Phase Separation In Solutions Research Articles

Uncovering the molecular mechanism for dual effect of ATP on phase separation in FUS solution.

Recent studies reported that adenosine triphosphate (ATP) could inhibit and enhance the phase separation in prion-like proteins. The molecular mechanism underlying such a puzzling phenomenon remains elusive. Here, taking the fused in sarcoma (FUS) solution as an example, we comprehensively reveal the underlying mechanism by which ATP regulates phase separation by combining the semiempirical quantum mechanical method, mean-field theory, and molecular simulation. At the microscopic level, ATP acts as a bivalent or trivalent binder; at the macroscopic level, the reentrant phase separation occurs in dilute FUS solutions, resulting from the ATP concentration–dependent binding ability under different conditions. The ATP concentration for dissolving the protein condensates is about 10 mM, agreeing with experimental results. Furthermore, from a dynamic point of view, the effect of ATP on phase separation is also nonmonotonic. This work provides a clear physical description of the microscopic interaction and macroscopic phase diagram of the ATP-modulated phase separation.

Tuning the thermodynamic, optical, and rheological properties of thermoresponsive polymer solutions via silica nanoparticle shape and concentration

HypothesisThe shape and quantity of hydrophilic silica nanoparticles (NPs) can be used to tune the microstructure, rheology, and stability of phase-separating polymer solutions. In thermoresponsive polymer systems, silica nanospheres are well-studied whereas anisotropic NPs have little literature precedent. Here, we hypothesize that NP shape and concentration lower the onset of rheological and turbidimetric transitions of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions. ExperimentsDifferential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), turbidimetry, and oscillatory rheology are utilized to examine interactions between NPs, PNIPAM, and water and to track changes in phase separation and rheological properties due to NP concentration and shape. FindingsNP addition reduces phase separation enthalpy due to PNIPAM-NP hydrogen bonding interactions, the degree to which depends on polymer content. While NP addition minorly impacts thermodynamic and optical properties, rheological transitions and associated rheological properties are dramatically altered with increasing temperature, and depend on NP quantity, shape, and polymer molecular weight. Thus NP content and shape can be used to finely tune transition temperatures and mechanical properties for applications in stimuli-responsive materials.

Experimental and theoretical study on the complete phase separation of ceria-zirconia solid solution into two end members, ceria and zirconia

Solid solution CeO2–ZrO2 has long been used as a non-noble metal oxide promoter for three-way catalysts owing to its high oxygen storage capacity. However, the stability issue of the CeO2–ZrO2 has been controversial for a long time. In particular, the phenomena observed by phase instability are so diverse and inconsistent that the related causal analysis is still a matter of debate. In this study, for the first time, it was demonstrated theoretically and experimentally that a Ce0.75Zr0.25O2 (CZO) solid solution must be completely separated into CeO2 and ZrO2 phases owing to its inherent thermodynamic instability. According to an extensive evaluation via defect chemical calculations and well-controlled model experiments with grain-boundary-free epitaxial thin film samples, CZO materials undergo phase separation until they are completely separated, and the separation rate is particularly high in a reducing atmosphere. The underlying inherent stability problem and enhanced phase separation kinetics of the CZO material are attributed to the enhanced cation diffusion in a reducing atmosphere, where more mobile cationic defects (interstitial cations) are generated and an easier pathway with a lower migration energy is available.

Phase-field simulation for the formation of porous microstructures due to phase separation in polymer solutions on substrates with different wettabilities

The porous microstructure has been widely observed in a variety of polymer solutions that have been broadly applied in many industry fields. Phase separation is one of the common mechanisms for the formation of the porous microstructure in binary polymeric mixtures. Previous studies for the formation of porous microstructures mostly focus on the separation of the bulk phase. However, there is a paucity of investigation for the phase separation of polymer mixtures contacting the solid substrate. When the polymeric liquid mixtures interact with the solid substrate, the wetting boundary condition has to be taken into account. In this work, we present a phase-field model which is coupled with the wetting boundary condition to study the phase separation in binary polymer solutions. Our consideration is based on the polymerization-induced phase separation, and thermally induced phase separation by using the Flory–Huggins model. By taking the wetting effect into account, we find that polymer droplets spontaneously occur in the microstructure, even though the bulk composition is outside the spinodal region. This phenomenon is caused by the surface composition resulting from the wetting effect that was often overlooked in literature. For the phase separation in the binary polymer mixture, we also study the impact of the temperature gradient on the microstructural evolution. The porosity, the number of droplets, and the mean radius of the droplets are rationalized with the temperature gradient.

Development of Analytical Platforms Utilizing Micro/Nanospaces Generated by Phase Separation of Aqueous Solutions

Development of Analytical Platforms Utilizing Micro/Nanospaces Generated by Phase Separation of Aqueous Solutions

Manipulation of coacervate droplets with an electric field

Many biopolymers are highly charged, and as in the case of many polymer mixtures, they tend to phase separate as a natural consequence of chain connectivity and an associated relatively low entropy of polymer mixing. Recently, it has become appreciated that the phase-separated structures formed by such polyelectrolyte blends, called "complex coacervates," underlie numerous biological structures and processes essential to living systems, and there has been intense interest in understanding the unique physical features of this type of phase-separation process. In the present work, we are particularly concerned with the field responsiveness of stabilized coacervate droplets formed after the phase separation of polyelectrolyte blend solution and then exposed to deionized water, making the droplet interfacial layer acquire a viscoelastic character that strongly stabilizes it against coalescence. We show that we can precisely control the positions of individual droplets and arrays of them with relatively low-voltage electric fields (on the order of 10 V/cm) and that the imposition of an oscillatory field gives rise to chain formation with coarsening of these chains into long fibers. Such a phase-separation-like process is generally observed in electrorheological fluids of solid colloidal particles subjected to much larger field strengths. The key to these coacervates' electrorheological properties is the altered interfacial viscoelastic properties when the droplets are introduced into deionized water and the associated high polarizability of the droplets, similar to the properties of many living cells. Since many different molecular payloads can be incorporated into these stable droplets, we anticipate many applications.

Thin film combinatorial sputtering of Al-Ce alloys: Investigating the phase separation of as-deposited solid solutions and determining the coefficient of thermal expansion

AlxCe100−x thin films with a composition range of ~75.0 < x < 99.5 at% (36.5 < x < 97.5 wt%) were synthesized via combinatorial co-sputtering from an Al and an Al50Ce50 target. The crystal structure, phase fraction, film morphology, electrical resistivity, and temperature-dependent coefficients of thermal expansion (CTE) are all correlated to the AlxCe100−x composition. The as-deposited films form a metastable solid-solution, and annealing leads to the formation of the thermodynamically stable two-phase system of Al and the α-Al11Ce3 intermetallic. Temperature dependent x-ray diffraction (XRD) reveals that the two phases expand independently of one another, and the thin film Al temperature-dependent CTE is similar to bulk Al. The thin film Al11Ce3 intermetallic phase has a nearly constant CTE of ~1.5 × 10−5/°C within the temperature range studied (25–550 °C). To confirm the thin film Al11Ce3 results, bulk stoichiometric Al11Ce3 and +/- 1 wt% Ce samples were prepared and the CTE of each was measured with the same conditions. A Rietveld analysis of the bulk data enabled an estimation of the CTE in each of the 3 orthorhombic lattice parameters, which displayed anisotropic behavior. The thin film and bulk CTE measurements were in very good agreement. Estimations of the temperature dependent CTE of the two-phase alloys are made via the Reuss and Voigt models. By demonstrating the efficacy of the approach, more complex multi-component rapid materials discovery of low CTE Al-alloys can be pursued via the combinatorial thin film synthesis and XRD measurement.

Cover Feature: Suppression of Liquid‐Liquid Phase Separation and Aggregation of Antibodies by Modest Pressure Application (Chem. Eur. J. 48/2022)

A high colloidal stability is important for pharmaceutical applications of antibody solutions. We demonstrate a high pressure sensitivity of antibody condensates as a suitable means to suppress liquid–liquid phase separation and subsequent aggregation of concentrated antibody solutions. The immunoglobulin molecules themselves are highly pressure resistant against unfolding, however, and can sustain high pressures without changing conformation. More information can be found in the Research Article by R. Winter and co-workers (DOI: 10.1002/chem.202201658).

Global existence of weak solutions to viscoelastic phase separation: part II. Degenerate case

The aim of this paper is to prove global in time existence of weak solutions for a viscoelastic phase separation. We consider the case with singular potentials and degenerate mobilities. Our model couples the diffusive interface model with the Peterlin–Navier–Stokes equations for viscoelastic fluids. To obtain the global in time existence of weak solutions we consider appropriate approximations by solutions of the viscoelastic phase separation with a regular potential and build on the corresponding energy and entropy estimates.

Fabrication of moldable chitosan gels via thermally induced phase separation in aqueous alcohol solutions

Wide application of chitosan in modern technologies is limited by the lack of reliable and low-cost techniques to prepare size-tuned constructs with a complex surface morphology, improved optical and mechanical properties. We report a new simple method for preparation of transparent thermoreversible chitosan alcogels from chitosan/H2O/ethanol ternary systems. This method, termed “low temperature thermally induced phase separation under non-freezing conditions” (LT-TIPS-NF), fine tunes gelation by adjusting only temperature (from 5 to −25 °C) and varying the initial content of chitosan (from 0.5 to 2.0 wt%) and ethanol (from 28.5 to 47.5 vol%). Transparent non-swelling final constructs of complex shape are prepared by fixing the pre-formed alcogels with a base solution. The size of the gel constructs is limited only by the dimensions of the mold and the cooling chamber. The LT-TIPS-NF is applicable both in injection molding and 3D printing techniques. The in vitro and in vivo experiments show the absence of prominent cytotoxicity and well-defined cell adhesion on the obtained hydrogels. Thus, this facile and scalable technique provides the multifunctional chitosan gel preparation with easily controlled properties exploiting inexpensive, renewable, and environmentally friendly source polysaccharide. These materials have prospects for a variety of uses, especially for biomedical applications.

Light Scattering of Electrospinning Jet with Internal Structures by Flow-Induced Phase Separation.

Herein, the direct morphological evidence of the extension-induced phase-separated structures in the electrospinning jet observed by high-speed video imaging and by light scattering technique is reported. Model solutions of poly(vinyl alcohol) (PVA)/water are electrospun. Two types of internal structures, that is, long strings and short ellipsoids, are found. A light scattering model is derived for the Vv scattering configuration to account for the scattered intensities contributed from the liquid jet itself and those from the internal structures. For the severely stretching jet of PVA/water, the Vv intensity profile is dominant by the internal structures to mask the scattering contribution from the jet itself. Moreover, the Hv intensity profile reflects the anisotropy of the oriented chains parallel to the jet axis. For the 7 wt% solution, the derived extension rate in the vicinity of the Taylor cone apex is about 3420 s-1 , which is higher than the Rouse relaxation rate measured by rheometer. It is concluded that extension-induced phase separation of the single-phase PVA solution is likely to occur in Taylor-cone apex to trigger the self-assembly process for producing strings (and/or bulges) in the flowing jet, which eventually transform to become the nanofibers, after solvent removal, to be collected on the grounded collector.

Fabricating porous monolithic ceramic materials via phase separations in solutions of poly(Vinyl alcohol) and sol nanoparticles

Fabricating porous monolithic ceramic materials via phase separations in solutions of poly(Vinyl alcohol) and sol nanoparticles

Nucleic acid partitioning in PEG-Ficoll protocells.

The phase separation of aqueous polymer solutions is a widely used method for producing self-assembled, membraneless droplet protocells. Non-ionic synthetic polymers forming an aqueous two-phase system (ATPS) have been shown to reliably form protocells that, when equipped with biological materials, are useful for applications such as analyte detection. Previous characterization of an ATPS-templated protocell did not investigate the effects of its biological components on phase stability. Here we report the phase diagram of a PEG 35k-Ficoll 400k-water ATPS at baseline and in the presence of necessary protocell components. Because the stability of an ATPS can be sensitive to small changes in composition, which in turn impacts solute partitioning, we present partitioning data of a variety of nucleic acids in response to protocell additives. The results show that the additives-particularly a mixture of salts and small organic molecules-have profound positive effects on ATPS stability and nucleic acid partitioning, both of which significantly contribute to protocell function. Our data uncovers several new areas of optimization for future protocell engineering.

Formation of Core-Sheath Polymer Fibers by Free Surface Spinning of Aqueous Two-Phase Systems.

Core-sheath fibers have numerous applications ranging from composite materials for advanced manufacturing to materials for drug delivery and regenerative medicine. Here, a simple and tunable approach for the generation of core-sheath fibers from immiscible solutions of dextran and polyethylene oxide is described. This approach exploits the entanglement of polymer molecules within the dextran and polyethylene oxide phases for free surface spinning into dry fibers. The mechanism by which these core-sheath fibers are produced after contact with a solid substrate (such as a microneedle) involves complex flows of the phase-separating polymer solutions, giving rise to a liquid-liquid core-sheath flow that is drawn into a liquid bridge. This liquid bridge then elongates into a core-sheath fiber through extensional flow as the contacting substrate is withdrawn. The core-sheath structure of the fibers produced by this approach is confirmed by attenuated total reflection Fourier-transform infrared spectroscopy and confocal microscopy. Tuning of the core diameter is also demonstrated by varying the weight percentage of dextran added to the reservoir from which the fibers are formed.

Size Effect in the Phase Separation in Three-Component Solutions

Size Effect in the Phase Separation in Three-Component Solutions

Temporal and spatial characterisation of protein liquid-liquid phase separation using NMR spectroscopy

Liquid-liquid phase separation (LLPS) of protein solutions is increasingly recognised as an important phenomenon in cell biology and biotechnology. However, opalescence and concentration fluctuations render LLPS difficult to study, particularly when characterising the kinetics of the phase transition and layer separation. Here, we demonstrate the use of a probe molecule trifluoroethanol (TFE) to characterise the kinetics of protein LLPS by NMR spectroscopy. The chemical shift and linewidth of the probe molecule are sensitive to local protein concentration, with this sensitivity resulting in different characteristic signals arising from the dense and lean phases. Monitoring of these probe signals by conventional bulk-detection 19F NMR reports on the formation and evolution of both phases throughout the sample, including their concentrations and volumes. Meanwhile, spatially-selective 19F NMR, in which spectra are recorded from smaller slices of the sample, was used to track the distribution of the different phases during layer separation. This experimental strategy enables comprehensive characterisation of the process and kinetics of LLPS, and may be useful to study phase separation in protein systems as a function of their environment.

Phase separation in surfactant-containing amorphous solid dispersions: Orthogonal analytical methods to probe the effects of surfactants on morphology and phase composition

Amorphous–amorphous phase separation (AAPS) is an important phase transition process for amorphous solid dispersion (ASD) performance both in terms of drug release as well as physical and chemical stability during storage. Addition of surfactants to ASD systems can impact both of these processes. One possible mechanism through which surfactants affect ASD performance is via their impact on AAPS. Unfortunately, despite their increasing usage in ASD formulations, the effect of surfactant on AAPS is still poorly understood, and there are limited analytical techniques that provide microstructural and composition information about phase separated ASDs. In this study, the impact of four surfactants (sodium dodecyl sulfate, Tween 80, Span 20 and Span 85) on water-induced phase separation in ASDs formulated with ritonavir and polyvinylpyrrolidone/vinyl acetate (PVPVA) was investigated using a variety of orthogonal analytical methods. Transparent films of ASDs with different compositions were prepared by spin coating. Fluorescence confocal microscopy in combination with an in situ humidity chamber was used to monitor the kinetics and morphology of phase separation following exposure to high relative humidity. Optical photothermal IR analysis of phase separated films enabled characterization of domain composition and surfactant distribution. Liquid-liquid phase separation concentration, zeta potential and solution nuclear magnetic resonance spectroscopy measurements enabled interpretation of interaction with and partition of surfactants into the drug-rich phase. It was found that phase separation kinetics and morphology were notably changed by the surfactants. Further, the surfactants showed different affinities for the drug-rich versus the aqueous/polymer-rich phases. The employed analytical techniques were found to be complementary in providing insight into surfactant location in phase separated systems. This study highlights the complexity of phase separation, especially in the presence of surfactants, and provides a foundation to understand the impact of AAPS on ASD performance.

Micellar extraction and spectrophotometric determination of quinoline yellow in drugs

A distinctive feature of modern drugs is a complex multicomponent composition, including both medicinal and auxiliary substances. The synthetic food dye Quinoline yellow (QY) is widely used for color correction, however, the determination of QY by the spectrophotometric method is impossible without separating the preparation from the matrix. Micellar extraction with polyoxyethylated alkylphenols Triton X-100 and OP-10 is proposed as an alternative to solid-phase extraction and traditional extraction with organic solvents. The phase separation of aqueous and aqueous-salt solutions of Triton X-100 and OP-10 with a con-centration of 1 to 10% is studied in various modes: polythermal (when heated to cloud point) and isothermal (salting out at 25°C). Sodium and ammonium sulfates and sodium carbonate are used as salting-out agents. Their salting-out ability decreases in the series Na2CO3 &gt; Na2SO4 &gt; (NH4)2SO4. The effect of the acidity of the medium and the nature of the electrolyte on the state of the QY in aqueous and aqueous micellar solutions is also studied. The form of the dye does not change within the pH range 1 – 8 and with the addition of Na2SO4, (NH4)2SO4. At higher pH values and in the presence of Na2CO3, structural changes occur in the molecule. The intensity and position of the maximum in the absorption spectrum change in the presence of surfactant micelles (bathochromic shift, Δλ = 8 nm). The dye distribution between the aqueous and micellar phases is studied in different modes of phase separation. It is shown that the systems with the addition of sodium and ammonium sulfates in the salting-out mode (R &gt; 97%) have the best extraction characteristics. Optimal conditions for the maximum single extraction of the dye in the concentration range of 1 – 10 mg/liter in the aqueous solution C(surfactant) — 10%, solution volume — 10 ml, Na2SO4 — 0.84 g, temperature — 25°C, time — 30 min. A rapid and easy to use method of QY extraction concentration from orodispersible tablets (lozenges) is developed. The error of the method does not exceed 5%. The verification of the correctness of the method, carried out by HPLC, proved the absence of a systematic error.

Building micro-capsules using water-in-water emulsion droplets as templates

The use of templates in materials chemistry is a well-established approach for producing membrane-bounded hollow spheres used for microencapsulation applications, but also in synthetic biology to assemble artificial cell-like compartments. Sacrificial solid or gel micro-particles, but also liquid-like oil-in-water or water-in-oil emulsion droplets are routinely used as templates to produce capsules. Yet, disruption of the core sacrificial material often requires harsh experimental conditions, such as organic solvents, which limits the use of such approach to encapsulate fragile solutes, including biomolecules. Recently, water-in-water emulsion droplets have emerged as promising alternative templates to produce capsules in solvent-free conditions. These water-in-water droplets result from liquid-liquid phase separation in dilute aqueous polymer or surfactants solutions. Their ease of preparation, the large palette of components they can be assembled from and the lack of harsh solvent or oil used for their production make water-in-water emulsions of practical importance in materials chemistry. Water-in-water droplets can also spontaneously sequester solutes by equilibrium partitioning, which provides a simple strategy to locally accumulate molecules of interest and encapsulate them in capsules after interfacial shell formation. Here, we review recent works that employ water-in-water emulsion droplets to prepare capsules and suggest possible additional applications in materials chemistry.

Effects of self-hydrogen bonding among formamide molecules on the UCST-type liquid-liquid phase separation of binary solutions with imidazolium-based ionic liquid, [Cnmim][TFSI], studied by NMR, IR, MD simulations, and SANS.

The upper critical solution temperature (UCST)-type liquid-liquid phase separation of imidazolium-based ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI], where n represents the alkyl chain length of the cation, n = 6, 8, 10, and 12) binary solutions with formamide (FA) was examined as a function of temperature and the FA mole fraction xFA. The two-phase region (immiscible region) of the solutions is much larger and expands more with the increase in n, in comparison with the previous [Cnmim][TFSI]-1,4-dioxane (1,4-DIO) systems. An array of spectroscopic techniques, including 1H and 13C NMR and IR combined with molecular dynamics (MD) simulations, was conducted on the present binary systems to clarify the microscopic interactions that contribute to the phase-separation mechanism. The hydrogen-bonding interactions of the imidazolium ring H atoms are more favorable with the O atoms of the FA molecules than with 1,4-DIO molecules, whereas the latter interact more favorably with the alkyl chain of the cation. Upon lowering the temperature, the FA molecules gradually self-aggregate through self-hydrogen bonding to form FA clusters. Concomitantly, clusters of ILs are formed via the electrostatic interaction between the counter ions and the dispersion force among the IL alkyl chains. Small-angle neutron scattering (SANS) experiments on the [C6mim][TFSI]-FA-d2 and [C8mim][TFSI]-FA-d2 systems revealed, similarly to [Cnmim][TFSI]-1,4-DIO systems, the crossover of the mechanism from the 3D-Ising mechanism around the UCST xFA to the mean-field mechanism at both sides of the mole fraction. Interestingly, the xFA range of the 3D-Ising mechanism for the FA systems is wider compared with the range of the 1,4-DIO systems. In this way, the self-hydrogen bonding among FA molecules most significantly governs the phase equilibria of the [Cnmim][TFSI]-FA systems.