Phase Separation In Solutions Research Articles

Continuity of Short-Time Dynamics Crossing the Liquid-Liquid Phase Separation in Charge-Tuned Protein Solutions.

Liquid-liquid phase separation (LLPS) constitutes a crucial phenomenon in biological self-organization, not only intervening in the formation of membraneless organelles but also triggering pathological protein aggregation, which is a hallmark in neurodegenerative diseases. Employing incoherent quasi-elastic neutron spectroscopy (QENS), we examine the short-time self-diffusion of a model protein undergoing LLPS as a function of phase splitting and temperature to access information on the nanosecond hydrodynamic response to the cluster formation both within and outside the LLPS regime. We investigate the samples as they dissociate into microdroplets of a dense protein phase dispersed in a dilute phase as well as the separated dense and dilute phases obtained from centrifugation. By interpreting the QENS results in terms of the local concentrations in the two phases determined by UV-vis spectroscopy, we hypothesize that the short-time transient protein cluster size distribution is conserved at the transition point while the local volume fractions separate.

Excipient Induced Unusual Phase Separation in Bovine Serum Albumin Solution: An Explicit Role Played by Ion-Hydration.

We report an instantaneous room-temperature phase separation of 1 mM bovine serum albumin solution in the presence of (20% acetic acid+0.2 M NaCl), a routinely used food preservative; an opaque liquid-like phase (L) coexists in equilibrium with a granular gel like phase (G). Interestingly, neither 20% acetic acid nor 0.2 M NaCl individually induces such a phase separation. Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) imaging show aggregated proteins to be dispersed in the upper phase, while the lower phase is composed of cross-linked fibrils (hydrogels). Mid-IR FTIR, Raman scattering, and circular dichroism (CD) experiments reveal a significant increase in the β-sheet content in BSA, which confirms the formation of amyloids in the presence of the excipient. Both L and G phases undergo distinct visual and microscopic changes upon incubation at 25 and 80 °C. It is evident that the added salt plays a pivotal role in bringing about this otherwise unique phase behavior. We divulge the explicit role of the ion associated hydration using THz-FTIR measurements in the 1.5-16.7 THz (50-550 cm-1) frequency window. Systematic alteration in the ion-induced THz-active mode of water envisions the key role of ions in shaping the various phases. Our study depicts an intriguing observation of severe amyloidosis of BSA upon the addition of a food preservative, even at room temperature, which is expected to add new insight into amyloid research. Considering the increasing number of individuals suffering from several neurodegenerative disorders (Alzheimer's, Parkinson's, type-2 diabetes, obesity, cancer, etc.), this study leads a caution toward critically revisiting the usage of known food preservatives.

Enhanced antifouling PSE hollow fiber membrane via zwitterionic copolymer segregation

Blending hydrophilic additives is an effective method to improve the surface hydrophilcility and antifouling property of ultrafiltration membranes. In this study, we prepared a series of polysulfate (PSE) hollow fiber membranes (HFMs) containing a zwitterion-based copolymer, poly(4-vinylpyridine-co-methylacryloxyethyl phosphocholine), with varying monomer ratios and blending quantities. The relationship between cast solution properties and phase separation behavior was investigated, as well as the impacts of copolymer composition and amount on the separation performances and antifouling abilities of the membranes. A higher hydrophilic monomer ratio and more copolymer addition of zwitterionic copolymer would facilitate surface segregation, increasing the hydrophilicity of membrane surface and generating a dense hydration layer. This layer can resist macromolecule contaminants and promote water molecular transport. Furthermore, a more compacted skin layer improves separation ability. The optimized PSE HFMs had water fluxes around 140 L m−2 h−1, BSA rejections over 97 %, and flux recovery rates over 92 % during operation. Moreover, the membrane demonstrated ultra-low flux-sacrifice when applied to protein solutions while maintaining a high rejection rate, which indicates the distinctive and strong competitiveness of PSE/P(4VP-co-MPC) HFMs.

Conformations of a low-complexity protein in homogeneous and phase-separated frozen solutions

Solutions of the intrinsically disordered, low-complexity domain of the FUS protein (FUS-LC) undergo liquid-liquid phase separation (LLPS) below a temperature TLLPS. To investigate whether local conformational distributions are detectably different in the homogeneous (i.e., single-phase) and phase-separated states of FUS-LC, we performed solid-state NMR (ssNMR) measurements on solutions that were frozen on submillisecond timescales after equilibration at temperatures well above (50°C) or well below (4°C) TLLPS. Measurements were performed at 25 K with signal enhancements from dynamic nuclear polarization. Crosspeak patterns in two-dimensional ssNMR spectra of rapidly frozen solutions in which FUS-LC was uniformly 15N,13C labeled were found to be nearly identical for the two states. Similar results were obtained for solutions in which FUS-LC was labeled only at Thr, Tyr, and Gly residues, as well as solutions of a FUS construct in which five specific residues were labeled by ligation of synthetic and recombinant fragments. These experiments show that local conformational distributions are nearly the same in the homogeneous and phase-separated solutions, despite the much greater protein concentrations and more abundant intermolecular interactions within phase-separated, protein-rich “droplets.” Comparison of the experimental results with simulations of the sensitivity of two-dimensional ssNMR crosspeaks to changes in populations of β strand-like conformations suggests that changes in conformational distributions are no larger than 5–10%.

In situ construction of one-dimensional structures induced by Ba doping in Al2O3-TiO2 ceramics derived from quenched powders

In this work, we propose a strategy for in situ construction of rod-like grains in Al2O3-TiO2 ceramics through Ba doping. Ba-doped Al2O3-13 wt% TiO2 composite powder was initially synthesized using combustion synthesis-air atomization, where feedstocks were melted by the Al-O2 combustion reaction and subsequently atomized and rapidly cooled in air, producing quenched powders rich in metastable phases. Upon heat treatment at 1100℃, the metastable phases transformed into stable forms, accompanied by phase separation and solid solution precipitation. Notably, Ba doping induced the formation of rod-like hollandite grains with preferential growth along the [001] direction. Bulk ceramics were prepared through pressureless sintering, and the sample sintered at 1350℃ exhibited a hardness of 14.14±0.61 GPa and a fracture toughness of 5.17±0.49 MPa∙m1/2. The toughening behavior of rod-like grains, including crack deflection and pull-out/bridging effects, was observed. This study provides insights into the evolution of quenched oxides and the design of ceramic microstructures.

High-Speed Electrospinning of Ethyl Cellulose Nanofibers via Taylor Cone Optimization.

Ethyl cellulose (EC) is one of the most widely used cellulose derivatives. Nevertheless, challenges such as the formation of beaded fibers, low yield, and nonporous internal structure persist in electrospinning, limiting functional improvements and industrial applications. This study invented a groundbreaking high-speed electrospinning technique through sheath liquid assistance to optimize the Taylor cone, dramatically enhancing the yield, morphology, and formation of porous structures of EC nanofibers beyond what has been seen in the literature to date. Our study emphasizes the crucial role of the sheath liquid's physical and chemical properties in controlling the morphology and diameter of EC nanofibers. It was discovered that highly polar and viscous sheath liquids led to the formation of beaded structures. Most importantly, the sheath liquid-assisted method substantially increased the ejection rate of the EC solution tens and hundreds of times compared to the current low-speed electrospinning method (0.1-1 mL/h) by refining the shape of the Taylor cone and resolving low productivity challenges in conventional nanofiber production. Meanwhile, increasing the flow rate of the EC or the sheath liquid accelerated the phase separation of EC solutions, thereby promoting the formation of porous structures in EC nanofibers. A pronounced porous structure was observed when the core EC flow rate reached 25 mL/h or the sheath chloroform flow rate reached 20 mL/h. Furthermore, our sheath liquid-assisted high-speed electrospinning technique demonstrated universal applicability to ECs with varying molecular weights. This study comprehensively addressed challenges in controlling the yield, morphology, and internal structure of EC nanofibers through sheath-solution-assisted high-speed electrospinning technology. These findings provide an innovative approach to developing next-generation electrospinning technologies to enhance the yield and properties of natural polymers for sustainability.

Efficient β-carotene recovery from surfactant-based aqueous solutions: Advancing from experimental to process simulation

β-carotene is a carotenoid present in the human diet with numerous functions in the body. This work suggests a new platform for efficiently recovering this bioactive compound from aqueous solutions. For the first time, a ternary deep eutectic solvent (DES) is proposed to promote phase separation in aqueous solutions of non-ionic surfactants (Triton X-102 and Tween 20). The influence of temperature on the miscibility regions was investigated from 298.15 K to 308.15 K as a preliminary step. The obtained phase diagrams at three temperatures were accurately correlated using four empirical equations. The extraction capacity of these novel combinations was analysed by means of the Tie-Lines (TL) and their derived magnitudes: Tie-Line Length (TLL) and Slope (S). The reliability of the TLs was ascertained through three empirical equations. Analysis of the data showed that more than 99 % of the model carotene could be extracted using ChCl:U:Gly from a Triton X-102 aqueous solution at 308.15 K. Process simulation using SuperPro Designer confirmed that an effective and sustainable process for recovering β-carotene from algal biomass can be designed using a simple approach.

Design of green DES-based aqueous two phase systems for lipolytic enzymes extraction

This study pioneers a novel green and cost-effective separation process using reline deep eutectic solvent (DES) for extracting Thermomyces lanuginosus lipase (TlL) from aqueous solutions. For the first time, it has been shown that various potassium organic salts combined with reline DES can induce phase separation in aqueous solutions of the biodegradable non-ionic surfactant Tergitol 15-S9, presenting a groundbreaking alternative to the banned surfactant Triton X-100. This work uniquely applies three different equations to describe the experimental solubility curves. The selection of reline DES is particularly innovative as it avoids significant deactivation effects with three commercial lipases: Candida antarctica lipases A and B, and TlL, with the latter undergoing a detailed study. This includes an unprecedented analysis of its thermodeactivation kinetics in reline DES aqueous solutions. Additionally, a novel investigation of immiscibility regions at different temperatures, involving comprehensive Tie-Line characterizations (slope and length), preceded the evaluation of lipase extraction. Remarkably, the study demonstrates that optimizing the feed composition to contain higher water concentrations can achieve exceptionally high extraction efficiencies (approximately 90%), suggesting a transformative potential for future applications in real aqueous cultures.

Highly efficient direct air capture using solid–liquid phase separation in aqueous diamine solution as sorbent

Abstract To reduce climate change, absorbing CO2 directly from the air (DAC) with high-efficient CO2 absorption, low-cost, and environmentally friendly system has been attracted much attention for several decades. In this work, a series of aqueous diamine solutions was examined for 400 ppm CO2 absorption at ambient temperature. The absorbents exhibited CO2 absorption with molar ratio of 1 molCO2/molamine, and aqueous isophorone diamine (IPDA) in particular showed >99% CO2 removal even under a 500 mL min−1 flow of 400 ppm CO2–N2 with the contact rate of 13,761.5 h−1 between CO2 and IPDA aqueous solution and the CO2 absorption rate of 4.46 mmol/L min. A precipitate of carbamic acid of IPDA was formed by reaction with CO2, and the CO2 removal efficiency was enhanced by increasing the solution viscosity by the formation of this precipitate. The CO2 was absorbed in aqueous IPDA solution as carbamic acid of IPDA and bicarbonate/carbonate species, and the absorbed CO2 could desorb by heating under O2-containing gas flow, which indicates our system is applicable to the CO2 condensation for a plant growth. This work provides fundamental information to establishing a solid–liquid phase change system with a high-efficient and environmentally friendly DAC system using aqueous solvent.

In Situ Morphology Control for Solution‐Printable Organic Photovoltaics

AbstractThe morphology of the photoactive layer plays an important role in both the photoelectric effect and device performance of solution‐processed organic solar cells (OSCs). Optimizing the morphology requires precise control over the complex film formation kinetics, which are influenced by a range of factors from the solution state to the solid‐film state. This review delves into the in situ characterization technologies employed to understand the active layer formation process and explores strategies for controlling film formation during key stages, including solution aggregation, nucleation, crystal growth, and phase separation. Special attention is given to the mechanism by which these strategies enable real‐time morphology control during the printing process and their potential to facilitate direct printing of active layers with optimized morphology. The goal is to offer valuable insights and guidance for managing film formation kinetics in solution‐processed OSCs, ultimately addressing the challenges of real‐time morphology control in scale‐up printing and paving the way for high‐throughput production of post‐processing‐free devices.

Dominance analysis to assess solute contributions to multicomponent phase equilibria

Phase separation in aqueous solutions of macromolecules underlies the generation of biomolecular condensates in cells. Condensates are membraneless bodies, representing dense, macromolecule-rich phases that coexist with the dilute, macromolecule-deficient phases. In cells, condensates comprise hundreds of different macromolecular and small molecule solutes. How do different solutes contribute to the driving forces for phase separation? To answer this question, we introduce a formalism we term energy dominance analysis. This approach rests on analysis of shapes of the dilute phase boundaries, slopes of tie lines, and changes to dilute phase concentrations in response to perturbations of concentrations of different solutes. The framework is based solely on conditions for phase equilibria in systems with arbitrary numbers of macromolecules and solution components. Its practical application relies on being able to measure dilute phase concentrations of the components of interest. The dominance framework is both theoretically facile and experimentally applicable. We present the formalism that underlies dominance analysis and establish its accuracy and flexibility by deploying it to analyze phase diagrams probed in simulations and in experiments.

Conformations of a Low-Complexity Protein in Homogeneous and Phase-Separated Frozen Solutions.

Liquid-liquid phase separation (LLPS) in solutions of proteins with intrinsically disordered domains has attracted recent attention because of its relevance to multiple biological processes and its inherent interest from the standpoint of protein biophysics. The high protein concentrations and abundant intermolecular interactions within protein-rich, phase-separated "droplets" suggests that conformational distributions of intrinsically disordered proteins may differ in homogeneous and phase-separated solutions. To investigate whether detectable differences exist, we performed experiments on the low-complexity domain of the FUS protein (FUS-LC) in which FUS-LC solutions were first equilibrated at temperatures well above or well below their LLPS transition temperatures, then rapidly frozen and examined at very low temperatures by solid state nuclear magnetic resonance (ssNMR) spectroscopy. The ssNMR data for homogeneous and phase-separated frozen solutions of FUS-LC were found to be nearly identical, showing that LLPS is not accompanied by substantial changes in the local conformational distributions of this intrinsically disordered protein.

Exact analytical solution of the Flory-Huggins model and extensions to multicomponent systems.

The Flory-Huggins theory describes the phase separation of solutions containing polymers. Although it finds widespread application from polymer physics to materials science to biology, the concentrations that coexist in separate phases at equilibrium have not been determined analytically, and numerical techniques are required that restrict the theory's ease of application. In this work, we derive an implicit analytical solution to the Flory-Huggins theory of one polymer in a solvent by applying a procedure that we call the implicit substitution method. While the solutions are implicit and in the form of composite variables, they can be mapped explicitly to a phase diagram in composition space. We apply the same formalism to multicomponent polymeric systems, where we find analytical solutions for polydisperse mixtures of polymers of one type. Finally, while complete analytical solutions are not possible for arbitrary mixtures, we propose computationally efficient strategies to map out coexistence curves for systems with many components of different polymer types.

Rheological and light scattering analyses for characterizing phase separation of polymer solutions in lithium-ion battery separator coating system

Rheological and light scattering analyses for characterizing phase separation of polymer solutions in lithium-ion battery separator coating system

A dynamic phase separation model for glass transition behavior in water-triggered shape memory polymer towards programmable recovery onset

Water-triggered shape memory polymers (SMPs) have been extensively studied for biomedical applications due to their advantages of non-thermal actuation capability. However, few studies have been carried out to explore the working principle of shape recovery onset, which is essentially determined by the complex reactions between polymer macromolecules and water molecules. In this study, we developed a phase separation model to describe the dynamic glass transition in water-triggered SMPs. Based on the phase transition theory, dense and dilute phase separations of polymer macromolecules can be achieved when the dynamic diffusions of water molecules in the SMPs undergo dehydration and absorption processes, respectively. Then, the dynamic glass transition is resulted from the dehydration and absorption of water molecules, leading to the dense and dilute phases in the SMPs. Therefore, a free-energy equation has been developed to characterize the recovery onset, in which the mixing free energy and elastic free energy are originated from the Flory–Huggins solution theory and phase separation model, respectively. Moreover, the glass transition and its connection to shape recovery behaviors, i.e. recovery ratio, relaxation time and dynamic mechanical modulus, have also been investigated, according to the Fick’s diffusion law. Meanwhile, onset of programmable recovery has been explained by the dynamic phase separation, based on the transpiration theory and permeability model. Finally, the proposed model is verified using the experimental results reported in the literature. This study is expected to provide a fundamental approach to formulate the constitutive relationship between the dynamic phase separation and programmable recovery onset in the water-triggered SMPs.

The beneficial effect of lauric acid addition in nucleation stage on the soot catalytic combustion performance of cerium-manganese catalyst

For cerium-manganese catalyst system, increasing the threshold of the amount of Mnx+ entering into the CeO2 lattice can generate more oxygen vacancies and adsorb more active oxygen species, thus promoting its soot catalytic combustion. However, this is difficult to achieve under the premise of fixed cerium-manganese ratio of the catalyst. Fortunately, the results of this study show that the addition of lauric acid at the nucleation stage of the cerium-manganese catalyst can effectively improve its activity and high temperature aging resistance. Combined with a series of characterization results, the addition of lauric acid can increase the threshold of Mnx+ content in CeO2 lattice, improve the structural performance of the catalyst, increase the specific surface area and pore volume of the catalyst, inhibit the secondary aggregation of catalyst particles, increase the content of surface Ce3+, increase the low temperature reduction performance and the content of surface chemical desorbed oxygen of the catalyst. In addition, it can also prevent the phase separation of cerium-manganese solid solution, the growth of grains, the increase of reduction peak temperature and the decrease of H2 consumption during high temperature aging. Moreover, the addition of lauric acid also greatly improves the release performance of active oxygen in cerium-manganese catalyst. Therefore, this study plays a positive role in promoting the commercial application of highly active cerium-manganese catalyst.

Lipid droplets as substrates for protein phase separation

Membrane-associated protein phase separation plays critical roles in cell biology, driving essential cellular phenomena from immune signaling to membrane traffic. Importantly, by reducing dimensionality from three to two dimensions, lipid bilayers can nucleate phase separation at far lower concentrations compared with those required for phase separation in solution. How might other intracellular lipid substrates, such as lipid droplets, contribute to nucleation of phase separation? Distinct from bilayer membranes, lipid droplets consist of a phospholipid monolayer surrounding a core of neutral lipids, and they are energy storage organelles that protect cells from lipotoxicity and oxidative stress. Here, we show that intrinsically disordered proteins can undergo phase separation on the surface of synthetic and cell-derived lipid droplets. Specifically, we find that the model disordered domains FUS LC and LAF-1 RGG separate into protein-rich and protein-depleted phases on the surfaces of lipid droplets. Owing to the hydrophobic nature of interactions between FUS LC proteins, increasing ionic strength drives an increase in its phase separation on droplet surfaces. The opposite is true for LAF-1 RGG, owing to the electrostatic nature of its interprotein interactions. In both cases, protein-rich phases on the surfaces of synthetic and cell-derived lipid droplets demonstrate molecular mobility indicative of a liquid-like state. Our results show that lipid droplets can nucleate protein condensates, suggesting that protein phase separation could be key in organizing biological processes involving lipid droplets.

Advantages of the low-temperature secondary emission mass spectrometry in analysis of metal ions in water samples revisited

A problem of necessity of concentrating trace admixtures of metal ions required for ecological water analysis can be overcome by harnessing a physical phenomenon of phase separation in aqueous solutions during their freezing. It is shown that the accumulation of metal-containing solutes in the channels between ice crystallites in the frozen solids is sufficient for their successful detection by means of low-temperature secondary emission mass spectrometry. Sufficiency of microliters volumes of water is an advantage of such an approach. Observation of various types of metal ions in frozen water samples is demonstrated on the examples of tap water, sea water, snow and a medicinal preparation. Revisiting and summation of physical basics of mass spectrometric examining of frozen water-inorganic salt solutions and estimates of advancement of mass spectrometric instrumentation permit us to propose a workflow for accelerated and simplified mass spectrometric detection of metal pollutants in water.

The Effect P Additive on the CeZrAl Support Properties and the Activity of the Pd Catalysts in Propane Oxidation.

The properties of a catalyst support are closely related to the catalyst activity, yet the focus is often placed on the active species, with little attention given to the support properties. In this work, we specifically investigated the changes in support properties after the addition of P, as well as their impact on catalyst activity when used for catalyst preparation. We prepared the CeO2-ZrO2-P2O5-Al2O3 (CeZrPAl) composite oxides using the sol-gel, impregnation, and mechanical mixing methods, and characterized the support properties using techniques such as XRD, XPS, SEM-EDS, N2 adsorption-desorption, and Raman spectra. The results showed that the support prepared using the sol-gel method can exhibit a more stable phase structure, larger surface area, higher adsorption capacity for oxygen species, and greater oxygen storage capacity. The addition of an appropriate amount of P is necessary. On the one hand, the crystallization and growth of CePO4 can lead to a decrease in the Ce content in the cubic phase ceria-zirconia solid solution, resulting in a phase separation of the ceria-zirconia solid solution. On the other hand, CePO4 can lock some of the Ce3+/Ce4+ redox pairs, leading to a reduction in the adsorption of oxygen species and a decrease in the oxygen storage capacity of the CeZrPAl composite oxides. The research results indicated that the optimal P addition is 6 wt.% in the support. Therefore, we prepared a Pd/CeZrPAl catalyst using CeZrAl with 6 wt.% P2O5 as the support and conducted the catalytic oxidation of C3H8. Compared with the support without P added, the catalyst activity of the support loaded with P was significantly improved. The fresh and aged (1000 °C/5 h) catalysts decreased by 20 °C and 5 °C in T50 (C3H8 conversion temperature of 50%), and by 81 °C and 15 °C in T90 (C3H8 conversion temperature of 90%), respectively.

Phase Change Study of a New Two-Phase Absorbent Based on DAP.

In order to overcome the drawbacks of conventional absorbents, which exhibit slow absorption rates and low absorption loads, this study suggests enhancing the absorbent system for CO2 absorption by incorporating a nonaqueous solvent into 1,3-propanediamine (DAP) and tetramethylethylenediamine (TMEDA), resulting in a two-phase system. The mechanism of solvent absorption of CO2 was investigated using nuclear magnetic resonance (NMR) carbon spectroscopy. By comparing the absorption load, fraction ratio, and viscosity of different absorbents after absorbing carbon dioxide, the two-phase absorbents with good performance were selected. The poor water absorbent consisting of the DAP/TMEDA system exhibited an absorption load of 3.8 mol/kg, surpassing that of the conventional 30% ethanolamine solution. A nonaqueous solvent is added to the system to replace some of the water to reduce the fraction. After adding different nonaqueous solvents, the phase separation system was screened after 2 h of CO2 absorption. The system with good performance was tested for the absorption of the solution under different amine concentration and water concentration tests. It is found that the absorption load of the DAP/TMEDA/diglyme system is 3.2 mol/kg, but the fraction can be reduced to 38%. The significant reduction in rich phase volume is beneficial for reducing the size and cost of regeneration tower. According to NMR detection and quantum chemical calculations, it was found that DAP/TMEDA absorbs carbon dioxide to form carbamate. DAP acts as the main absorbent, while TMEDA and nonaqueous solvents do not participate in the absorption reaction. Nonaqueous solvents were found to accelerate the solution phase separation due to the salt precipitation reaction.