Spinodal Mechanism Research Articles

Influence of pH and lipid membrane on the liquid–liquid phase separation of wheat γ-gliadin in aqueous conditions

Protein body (PB) formation in wheat seeds is a critical process influencing seed content and nutritional quality. In this study, we investigate the potential mechanisms governing PB formation through an in vitro approach, focusing on γ-gliadin, a key wheat storage protein. We used a microfluidic technique to encapsulate γ-gliadin within giant unilamellar vesicles (GUVs) and tune the physicochemical conditions in a controlled and rapid way. We examined the influence of pH and protein concentration on LLPS and protein-membrane interactions using various microscopy and spectroscopy techniques. We showed that γ-gliadin encapsulated in GUVs can undergo a pH-triggered liquid–liquid phase separation (LLPS) by two distinct mechanisms depending on the γ-gliadin concentration. At low protein concentrations, γ-gliadins phase separate by a nucleation and growth-like process, while, at higher protein concentration and pH above 6.0, γ-gliadin formed a bi-continuous phase suggesting a spinodal decomposition-like mechanism. Fluorescence and microscopy data suggested that γ-gliadin dense phase exhibited affinity for the GUV membrane, forming a layer at the interface and affecting the reversibility of the phase separation.

Modulated distribution of vacancies within the post-irradiated bcc metals

The criterion of formation of a modulated structure by means of the spinodal mechanism in a spatial distribution of interacting vacancies (as strong concentrators of mechanical stresses) in metals as a target after irradiation is analyzed. For the irradiated body-centered cubic vanadium and tungsten, temperature dependences of the spatial periods of such a structure of the substitutional-vacancies’ subsystem are predicted taking into account the total mixing energies consisting of the energies of the (electro)chemical and strain-induced interactions between vacancies, which are cohesive by the nature in short distances and elastic by character at long distances, respectively.

Frequency-Dependent Dewetting of Thin Liquid Films Using External ac Electric Field.

The stability of thin liquid films on a surface can be controlled by using external stimuli, such as an electric field, temperature, or light, by manipulating the total excess free energy of the system. It has been previously shown that thin lubricating films on slippery surfaces can be destabilized via the spinodal mechanism using an external electric field, which returns to the original stable configuration upon the electric field. However, the role of the frequency of the applied ac electric field is not clear, which is the main topic of study in this report. When an ac electric field of fixed voltage and varying frequency is applied across thin lubricating films of slippery surfaces, a different dewetting behavior is observed. Characteristic length and time scales of dewetting depend strongly on the frequency of the applied voltage, which is primarily due to the change in the dielectric behavior of the lubricating fluid. In addition, the interplay of various time scales involved in the dewetting process also depends on the frequency.

Oxygen intake and giant thermo-chemical expansion of ceramics in the non-stoichiometric CaBaFe4O7+δ ferrite

The high-precision coulometric titration measurements were used in order to find the temperature and oxygen pressure dependent variations of oxygen homogeneous fields in CaBaFe4O7+δ1 (CBF7) and CaBaFe4O8–δ2 (CBF8) ferrites and to demonstrate a miscibility gap separating bordering compositions CaBaFe4O7.1 and CaBaFe4O7.8. The spinodal mechanism of the structural transition between CBF7 and CBF8 is proposed to be responsible for the excellent mechanical robustness and unusually large thermal expansion coefficient (156∙10−6 К−1 at 400 – 600 °C) of ceramic samples formed during the heating and oxidation of the CBF7 phase in air.

Rational design and multi-stage formation mechanisms of FeCrNiAl medium-entropy alloy strengthened by multi-scaled dual phases

Constructing multimodal microstructure in high/medium-entropy alloys (H/MEAs) is expected to further improve the performance via introducing heterostructure strengthening mechanism. In this study, FeCrNiAl-based MEAs were rationally designed to form a special microstructure with trimodal B2 nanoparticles and rod-shaped Laves phase into body-centered-cubic (BCC) structured matrix, via the CALPHAD method and composition adjustment. To systematically exhibit the microstructure evolution, phase formation and stabilization mechanisms, we reported the representative Fe61.93Al15.62Cr13.88Ni6.25Nb0.97Mo1.16Ta0.19 (at.%) alloy. It is found that the multi-scaled B2 particles with distinct mean radii of 225 nm, 15 nm, 1–5 nm precipitate in the melt solidification, aging and cooling processes in turn, and the Laves phase also forms in the aging stage. The primary and secondary B2 particles precipitate in the classical nucleation and growth pathway, while the ultrafine B2 particles follow a spinodal decomposed mechanism. By co-alloying Mo, Nb, and Ta elements, the thermal stability of B2 and Laves phase is significantly improved, resulting in a much lower coarsening rate (k = 8 × 10−27 m3/s) than that in common B2-strengthened BCC alloys at 800 °C. This ultra-stable and heterostructured alloy should have good application potential at elevated temperature, and should be a paradigm for future development of multi-modal precipitate strengthened alloys.

Concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in ferritic steel containing copper during aging

ABSTRACT The concurrent (Fe,Mo)2C carbides and Cu-rich clusters precipitation in the ferritic steel containing copper after aging at 400°C for 4000 h have been investigated using transmission electron microscopy (TEM) and atom probe tomography (APT). The results show that spinodal decomposition and an atomic ordering reaction occur in the ferritic steel containing copper. After aging, the retained austenite decomposed by the spinodal mechanism into C-rich and C-lean regions. The C-rich phase transforms into the (Fe,Mo)2C carbides via the ordering reaction, while Cu-rich clusters formed in the C-lean regions. The experimental results can be interpreted on the basis of phase separation via spinodal decomposition followed by chemical ordering. The small size of Cu-rich clusters can be attributed to the lower diffusion coefficient of Cu in the retained austenite.

Influence of annealing on microstructures and mechanical properties of arc-deposited AlCrTiSiN coating

A AlCrTiSiN nanomultilayered coating, mainly consisting of fcc-AlCrTiSiN solid solution and some hcp-clusters at fcc-AlCrTiSiN nanotwin boundaries, was isothermally annealed at 800–1100 °C. Thermal stability and changes in microstructure were studied carefully to illustrate its thermal dissolution mechanism. A thermal induced transformation of hcp to fcc is observed by emission of partial dislocation at hcp/fcc interfaces when annealed at 800 °C. Furthermore, we observe the onset of decomposition of fcc-AlCrTiSiN solid solution to coherently Al-rich and TiCr-rich fcc domains at 1000 °C via spinodal mechanism, accompanied by the precipitation of semi-coherent hcp-clusters within Al-rich fcc sublayers by nucleation mechanism. This transformation results in a notable hardening due to the refinement of grains and the coherency strains caused by spinodal decomposition and the formation of semi-coherent hcp-clusters. Later, annealing at 1100 °C promotes the dissolution of layered structures by pinching off of hcp sublayers, the transformation of fcc-AlCrTiSiN solid solution to Cr, Cr2N and hcp-AlN particles and the coarsening of hcp-AlN particles, resulting in a notable loss in hardness.

Revisiting the formation mechanism of intragranular κ-carbide in austenite of a Fe-Mn-Al-Cr-C low-density steel

It was usually believed that the formation of intragranular κ-carbide in γ-austenite was attributed to spinodal decomposition followed by ordering reaction. In this work, near-atomic scale characterization of an austenite-based Fe-20Mn-9Al-3Cr-1.2C (wt. %) low-density steel, using (high-resolution) scanning transmission electron microscopy and atomic probe tomography, reveals that the initially-formed κ-carbides (2-3 nm in particle size) are featured with an ordered L′12 structure but without detectable chemical partitioning. The Gibbs energy of the FCC phase obtained by thermodynamic calculations always shows a positive curvature (i.e. d2Gdx2 < 0) with the variable contents of Al and C in the temperature range 400-800 °C. Both the results demonstrate that the ordered nuclei of κ-carbide can form directly in the disordered γ-austenite rather than through the well-known spinodal decomposition-ordering mechanism. The extremely low nucleation barrier is due to the similar lattice structure, same composition and complete coherency between the γ-austenite matrix and κ-carbides.

Mechanisms of Pulsed Laser-Induced Dewetting of Thin Platinum Films on Tantalum Substrates—A Quantitative Study

The mechanism of pulsed laser-induced dewetting (PLiD) of Pt thin films in the thickness range from 3.2 to 8.9 nm was investigated on smooth chemically polished Ta (PT) and patterned dimpled Ta (DT) substrates, both of which have a thin Ta2O5 layer on the surface. Complete dewetting was achieved for a film thickness of 3.2–4.6 nm. Beyond that, a distinct morphological evolution in the intermediate stages from bicontinuous to polygonal structures was observed with the change in thin-film thickness, enabling the determination of the transition thickness for Pt on Ta2O5/DT substrates to be between 5.9 and 7.7 nm. Furthermore, by examining the dependence of Pt nanoparticle (NP) size (D), nearest neighbor interparticle distance (L), and NP surface density (N) on the Pt film thickness (h), quantitative evidence was provided to demonstrate that PLiD of Pt thin films on Ta2O5/Ta substrates occurred via the spinodal dewetting mechanism. In particular, a power-law fit to the data obtained from Pt NPs on the Ta2O5/PT substrate showed that L has a quadratic dependence on h, that is, L = 5.13 h2.04. Also, the thickness dependence of D and N on Ta2O5/PT showed a power-law relationship of D = 3.74 h1.76 and N = 2.93 × 1012 h-4.03, respectively. These results are in excellent agreement with predictions from the spinodal dewetting theory. It has also been shown that the patterned DT surface underneath the Pt films exerted extra control on the NP morphology, causing a deviation from the power law as predicted by the spinodal dewetting mechanism. From the thickness dependence of L, D, and N, the Hamaker constant (A) of Pt, the proportional constant (a) correlating the characteristic spinodal length scale (Λ) and L, and the geometric factor (f (θ)) were determined.

Universal dynamics of coarsening during polymer-polymer thin-film spinodal dewetting kinetics.

The dewetting dynamics of a supported bilayer polymer thin film on a solid substrate is investigated using grazing incidence x-ray photon correlation spectroscopy. We find that the top layer dewets via the spinodal mechanism. The kinetics of the dewetting is studied by monitoring the time evolution of the surface diffuse x-ray scattering intensity. We study the time evolution of fluctuations about the average surface structure by measuring the two-time x-ray intensity fluctuation correlation functions. Using these two-time correlation functions we quantify the crossover from early-time diffusive dynamics to hydrodynamics. The early diffusive regime satisfies dynamic universality. The two-time correlation functions also quantify the onset of hydrodynamic effects. The hydrodynamic regime is observed during the spinodal dewetting process as these interactions are not screened.

Dewetting behavior of Ge layers on SiO2 under annealing

The solid-state dewetting phenomenon in Ge layers on SiO2 is investigated as a function of layer thickness dGe (from 10 to 86 nm) and annealing temperature. The dewetting is initiated at about 580–700 °C, depending on dGe, through the appearance of surface undulation leading to the particle formation and the rupture of Ge layers by narrow channels or rounded holes in the layers with the thicknesses of 10–60 and 86 nm, respectively. The channel widths are significantly narrower than the distance between the particles that causes the formation of thinned Ge layer areas between particles at the middle dewetting stage. The thinned areas are then agglomerated into particles of smaller sizes, leading to the bimodal distributions of the Ge particles which are different in shape and size. The existence of a maximum in the particle pair correlation functions, along with the quadratic dependence of the corresponding particle spacing on dGe, may indicate the spinodal mechanism of the dewetting in the case of relatively thin Ge layers. Despite the fact that the particle shape, during the solid-state dewetting, is not thermodynamically equilibrium, the use of the Young’s equation and contact angles allows us to estimate the particle/substrate interface energy.

Effect of tertiary polysiloxane on the phase separation and properties of epoxy/PEI blend

AbstractEpoxy functional siloxane (DMS‐E09) was blended with epoxy resin (DGEBA) and thermoplastic polyetherimide (PEI). The results of morphology monitoring indicated that the reaction induced phase separation for all blends followed the spinodal phase separation mechanism. The microstructure changed from co‐continuous of 25 wt% epoxy/PEI system to phase‐inversion structure of 30 wt% epoxy/PEI system regardless of the content of the tertiary component DMS‐E09. By comparing the onset time of phase separation between the two designated systems, the sequential occurrence of primary macrophase separation in co‐continuous phase and secondary microphase separation in PEI‐rich phase for 25 wt% epoxy/PEI system was identified. Studies of the thermomechanical properties of the DGEBA/PEI/DMS‐E09 blends found that storage modulus increased with the addition of PEI but decreased with DMS‐E09 monotonically. The value of Tg decreased with the addition of the tertiary DMS‐E09 but was offset partially by the presence of PEI.

Pulsed laser induced dewetting of Au thin films on Ta2O5 substrates

Au nanoparticle arrays are formed by pulsed laser-induced dewetting from chemically polished and anodically formed templated (dimpled) Ta. Here we demonstrate clear evidence that pulsed laser-induced dewetting (PLiD) of thin films of Au on Ta 2 O 5 /Ta follows the spinodal dewetting mechanism, which was further found to be dependent on the surface topology of the substrate. We examine two different Ta 2 O 5 -coated Ta substrates (dimpled Ta and chemically polished Ta), and find that for Au nanoparticles (NPs) formed on polished Ta, the diameter, spacing and NP number density were related to the initial Au film thickness ( h ) by h 5/3 , h 2 and h −4 , respectively. The diameter, spacing and number density of NPs formed on chemically polished Ta were found to not vary with either laser fluence (260–300 mJ·cm −2 ) or irradiation time (0.1–60 s). On dimpled/patterned Ta substrates, thicker (>4 nm) Au films resulted in Au NPs that exhibit a more uniform diameter and spacing that mirrors the dimpled Ta template, and the dewetting is thought to proceed by an alternative mechanism.

Morphology Control During Heat Treatment of GeTe-PbTe Alloys

Abstract Microstructural evolution of GexPb1–xTe (x=0.5, 0.87, 0.9) alloys with respect to spinodal decomposition and continuous/discontinuous precipitation is investigated. Solution treatment at 630 °C for 10 days leads to a single-phase grain structure with homogeneous concentration distribution. In Ge0.5Pb0.5Te, after aging at 300, 400, and 450 °C for 3 days a lamellar spinodally decomposed microstructure was observed. For the alloys with higher Ge content, a diffusion controlled decomposition of the supersaturated solid solution occurs, during which two different microstructures form either simultaneously or separately. Inside the miscibility gap, but outside the spinodal line, a nucleation and growth mechanism leads to continuous and discontinuous precipitation at the grain boundaries, followed by continuous precipitation in the grain interior.

A hierarchical dual-phase photoetching template route to assembling functional layers on Si photoanode with tunable nanostructures for efficient water splitting

Surface functionalization is closely associated with the light harvesting and the charge separation, transfer, and injection efficiencies of water-splitting photoelectrode. Here, a dual-phase photoetching template with hierarchical structure, polyphenylsilsequioxane nanopillars and bicontinuous polyphenylsilsequioxane + polystyrene network layer, is patterned on the Si photoanode via a spinodal phase separation mechanism. Controllably photoetching the polymer template allows us to physically deposit functional layers with tunable nanostructures from net to dispersed dot. As a demonstration, the broken Ni/NiOx net modified Si photoanode exhibits a low onset potential of 0.93 VRHE, a high saturated photocurrent density of 40 mA cm−2 and a stability of 50 h in 1.0 M K-borate under AM1.5 G illumination, resulting from the inhomogeneous barrier height driven efficient charge extraction and low light loss by the dispersed surface modification. The proposed dual-phase lithographic template may open a new avenue to easily assemble functional layers on photoelectrodes for efficient solar energy conversion.

Dynamical solid-liquid transition through oscillatory shear.

Starting from an ideal crystalline state, we numerically study a nonequilibrium dynamical order-disorder transition promoted by the application of a periodic shearing protocol at low temperatures in model systems in three dimensions. We observe a discontinuous dynamical transition from an ordered to a disordered steady state. Through the analysis of large-scale simulations, we show that the amorphization mechanism around the discontinuous transition is reminiscent of spinodal decomposition.

Nanostructured gradient coating based on carbide of tungsten in carbon steel

Structural and phase transformations in tungsten-containing functional coatings of carbon steels, obtained in high-energy processes of implanting tungsten carbide micropowders by complex pulse electromechanical processing method, are studied. It is shown that during thermosilic action in the deformation zone, an intensive austenisation of steel occurs with the dissolution of tungsten carbide with the subsequent formation of composite gradient structures as a result of the decomposition of supercooled austenite supersaturated with tungsten both by the diffusion mechanism and by the spinodal decay mechanism. In the case of spinodal decay, in the general case, the diffusion flux is determined not by the concentration gradient, but by the gradient of the chemical potential. In this case, the diffusion processes lead to a state characterised by the condition that the chemical potential μ is constant in a given volume and the system bundles into concentration zones where the condensed phases crystallise. It is shown that individual zones of the tungsten-containing phases of the alloy are in the liquid-phase state and also undergo spinodal decomposition with the formation of highly disperse carbide phases of globular morphology.

Configurational thermodynamics of C in body-centered cubic/tetragonal Fe: A combined computational study

Configurational thermodynamics of C in body-centered cubic (bcc) or tetragonal (bct) Fe is investigated combining several computational techniques. Pairwise CC interaction energies in bcc Fe are calculated by density functional theory (DFT) and embedded atom method (EAM) potential respectively. The interaction between C atom and homogeneous strain is calculated assuming C acts as force dipoles in linear elastic medium of Fe. The CC and C–strain interactions are input into Monte Carlo (MC) simulations to find equilibrium C configuration on octahedral interstitial sublattices (OISs) in bcc/bct Fe and corresponding thermodynamic properties. In bcc Fe, DFT-MC and EAM-MC both give a single-phase region with C distributed with disorder on all the three OISs (α) at high temperature, and a two-phase region with ferrite and an ordered compound (α‴) at low temperature. The compound is Fe16C1 according to DFT or Fe16C2 according to EAM inputs, both having two OISs occupied. When a homogeneous tetragonal lattice strain is applied, the disordered phase exhibits a preferential sublattice occupation (Zener ordered α′), which is primarily caused by C–strain interaction and is mitigated by CC interactions. The ordered compound may also have two (α‴) or one (α″) OIS occupied. C clustering in bcc/bct Fe follows a conditional spinodal mechanism, namely long-range order being a prerequisite of spinodal decomposition. This is verified by the difference in solution thermodynamics of α/α′ (ordering-type) and α‴/α″ (clustering-type), as well as kinetic Ising model simulations which reveal a temporal sequence of short-range ordering, long-range ordering, and eventually C clustering.

Thermodynamic and thermokinetic processes of formation disperse structures of bitumen

ABSTRACTThe present experiment analyzes structural and thermal properties of bitumen carried out by temperature-modulated differential scanning calorimetry. It is shown that the bitumen in specific time-temperature conditions is a dispersed system of variable composition and structure. The dispersed phase can be represented by two types of domains. Paraffinic hydrocarbons form aggregative solid, structural crystalline phase at thermodynamic laws of structural phase transitions and nucleation thermodynamic mechanism of phase separation. The asphaltenes form for a relatively long time, an aggregative solid is structurally amorphous phase, as a result of thermokinetic structural relaxation glass transition by spinodal thermodynamic phase separation mechanism.

Formation of phase composition of petroleum bitumen according to data of temperature modulated differential scanning calorimetry

The analysis of structural and thermal properties of petroleum bitumen is carried out by temperature modulated differential scanning calorimetry. The technique allows to separate equilibrium and non-equilibrium thermal events and makes it possible to identify and observe structure transition invisible or overlapping on curves of conventional differential scanning calorimetry. It is shown that bitumen is a dispersion system only in specific time–temperature conditions. The dispersed phase can be represented by two types of aggregates. Saturates form aggregative solid, structural crystalline phase in accordance with thermodynamic law of structural phase transitions and nucleation thermodynamic mechanism of phase separation. The asphaltenes form for a relatively long time, an aggregative solid structurally amorphous phase as a result of thermokinetic structural relaxation glass transition by spinodal thermodynamic phase separation mechanism.