Early Stage Of Phase Separation Research Articles

Deciphering the molecular mechanism underlying morphology transition in two-component DNA-protein cophase separation.

Nucleic acid and protein co-condensates exhibit diverse morphologies crucial for fundamental cellular processes. Despite many previous studies that advanced our understanding of this topic, several interesting biophysical questions regarding the underlying molecular mechanisms remain. We investigated DNA and human transcription factor p53 co-condensates-a scenario where neither dsDNA nor the protein demonstrates phase-separation behavior individually. Through a combination of experimental assays and theoretical approaches, we elucidated: (1) the phase diagram of DNA-protein co-condensates at a certain observation time, identifying a phase transition between viscoelastic fluid and viscoelastic solid states, and a morphology transition from droplet-like to "pearl chain"-like co-condensates; (2) the growth dynamics of co-condensates. Droplet-like and "pearl chain"-like co-condensates share a common initial critical microscopic cluster size at the nanometer scale during the early stage of phase separation. These findings provide important insights into the biophysical mechanisms underlying multi-component phase separation within cellular environments.

Early Stages of FUS Droplet Formation via Liquid-Liquid Phase Separation.

The phase behavior of complex biomolecular solutions may explain different cellular processes, including the organization of cells by membraneless organelles. The early stages of phase separation are crucial to understanding the underlying mechanism and identifying biomolecules that trigger or drive the transition. Here, we analyze the early events of liquid-liquid phase separation (LLPS) of FUS by multiangle time-resolved static and dynamic light scattering. LLPS was triggered by TEV-catalyzed cleavage of the MBP-tag from FUS-MBP. The light scattering measurements revealed the existence of at least two fractions of FUS-MBP aggregates already prior to the onset of LLPS. The orders of magnitude of the aggregate size in these two fractions are 10 and 100 nm, respectively. LLPS started after an induction period, which depended on the concentration of FUS-MBP. The data from time-dependent light scattering revealed a coalescence of droplets also denoted as a step growth process. A step growth process instead of nucleation and growth via monomer addition suggests that LLPS takes place within the spinodal rather than between the binodal and the spinodal.

Nanostructure, Mechanical Properties, and Corrosion Resistance of Super Duplex Stainless Steel 2507 Aged at 500 °C

In order to investigate the effect of phase separation (PS) on the super duplex stainless steel SAF 2507, the evolution of the nanostructure, mechanical properties, and corrosion resistance of the alloy was studied after aging at 500 °C for 1, 10, 100, and 1000 h. The nanostructure of PS was quantitatively characterized by small-angle neutron scattering. The hardness, impact toughness, and pitting corrosion resistance were measured for different conditions. The results show that the early stage of PS had a more significant impact on the nanostructure and properties of SAF 2507. The fracture behavior of the alloy was likely determined by the mechanical properties of ferrite for aged conditions. The pitting corrosion resistance of SAF 2507 aged at 500 °C was closely related to the Cr depletion caused by PS, and the resistance became weaker with the progression of PS. The evolution of the passivation region with aging time correlated well with that of mechanical properties and characteristic parameters of PS, indicating that it is possible to develop a new nondestructive electrochemical method to quantify the evolution of PS in SAF 2507.

Domain boundary assisted spinodal decomposition in magnetic materials

Spinodal decomposition involves a composition modulation that grows with time which leads to phase separation. Surfaces, grain boundaries, and other defect sites possessing higher energy also assist spinodal decomposition. This work explores the possibility of magnetic domain boundary-assisted spinodal decomposition in a binary magnetic alloy using phase-field simulations. We observe a uniquely aligned microstructure in the early stage of phase separation, as the second phase paramagnetic particles evolve along the magnetic domain boundaries in a ferromagnetic matrix. Moreover, it significantly affects the coarsening dynamics post phase separation similar to that found in recent studies.

In Situ Monitoring of Scale Effects on Phase Selection and Plasmonic Shifts during the Growth of AgCu Alloy Nanostructures for Anticounterfeiting Applications

Tailoring of plasmon resonances is essential for applications in anticounterfeiting. This is readily achieved by tuning the composition of alloyed metal clusters; in the simplest case, binary alloys are used. Yet, one challenge is the correlation of cluster morphology and composition with the changing optoelectronic properties. Hitherto, the early stages of metal alloy nanocluster formation in immiscible binary systems such as silver and copper have been accessible by molecular dynamics (MD) simulations and transmission electron microscopy (TEM). Here, we investigate in real time the formation of supported silver, copper, and silver–copper-alloy nanoclusters during sputter deposition on poly(methyl methacrylate) by combining in situ surface-sensitive X-ray scattering with optical spectroscopy. While following the transient growth morphologies, we quantify the early stages of phase separation at the nanoscale, follow the shifts of surface plasmon resonances, and quantify the growth kinetics of the nanogranular layers at different thresholds. We are able to extract the influence of scaling effects on the nucleation and phase selection. The internal structure of the alloy cluster shows a copper-rich core/silver-rich shell structure because the copper core yields a lower mobility and higher crystallization tendency than the silver fraction. We compare our results to MD simulation and TEM data. This demonstrates a route to tailor accurately the plasmon resonances of nanosized, polymer-supported clusters which is a crucial prerequisite for anticounterfeiting.

Phase decomposition in nanocrystalline Cr0.8Cu0.2 thin films

Metastable Cr0.8Cu0.2 alloy thin films with nominal thickness of 360 nm have been deposited on Si(100) substrate by co-evaporation of Cu and Cr using molecular beam epitaxy (MBE). Phase evolution, microstructure, stress development, and crystallographic texture in Cr0.8Cu0.2 thin films have been investigated by X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS) during annealing of the films in the temperature range 200–450 °C. X-ray diffraction of the as-deposited thin film shows single phase bcc crystal structure of the film whereas APT observation of fine precipitates in the film matrix due to inherent compositional fluctuation indicates onset of phase separation via spinodal decomposition regime. XRD (in-situ) and APT investigation of 300 °C annealed film reveals that the early stage of phase separation involves localized formation of metastable intermediate bcc precipitate phase having 60 at% Cr and 40 at% Cu approximately (~Cr0.6Cu0.4). For longer duration of annealing at temperature ≥350 °C, such metastable bcc precipitates act as heterogeneous nucleation sites for the onset of precipitation of Cu rich fcc Cu(Cr) phase which indicates a change of phase separation mechanism from ‘spinodal decomposition’ to ‘nucleation and growth’. Annealing of the film at temperature ≥400 °C for longer duration leads to the formation of a two phase structure with Cu rich fcc precipitate phase in a Cr rich bcc matrix. Observed phase decomposition is accompanied by significant changes in the microstructure, residual stress and crystallographic texture in the Cr rich bcc film matrix which leads to the minimization of both surface and strain energies and thereby a reduction of total Gibbs free energy of the thin film. Thermodynamic model calculation has been presented in order to understand the nucleation pathway of Cu rich stable fcc Cu(Cr) precipitates via non-classical nucleation of metastable intermediate bcc Cr0.6Cu0.4 phase.

Quantitative evaluation of spinodal decomposition in thermally aged binary Fe-35 at.% Cr alloys by correlative atom probe tomography and small angle neutron scattering analyses

In this work, spinodal decomposition (SD) in Fe-35 at.% Cr alloy is quantified by correlatively combining two complimentary techniques namely, Atom Probe Tomography (APT) and Small Angle Neutron Scattering (SANS). In order to overcome the uncertainty often encountered in quantification of the characteristic SD parameters (wavelength λSD, amplitude A and volume fraction of Cr-rich α/-phase Φ), we adopt the following: (i) utilize the unique specific attribute of a technique suitable for evaluating any particular SD parameter; (ii) incorporate such reliably extracted parameter as input for evaluating other parameters wherever applicable. This novel correlative approach builds on each other's strength and provides improved accuracy. λSD is determined independently from APT and SANS analyses. For evaluation of A and Φ, APT analysis utilizes the value of λSD determined from SANS, whereas the phase compositions evaluated by APT are utilized in SANS analysis. With progressive phase separation, α/α/ compositional difference increases continually (from 19.8% after 10 h to 48.2% after 500 h) along with concomitant contraction of the interface (from 1.92 nm to 1.55 nm), underscoring the distinctive characteristics of SD process. Signature of rarely observed early stage of phase separation in the form of a dense population (9.78 × 1024/m3) of extremely small (0.67 nm radius) Cr-rich nanoclusters is registered after aging only for 1 h. In addition, temporal evolution of λSD clearly distinguishes early stage of SD (time exponent of 0.15) from the coarsening stage (time exponent of 0.29, 120 h onwards).

Quantitative Evaluation of Spinodal Decomposition in Thermally Aged Binary Fe-35 At.% Cr Alloys by Correlative APT and SANS Analyses

In this work, spinodal decomposition (SD) in Fe-35 at.% Cr alloy is quantified by correlatively combining two complimentary techniques namely, Atom Probe Tomography (APT) and Small Angle Neutron Scattering (SANS). In order to overcome the uncertainty often encountered in quantification of the characteristic SD parameters (wavelength λSD , amplitude A and volume fraction of Cr-rich α/ -phase Φ), we adopt the following: (i) utilize the unique specific attribute of a technique suitable for evaluating any particular SD parameter; (ii) incorporate such reliably extracted parameter as input for evaluating other parameters wherever applicable. This novel correlative approach builds on each other’s strength and provides improved accuracy. λSD is determined independently from APT and SANS analyses. For evaluation of A and Φ, APT analysis utilizes the value of λSD determined from SANS, whereas the phase compositions evaluated by APT are utilized in SANS analysis. With progressive phase separation, α/α/ compositional difference increases continually (from 19.8% after 10 h to 48.2% after 500 h) along with concomitant contraction of the interface (from 1.92 nm to 1.55 nm), underscoring the distinctive characteristics of SD process. Signature of rarely observed early stage of phase separation in the form of a dense population (9.78x1024 /m3 ) of extremely small (0.67 nm radius) Cr-rich nanoclusters is registered after aging only for 1 h. In addition, temporal evolution of λSD clearly distinguishes early stage of SD (time exponent of 0.15) from the coarsening stage (time exponent of 0.29, 120 h onwards).

Morphology, thermal and mechanical performance of epoxy/polysulfone composites improved by curing with two different aromatic diamines

AbstractEpoxy/polysufone (PSF) composites cured with 4,4'‐diaminodiphenyl sulfone (DDS) and 4,4'‐diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy‐DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25‐DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25‐DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross‐link density.

Early stage phase separation of AlCoCr0.75Cu0.5FeNi high-entropy powder at the nanoscale

High entropy alloys are generally considered to be single phase material. This state is, however, typically a non-equilibrium state after fabrication at high cooling rates. Phase constitution after fabrication or heat treatment is mostly known for isothermal annealing only and for casts as well as rapidly quenched alloys. Knowledge on early phase separation stages of high entropy alloys and their mechanisms are missing so far. Here, we present results on phase separation at intermediate cooling rates, by characterization of gas atomized powder of the AlCoCr0.75Cu0.5FeNi alloy. Although investigation by X-ray diffraction and Electron Backscatter Diffraction indicates a single-phase nature of the powder particles, aberration-corrected scanning transmission electron microscopy and atom probe tomography reveal a nanoscale phase separation into Ni–Al-rich B2 and Fe–Cr-rich A2 regions as well as a high number density of 3.1 × 1024 Cu-rich clusters per m3 in the B2 matrix. The observed phase separation and cluster formation are linked to spinodal decomposition and nucleation processes, respectively. The study highlights that adequate characterization techniques need to be chosen when making statements about phase stability and structural evolution in compositionally complex alloys.

Jumping In and Out of the Phase Diagram Using Electric Fields: Time Scale for Remixing of Polystyrene/Poly(vinyl methyl ether) Blends.

We demonstrate it is possible to repeatedly jump polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends from the one-phase to two-phase region by simply turning on and off an electric field at a fixed temperature near the phase boundary. This builds on our previous work that established electric fields enhance the miscibility of PS/PVME blends by shifting the phase separation temperature TS(E) of 50/50 blends up by 13.5 ± 1.4 K when field strengths of E = 1.7 × 107 V/m are applied (J. Chem. Phys. 2014, 141, 134908). Monitoring the early stages of phase separation and remixing by fluorescence, we measure the remixing time scale τ(T) with and without electric fields, finding τ(T) is unchanged by the presence of the field and well fit by a Vogel-Fulcher-Tammann expression. These observations are consistent with a mobility-limited process several degrees from the phase boundary where electric fields have shifted the miscibility transition.

Modeling the Early Stages of Phase Separation in Disordered Elastin-like Proteins

Elastin-like proteins (ELPs) are known to undergo liquid-liquid phase separation reversibly above a concentration-dependent transition temperature. Previous studies suggested that, as temperature increases, ELPs experience an increased propensity for type II β-turns. However, how the ELPs behave below the phase transition temperature itself is still elusive. Here, we investigate the importance of β-turn formation during the early stages of ELP self-association. We examined the behavior of two ELPs, a 150-repeat construct that had been investigated previously (ELP[V5G3A2-150] as well as a new 40-repeat construct (ELP40) suitable for nuclear magnetic resonance measurements. Structural analysis of ELP40 reveals a disordered conformation, and chemical shifts throughout the sequence are insensitive to changes in temperature over 20°C. However, a low population of β-turn conformation cannot be ruled out based on chemical shifts alone. To examine the structural consequences of β-turns in ELPs, a series of structural ensembles of ELP[V5G3A2-150] were generated, incorporating differing amounts of β-turn bias throughout the chain. To mimic the early stages of the phase change, two monomers were paired, assuming preferential interaction at β-turn regions. This approach was justified by the observation that buried hydrophobic turns are commonly observed to interact in the Protein Data Bank. After dimerization, the ensemble-averaged hydrodynamic properties were calculated for each degree of β-turn bias, and the results were compared with analytical ultracentrifugation experiments at various temperatures. We find that the temperature dependence of the sedimentation coefficient (s20,wo) can be reproduced by increasing the β-turn content in the structural ensemble. This analysis allows us to estimate the presence of β-turns and weak associations under experimental conditions. Because disordered proteins frequently exhibit weak biases in secondary structure propensity, these experimentally-driven ensemble calculations may complement existing methods for modeling disordered proteins generally.

Effect of applied strain on phase separation of Fe–28 at.% Cr alloy: 3D phase-field simulation

A quantitative simulation of the separation of the α′ phase in Fe–28 at.% Cr alloy under the effects of applied strain is performed by utilizing a three-dimensional phase-field model. The elongation of the Cr-enriched α′ phase becomes obvious with the influence of applied uniaxial strain for the phase separation transforms from spinodal decomposition of 700 K to nucleation and growth of 773 K. The applied strain shows a significant influence on the early stage phase separation, and the influence is enlarged with the elevated temperature. The steady-state coarsening with the mechanism of spinodal decomposition is substantially affected by the applied strain for low-temperature aging, while the influence is reduced as the temperature increases and as the phase separation mechanism changes to nucleation and growth. The peak value of particle size distribution decreases, and the PSD for 773 K becomes more widely influenced by the applied strain. The simulation results of separation of the Cr-enriched α′ phase with the applied strain provide a further understanding of the strain effect on the phase separation of Fe–Cr alloys from the metastable region to spinodal regions.

Molecular dynamics simulation of Ag–Cu cluster growth on a thin polymer film

We present molecular dynamics (MD) simulation results for the growth of silver–copper nanoparticles on a polymeric surface during sputter deposition. The simulation procedure extends a previous implementation for gold nanoparticles to bimetallic nanoparticles. Making use of an accelerated version of MD, the timescales of the simulations become comparable to those of an actual deposition process, which may take several minutes in experiments. While silver and copper are known to be immiscible in the bulk, we trace the concentration profiles of Ag and Cu atoms in the clusters for film thicknesses up to 1.8 nm and are thus able to investigate the early stages of phase separation on the nanoscale.

A Combinatorial Approach for Assessing the Magnetic Properties of High Entropy Alloys: Role of Cr in AlCoxCr1–xFeNi

A combinatorial assessment of composition‐microstructure‐magnetic property relationships in magnetic high entropy AlCoxCr1‐xFeNi alloy (0 ≤ x ≤ 1) system has been carried out using compositionally graded alloys fabricated via laser additive manufacturing. At one end, the AlCoFeNi composition (x = 1) consisted of equiaxed B2 grains, exhibiting very early stages of phase separation (only compositional partitioning) into Ni–Al rich and Fe–Co rich regions within grains of the B2 phase. At the other extreme, the AlCrFeNi composition (x = 0) exhibited grains with pronounced spinodal decomposition, resulting in a B2 + bcc microstructure with the degree of spinodal decomposition progressively increasing with Cr content in these AlCoxCr1–xFeNi alloys. While the saturation magnetization (Ms) monotonically increases six times from x = 0 to x = 1, the coercivity (Hc) variation is non‐monotonic, increasing seven times from x = 0 to x = 0.4, and subsequently decreasing fourteen times from x = 0.4 to x = 1.0. The magnetic phase transition temperature (Tc) for these alloys also increases monotonically with increasing Co content with a second phase transition exhibited in a certain range of compositions between x = 0.6 to x = 0.8. Such substantial changes in the magnetization behavior and properties of magnetic high entropy systems opens possibilities of tuning these alloys for specific soft or hard magnetic component applications.

Viscoelastic phase separation of polystyrene/poly(vinyl methyl ether) blends with different dynamic asymmetry

Viscoelastic phase separation (VPS) can be induced in dynamically asymmetric polystyrene/poly(vinyl methyl ether) (PS/PVME) blend in which there is a large difference between glass transition temperature of the components (about 125 °C). In this study, the effect of molecular weight of the slower component, PS, on VPS mechanism is investigated. The correlation between the time evolution of the phase-separating morphologies and their linear and nonlinear rheological behavior is studied for blends with three different PSs. Rheological measurements and morphological observations are carried out at quench depth of 14 °C. While it was previously found that depending on composition of blend, three different types of VPS behavior can be observed due to self-induced stresses in the early stage of phase separation—(i) the transient gel induced VPS (TG-VPS), (ii) coalescence induced VPS (C-VPS), and (iii) aggregating nucleation and growth (ANG)—in this study, we show that different types of VPS can be observed for a single composition by changing the molecular weight of PS. In other words, dynamic asymmetry between PS-rich and PVME-rich phases decreases with a decrease of molecular weight of PS which results in weaker transient gel in the early stage of phase separation. Consequently, the phase separation mechanism changes for 10/90 blend from TG-VPS to C-VPS and, for 5/95 blend from C-VPS to ANG or NNG (normal nucleation and growth). Furthermore, the variation of fractal dimension by phase separation is studied for 10/90 blends containing PS with different molecular weights.

Evolution of concentration fluctuation during phase separation of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The influence of nanosilica on the concentration fluctuation of polystyrene/poly (vinyl methyl ether) (PS/PVME) mixtures was investigated during phase separation. The amplitude of concentration fluctuation was quantified by dielectric spectrums based on the idea of Lodge–Mcleish model and the linearized Cahn–Hilliard theory could describe the amplitude evolution of concentration fluctuation at the early stage of phase separation. Hydrophilic nanosilica A200 dispersed in PVME-rich phase behaved an obvious inhibition effect on the concentration fluctuation of blend matrix, while hydrophobic nanosilica R974 dispersed in PS-rich phase had little effect on the concentration fluctuation. The kinetics and amplitude evolution of concentration fluctuation during phase separation for PS/PVME/A200 nanocomposites were remarkably restrained due to the surface adsorption of PVME on A200. As the segmental dynamics of PVME and PS in homogeneous matrix was hardly influenced by A200 and R974, the enhanced miscibility and the significantly constrained flow relaxation of PVME chains might contribute to the retarded concentration fluctuation of PS/PVME/A200 nanocomposites. While the weak interaction between R974 and components of blend matrix and little effect of R974 on the molecular dynamics of PS chains may result in the weak retardation of concentration fluctuation for blend matrix. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Interdiffusion and phase separation upon curing in thermoset-thermoplastic interphases unravelled by the characterization of partially cured systems

The evolution upon curing of interdiffusion as well as phase separation is characterized at the interphase between a high Tg poly(ether sulfone) thermoplastic (TP) and a high density thermosetting network (TS), both components being initially miscible. We show that the late stages of the diffusion process overlap with the early stages of phase separation, which is contrary to the expectations from the current state of the art. The penetration depth of the TS into the TP is found to increase with decreasing gelation time within the investigated operating window. This is due to the stronger thermal activation of diffusion over reaction at the early stages of curing. A chemometric model is developed based on Raman spectroscopy data in order to further analyze these results. The predictions of the model are compared with the profiles generated by image analysis carried on microtomed sections of fully cured interphases. The concentration profiles of partially cured interphases are predicted as well and used to correlate the degree of curing of the TS with the front velocity for each profile.

Early stage phase separation in ternary alloys: A test of continuum simulations

Phase separation in the γ−γ’ alloy 5.2%Al–14.2%Cr-Ni at 873.15 K has been investigated by three-dimensional phase-field simulations, employing a model where both thermodynamic and kinetic parameters were experimentally verified. 510 individual nuclei corresponding to a density of 1024 m−3 were introduced in accordance with classical nucleation theory, and the microstructural evolution was simulated up to a time of 32 h. The microstructural evolution was characterized, and regimes were identified according to the dominant mechanisms for microstructural evolution, where the final regime was found to be a coarsening regime obeying well-known power laws for the particle density and the average γ’ particle radius. The evolution of the volume-averaged composition of the particles was found to follow a complicated trajectory, while the composition of individual particles were found to depart significantly from the average. The simulations were compared to experimental results from the literature based on atom probe tomography, and in general good qualitative correspondence was found, albeit with quantitative differences. These are discussed in terms of the assumptions inherent to the phase-field model, and by extension to most common continuum models of diffusive phase transformations.

A computational study of long range surface-directed phase separation in polymer blends under a temperature gradient

The surface-directed phase separation phenomena of a model binary polymer blend quenched into the unstable region of its binary symmetric phase diagram was studied numerically using the nonlinear Cahn–Hilliard theory coupled with the Flory–Huggins–de-Gennes theory. Long range surface potential within a square geometry, where one side of the domain is exposed to a surface with preferential attraction to one component of a binary polymer blend under a temperature gradient in the x-direction, was incorporated in the model. No transition from complete wetting to partial wetting for all quench depths and/or long range surface potentials was observed. The structure factor analysis for the bulk presented an exponential growth rate at the early stage of phase separation, which slowed down at the intermediate stage with a slope of 0.33, which is in agreement with the Lifshitz–Slyozov power law. As the diffusion coefficient increased, the rate of phase separation increased accordingly in the bulk. This led to faster transition time from the early to intermediate stage within the bulk. In deeper quenches, a higher rate of phase separation was observed along with lower surface enrichment. Deeper quenches also led to the faster rupture of spinodal waves in the bulk. The process of surface enrichment, however, was continuous for all quench depths studied. The effect of different temperature gradient values on the surface enrichment rate was studied for the first time within a long range surface potential setting. No noticeable change in surface enrichment was observed for different temperature gradients.