Phase Separation Temperature Research Articles

Physical Gels of Atactic Poly(N-isopropylacrylamide) in Water: Rheological Properties and As-Derived Spinodal Temperature

Aqueous solutions of atactic poly(N-isopropylacrylamide) (a-PNIPAM) undergo complex phase transitions at 20-33 °C. In this temperature range, the a-PNIPAM solution exhibits a phase behavior of lower critical solution temperature at the binodal temperature (Tb) and physical gel formation at the gel temperature (Tgel). On slow heating of the one-phase solution containing linear a-PNIPAM chains, branched chains are gradually developed to proceed with the physical gelation before phase separation considering that Tgel < Tb. Thus, the phase separation temperature determined from the conventional approaches, either by turbidity to derive the Tb or by scattering to derive the spindal temperature (Ts) from the Ornstein-Zernike analysis, is strictly the transition temperature associated with the a-PNIPAM hydrogel (or highly branched chains newly developed at elevated temperatures), rather than the initial a-PNIPAM solution prepared. Herein, the spinodal temperatures of a-PNIPAM hydrogels (Ts,gel) of various concentrations were determined from rheological measurements at a heating rate of 0.2 °C/min. Analyses of the temperature dependence of loss modulus G″ and storage modulus G' give rise to the Ts,gel, based on the Fredrickson-Larson-Ajji-Choplin mean field theory. In addition, the specific temperature (T1) above which the one-phase solution starts to dramatically form the aggregated structure (e.g., branched chains) was also derived from the onset temperature of G' increase; this is because as solution temperature approaches the spinodal point, the concentration fluctuations become significant, which is manifested with the elastic response to enhance G' at T > T1. Depending on the solution concentration, the measured Ts,gel is approximately 5-10 °C higher than the derived T1. On the other hand, Ts,gel is independent of solution concentration to be constant at 32.8 °C. A phase diagram of the a-PNIPAM/H2O mixture is thoroughly constructed together with the previous data of Tgel and Tb.

Synthesis, Characterization, Conformation in Solution, and Thermoresponsiveness of Polymer Brushes of methoxy[oligo (propylene glycol)-block-oligo(ethylene glycol)]methacrylate and N-[3-(dimethylamino)propyl]methacrylamide Obtained via RAFT Polymerization

The thermo- and pH-responsive polymer brushes based on methoxy[oligo(propyleneglycol)8-block-oligo(ethyleneglycol)8]methacrylate with different concentrations of N-[3-(dimethylamino)propyl]methacrylamide (from 0% to 20%) were synthesized via RAFT polymerization. The "grafting-through" approach was used to prepare the low-molar-mass dispersion samples (Mw/Mn ≈ 1.3). Molar masses and hydrodynamic characteristics were obtained using static and dynamic light scattering and viscometry. The solvents used were acetonitrile, DMFA, and water. The molar masses of the prepared samples ranged from 40,000 to 60,000 g·mol-1. The macromolecules of these polymer brushes were modeled using a prolate revolution ellipsoid or a cylinder with spherical ends. In water, micelle-like aggregates were formed. Critical micelle concentrations decreased with the content of N-[3-(dimethylamino)propyl]methacrylamide. Molecular brushes demonstrated thermo- and pH-responsiveness in water-salt solutions. It was shown that at a given molecular mass and at close pH values, the increase in the number of N-[3-(dimethylamino)propyl]methacrylamide units led to an increase in phase separation temperatures.

Raumzeitliche Propagation eines minimalen katalytischen RNA‐Netzwerkes in GUV‐Protozellen durch Temperaturzyklen und Phasenseparation

AbstractKompartimentierung ist der Schlüssel zu vielen zellulären Prozessen und kritische Bedingung für minimales Leben. In Zellen sorgt eine komplexe Chemie dafür, Biomoleküle zur richtigen Zeit am richtigen Ort zusammenzubringen oder sie zu separieren. Durch die Selbstorganisation von Lipiden, Nukleinsäuren und Proteinen entstehen hochspezialisierte Mikroumgebungen mit funktionalen Grenzflächen und Schnittstellen. Wir stellen hier auf Basis von reversibler RNA‐basierter Flüssig‐Flüssig‐Phasenseparation (LLPS) in Riesenvesikeln (GUVs) ein effizientes System zur funktionalen Kompartimentierung vor. Dieses ist in der Lage, eine RNA‐basierte enzymatische Reaktion mithilfe von Frost‐Tau‐(FT)‐Zyklen innerhalb einer Population von GUVs zu propagieren. Wir zeigen, dass eine solche enzymatische Reaktion dadurch beschleunigt werden kann, dass die Reaktanden in der kondensierten RNA‐reichen Phase aufkonzentriert werden. Die gleichmäßige Verteilung von RNA‐Substraten im dekondensierten Zustand ermöglicht den Austausch zwischen den Vesikeln während des Einfrierens und Auftauens. In der vorliegenden Studie wurde untersucht, inwieweit ein minimales reversibles Phasenseparationssystem in Lipidvesikeln raumzeitliche Kontrolle in zyklischen Prozessen erlaubt, so wie es in Minimalzellen erforderlich wäre.

Spatiotemporal Propagation of a Minimal Catalytic RNA Network in GUV Protocells by Temperature Cycling and Phase Separation.

Compartmentalization is key to many cellular processes and a critical bottleneck of any minimal life approach. In cells, a complex chemistry is responsible for bringing together or separating biomolecules at the right place at the right time. Lipids, nucleic acids and proteins self-organize, thereby creating boundaries, interfaces and specialized microenvironments. Exploiting reversible RNA-based liquid-liquid phase separation (LLPS) inside giant unilamellar vesicles (GUVs), we present an efficient system capable of propagating an RNA-based enzymatic reaction across a population of GUVs upon freezing-thawing (FT) temperature cycles. We report that compartmentalization in the condensed RNA-rich phase can accelerate such an enzymatic reaction. In the decondensed state, RNA substrates become homogeneously dispersed, enabling content exchange between vesicles during freeze-thawing. This work explores how a minimal reversible phase separation system in lipid vesicles could help to implement spatiotemporal control in cyclic processes, as required for minimal cells.

Thermo-switchable hydrophobic solvents formulated with weak acid and base for greener separation processes

Switchable solvents are changing properties when exposed to an external stimulus. As example, for thermomorphic multiphasic system (TMS), temperature changes can induce phase separations. Aqueous systems presented here are formulated with a carboxylic acid (weak acid) and an amphiphilic tertiary amine (weak base). They show thermo-switchable hydrophobicity and after separation, the weak acid and base are mainly found in the organic phase while the aqueous phase is mostly composed of water, up to 99 wt%. The phase separation temperature (cloud point) can be tuned from 20 to 80 °C depending on the choice of the carboxylic acid and on the acid: base molar ratio. A collection of saturated aliphatic carboxylic acids and benzoic acid derivatives have been investigated to evaluate the impact of different physico-chemical properties on the cloud point. The octanol/water partition coefficient (log P) and acidic constant (pKa) were identified as key physico-chemical properties to adjust the phase separation temperature. Finally, as illustration of the efficiency of these systems to remove a chemical from water, it has been shown that 99 % extraction of an anionic dye, methyl orange, could be achieved with most of the tested TMS.

Preparation of monodispersed SiO2-Al2O3 microspheres based on fly ash by thermally induced phase separation

In this study, we successfully prepared fly ash-based SiO2-Al2O3 microspheres using phase separation followed by acid leaching. Thermal analysis and X-ray diffraction were used to identify the optimal temperature range of heat treatment. The chemical composition and surface property of the microspheres were analyzed using X-ray fluorescence and contact angle measurements, and scanning electron microscopy was used to characterize the appearance of the microspheres. The results showed that the SiO2-Al2O3 microspheres were composed of 60–80 wt% SiO2 and 10–12 wt% Al2O3 with a uniform particle size, a hydrophilic surface, and high alkali resistance. Heat treatment studies revealed that the phase separation temperature should not exceed 900 °C to avoid crystallization. The mean particle size of the SiO2-Al2O3 microspheres decreased with an increase in the heat treatment temperature. Additionally, observing the evolution of the phase structure at 800 °C showed that there was fusion between the SiO2-Al2O3-enriched phases via interfacial tension in the later stage, resulting in larger spherical phase structures. Further, an increase in the Al2O3, Fe2O3, and CaO composition decreased the SiO2-Al2O3 microspheres particle size, and therefore inhibited phase separation.

Metastable phase separation and duplex metallic glass formation of liquid Zr&lt;sub&gt;35&lt;/sub&gt;Al&lt;sub&gt;23&lt;/sub&gt;Ni&lt;sub&gt;22&lt;/sub&gt;Gd&lt;sub&gt;20&lt;/sub&gt; alloy

Duplex metallic glass with two amorphous phases has been extensively investigated for desirable strength and plasticity. In this paper, the metastable phase separation and dual amorphous phase formation of liquid Zr&lt;sub&gt;35&lt;/sub&gt;Al&lt;sub&gt;23&lt;/sub&gt;Ni&lt;sub&gt;22&lt;/sub&gt;Gd&lt;sub&gt;20&lt;/sub&gt; alloy under substantial undercooling condition and rapid cooling condition are studied by drop tube technology. The equilibrium solidification structure consists of three crystalline phases, while the critical undercooling temperature of metastable phase separation is determined to be 516 K (0.37&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;L&lt;/sub&gt;). The separated Zr-rich liquid phase undergoes amorphous transition and becomes amorphous AM-Zr phase with the composition of Zr&lt;sub&gt;45&lt;/sub&gt;Ni&lt;sub&gt;23&lt;/sub&gt;Al&lt;sub&gt;23&lt;/sub&gt;Gd&lt;sub&gt;9&lt;/sub&gt; when alloy undercooling is increased to 624 K (0.45&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;L&lt;/sub&gt;). After that, the Gd-rich liquid phase forms amorphous AM-Gd phase with the composition of Gd&lt;sub&gt;39&lt;/sub&gt;Al&lt;sub&gt;22&lt;/sub&gt;Ni&lt;sub&gt;20&lt;/sub&gt;Zr&lt;sub&gt;19&lt;/sub&gt; at larger undercooling of 714 K (0.52&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;L&lt;/sub&gt;). With the increase of liquid undercooling and cooling rate, the kinetic mechanism of metastable phase separation changes from nucleation and growth type to spinodal decomposition type, and consequently the microstructure of dual amorphous phases transforms from a spherical morphology to a reticular structure. The average hardness and Young’s modulus, which are influenced by free volume, phase volume fraction and structure of dual amorphous phases, exhibit a complex variation of first increasing and then decreasing with the decrease of alloy droplet size. The formation of dual amorphous phases is in favor of the energy dissipation and the generation of multiple shear bands during mechanical compression, which improves the plasticity for this kind of amorphous alloy.

Multi-scale molecular simulation of random peptide phase separation and its extended-to-compact structure transition driven by hydrophobic interactions.

Intrinsically disordered proteins (IDPs) often undergo liquid-liquid phase separation (LLPS) and form membraneless organelles or protein condensates. One of the core problems is how do electrostatic repulsion and hydrophobic interactions in peptides regulate the phase separation process? To answer this question, this study uses random peptides composed of positively charged arginine (Arg, R) and hydrophobic isoleucine (Ile, I) as the model systems, and conduct large-scale simulations using all atom and coarse-grained model multi-scale simulation methods. In this article, we investigate the phase separation of different sequences using a coarse-grained model. It is found that the stronger the electrostatic repulsion in the system, the more extended the single-chain structure, and the more likely the system forms a low-density homogeneous phase. In contrast, the stronger the hydrophobic effect of the system, the more compact the single-chain structure, the easier phase separation, and the higher the critical temperature of phase separation. Overall, by taking the random polypeptides composed of two types of amino acid residues as model systems, this study discusses the relationship between the protein sequence and phase behaviour, and provides theoretical insights into the interactions within or between proteins. It is expected to provide essential physical information for the sequence design of functional IDPs, as well as data to support the diagnosis and treatment of the LLPS-associated diseases.

Temperature-Responsive Deep Eutectic Solvents for Highly Selective Separation of 5-Hydroxymethylfurfural from Reaction Mixture

5-Hydroxymethylfurfural (HMF) is a key biobased platform compound for the production of high-value chemicals and fuels. However, separation and purification of HMF is currently the bottleneck for HMF production. In this work, a novel class of temperature-responsive deep eutectic solvent (DES)–water systems have been explored to selectively separate HMF from reaction mixtures. The fructose dehydration reaction was conducted in homogeneous DES–H2O systems, and then, the produced HMF was migrated to the DES-rich phase while the unreacted fructose was retained in the H2O-rich phase upon cooling. Thus, selective separation of HMF was realized. It was found that water–water and DES–DES interactions predominate over DES–water interactions during cooling, thus resulting in upper critical solution temperature phase separation. Under optimal conditions, the partition coefficient and separation factor of HMF could reach up to 78 and 609, respectively, which is about 5 and 13 times those reported in ionic liquid-based aqueous biphasic systems. Furthermore, HMF could be removed from the DES-rich phase, giving a high recovery efficiency of 69%, which is much higher than the best value reported in the literature. At the same time, DES was regenerated and reused in the next process, and no obvious decrease in partition coefficient of HMF was observed after six cycles.

Experimental study of phase separation in dynamically asymmetric unentangled polymer blend.

We examined a phase separation process of a dynamically asymmetric blend of unentangled polyisoprene (PI) and poly(4-ethylstyrene) (PC2St) exhibiting the upper critical solution temperature. PI having the type-A dipole was the dielectrically active fast component, whereas PC2St was the dielectrically inert slow component whose dynamics can be detected by rheological measurements. To precisely model the phase separation process, it is important to estimate the composition dependence of the mobility, which is needed to describe the phase separation dynamics. For that purpose, we conducted dielectric and rheological measurements to determine the friction coefficient of each component in a homogeneous state sufficiently above the phase separation temperature. The temperature dependence of the friction coefficient of each component was reasonably expressed by the Williams-Landel-Ferry equation. Extrapolating this dependence obtained for blends of various compositions to the test temperature T* below the phase separation temperature, we were able to estimate the friction coefficient of the chain at T* as a function of the composition. This friction coefficient was then used to determine the mobility Λ defined for the material fluxes at T*. The time-dependent Ginzburg-Landau (TDGL) equation incorporating this Λ well described the experimentally observed phase separation dynamics. In particular, the 2D TDGL simulation with this Λ qualitatively captured the phase-separated structure observed with the optical microscope as well as broad dielectric mode distribution of the blend at T*.

Liquid-liquid phase separation in borosilicate glass enriched in MoO3 – experimental investigations and thermodynamic calculations

Phase separation in sodium borosilicate glasses containing molybdenum oxide has been studied in a compositional range of interest for nuclear glasses. Two series of quaternary compositions (63.5SiO2-19.6Na2O-16.9B2O3)1-x(MoO3)x with 0 ≤ x ≤ 3 mol.% MoO3 have been synthesized and characterized, by a range of complementary experimental techniques both in situ in temperature, by viscometry and hot stage SEM, and ex-situ, by HRTEM, PXRD, EPMA and dissolution calorimetry. The phase separation temperatures between silicate and molybdenum oxide rich liquids were determined for each composition. Molybdenum oxide solubility limits were established for quenched and annealed glasses.For molybdenum oxide contents exceeding these limits, crystalline sodium mono-molybdate precipitates in the glasses as shown by XRD results and the fractions of precipitates were indirectly quantified by MoO3 mole balance and enthalpy balance relying on solution calorimetry experiments. The experimental results were compared with thermodynamic calculations performed with Thermo-Calc software and a CALPHAD database of the SiO2-Na2O-MoO3 ternary system. The ternary model allows the calculation of the nature and quantity of the precipitated phases in reasonable agreement with the experiments, even if, in the current state of development of the thermodynamic database, the absence of boron restricts the relevance of the calculations. Thus, for the construction of a predictive thermodynamic calculation tool, the addition of boron to the database is the most promising prospect.

Effect of natural convection and diffusion on liquid-liquid phase separation behaviors of partially miscible solutions with lower critical solution temperature

Partially miscible solutions with lower critical solution temperature (LCST) have significant potential in improving the cooling performance of microchannel heat sinks, reducing pressure drop, and ensuring stable operation of the cooling system. Thereby, it is essential and meaningful to clearly understand the liquid-liquid phase separation process driven by natural convection and diffusion to enhance the cooling performance in microchannels further. In this paper, the liquid-liquid phase separation behaviors of 2-Butoxyethanol/water solutions in a slit cavity were visually investigated. Moreover, the effect of driven force was discussed on the temperature distribution, motion of boundaries and phase separation rate. Furthermore, the effect of the mass fraction was discussed on the phase separation temperature range and phase separation rate. The results proved that the phase separation rate was kept at 0.39%·s−1 on average in the whole slit cavity by the natural convection, whereas the driving force of diffusion was so weak that the phase separation rate rapidly decreased along the vertical direction. That means reasonable enhancements of the disturbance in the microchannel could significantly increase the phase separation rate. Moreover, the phase separation rate increased with an increase in the mass fraction, and the solution with the best cooling performance could be found at 27.4%≤ω2-BE≤35%. The results are expected to provide theoretical guidance to prepare solutions with suitable phase separation temperature range and excellent cooling performance.

Mechanistic Insights into the Phase Separation Behavior and Pathway‐Directed Information Exchange in all‐DNA Droplets

AbstractLiquid‐liquid phase separation provides a versatile approach to fabricating cell‐mimicking coacervates. Recently, it was discovered that phase separation of single‐stranded DNA (ssDNA) allows for forming protocells and microgels in multicomponent systems. However, the mechanism of the ssDNA phase separation is not comprehensively understood. Here, we present mechanistic insights into the metal‐dependent phase separation of ssDNA and leverage this understanding for a straightforward formation of all‐DNA droplets. Two phase separation temperatures are found that correspond to the formation of primary nuclei and a growth process. Ca2+ allows for irreversible, whereas Mg2+ leads to reversible phase separation. Capitalizing on these differences makes it possible to control the information transfer of one‐component DNA droplets and two‐component core–shell protocells. This study introduces new kinetic traps of phase separating ssDNA that lead to new phenomena in cell‐mimicking systems.

Mechanistic Insights into the Phase Separation Behavior and Pathway-Directed Information Exchange in all-DNA Droplets.

Liquid-liquid phase separation provides a versatile approach to fabricating cell-mimicking coacervates. Recently, it was discovered that phase separation of single-stranded DNA (ssDNA) allows for forming protocells and microgels in multicomponent systems. However, the mechanism of the ssDNA phase separation is not comprehensively understood. Here, we present mechanistic insights into the metal-dependent phase separation of ssDNA and leverage this understanding for a straightforward formation of all-DNA droplets. Two phase separation temperatures are found that correspond to the formation of primary nuclei and a growth process. Ca2+ allows for irreversible, whereas Mg2+ leads to reversible phase separation. Capitalizing on these differences makes it possible to control the information transfer of one-component DNA droplets and two-component core-shell protocells. This study introduces new kinetic traps of phase separating ssDNA that lead to new phenomena in cell-mimicking systems.

Amphiphile regulated ionic-liquid-based aqueous biphasic systems with tunable LCST and extraction behavior

Ionic liquid (IL)/H2O mixtures with tunable lower critical solution temperature (LCST) behavior exhibit tantalizing prospect in the field of liquid-liquid phase separation and purification. Herein, different types of amphiphiles were evaluated for the facile regulation of IL ([P4444][DMBS]) based aqueous biphasic systems (ABSs). Interestingly, the addition of zwitterionic 3-(1-dodecyl-3-imidazolio) propanesulfonate (DIPS) remarkably increases the phase separation temperature of IL aqueous solution, while the addition of anionic sodium dodecyl benzene sulfonate (SDBS) and dodecyl-benzenesulphonic acid (DBSA) results in decreasing of the phase separation temperature. The tunable phase separation temperature ranges from 10 to 90 °C, which almost cover the full usable temperature range of ABSs. The regulation mechanism of amphiphile additives on the LCST behavior of IL/H2O mixtures was investigated through isothermal titration calorimetry, 1H NMR spectroscopy and molecular dynamics simulations. Briefly, the addition of zwitterionic DIPS increased LCST through electrostatic shielding effect, while the addition of anionic SDBS and DBSA decreased LCST through ion exchange effect. As a proof of concept, the amphiphile regulated ABSs were demonstrated to selectively separate aliphatic and aromatic amino acids.

Smart Protein Refolding System Based on UCST-Type Ureido Polymers.

We have reported that ureido polymers exhibit upper critical solution temperature (UCST)-type phase behavior in solution, which is the opposite of lower critical solution temperature (LCST)-type behavior. Furthermore, UCST-type ureido polymers undergo liquid-liquid phase separation (LLPS) upon cooling rather than the liquid-solid phase transition of the typical LCST-type polymers. In this study, ureido polymers with hydrophobic groups were prepared to evaluate the effects of cooling-induced LLPS of UCST-type polymers on refolding of proteins. When protein was heated with a ureido polymer functionalized with undecyl groups, aggregation of the protein was prevented. Subsequent cooling incubation resulted in the spontaneous release of the protein from the polymer. The released protein had enzymatic activity, suggesting that the protein refolded properly. Interestingly, efficient refolding was observed when the solution of the UCST-type ureido polymer and protein was incubated at around the phase separation temperature of the polymer, implying that cooling-induced LLPS of the polymer enhanced the release of the protein. Additionally, by centrifugation at 4 °C, the refolded protein was readily separated from the ureido polymers, which precipitated upon cooling.

Natural Deep Eutectic Solvent-Based Dispersive Liquid-Liquid Microextraction Coupled with Direct Analysis in Real Time Mass Spectrometry: A Green Temperature-Mediated Analytical Strategy.

Green analytical chemistry (GAC) represents a rapidly growing research field that aims at developing novel analytical approaches with minimal consumption of hazardous reagents and solvents. The current study reports on a GAC methodology exploiting the unique physicochemical properties of natural deep eutectic solvents (NADESs), a supposedly environmentally friendly class of solvents. Based on a temperature-mediated strategy, the NADESs were manipulated to undergo multiple phase transitions for favorable functionality and performance. As proof-of-concept demonstrations, both hydrophobic and hydrophilic NADESs were prepared for the extraction and analysis of eight phthalate esters in aqueous samples (food simulants) and three aflatoxins in oily samples (edible oils), respectively. NADES-based dispersive liquid-liquid microextraction (DLLME) was employed to achieve high-efficiency sample pretreatment. Afterward, the NADESs were transformed from liquids into solids by tuning the peripheral temperature for a convenient phase separation from the sample matrices. The solidified NADES extracts were melted and vaporized at elevated temperatures by transmission-mode direct analysis in real time (DART) for further quadrupole-Orbitrap high-resolution mass spectrometry (Q-Orbitrap HRMS) analysis. The developed protocol was validated, achieving good repeatability with relative standard deviations (RSDs) of less than 9% and satisfactory sensitivity with limits of detection (LODs) and quantitation (LOQs) ranging from 0.1 to 0.8 and 0.2 to 2.0 μg/kg, respectively. The greenness of the analytical methodology was assessed with the calculated scores of 0.66 and 0.57 for the hydrophobic and hydrophilic NADES-based protocols, respectively. The method was applied to marketed samples, highlighting the great potential for green chemical analysis.

Membrane Manipulation of Giant Unilamellar Polymer Vesicles with a Temperature-Responsive Polymer.

Understanding the complex behavior and dynamics of cellular membranes is integral to gain insight into cellular division and fusion processes. Bottom-up synthetic cells are as a platform for replicating and probing cellular behavior. Giant polymer vesicles are more robust than liposomal counterparts, as well as having a broad range of chemical functionalities. However, the stability of the membrane can prohibit dynamic processes such as membrane phase separation and division. Here, we present a method for manipulating the membrane of giant polymersomes using a temperature responsive polymer. Upon elevation of temperature deformation and phase separation of the membrane was observed. Upon cooling, the membrane relaxed and became homogeneous again, with infrequent division of the synthetic cells.

Membrane Manipulation of Giant Unilamellar Polymer Vesicles with a Temperature‐Responsive Polymer

AbstractUnderstanding the complex behavior and dynamics of cellular membranes is integral to gain insight into cellular division and fusion processes. Bottom‐up synthetic cells are as a platform for replicating and probing cellular behavior. Giant polymer vesicles are more robust than liposomal counterparts, as well as having a broad range of chemical functionalities. However, the stability of the membrane can prohibit dynamic processes such as membrane phase separation and division. Here, we present a method for manipulating the membrane of giant polymersomes using a temperature responsive polymer. Upon elevation of temperature deformation and phase separation of the membrane was observed. Upon cooling, the membrane relaxed and became homogeneous again, with infrequent division of the synthetic cells.

Controlling phase separation behavior of thermo-responsive ionic liquids through the directed distribution of anionic charge

Thermoresponsive ionic liquids (TR-ILs) are room temperature liquid salt electrolytes with dynamic physical properties which have been hailed as potential solutions to inefficiencies in energy storage and material separations. That potential is hindered by the sensitivity of TR-IL phase separation to chemical structure. An accurate assessment of the effect of ion structure on molecular bonding is required for rational design as bonding changes translate to bulk material behavior. We systematically modify the structure of TR-ILs which exhibit either lower critical solution temperature (LCST) or upper critical solution temperature (UCST) phase separation to isolate the effect of specific types of bonding on eight tetrabutylphosphonium benzoate derived ILs through COSMO-RS sigma profile analysis and variable temperature (VT) 1H NMR. Our results reveal that in addition to Hydrogen bonding, cation conformational flexibility, functional group availability, cation–anion coordination strength and directionality of hydrogen bonds play key roles in governing the IL phase separation behavior. © 2017 Elsevier Inc. All rights reserved.