the fluidity of its lipid matrix, which is strongly modulated by the lipid composition and temperature. The present work, employing extensive atomistic simulations, provides the first atomistic view of the phase transition and domain coexistence in a model membrane composed of thylakoid lipids of a commercially important red alga Gracilaria corticata between 10 and 40 °C. The growth and photosynthetic activity of marine algae are greatly influenced by the seawater temperature. So far, little is known about the molecular organization of lipids in thylakoid membranes, in particular their adaptive arrangements under temperature stress. Our simulations show that the algal thylakoid membrane undergoes a transition from a gel-like phase at a low temperature, 10-15 °C, to a homogeneous liquid-crystalline phase at a high temperature, 40 °C. Clear evidence of spontaneous phase separation into coexisting nanoscale domains is detected at intermediate temperatures nearing the optimal growth temperature range. Particularly, at 25-30 °C, we identified the formation of a stable ripple phase, where the gel-like domains rich in saturated and nearly hexagonally packed lipids were separated from fluid-like domains enriched in lipids containing PUFA chains. The phase separation is driven by the spontaneous and preferential segregation of lipids into differentially ordered domains, mainly depending on the acyl chain types. Cholesterol impairs the phase transition and the emergence of domains and induces a fairly uniform liquid-ordered phase in the membrane over the temperatures studied. This work improves the understanding of the properties and reorganization of lipids in the thylakoid membrane in response to temperature variation.

Self-Organized Growth of Nanowires on a Graphene Film

The self-organized growth of nanowires (NWs) on a graphene film is realized through the van der Waals epitaxy mechanism by metalorganic chemical vapor deposition. It is a fundamental phenomenon which is qualitatively different from the known growth mechanisms, such as self- and metal-catalyzed NW growth. We present a theoretical model that explains the self-organized nucleation of InGaAs NWs on graphene, starting from the formation of InAs NW segments. Then, newly formed InAs NWs act just like seeds to initiate the subsequent growth of InAs/InxGa1–xAs core–shell NWs with spontaneous phase segregation. The model shows that due to the introduction of the graphene film, the nucleation speed of InAs and InGaAs nanoislands in the horizontal direction far exceeds that of the vertical direction. It also elucidates why the radius of the InAs core is two times larger than the InGaAs shell thickness by considering the adatom collection ability of the InAs core and InGaAs shell, respectively, during the transformative process. Thus, the theoretical analysis of the self-organized NW growth on a graphene film is of vital importance for further optimizing the fabrication procedures of two-dimensional material-based NWs.

Interface engineering toward self-corrosion inhibited alkaline aluminum-air battery via optimized electrolyte system

In this manuscript, an introduced ionic liquids-ethylene glycol-KOH electrolyte system is proposed. Theoretical calculations and experiments show that ionic liquids with stronger hydrophobicity provide better corrosion inhibition for their spontaneous adsorption behavior and water molecule segregation. In this process, the imidazole ring cations play a major role. The electrolyte system reconstructs the Al/electrolyte interface with poor H2O, thus has lower self-corrosion rate for [BMIM]PF6 and contributes to the uniform dissolution of Al anode. Additionally, discharge performance of the full-cell feature same trend, endowing an outstanding capacity of 1971 mAh g−1 and anode utilization of 66.2% in alkaline [BMIM]PF6-ethylene glycol electrolyte. In terms of maintaining the activity of the Al-6061 anode whilst keeping low corrosion rate level, the proposed electrolyte system seems to be potential alternative.

Microstructured click hydrogels for cell contact guidance in 3D.

The topography of the extracellular matrix (ECM) is a major biophysical regulator of cell behavior. While this has inspired the design of cell-instructive biomaterials, the ability to present topographic cues to cells in a true 3D setting remains challenging, particularly in ECM-like hydrogels made from a single polymer. Herein, we report the design of microstructured alginate hydrogels for injectable cell delivery and show their ability to orchestrate morphogenesis via cellular contact guidance in 3D. Alginate was grafted with hydrophobic cyclooctyne groups (ALG-K), yielding amphiphilic derivatives with self-associative potential and ionic crosslinking ability. This allowed the formation of microstructured ALG-KH hydrogels, triggered by the spontaneous segregation between hydrophobic/hydrophilic regions of the polymer that generated 3D networks with stiffer microdomains within a softer lattice. The azide-reactivity of cyclooctynes also allowed ALG-K functionalization with bioactive peptides via cytocompatible strain-promoted azide-alkyne cycloaddition (SPAAC). Hydrogel-embedded mesenchymal stem cells (MSCs) were able to integrate spatial information and to mechano-sense the 3D topography, which regulated cell shape and stress fiber organization. MSCs clusters initially formed on microstructured regions could then act as seeds for neo-tissue formation, inducing cells to produce their own ECM and self-organize into multicellular structures throughout the hydrogel. By combining 3D topography, click functionalization, and injectability, using a single polymer, ALG-K hydrogels provide a unique cell delivery platform for tissue regeneration.

Chiral and Morphological Anisotropy of Supramolecular Polymers Shaped by a Singularity in Solvent Composition.

Understanding the role of solvent in translating molecular anisotropy to supramolecular polymers is in the early stages. A solvent's influence on the strength of different noncovalent interactions can explain anisotropic growth in some cases, but its effect on cooperative processes, particularly in mixed solvents, remains obscure. We report the self-assembly of a series of chiral perylene bisimides in water-cosolvent mixtures, and the results highlight the fascinating influence of solvent-solute interactions on supramolecular anisotropy, both chiral and morphological. The initial assembly is agnostic to solvent composition, resulting in weakly chiral, spherical nanostructures. In an extremely narrow solvent composition range, the nanospheres transform into long, prominently chiral supramolecular polymers. Further, chirality can be fully reversed by changing the good (achiral) cosolvent. We elucidate how solvent modulates specific noncovalent interactions and governs the kinetics and thermodynamics of key processes, such as spontaneous phase segregation, secondary nucleation, and cooperative growth. In the context of supramolecular polymerization, our results encourage one to steer the focus away from the physical attributes of a solvent (polarity, phase diagram, etc.) and toward the complexities of solvent-solute interactions.

Spontaneous mirror symmetry breaking and chiral segregation in the achiral ferronematic compound DIO.

An achiral compound, DIO, known to exhibit three nematic phases namely N, NX and NF, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic NF shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.

Construction of multiphasic membraneless organelles towards spontaneous spatial segregation and directional flow of biochemical reactions.

Many intracellular membraneless organelles (MLOs) appear to adapt a hierarchical multicompartment organization for efficient coordination of highly complex reaction networks. Recapitulating such an internal architecture in biomimetic platforms is, therefore, an important step to facilitate the functional understanding of MLOs and to enable the design of advanced microreactors. Herein, we present a modular bottom-up approach for building synthetic multiphasic condensates using a set of engineered multivalent polymer-oligopeptide hybrids. These hybrid constructs exhibit dynamic phase separation behaviour generating membraneless droplets with a subdivided interior featuring distinct chemical and physical properties, whereby a range of functional biomolecules can be spontaneously enriched and spatially segregated. The platform also attains separated confinement of transcription and translation reactions in proximal compartments, while allowing inter-compartment communication via a directional flow of reactants. With advanced structural and functional features attained, this system can be of great value as a MLO model and as a cell-free system for multiplex chemical biosynthesis.

On-surface synthesis and spontaneous segregation of conjugated tetraphenylethylene macrocycles

Creating conjugated macrocycles has attracted extensive research interest because their unique chemical and physical properties, such as conformational flexibility, intrinsic inner cavities and aromaticity/antiaromaticity, make these systems appealing building blocks for functional supramolecular materials. Here, we report the synthesis of four-, six- and eight-membered tetraphenylethylene (TPE)-based macrocycles on Ag(111) via on-surface Ullmann coupling reactions. The as-synthesized macrocycles are spontaneously segregated on the surface and self-assemble as large-area two-dimensional mono-component supramolecular crystals, as characterized by scanning tunneling microscopy (STM). We propose that the synthesis benefits from the conformational flexibility of the TPE backbone in distinctive multi-step reaction pathways. This study opens up opportunities for exploring the photophysical properties of TPE-based macrocycles.

Simultaneously enhanced separation and antifouling properties by synergistic effect of pore-formation and surface segregation through incorporating bowl-like amphiphiles

Herein, we propose a new strategy to improve the separation and antifouling properties of ethylene vinyl alcohol (EVAL) membranes by a dual pore formation mechanism modified with natural macrocyclic amphiphiles cyclodextrin (CDs). The amphiphilic bowl-like geometry of CDs, consisting of a hydrophobic cavity and hydrophilic rim, induces spontaneous surface segregation during the non-solvent induced phase separation to form a CD-enriched layer. Here, CDs play multiple roles, including pore-forming and antifouling enhancement agents, by modifying the morphological, physical, permeation, and separation properties of the membranes. The three-dimensional honeycomb sponge-like structure was determined by SEM analysis, and the elemental composition was examined by SEM-EDX analysis. The O element indicated a gradient decrease distribution from the top to the bottom layer of the cross-section, concomitant with the combination of pore-forming and surface segregation functions. The introduction of amphiphilic CDs increases the roughness, hydrophilicity, and porosity of the membranes. Furthermore, the CDs-modified EVAL (d-M) membranes have excellent mechanical properties, a high water flux (148 L/m2h) with superior rejection to BSA (98%), and can be used for dye separation (Congo Red: 99.7%, Coomassie brilliant blue: 97.5%, Trypan blue: 92.4%). Moreover, the modified EVAL with the best performance has excellent antifouling capacity and long-term stability. This work demonstrates the effect of the addition of CDs and octanol as dual pore formers on the fabrication of hydrophilic antifouling membranes for efficient separation.

Spontaneous Phase Segregation Enabling Clogging Aversion in Continuous Flow Microfluidic Synthesis of Nanocrystals Supported on Reduced Graphene Oxide

Eliminating clogging in capillary tube reactors is critical but challenging for enabling continuous-flow microfluidic synthesis of nanoparticles. Creating immiscible segments in a microfluidic flow is a promising approach to maintaining a continuous flow in the microfluidic channel because the segments with low surface energy do not adsorb onto the internal wall of the microchannel. Herein we report the spontaneous self-agglomeration of reduced graphene oxide (rGO) nanosheets in polyol flow, which arises because the reduction of graphene oxide (GO) nanosheets by hot polyol changes the nanosheets from hydrophilic to hydrophobic. The agglomerated rGO nanosheets form immiscible solid segments in the polyol flow, realizing the liquid-solid segmented flow to enable clogging aversion in continuous-flow microfluidic synthesis. Simultaneous reduction of precursor species in hot polyol deposits nanocrystals uniformly dispersed on the rGO nanosheets even without surfactant. Cuprous oxide (Cu2O) nanocubes of varying edge lengths and ultrafine metal nanoparticles of platinum (Pt) and palladium (Pd) dispersed on rGO nanosheets have been continuously synthesized using the liquid-solid segmented flow microfluidic method, shedding light on the promise of microfluidic reactors in synthesizing functional nanomaterials.

Q-learning-based migration leading to spontaneous emergence of segregation

Understanding population segregation and aggregation is a critical topic in social science. However, the mechanisms behind segregation are not well understood, especially in the context of conflicting profits. Here, in the context of evolutionary game theory, we study segregation by extending the prisoner’s dilemma game to mobile populations. In the extended model, individuals’ types are distinguished by their strategies, which may change adaptively according to their associated payoffs. In addition, individuals’ migration decisions are determined by the Q-learning algorithm. On the one hand, we find that such a simple extension allows the formation of three different types of spontaneous segregation: (a) environmentally selective segregation; (b) exclusionary segregation; and (c) subgroup segregation. On the other hand, adaptive migration enhances network reciprocity and enables the dominance of cooperation in a dense population. The formation of these types of segregation and the enhanced network reciprocity are related to individuals’ peer preference and profit preference. Our findings shed light on the importance of adaptive migration in self-organization processes and contribute to the understanding of segregation formation processes in evolving populations.

Improved electrochemical performance in Sc-doped nanocrystalline LiMn2O4

• Design of stable interfaces for cathode nanomaterials enhanced capacity in Li-ion battery. • Sc 3+ spontaneously segregates to both surfaces and grain boundaries in LiMn 2 O 4 nanoparticles. • Sc 3+ -LMO showed capacity retention of 97.3% compared LMO with only 88.3%. Jahn-Teller effects have been widely known to cause capacity fading in LiMn 2 O 4 (LMO) cathode materials due to Mn dissolution from the cathode/electrolyte interfaces. This effect is more pronounced in nanoscale materials due to their high surface reactivity. Although surface coatings can help mitigate the phenomenon, there is still limited understanding of the correlation between the spontaneous segregation of dopants to interfaces and the cathode electrochemical performance. This work demonstrates that an interfacial dopant, Sc 3+ , selected on a thermodynamic principle, segregates to surfaces and grain boundaries and acts as a system stabilizer. The electrochemical performance in Li/LMO half-cells showed nanostructured Sc 3+ -doped LMO delivers capacity retention of 97.3% after 50 cycles at 0.2C compared to an equivalent undoped LMO with only 88.3%. Sc-doping reduces the charge transfer resistance while maintaining its high characteristic diffusion coefficient (D Li+ ) of 9.089 × 10 -11 cm 2 /s. The work highlights that understanding the thermodynamic stabilization of cathode materials can provide a pathway to advance cathode technologies even beyond Lithium.

On the problem of stability/instability of bimetallic core-shell nanostructures: Molecular dynamics and thermodynamic simulations

Earlier we put forward a hypothesis about relationship between the spontaneous surface segregation of one of the components of binary A-B nanoparticles and stability/instability of one of the two alternative core-shell nanostructures A@B or B@A. Here, the first symbol (before the @ sign) corresponds to the particle core, and the second (after @) to its shell. In accordance with our hypothesis, stable or at least more stable should be that of the two alternative nanostructures, the shell of which corresponds to the component spontaneously segregating to the surface. Verification of this hypothesis and revealing possible deviations from it have been carried out by using molecular dynamics simulation of Co@Au, Au@Co, Ni@Cu, Cu@Ni, Al@Ni and Ni@Al nanostructures. In addition, the atomistic and thermodynamic simulations were involved to predict the surface segregation in corresponding binary nanoalloys (Co-Au, Ni-Cu and Ni-Al). The thermodynamic simulation of segregation in binary metal nanoparticles was based on numerical solution of the Butler equation for a two-cell particle model. It has been established that the above hypothesis is indeed fulfilled but in some certain temperature ranges. During discussion of the results obtained, the concept was put forward of thermodynamic and kinetic factors of the core-shell nanostructure stability.