Phase Separation In Solutions Research Articles

Segregative phase separation of gelatin and tragacanth gum solution and Mickering stabilization of their water-in-water emulsion with microgel particles prepared by complex coacervation

This study aimed to investigate the segregative interaction of gelatin (G) and tragacanth gum (TG) and the stabilization of their water-in-water (W/W) emulsion by G-TG complex coacervate particles. Segregation was studied at different pHs, ionic strengths and biopolymer concentrations. Results showed that incompatibility was affected by increasing the biopolymer concentrations. So, three reigns were demonstrated in the phase diagram of the salt-free samples. NaCl significantly changed the phase behavior via enhancement of self–association of polysaccharide and changing solvent quality due to the charge screening effect of ions. The W/W emulsion prepared from these two biopolymers and stabilized with G-TG complex particles was stable for at least one week. The microgel particles improved emulsion stability by adsorption to the interface and creating a physical barrier. A fibrous and network-like structure of the G-TG microgels was observed by scanning electron microscopy images suggesting the Mickering emulsion stabilization mechanism. It was confirmed that the bridging flocculation between the microgel polymers led to phase separation after the stability period. Biopolymer incompatibility investigation is a useful tool to obtain beneficial knowledge for preparation new food formulation, especially no contain oil emulsions for low- calorie diets.

Novel multiscale simulations on the membrane formation via hybrid induced phase separation process based on dissipative particle dynamics

A novel simulation methodology, that was based on dissipative particle dynamics (DPD) combined with information from molecular dynamics (MD) and calculations of an extended Maxwell-Stefan (MS) equations, was established to obtain multiscale analysis on the dynamics of hybrid induced phase separation (HIPS), taking polyvinylidene fluoride-diphenyl carbonate/water–ethanol (PVDF-DPC/water–ethanol) system as an example. Firstly, MS equations were derived to describe the heat transfer across the interface between the casting solution and coagulation to get the temperature profiles of the casting solution. Secondly, MD simulations for the PVDF-DPC solution were conducted to acquire bond and angle distributions of the PVDF chains. And compared to the DPD particle distributions, a novel DPD force field to describe the real flexibility of PVDF chains and a coarse-graining mapping between the MD and DPD were developed. Thirdly, based on the quenching time calculated by the MS equations and the DPD time scale, DPD simulations were carried out to demonstrate the dynamics of phase separation and membrane formation for different parts of the polymer solution via HIPS and compared to that via thermally induced phase separation (TIPS). The simulation results indicated that the mass transfer had a decisive effect on the phase separation of polymer solution near the interface and resulted in a highly asymmetric structure with a denser polymer top layer and porous sublayer, and this effect was together decided by the quenching rate and polymer solidification. For the inner parts of the polymer solution, a mainly isotropic structure was formed due to heat transfer. Based on experimental verification and simulation results, it can be known that the multiscale simulation was much closer to reality and can provide deep insights into the membrane formation prepared via the HIPS process.

Spontaneous transfer of amphiphilic molecules from evaporating water to involatile oil and its effects on the rate of water evaporation

We have investigated the evaporation kinetics of water through an involatile oil layer with amphiphilic molecules dissolved in both the water and oil phases. As water evaporated, the concentration of amphiphilic molecules in the water phase increased, which induced spontaneous transfer of the amphiphilic molecules to the oil phase. The volume of the oil phase increased owing to the phase transfer, which caused a decrease in the rate of water evaporation. However, the evaporation flux of water was not explained by only the thickness of the oil layer, and the amount of dissolved amphiphilic molecules in the oil phase also affected the evaporation flux. We propose that the amphiphilic molecules in the oil phase affected transport of water molecules through the oil layer because there would be a strong interaction between the amphiphilic molecules and water molecules in the oil phase. A simple mathematical model based on retarded diffusion reasonably explained the experimental data. Phase transfer of the amphiphilic molecules is important to understand the evaporation kinetics of water in phase-separated solutions, such as emulsions. The kinetics of water evaporation and the compositions of the amphiphilic molecules compared with those at equilibrium are discussed.

Tough monolithic TiO2 materials fabricated by the sol-gel process accompanied with phase separation in solutions of SiC nanofibers and preceramic polymers

In recent decades, the sol-gel process accompanied with phase separation has been employed to fabricate porous monolithic ceramic materials. However, it is challenging to obtain crack-free samples by using this method, due to the fragile nature of porous ceramic materials and the large internal stress generated from drying and calcination process. In this work, tough monolithic titania (TiO2) materials were fabricated by the sol-gel process accompanied with phase separation in solutions of silicon carbide (SiC) nanofibers and preceramic polymers. It was found that polyethylene oxide (PEO) and ethylenediamine (EDA) can promote phase separation and sol-gel process respectively, and the micro-morphology of porous monolithic TiO2 materials can be flexibly tuned by adjusting the contents of PEO and EDA. The addition of SiC nanofibers effectively enhanced the mechanical performance and photocatalytic activity of porous TiO2 materials without altering their bicontinuous micro-morphology. Taking TiO2 materials as an example, this work demonstrates a novel methodology to fabricate ceramic nanofibers reinforced porous monolithic ceramic materials.

X-ray Reflectometry of Thin Films Formed during Phase Separation of Organic Solutions of Aliphatic Polyethers in Water

X-ray Reflectometry of Thin Films Formed during Phase Separation of Organic Solutions of Aliphatic Polyethers in Water

Kinetics of Micellization and Liquid-Liquid Phase Separation in Dilute Block Copolymer Solutions.

A lattice theory for block copolymer solutions near the boundary between the micellization and liquid-liquid phase separation regions proposes a new kinetic process of micellization where small concentrated-phase droplets are first formed and then transformed into micelles in the early stage of micellization. Moreover, the thermodynamically stable concentrated phase formed from metastable micelles by a unique ripening process in the late stage of phase separation, where the growing concentrated-phase droplet size is proportional to the square root of the time.

Phase separation and dynamical arrest of protein solutions dominated by short-range attractions.

The interplay of liquid-liquid phase separation (LLPS) and dynamical arrest can lead to the formation of gels and glasses, which is relevant for such diverse fields as condensed matter physics, materials science, food engineering, and the pharmaceutical industry. In this context, protein solutions exhibit remarkable equilibrium and non-equilibrium behaviors. In the regime where attractive and repulsive forces compete, it has been demonstrated, for example, that the location of the dynamical arrest line seems to be independent of ionic strength, so that the arrest lines at different ionic screening lengths overlap, in contrast to the LLPS coexistence curves, which strongly depend on the salt concentration. In this work, we show that the same phenomenology can also be observed when the electrostatic repulsions are largely screened, and the range and strength of the attractions are varied. In particular, using lysozyme in brine as a model system, the metastable gas-liquid binodal and the dynamical arrest line as well as the second virial coefficient have been determined for various solution conditions by cloud-point measurements, optical microscopy, centrifugation experiments, and light scattering. With the aim of understanding this new experimental phenomenology, we apply the non-equilibrium self-consistent generalized Langevin equation theory to a simple model system with only excluded volume plus short-range attractions, to study the dependence of the predicted arrest lines on the range of the attractive interaction. The theoretical predictions find a good qualitative agreement with experiments when the range of the attraction is not too small compared with the size of the protein.

Plant cell-like tip-growing polymer precipitate with structurally embedded multistimuli sensing ability

Soft systems that respond to external stimuli, such as heat, magnetic field, and light, find applications in a range of fields including soft robotics, energy harvesting, and biomedicine. However, most of the existing systems exhibit nondirectional, nastic movement as they can neither grow nor sense the direction of stimuli. In this regard, artificial systems are outperformed by organisms capable of directional growth in response to the sense of stimuli or tropic growth. Inspired by tropic growth schemes of plant cells and fungal hyphae, here we report an artificial multistimuli-responsive tropic tip-growing system based on nonsolvent-induced phase separation of polymer solution, where polymer precipitates as its solvent dissolves into surrounding nonsolvent. We provide a theoretical framework to predict the size and velocity of growing precipitates and demonstrate its capability of sensing the directions of gravity, mechanical contact, and light and adjusting its growing direction in response. Exploiting the embedded physical intelligence of sensing and responding to external stimuli, our soft material system achieves multiple tasks including printing 3D structures in a confined space, bypassing mechanical obstacles, and shielded transport of liquids within water.

Chemical control of phase separation in DNA solutions.

We designed a series of DNA sequences comprising a trinucleotide repeat segment and a small molecule-binding aptamer. Optimization of the DNA sequences and reaction conditions enabled chemical control of phase separation of DNA condensates. Our results demonstrate a new strategy to regulate biomolecular phase transition.

Protein solutions close to liquid-liquid phase separation exhibit a universal osmotic equation of state and dynamical behavior.

Liquid-liquid phase separation (LLPS) of protein solutions is governed by highly complex protein-protein interactions. Nevertheless, it has been suggested that based on the extended law of corresponding states (ELCS), as proposed for colloids with short-range attractions, one can rationalize not only the thermodynamics, but also the structure and dynamics of such systems. This claim is systematically and comprehensively tested here by static and dynamic light scattering experiments. Spinodal lines, the isothermal osmotic compressibility κT and the relaxation rate of concentration fluctuations Γ are determined for protein solutions in the vicinity of LLPS. All these quantities are found to exhibit a corresponding-states behavior. This means that, for different solution conditions, these quantities are essentially the same if considered at similar reduced temperature or second virial coefficient. For moderately concentrated solutions, the volume fraction ϕ dependence of κT and Γ can be consistently described by Baxter's model of adhesive hard spheres. The off-critical, asymptotic T behavior of κT and Γ close to LLPS is consistent with the scaling laws predicted by mean-field theory. Thus, the present work aims at a comprehensive experimental test of the applicability of the ELCS to structural and dynamical properties of concentrated protein solutions.

LLPS vs. LLCPS: analogies and differences.

We compare the process of Liquid-Liquid Phase Separation (LLPS) of flexible macromolecular solutions, with the Liquid-Liquid Crystalline Phase Separation (LLCPS) of semiflexible polymers and rigid filamentous colloids, which involves the formation of a liquid phase that possesses a directional alignment. Although the observed phase separation follows a similar dynamic path, namely nucleation and growth or spinodal decomposition separating two phases of dilute and concentrated compositions, the underlying physics that defines the theoretical framework of LLCPS is completely different from the one of LLPS. We review the main theories that describe the phase separation processes and relying on thermodynamics and dynamical arguments, we highlight the differences and analogies between these two phase separation phenomena, attempting to clarify the inner mechanisms that regulate those two processes. A particular focus is given to metastable phases, as these intermediate states represent a key element in understanding how phase separation works.

Extraction and determination of aflatoxin B1 in cereal samples using pH-switchable hydrophobic deep eutectic solvents followed by HPLC-FL analysis.

A quick, simple and environmentally friendly liquid phase microextraction (LPME) sample pretreatment procedure was proposed based on pH-switchable hydrophobic deep eutectic solvents (HDESs) and high performance liquid chromatography coupled with a fluorescence detector (HPLC-FL). This method was used for the quantitative study of aflatoxin B1 (AFB1) and applied to eight widely consumed cereal samples. In this method, six different DESs were synthesized and then their pH-switchability was investigated. DESs that could be switched with pH were employed for separation and preconcentration of AFB1 in cereal samples. In this method, dispersing the extractant phase in the aqueous solution and subsequent phase separation are performed only by changing the pH. Important parameters affecting extraction, such as the type of DES and its volume, concentration of KOH, volume of HCL, effect of salt and extraction time were investigated and optimum conditions were obtained. Under the optimum conditions, relative standard deviation (RSD) values for intra-day and inter-day of the method based on seven replicate measurements of 5.0 μg kg-1 of AFB1 in cereal samples were 3.3 and 5.2%, respectively. The calibration graphs were linear in the range of 0.007-20 μg kg-1 and limit of detection (LOD) was 0.002 μg kg-1. The relative recoveries of real cereal samples which have been spiked with different levels of AFB1 were 90.8-107.5%.

In situ experimental observation and determination of speciation in phase-separated mixtures of aqueous uranyl sulfate and sulfuric acid under hydrothermal conditions by Raman spectroscopy

Liquid-liquid phase-separated aqueous solutions of [UO2SO4 + H2SO4] were investigated by quantitative Raman methods at temperatures from 300 to 425 °C and 25 MPa, using quartz-capillary optical cells. UO2SO4 concentrations ranged from 0.3 to 0.8 mol·kg-1, and the ratio of SO4/U was varied from 1 to 3.5 by the addition of sulfuric acid. Phase transition temperatures were determined by direct visual observation. The Raman spectra of the homogeneous phase solutions, at temperatures just below the lower critical solution temperature, were used as an external standard to quantify the concentrations of the species present in each of the phase-separated solutions. Deconvolution of the Raman spectra in both the dense and dilute aqueous phases showed that the uranyl ion is completely associated into the complexes UO2SO40(aq) and UO2(SO4)22−(aq). UO2SO40(aq) is the dominant species at 350 °C, and its relative concentration increases further upon heating. HSO4−(aq) was found to exist in appreciable concentrations in the dense phase only at t ≥ 400 °C. The concentration of HSO4−(aq) in the dilute phase is significant at 350 °C and increases above 375 °C. Raising the temperature to 400 °C resulted in no detectable concentration of uranium or sulfate species in the dilute phase. A solid phase formed inside the uranium-rich phase of solutions of UO2SO4 without added sulfuric acid, and is presumed to be UO3·H2O(s).

Ultrathin and highly breathable electronic tattoo for sensing multiple signals imperceptibly on the skin

The ideal epidermal electronics is desired to be comfortable to wear (e.g., imperceptible and breathable), simple to prepare without losing functionality. But real epidermal electronics always trade off its functionality, comfortability, and fabrication complexity. Herein, we present an ultrathin, breathable (20.5 mg/cm2h), multifunctional electronic tattoo (e-tattoo) that can be manufactured efficiently and cheaply. Ultrathin (0.15–11.09 µm) and porous thermoplastic polyurethane (TPU) film, obtained by combining simple rod-coating and polymer solution phase separation, provide excellent breathability for the devices. Silver nanowires (AgNWs) are sprayed on the porous film surface to form a strain-insensitive conductive layer. Based on porous films, a series of functional modules such as electrophysiological sensing, epidermal moisture sensing, touch sensing (with self-signal recognition), and pressure sensing (no interference with skin sensation) are described in the work. Experiments have shown that ultrathin and breathable e-tattoos have good conformability and can work imperceptibly on the skin for a long time. This e-tattoo with excellent comprehensive performance provides new ideas in health monitoring, human-computer interaction, and tactile information detection, and contributes to the development of next-generation epidermal electronic platforms.

Emulsion imaging of a DNA nanostar condensate phase diagram reveals valence and electrostatic effects.

Liquid-liquid phase separation (LLPS) in macromolecular solutions (e.g., coacervation) is relevant both to technology and to the process of mesoscale structure formation in cells. The LLPS process is characterized by a phase diagram, i.e., binodal lines in the temperature/concentration plane, which must be quantified to predict the system's behavior. Experimentally, this can be difficult due to complications in handling the dense macromolecular phase. Here, we develop a method for accurately quantifying the phase diagram without direct handling: We confine the sample within micron-scale, water-in-oil emulsion droplets and then use precision fluorescent imaging to measure the volume fraction of the condensate within the droplet. We find that this volume fraction grows linearly with macromolecule concentration; thus, by applying the lever rule, we can directly extract the dense and dilute binodal concentrations. We use this approach to study a model LLPS system of self-assembled, fixed-valence DNA particles termed nanostars (NSs). We find that temperature/concentration phase diagrams of NSs display, with certain exceptions, a larger co-existence regime upon increasing salt or valence, in line with expectations. Aspects of the measured phase behavior validate recent predictions that account for the role of valence in modulating the connectivity of the condensed phase. Generally, our results on NS phase diagrams give fundamental insight into limited-valence phase separation, while the method we have developed will likely be useful in the study of other LLPS systems.

Analysis of polycyclic-aromatic hydrocarbons in blood serum samples obtained from oil refinery workers. Determination of occupational exposure

The present study was undertaken to evaluate the occupational exposure to PAHs of long-term workers in a specific petroleum refinery in Albania. The main route of exposure to these pollutants is via inhalation within a highly contaminated work environment. Serum samples from workers were collected and analyzed. A cloud-point extraction method was applied to isolate and concentrate PAHs from samples using Triton X-100 as the extraction agent. The phase separation of micellar serum solutions was induced with the addition of sodium chloride. The analyses were performed by gas chromatography/mass spectrometry using a capillary column HP-5MS. The PAHs analyzed were acenaphthene, acenaphthylene, anthracene, benzo[α]anthracene, benzo[α]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[g,h,i]perylen, chrysene, dibenzo[α,h]anthracene, fluorene, indeno [1,2,3-cd]pyrene, naphthalene, phenanthrene and pyrene. Mean concentration of analytes ranged from 4 ng mL−1 for fluorene and anthracene to 110 ng mL−1 for dibenzo[α,h]anthracene. The compositional profile of the PAHs was primarily 4–6 rings PAHs. Diagnostic isomeric ratios of benzo[α]anthracene/(benzo[α]anthracene + chrysene) and phenanthrene/anthracene suggest that the PAHs in the serum were primarily pyrogenic PAHs. The bioaccumulation trend of the PAHs in the workers proved conditional to their physical location within the workplace.

Effect of Acetone as Co-Solvent on Fabrication of Polyacrylonitrile Ultrafiltration Membranes by Non-Solvent Induced Phase Separation.

For the first time, the presence of acetone in the casting solutions of polyacrylonitrile (PAN) in dimethylsulfoxide or N-methyl-2-pyrrolidone was studied with regards to thermodynamical aspects of phase separation of polymeric solutions induced by contact with non-solvent (water), formation and performance of porous membranes of ultrafiltration range. The positions of the liquid equilibrium binodals on the phase diagrams of these three-component and pseudo-three-component mixtures were determined. For PAN-N-methyl-2-pyrrolidone-water glass transition curve on a ternary phase diagram was plotted experimentally for the first time. The real-time evolution of the structure of mixtures of PAN with solvents (co-solvents) upon contact with a non-solvent (water) has been studied. The thermodynamic analysis of the phase diagrams of these mixtures, together with optical data, made it possible to propose a mechanism of structure formation during non-solvent induced phase separation of different mixtures. The addition of acetone promotes the formation of a spongy layer on the membrane surface, which decreases the probability of defect formation on the membrane surface and keeps finger-like macrovoids from the underlying layers of the membrane. It was shown that the molecular weight cut-off (MWCO) of the membranes can be improved from 58 down to 1.8 kg/mol by changing the acetone content, while polymer concentration remained the same.

(Battery Division Research Award) Structure-Property Relationships: A Journey From LFP to Lithium Metal

Conceptual importance of “Matastable Phase Diagram” and “Liquid Madelung Potential” will be demonstrated by picking up some of my mechanism-solving works on LFP and lithium metal.In Li x FePO4, the ground state phase separation and metastable solid solution are energetically competitive, and the solid solution phase is induced in a non-equilibrium electrochemical reaction, playing critical role for fast kinetics. However, there had been no discussion or experimental report of the crystal structure, optical and transport properties of the metastable solid solution phase due to the extreme technical difficulties; the solid-solution phase Li x FePO4 is metastable during electrochemical process and disappears within a few seconds. We overcame this limitation by quenching Li x FePO4 (x = 2/3) at 350 °C to room temperature. This quenched phase remained stable for a couple of weeks, which enabled sufficient time to measure the several intrinsic properties, including polaron-crystallized superstructure, optical properties with emerging inter-valence charge transfer absorption, and enhanced conductivity over 103 in order.Since the Li/Li+ redox potential (E Li/Li+) positions outside of the thermodynamical potential window of the present electrolyte, suppressing side reactions is essential, which can be realized not only by kinetic suppression by SEI but also by thermodynamic stabilization viz. upshift of E Li/Li+. Remarkable improvement of Coulombic efficiency is exemplified in (locally) salt-concentrated electrolyte, where E Li/Li+ largely upshifts over 0.6 V. We revealed that the unusual upshift of E Li/Li+ is primarily dominated by Coulombic energy penalty of Li+ in the electrolytes rather than the simple Nernst equation with extremely high Li+ activity coefficient.[1] Overall energetics was verified and directly quantified by introducing the “liquid Madelung potential (E LM)” analogous to the conventional concept in solid-state science.[1] Namely, Li+ is electrostatically more stabilized by electron-localized solvents, while relatively less stabilized by electron-delocalized larger sized anion, thus decreasing the overall Coulombic energy gain of Li+ under progressive anion coordination.[1][1] N. Takenaka, S. Ko, A. Kitada, and A. Yamada, submitted (2022) Figure 1

Droplet Microfluidics for the Label-Free Extraction of Complete Phase Diagrams and Kinetics of Liquid-Liquid Phase Separation in Finite Volumes.

Liquid-liquid phase separation of polymer and protein solutions is central in many areas of biology and material sciences. Here, an experimental and theoretical framework is provided to investigate the thermodynamics and kinetics of liquid-liquid phase separation in volumes comparable to cells. The strategy leverages droplet microfluidics to accurately measure the volume ofthe dense phase generated by liquid-liquid phase separation of solutions confined in micro-sized compartments. It is shown that the measurement of the volume fraction of the dense phase at different temperatures allows the evaluation of the binodal lines that determine the coexistence region of the two phases in the temperature-concentration phase diagram. By applying a thermodynamic model of phase separation in finite volumes, it is further shown that the platform can predict and validate kinetic barriers associated with the formation of a dense droplet in a parent dilute phase, therefore connecting thermodynamics and kinetics of liquid-liquid phase separation.

Unraveling the Co-Crystallization-Charge Transport Relation in Conjugated Polymer Blends via Meniscus-Assisted Solution-Shearing.

The ability to craft the co-crystallization in conjugated polymer blends represents an important endeavor for the enhancement of charge transport. However, simple and efficient approaches to co-crystallization have yet to be realized. Herein, for the first time, a robust meniscus-assisted solution-shearing (MASS) strategy is reported to achieve co-crystallization in the poly(2,5-bis(3-hexylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C6) and poly(2,5-bis(3-decylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C10) blended films, and correlate this co-crystalline structure to the charge transport properties. The as-cast PBTTT-C6/PBTTT-C10 blends exhibit co-crystalline or phase-separated structures influenced by their molecular weights. Interestingly, confined-shearing of the initial phase-separated blended solution to MASS produces the formation of their co-crystallization. The co-crystallization kinetics accompanied by the chain packing change and optical properties are scrutinized. Finally, the resulting organic field-effect transistors (OFETs) signify the cocrystal-facilitated charge transport in the blends. Conceptually, this efficient MASS strategy in rendering the co-crystallization in conjugated polymer blends can be readily extended to other conjugated polymer blends of interest for a variety of device applications.