Initial Stage Of Phase Separation Research Articles

Phase separation and molecular ordering of the prion-like domain of the Arabidopsis thermosensory protein EARLY FLOWERING 3

Liquid-liquid phase separation (LLPS) is an important mechanism enabling the dynamic compartmentalization of macromolecules, including complex polymers such as proteins and nucleic acids, and occurs as a function of the physicochemical environment. In the model plant, Arabidopsis thaliana, LLPS by the protein EARLY FLOWERING3 (ELF3) occurs in a temperature-sensitive manner and controls thermoresponsive growth. ELF3 contains a largely unstructured prion-like domain (PrLD) that acts as a driver of LLPS in vivo and in vitro. The PrLD contains a poly-glutamine (polyQ) tract, whose length varies across natural Arabidopsis accessions. Here, we use a combination of biochemical, biophysical, and structural techniques to investigate the dilute and condensed phases of the ELF3 PrLD with varying polyQ lengths. We demonstrate that the dilute phase of the ELF3 PrLD forms a monodisperse higher-order oligomer that does not depend on the presence of the polyQ sequence. This species undergoes LLPS in a pH- and temperature-sensitive manner and the polyQ region of the protein tunes the initial stages of phase separation. The liquid phase rapidly undergoes aging and forms a hydrogel as shown by fluorescence and atomic force microscopies. Furthermore, we demonstrate that the hydrogel assumes a semiordered structure as determined by small-angle X-ray scattering, electron microscopy, and X-ray diffraction. These experiments demonstrate a rich structural landscape for a PrLD protein and provide a framework to describe the structural and biophysical properties of biomolecular condensates.

Features of L-Menthol Crystallization in Optically Active Medium Based on L- and D-Asparaginate Chitosan

The phase separation kinetics of an ethanolic L-menthol solution in an aqueous solution of optically and biologically active chitosan L- and D-aspartate was studied. It has been established that this process proceeds according to the extraction crystallization mechanism and combines two types of phase separation, namely: liquid–liquid and liquid–crystal. The effect of aspartic acid stereoisomer, chitosan molecular weight, and polymer: acid ratio on the optical, structural-morphological, and dimensional characteristics of dispersed phase droplets at the initial stage of phase separation and crystal aggregates of the L-menthol condensed phase at the final stage was assessed. In the chitosan D-aspartate medium, as well as with an increase in the concentration of components in the optically active medium and the molecular weight of the polymer, the rate of phase separation, the size of droplets and particles increase. It has been suggested that the system under study is promising for encapsulating hydrophobic drugs, creating chirooptic waveguides, and sensors for biomedical purposes, as well as developing new methods for studying the fundamental principles of phase separation in intracellular regulation of membraneless organelles and subcellular organization of biosystems, including under stress conditions of a living organism underlying the development of new pharmaceuticals to treat rare and currently incurable diseases.

Biocidal Activity of Chitosan Asparaginate Nanoparticles

Abstract—The biological activity of chitosan asparaginate particles formed in the chitosan‒L-aspartic acid‒water system at the initial stage of phase separation was investigated. Cultivation of Staphylococcus aureus 209 P and Escherichia coli 113-13 in the medium supplemented with nanoparticles resulted in massive death of bacterial cultures. The biocidal activity against gram-positive bacteria was most pronounced. Biological tests revealed high biocompatibility of chitosan nanoparticles and their ability to accelerate the proliferative activity of the cultures of epidermal and epithelial cells. Our results indicate that chitosan asparaginate nanoparticles are promising for medico-biological and pharmaceutical applications.

Atomic Pathways of Solute Segregation in the Vicinity of Nanoscale Defects.

Using GeSn semiconductor as a model system, this work unravels the atomic-level details of the behavior of solutes in the vicinity of a dislocation prior to surface segregation in strained, metastable thin layers. The dislocations appear in the 3D atom probe tomography maps as columnar regions, 3.5-4.0 nm wide, with solute concentrations 3-4 times higher than the sounding matrix. During the initial stage of phase separation, the migration of solute atoms toward the dislocation is associated with a gradual increase in Sn concentration and in density of atomic clusters, which reach 175-190 per 103 nm3 with 12-15 atoms/cluster close to dislocations. The latter provide, at advanced stages, fast diffusive channels for Sn mass-transport to the surface, thus bringing the matrix around the dislocation to the equilibrium concentration. In parallel, an increase in solute concentration (∼0.05 at. %/nm) and in the number of atomic clusters (12-16 clusters/33 nm) is observed along the dislocation core.

Effect of driving on coarsening dynamics in phase-separating systems

We consider the Cahn–Hilliard (CH) equation with a Burgers-type convective term that is used as a model of coarsening dynamics in laterally driven phase-separating systems. In the absence of driving, it is known that solutions to the standard CH equation are characterized by an initial stage of phase separation into regions of one phase surrounded by the other phase (i.e. clusters or drops/holes or islands are obtained) followed by the coarsening process, where the average size of the structures grows in time and their number decreases. Moreover, two main coarsening modes have been identified in the literature, namely, coarsening due to volume transfer and due to translation. In the opposite limit of strong driving, the well-known Kuramoto–Sivashinsky equation is recovered, which may produce complicated chaotic spatio-temporal oscillations. The primary aim of the present work is to perform a detailed and systematic investigation of the transitions in the solutions of the convective CH equation for a wide range of parameter values, and, in particular, to understand in detail how the coarsening dynamics is affected by an increase of the strength of the lateral driving force. Considering symmetric two-drop states, we find that one of the coarsening modes is stabilized at relatively weak driving, and the type of the remaining mode may change as driving increases. Furthermore, there exist intervals in the driving strength where coarsening is completely stabilized. In the intervals where the symmetric two-drop states are unstable they can evolve, for example, into one-drop states, two-drop states of broken symmetry or even time-periodic two-drop states that consist of two traveling drops that periodically exchange mass. We present detailed stability diagrams for symmetric two-drop states in various parameter planes and corroborate our findings by selected time simulations.

Investigation of Chemical and Physical Surface Changes of Thermally Conditioned Glass Fibres

A number of analytical techniques were applied to investigate changes to the surface of unsized boron-free E-glass fibres after thermal conditioning at temperatures up to 700 °C. Novel systematic studies were carried out to investigate the fundamental strength loss from thermal conditioning. Surface chemical changes studied using X-ray photoelectron spectroscopy (XPS) showed a consistent increase in the surface concentration of calcium with increasing conditioning temperature, although this did not correlate well with a loss of fibre strength. Scanning electron microscopy fractography confirmed the difficulty of analysing failure-inducing flaws on individual fibre fracture surfaces. Analysis by atomic force microscopy (AFM) did not reveal any likely surface cracks or flaws of significant dimensions to cause failure: the observation of cracks before fibre fracture may not be possible when using this technique. Fibre surface roughness increased over the whole range of the conditioning temperatures investigated. Although surface roughness did not correlate precisely with fibre strength, there was a clear inverse relationship at temperatures exceeding 400 °C. The interpretation of the surface topography that formed between 400–700 °C produced evidence that the initial stage of phase separation by spinodal decomposition may have occurred at the fibre surface.

Time-Resolved Structured Illumination Microscopy for Phase Separation Dynamics of Water and 2-Butoxyethanol Mixtures: Interpretation of "Early Stage" Involving Micelle-Like Structures.

Phase separation dynamics of a water/2-butoxyethanol (2BE) mixture was studied with newly developed time-resolved structured illumination microscopy (SIM). Interestingly, an employed hydrophobic fluorescent probe for SIM showed spectral shifts up to 500 ns after a laser-induced temperature jump, which suggests 2BE micellar-like aggregates become more hydrophobic at the initial stage of phase separation. This hydrophobic environment in 2BE aggregates, probably due to the ejection of water molecules, continued up to at least 10 μs. Time-resolved SIM and previously reported light scattering data clearly showed that the size of a periodic structure remained constant (ca. 300 nm) from 3 to 10 μs, and then the growth of periodic structures having the self-similarity started. We think that the former and the latter processes correspond to "early stage" (concentration growth) and "late stage" (size growth), respectively, in phase separation dynamics. Here we suggest that, in the early stage, the entity to bear 2BE phase be water-poor 2BE aggregates, and the number density of these aggregates would simply increase in time.

Retardation of the phase segregation of liquid mixtures with a critical point of miscibility

The phase transition extraction (PTE) process consists of bringing a partially miscible mixture from the single‐phase to the two‐phase region of its phase diagram. Its most important characteristic is that the resulting phase separation is very fast, and hardly affected by coalescence‐retarding impurities. In this work we study two counter‐cases, where the PTE process appears to be severely retarded. First, we consider the ouzo effect, where the mixture forms very stable metastable micro‐emulsions, showing that this process can be generalized, leading to a reverse ouzo effect, where a modifier is added in large quantities. The second retardation technique consists of using very viscous solvents. We found that, in agreement with the predictions of the phase field model, the growth rate of the nuclei during the initial stage of phase separation does not depend on viscosity, while, on the other hand, when the size of the nuclei exceed their capillary length, gravitational effects become relevant and the settling time is proportional to the viscosity of the continuous phase. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4047–4052, 2018

Kinetics of α’-phase nucleation during thermal aging of Fe–22% Cr alloy

The initial stage of phase separation of binary Fe–22 at % Cr alloy during thermal aging at 500°C is studied at the atomic-scale level by atom probe tomography. Upon the behavior analysis of pair-correlation function of chromium atoms, long-range correlations typical of spinodal decomposition are observed at short aging times, which disappear 25 h after aging. The analysis of 3D atomic maps shows that Cr-rich regions form at the initial steps of decomposition, where the chromium concentration increases with an increase in the aging time. At the aging time of ~100 h, the chromium concentration in the center of these regions reaches 80 at %, which corresponds to the α' phase.

Formation of solid solutions of gallium in Fe–Cr and Fe–Co alloys: Mössbauer studies and first-principles calculations

Investigation of Ga influence on the structure of Fe–Cr and Fe–Co alloys was performed with the use of Mössbauer spectroscopy and X-ray diffraction methods. The experimental results are compared with results of first-principles calculations of the mixing and solubility energies for Ga in an Fe–X (X=Co, Cr) alloy both in ferromagnetic and paramagnetic states. It is shown that Ga mainly goes into the solid solutions of the base alloys. In the alloys of the Fe–Cr system, doping with Ga handicaps the decomposition of solid solutions, observed in the binary alloys, and increases its stability. In the alloys with Co, Ga also favors the uniformity of solid solutions. The results of the first-principles calculations testify in favor of a preferable dissolution of Ga in the FeCo regions of a multicomponent structure rather than FeCr regions, both types of regions being in the ferromagnetic state at the temperature of annealing. The analysis of Mössbauer experiments gives some grounds to conclude that if, owing to liquation, clusterization, or initial stages of phase separation, there exist regions enriched in iron, some amount of Ga atoms prefer to enter the nearest surroundings of iron atoms, thus forming binary Fe–Ga regions (or phases).

Broadband luminescence in nanostructured glasses

The mechanism of broadband near-IR luminescence in the process of nanostructuring of Ni2+-activated glasses in the system R2O–Ga2O3–SiO2–GeO2 (R = Li, Na) at the initial stage of phase separation is described.

Early Stage Phase Separation in Pharmaceutical Solid Dispersion Thin Films under High Humidity: Improved Spatial Understanding Using Probe-Based Thermal and Spectroscopic Nanocharacterization Methods

Phase separation in pharmaceutical solid dispersion thin films under high humidity is still poorly understood on the submicrometer scale. This study investigated the phase separation of a model solid dispersion thin film, felodipine-PVP K29/32, prepared by spin-coating and analyzed using probe-based methods including atomic force microscopy, nanothermal analysis, and photothermal infrared microspectroscopy. The combined use of these techniques revealed that the phase separation process occurring in the thin films under high humidity is different from that in dry conditions reported previously. The initial stage of phase separation is primarily initiated in the bulk of the films as amorphous drug domains. Drug migration toward the surface of the solid dispersion film was then observed to occur under exposure to increased humidity. PVP cannot prevent phase separation of felodipine under high humidity but can minimize the crystallization of amorphous felodipine domains in the solid dispersion thin films. This study demonstrates the unique abilities of these nanocharacterization methods for studying, in three dimensions, the phase separation of thin films for pharmaceutical applications.

Similarity of the Signatures of the Initial Stages of Phase Separation in Metastable and Unstable Polymer Blends

Time-resolved small angle neutron scattering was used to probe the initial stages of liquid-liquid phase separation in both critical and off-critical binary polymer blends, and the critical (q(c)) and most probable (q(m)) wave vectors were identified for several quench depths. For the critical blend, the Cahn-Hilliard-Cook theory provides a framework for analyzing the data and explains the observed decrease in q(m) with time. For the off-critical blend, q(m) is independent of quench time, regardless of whether the quench is metastable or unstable.

Dynamics and pattern formation in thermally induced phase separation of polymer–solvent system

In this paper, the characteristic dynamics and pattern formation of polymer–solvent system, undergoing thermal induced phase separation (spinodal decomposition), have been studied using non-linear simulations. The modified Cahn–Hilliard equation with the incorporation of the Flory–Huggins free energy model is used. The development of a wide variety of initial and intermediate stage morphology is feasible either by introducing sharp/continuous spatial temperature variation or by altering the initial mean solvent concentration (Co) in the vicinity of the minima (Cm) of the spinodal parameter (second derivative of excess Gibbs free energy w.r.t concentration). For Co < Cm initial stage of phase separation proceeds by the formation of columns/island of the solvent rich phase dispersed in polymer rich continuous phase. On the contrary, Co > Cm, phase separation leads to formation of holes of polymer rich phase dispersed in the continuous solvent rich phase. For an intermediate mean concentration very close to Cm inter-connecting structures are evolved. A continuous variation of spatial temperature leads to the directional (rather than random) evolution of phase separated pattern. The initial stage of evolution always propagates from the lowest to the highest temperature regime. A spatial step variation of temperature leads to formation of localized novel phase separated patterns. For a flow system, the dynamics and pattern formation can be controlled by tuning the different timescales: timescale of convection, de-mixing and coalescence.

Low silica K2O – Nb2O5 – SiO2 nonlinear optical glasses

Glasses with the compositions (100 - x)KNbO 3 - xSiO 2 (x = 12 - 35), forming a transparent glass ceramic when heat-treated in the glass formation temperature range, have been obtained. The initial stages of phase separation are accompanied by the appearance of appreciable quadratic optical nonlinearity in the glasses. This nonlinearity can be used to develop high-efficiency electro-optic modulators by thermal poling.

A lattice Boltzmann method for thermal nonideal fluids

A Lattice Boltzmann Method for van der Waals fluids with variable temperature is described. Thermo-hydrodynamic equations are correctly reproduced at second order of a Chapman-Enskog expansion. The method is applied to study initial stages of phase separation of a fluid quenched by contact with colder walls. Thermal equilibration is favoured by pressure waves which propagate with the sound velocity.

Nanosized structural transformation and nonlinear optical properties of lithium niobium germanate glasses

Glass formation in Li2O–Nb2O5–GeO2 (LNG) system, the structure and crystallization behavior of glasses that have compositions near the ratio Li2O/Nb2O5∼1 corresponding to stoichiometry of ferroelectric phase LiNbO3 were examined by differential thermal analysis, X-ray diffraction, small-angle neutron scattering and second harmonic generation (SHG). LNG glasses were subjected to heat treatments at temperatures in the range between Tg and temperature of the first exothermic peak in order to initiate nonlinear optical activity by nanoheterogeneity formation. Transparent nanostructured glasses with second-order optical nonlinearity were obtained for compositions characterized by the Li2O/Nb2O5 molar ratio ranging from 0.83 to 1.2 and GeO2 40–45mol%. As prolonged heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO3 the origin of SHG in transparent LNG glasses is supposed to be connected predominantly with polarity of nanoheterogeneities formed at the initial stage of phase separation.

Second-order optical non-linearity initiated in Li 2O–Nb 2O 5–SiO 2 and Li 2O–ZnO–Nb 2O 5–SiO 2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 Å have been formed in glasses of the Li 2O–Nb 2O 5–SiO 2 (LNS) and Li 2O–ZnO–Nb 2O 5–SiO 2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher T g lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO 3 and non-polar LiZnNbO 4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO 3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO 4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO 3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

On the nature of the second-order optical nonlinearity of nanoinhomogeneous glasses in the Li2O-Nb2O5-SiO2 system

The submicroscopic structure of lithium niobium silicate glasses of the compositions 2xLiNbO3 · (1 − x)(Li2O · 2SiO2) (x = 0.40, 0.45, 0.50) and 30Li2O · 25Nb2O5 · 45SiO2 in the initial state and after heat treatment for different times at temperatures in the vicinity of the glass transition point T g are investigated using X-ray powder diffraction, small-angle neutron scattering (SANS), synchrotron small-angle X-ray scattering (SAXS), and electron microscopy. A nanostructure with inhomogeneities ∼40 A in size is formed in glasses at the initial stages of phase separation at temperatures in the range 600–670°C. This structure is responsible for the appearance of the second-order optical nonlinearity. The SANS, SAXS, and electron microscopic data on the inhomogeneity size are in good agreement with each other. According to the X-ray diffraction, SANS, and SAXS data, the ordering of the glass structure and the difference between the density of inhomogeneities and the density of the matrix increase in the course of heat treatment. At the initial stage of amorphous phase separation, the glass decomposes into regions enriched in SiO2 and regions with an increased content of lithium and niobium. An increase in the temperature or time of heat treatment results in the precipitation of LiNbO3 ferroelectric crystals. The results obtained allow us, for the first time, to make the inference that nanoscale changes in the glass structure lead to considerable changes (by one order of magnitude and more) in the quadratic optical nonlinearity, which can be controlled by heat treatment. The origin of the second-order optical nonlinearity is associated with both the nanosized modulations of the polarizability due to the inhomogeneous glass structure and the polarity of structural nanoinhomogeneities from which the LiNbO3 phase precipitates at the later stages of phase separation.

Residual Stress Evolution during Decomposition of Ti&lt;sub&gt;(1-x)&lt;/sub&gt;Al&lt;sub&gt;(x)&lt;/sub&gt;N Coatings Using High-Energy X-Rays

Residual stresses and microstructural changes during phase separation in Ti33Al67N coatings were examined using microfocused high energy x-rays from a synchrotron source. The transmission geometry allowed simultaneous acquisition of x-ray diffraction data over 360° and revealed that the decomposition at elevated temperatures occurred anisotropically, initiating preferentially along the film plane. The as-deposited compressive residual stress in the film plane first relaxed with annealing, before dramatically increasing concurrently with the initial stage of phase separation where metastable, nm-scale c-AlN platelets precipitated along the film direction. These findings were further supported from SAXS analyses.