Liquid-liquid Phase Separation Temperature Research Articles

Liquid–liquid phase separation in aqueous solutions of poly(ethylene glycol) methacrylate homopolymers

AbstractHere, the liquid–liquid phase separation (LLPS) in aqueous solutions containing poly(ethylene glycol) (PEG) methacrylate homopolymers is reported for the first time. In this study, the thermoresponse of concentrated solutions of DEGMA60 (two ethylene glycol, EG, groups) TEGMA71 (three EG groups), OEGMA300x (4.5 in average EG groups) of varying molar masses (MM), and OEGMA50028 (nine in average EG groups) is discussed. Interestingly, the temperature of LLPS (TLLPS) is controlled by the length of the PEG side chain, the MM of the OEGMA300x and the polymer concentration. More specifically, the transition temperature decreases with: (i) Decrease in the length of the PEG side chain, (ii) increase in MM of the OEGMA300x, and increase in concentration. In addition, LLPS is also observed in mixtures of OEGMA300x with Pluronic® F127. In conclusion, these systems present a thermally induced LLPS, with the transition temperature being finely tuned to room temperature when DEGMA is used. These systems find potential use in numerous applications, varying from purification to “water‐in‐water” emulsions.

Thermodynamic and sequential characteristics of phase separation and droplet formation for an intrinsically disordered region/protein ensemble.

Liquid–liquid phase separation (LLPS) of some IDPs/IDRs can lead to the formation of the membraneless organelles in vitro and in vivo, which are essential for many biological processes in the cell. Here we select three different IDR segments of chaperon Swc5 and develop a polymeric slab model at the residue-level. By performing the molecular dynamics simulations, LLPS can be observed at low temperatures even without charge interactions and disappear at high temperatures. Both the sequence length and the charge pattern of the Swc5 segments can influence the critical temperature of LLPS. The results suggest that the effects of the electrostatic interactions on the LLPS behaviors can change significantly with the ratios and distributions of the charged residues, especially the sequence charge decoration (SCD) values. In addition, three different forms of swc conformation can be distinguished on the phase diagram, which is different from the conventional behavior of the free IDP/IDR. Both the packed form (the condensed-phase) and the dispersed form (the dilute-phase) of swc chains are found to be coexisted when LLPS occurs. They change to the fully-spread form at high temperatures. These findings will be helpful for the investigation of the IDP/IDR ensemble behaviors as well as the fundamental mechanism of the LLPS process in bio-systems.

Possibilities of heat pulse probing method for determining the phase diagram of partially-miscible liquid mixtures

In the course of this research, the liquid-liquid equilibrium line for binary solutions characterized by the upper critical solution temperature was developed by the traditional method of visual observation and the method of heat pulse probing. The objects of study were solutions of perfluoromethylcyclohexan/hexene-1 and perfluorodimethylcyclohexan/hexene-1. Heat pulse probing mode was found, which allows us to recognize the approaching to the temperature of liquid-liquid phase separation. The possibility of pulse technique with a characteristic time of several milliseconds to determine the phase state and estimate the actual concentration of solutions in opaque vessels was revealed.

Formation of Dendrimer Nanoassemblies by Oligomerization-Induced Liquid–Liquid Phase Separation

Dendrimers are hyperbranched macromolecules with applications in host-guest chemistry, self-assembly, nanocatalysis, and nanomedicine. We show that dendrimer-based globular nanoparticles are formed by using dendrimer oligomerization to isothermally induce liquid-liquid phase separation (LLPS). We first determined that LLPS of aqueous mixtures of the fourth-generation amino-functionalized poly(amido amine) dendrimer is observed by lowering temperature in the presence of sodium sulfate. In relation to LLPS, we experimentally characterized the effect of salt and dendrimer concentrations on the LLPS temperature and salt-dendrimer isothermal partitioning. Our results were theoretically examined using a two-parameter thermodynamic model. We then showed that the addition of a small amount of glutaraldehyde, which leads to the formation of soluble dendrimer oligomers by chemical cross-linking, increases the LLPS temperature. This implies that a dendrimer aqueous mixture, which is initially homogeneous at room temperature and exhibits LLPS only at relatively low temperatures, can exhibit LLPS at room temperature due to dendrimer oligomerization. The high dendrimer concentration inside the nanodroplets, produced from LLPS, accelerates dendrimer cross-linking, thereby yielding stable globular nanoparticles. These nanomaterials retain the host-guest properties of the initial dendrimers, indicating potential applications as nanocatalysts, extracting agents and drug carriers. Our work provides the basis for a new approach for obtaining dendrimer-based nanoassemblies by employing low-generation dendrimers as building blocks.

Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °C

Lithium (Li) is an important component of hydrothermal fluids, especially submarine hydrothermal fluids. Investigation of the species and ion complexation of Li+ at elevated temperature and pressure can improve our knowledge on the behavior of Li under hydrothermal conditions. In this study, in situ optical and Raman spectroscopic experiments were conducted on the Li2SO4-H2SO4-H2O system and its D2O analogue at temperatures≤420°C. An unexpected liquid-liquid phase separation (immiscibility) was observed at temperatures above 336.5°C; the aqueous phase was separated into a sulfate-rich heavy liquid phase and a sulfate-poor light liquid phase at vapor-saturation pressures. The liquid-liquid phase separation temperature decreased as the Li2SO4 concentration increased in dilute solutions (≤1.25 m), increased as the Li2SO4 concentration increased in concentrated solutions (>1.25 m), and exhibited a lower critical solution temperature (LCST) at ~336.5°C. The presence of excess H2SO4 (or D2SO4) increased the liquid-liquid phase separation temperature at a constant Li2SO4 concentration. Liquid-liquid phase separation is common in organic-bearing solutions, and LCST is considered to be a macro-scale property of polymer solutions, indicating complicated ion pairing between Li+ and SO42− at high temperature. In situ Raman spectra of the v1(SO42−) band indicated the presence of “free” SO42−, LiSO4−, possible Li2SO40 and other poly-ion associations. The Li+-SO42− association increased with increasing temperature at a constant Li2SO4 concentration. These results indicate that Li+ can form contact ion pairs with ligands despite its strong hydration tendency.In submarine hydrothermal systems, various contact ion pairs should be important Li species during the high-temperature leaching of Li from basalts (e.g., >200°C). The formation of strong and various Li+-SO42− pairs can enhance the leaching of Li because the mobility and diffusion of the Li+-SO42− complex has been reported to be stronger than that of “free” ions. During the low-temperature (e.g., <150°C) uptake of Li+ into secondary minerals (e.g., clays), free Li+ and outer-sphere ion pairs are the dominant Li+ species. Contact ion pairs are also important Li species during the hydrothermal alteration/precipitation of Li-rich minerals in pegmatite systems. Moreover, liquid-liquid phase separation was found to play important roles in the formation of low-temperature minerals (e.g., calcite). However, similar crystallization pathways have rarely been documented for inorganic systems under high temperatures. Anhydrous Li2SO4 was observed to precipitate within the dense liquid phase at ≥360°C in 1.5 m Li2SO4, confirming that the immiscible dense liquid phase can serve as a precursor for the crystallization of sulfates and other minerals under hydrothermal conditions. The possible processes for the dense-liquid-based crystallization by particle attachment can be summarized as (1) strong and reversible ion association induces liquid-liquid phase separation, (2) nucleation and crystallization within the dense liquid phase, and (3) continued growth on the surface of early formed solid phase. Submarine hydrothermal fluids often contain low-dielectric components such as methane and other organic components, which lower the dielectric constant of hydrothermal fluids and promote ion association. Therefore, liquid-liquid phase separation may occur in submarine hydrothermal fluids and can play important roles in the precipitation of sulfates and other minerals.

Liquid-liquid equilibria in demixing amines: a thermodynamic approach

Carbon dioxide (CO2) Capture from post-combustion industrial effluents will substantially contribute to the reduction of anthropogenic emission of carbon responsible for global warming. The chemical absorption of CO2 in mixed solvents (typically aqueous solution of alkanolamines [1]) is considered as a promising avenue for its capture before transportation and storage [2]. Research projects are developed in order to reduce the energy costs of the regeneration step in process working on absorption-desorption cycles. CO2 desorption requires substantial heating of the whole system containing the products resulting from chemical reactions of CO2. This presentation concerns the use of demixing amines to reduce of the energy involved in capture process. These amines show a liquid-liquid phase separation at moderately elevated temperatures [3]. Such a phase separation occurring at the output of the absorber unit will concentrate carbon in water rich phase that is the only part of the solvent that needs to be regenerated. The presentation will focus on the study of those phase separations for water + amine mixtures. It is proposed to investigate a group of piperidine derivatives and to analyse the effect of substitution in different positions on the ring. First measurements will also be reported for evaluating the influence of CO2 on the temperature of liquid-liquid phase separation. The phase diagrams will be obtained in combining two different methods. A microcalorimeter from setaram was used to determine the liquid-liquid separation temperature. The calorimeter is based on calvet principle and is able to operate in scanning temperature mode from 253 K to 393 K. it allows to measure the differential thermal flux between the measuring cell filled with the solution and the reference cell filled with water as reference fluid. The liquid-liquid separation temperature is determined by evaluating the first point when the thermal flux diverges from the baseline. Simultaneously to these calorimetric measurements, a phase equilibrium cell was developed to get optical information on the liquid-liquid separation. The binary solution was introduced in the cell, and the solution was observed during scanning of temperature. The scanning rate chosen was similar to calorimetric measurements in order to be able to compare directly the results. The separation temperature was noted when the first turbidity is observed. REFERENCES [1] L. Rodier, K. Ballerat-Busserolles, J-Y. Coxam, J. Chem. Thermodynamics, 42, 773-780 (2010). [2] L. Raynal, P-A. Bouillon, A. Gomez, P. Broutin, Chemical Engineering Journal, 10.1016/j.cej.2011.01.008 [3] Y. Coulier, K. Ballerat-Busserolles, L. Rodier, J-Y. Coxam, Fluid Phase Equilibria, 296, 206-212 (2010)

Liquid−Liquid Phase Transition of Protein Aqueous Solutions Isothermally Induced by Protein Cross-Linking

We experimentally demonstrated that liquid-liquid phase separation (LLPS) of protein aqueous solutions can be induced by isothermal protein oligomerization. This phenomenon is analogous to LLPS induced by the polymerization of small organic molecules in solution. Specifically, using glutaraldehyde for protein cross-linking, we observed the formation of protein-rich liquid droplets for bovine serum albumin and chicken egg lysozyme at 25 degrees C. These droplets evolved into cross-linked protein microspheres. If the aqueous solutions of the protein monomer do not show LLPS at temperatures lower than the oligomerization temperature, protein-rich droplets are not observed. We experimentally linked the formation of these droplets to the increase of LLPS temperature during protein oligomerization. When macroscopic aggregation competes with LLPS, a rationale choice of pH, polyethylene glycol, and salt concentrations can be used to favor LLPS relative to aggregation. Although glutaraldehyde has been extensively used to cross-link protein molecules, to our knowledge, its use in homogeneous aqueous solutions to induce LLPS has not been previously described. This work contributes to the fundamental understanding of both phase transitions of protein solutions and the morphology of protein condensed phases. It also provides guidance for the development of new methods based on mild experimental conditions for the preparation of protein-based materials.

A Calorimetry and Light Scattering Study of the Formation and Shape Transition of Mixed Micelles of EO20PO68EO20Triblock Copolymer (P123) and Nonionic Surfactant (C12EO6)

The interaction between the nonionic surfactant C12EO6 and the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO20PO68EO20 (P123) has been investigated by means of isothermal titration and differential scanning calorimetry (DSC) as well as static and dynamic light scattering (SLS and DLS). P123 self-assembles in water into spherical micelles at ambient temperatures. At raised temperatures, the DSC data revealed a sphere-to-rod transition of the P123 micelles around 60 degrees C. C12EO6 interacts strongly with P123 micelles in aqueous solution to give mixed micelles with a critical micelle concentration (cmc) well below the cmc for pure C12EO6. The presence of C12EO6 also lowers the critical micelle temperature of P123 so aggregation starts at significantly lower temperatures. A new phenomenon was observed in the P123-C12EO6 system, namely, a well-defined sphere-to-rod transition of the mixed micelles. A visual phase study of mixtures containing 1.00 wt % P123 showed that in a narrow concentration range of C12EO6 both the sphere-to-rod transition and the liquid-liquid phase separation temperature are strongly depressed compared to the pure P123-water system. The hydrodynamic radius of spherical mixed micelles at a C12EO6/P123 molar ratio of 2.2 was estimated from DLS to be 9.1 nm, whereas it is 24.1 nm for the rodlike micelles. Furthermore, the hydrodynamic length of the rods at a molar ratio of 2.2 is in the range of 100 nm. The retarded kinetics of the shape transition was detected in titration calorimetric experiments at 40 degrees C and further studied by using time-resolved DLS and SLS. The rate of growth, which was slow (>2000 s), was found to increase with the total concentration.

Comparison between Protein−Polyethylene Glycol (PEG) Interactions and the Effect of PEG on Protein−Protein Interactions Using the Liquid−Liquid Phase Transition

Phase transitions of protein aqueous solutions are important for protein crystallization and biomaterials science in general. One source of thermodynamic complexity in protein solutions and their phase transitions is the required presence of additives such as polyethylene glycol (PEG). To investigate the effects of PEG on the thermodynamic behavior of protein solutions, we report measurements on the liquid-liquid phase separation (LLPS) of aqueous bovine serum albumin (BSA) in the presence of relatively small amounts of PEG with an average molecular weight of 1450 g/mol (PEG1450) as a model system. We experimentally characterize two thermodynamically independent properties of the phase boundary: (1) the effect of PEG1450 concentration on the LLPS temperature, (2) BSA/PEG1450 partitioning in the two liquid coexisting phases. We then use a thermodynamic perturbation theory to relate the first property to the effect of PEG concentration on protein-protein interactions and the second property to protein-PEG interactions. As criteria to determine the accuracy of a microscopic model, we examine the model's ability to describe both experimental thermodynamic properties. We believe that the parallel examination of these two properties is a valuable tool for verifying the validity of existing models and for developing more accurate ones. For our system, we have found that a depletion-interaction model satisfactorily explains both protein-PEG interactions and the effect of PEG concentration on protein-protein interactions. Finally, due to the general importance of LLPS, we will experimentally show that protein-PEG-buffer mixtures can exhibit two distinct types of liquid-liquid phase transitions.

Effect of Liquid−Liquid Phase Separation on the Lamellar Crystal Morphology in PEH/PEB Blend

Optical microscopy (OM) and atomic force microscopy (AFM) were used to investigate the effect of liquid−liquid phase separation (LLPS) on the lamellar crystal morphology in a statistical copolymer blend of poly(ethylene-co-hexene) (PEH) and poly(ethylene-co-butene) (PEB). The quench depth and the time of liquid−liquid phase separation (LLPS) exhibit obvious influences on the lamellar crystal morphology. The values of lamellar long period were measured from the AFM micrographs. It is interesting to find that the lamellar long periods of the blend show minimum values with respect to the LLPS temperature, LLPS time, and the crystallization temperature. The lamellar insertion and lamellar thickening models and inclusion/exclusion of the amorphous component in the lamellar stacks are considered to cause this puzzling phenomenon.

Observation of liquid-liquid phase separation for eye lens gammaS-crystallin.

gammaS-crystallin (gammaS) is an important human and bovine eye lens protein involved in maintaining the transparency of the eye. By adding small amounts of polyethylene glycol (PEG) to the binary aqueous bovine gammaS solutions, we have observed liquid-liquid phase separation (LLPS) at -8 degrees C and revealed that, in the binary gammaS-water system, this phase transition would occur at -28 degrees C. We have measured both the effect of PEG concentration on the LLPS temperature and proteinPEG partitioning between the two liquid coexisting phases. We use our measurements of proteinPEG partitioning to determine the nature and the magnitude of the gammaS-PEG interactions and to quantitatively assess the effectiveness of PEG as a crystallizing agent for gammaS. We use our measurements of LLPS temperature as a function of protein and PEG concentration to successfully determine the location of the critical point for the binary gammaS-water system. This phase transition cannot be observed in the absence of PEG because it is inaccessible due to the freezing of the system. Our findings indicate that the effective interactions between gammaS molecules in the binary gammaS-water system are attractive. We compare the magnitude of the attraction found for gammaS with the results obtained for the other gamma-crystallins for which the critical temperature is located above the freezing point of the system. This work suggests that PEG can be used to reveal the existence of LLPS for a much wider range of binary protein-water systems than known previously.

Effect of polyethylene glycol on the liquid–liquid phase transition in aqueous protein solutions

We have studied the effect of polyethylene glycol (PEG) on the liquid-liquid phase separation (LLPS) of aqueous solutions of bovine gammaD-crystallin (gammaD), a protein in the eye lens. We observe that the phase separation temperature increases with both PEG concentration and PEG molecular weight. PEG partitioning, which is the difference between the PEG concentration in the two coexisting phases, has been measured experimentally and observed to increase with PEG molecular weight. The measurements of both LLPS temperature and PEG partitioning in the ternary gammaD-PEG-water systems are used to successfully predict the location of the liquid-liquid phase boundary of the binary gammaD-water system. We show that our LLPS measurements can be also used to estimate the protein solubility as a function of the concentration of crystallizing agents. Moreover, the slope of the tie-lines and the dependence of LLPS temperature on polymer concentration provide a powerful and sensitive check of the validity of excluded volume models. Finally, we show that the increase of the LLPS temperature with PEG concentration is due to attractive protein-protein interactions.

Relation between liquid-liquid phase separation and crystallization in isotactic and syndiotactic polypropylene solutions

The effects of the stereospecificity of a polymer chain and of the interaction in polypropylene (PP) solutions on the relation between liquid-liquid phase separation and crystallization were investigated by using an isotactic PP (i-PP) and a syndiotactic PP (s-PP) of high stereoregularity and of similar molar mass. Dialkyl phthalate was used as a solvent. A series of dialkyl phthalates with a different number of carbon atoms in the alkyl chain was employed to control the interaction between polymer and solvent. Phase transition temperatures were measured by optical microscopy with a hot stage. Liquid-liquid phase separation temperature (TL-L) in the system of i-PP and dihexyl phthalate was located below its melting temperature (Tm). However, TL-L for the s-PP system in the same solvent was elevated much above its Tm due to a decreased Tm and increased TL-L. The reduced solubility of s-PP is primarily attrib- uted to enhanced hydrophobicity arising from alternate positioning of the methyl groups along the polymer chain. As the length of the alkyl chain in the phthalate increases, TL-L decreases significantly and Tm decreases slightly, resulting in the value of TL-L shifting below that of Tm for the solution of s-PP and dinonyl phthalate. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 159-163, 1998

Nonequilibrium liquid-liquid phase separation in crystallizable polymer solutions

The relation between liquid-liquid phase separation and crystallization was investigated by applying a systematic change in the interaction in isotactic polypropylene (i-PP) solutions with a proper selection of solvents. A series of dialkyl phthalates, with a different number of carbon atoms in the alkyl chain, was usded to control the solvent quality. The liquid-liquid phase separation temperature decreased remarkably when the interaction became favorable while the melting point curve remained constant. As the result of this systematic change in polymer-solvent interaction, the liquid-liquid phase separation was observed under nonequilibrium conditions below the equilibrium liquid-solid transition