Liquid-liquid Demixing Research Articles

Role of molecular complexation in solid-liquid phase diagram of poly-ethylene oxide/urea mixture

Thermodynamic phase diagram of polyethylene oxide (PEO)/urea blend has been investigated with emphasis on the formation of induced crystals driven by molecular complexation. Of particular interest is that the complexed α crystal is more stable than those of neat constituents. The experimental solid-liquid phase diagram of PEO/urea blends has been analyzed in the context of the combined Flory-Huggins free energy for liquid-liquid demixing and phase field free energy of crystal solidification. The self-consistently calculated coexistence lines of the PEO/urea mixture exhibit an azeotrope type, accompanied by eutectoid reactions in the submerged regions, wherein the complexed α crystal decomposes into two coexistence crystalline phases. These coexistence crystalline phases were further analyzed by means of polarized optical microscopy, Fourier transform infrared spectroscopy, and wide-angle x-ray diffraction. A possible phase diagram of the complexed PEO/urea is constructed and discussed.

Preparation of Interconnected Biomimetic Poly(vinylidene fluoride-co-chlorotrifluoroethylene) Hydrophobic Membrane by Tuning the Two-Stage Phase Inversion Process.

A facile strategy was applied for poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) hydrophobic membrane preparation by tuning the two-stage phase inversion process. The exposure stage was found to benefit the solid-liquid demixing process (gelation/crystallization) induced by the solvent evaporation and the subsequent phase inversion induced by immersion benefit the liquid-liquid demixing. It was confirmed that the electrospun nanostructure-like biomimetic surface and interconnected pore structure can be expected by controlling the exposure duration, and 300 s was considered as the inflection point of exposure duration for PVDF-CTFE membrane through which a tremendous variation would show. The micro/nanohierarchical structure in the membrane surface owing to the crystallization of PVDF-CTFE copolymer was responsible for the improvement of membrane roughness and hydrophobicity. Meanwhile, the interconnected pore structure in both the surface and the cross-section, which were formed because of the crystallization process, offers more mass transfer passages and enhances the permeate flux. The membrane then showed excellent MD performance with high permeate flux, high salt rejection, and relatively high stability during a 48 h continuous DCMD operation, according to the morphology, pore structure, and properties, which can be a substitute for hydrophobic membrane application.

Development and Characterization of Polysulfone/Polyvinylidene Flouride Blend Membrane Induced by Delayed Liquid-Liquid Demixing

Polysulfone (PSf)-Polyvinylidene fluoride (PVDF) membranes were fabricated via phase inversion method and immersion precipitation technique. In particular, the effect of varied amount of NMP addition into coagulation bath on permeability, mechanical properties, chemical resistance and thermal stability of membranes were investigated. The presence of solvent in coagulation bath caused delayed liquid-liquid demixing that caused increasing chance of disoriented interactions in PSf/PVDF blend membrane thus larger pore and dominated macrovoids membranes resulted. It was found that the increase of solvent addition lead to increasing of flux and decreasing of mechanical strength whereas a remarkably and enhanced chemical resistance has been achieved which showed excellent resistance in H 2 SO 4 but degraded upon exposure to a concentration of 15% NaOH solution. Furthermore, TGA analysis revealed that the membrane exhibit improved thermal stability while the morphology of membrane showed the formation of asymmetry structure.

Transferable thin films with sponge-like porous structure via improved phase separation

Abstract This study is the first to report highly efficient production of homogeneous large-scale thin polymer films with a sponge-like porous structure via an improved phase separation method. A mixture of tetrahydrofuran and methanol, which is used as a highly volatile solvent/nonsolvent pair, is crucial to induce phase separation and thus determines the resulting structure. The obtained porous structure is composed of intermingled sticks in a size range of 50–100 nanometers and bumps with a diameter of about 200 nanometers, revealing a morphology that resembles a bird's nest. The pore size and porosity of the porous film are finely controlled by varying the mixture composition. Furthermore, by employing a water-soluble interlayer before the phase separation process, the obtained porous film, even with extremely large area, can be easily detached from solid substrates without damaging the film. Notably, it possesses a skin-free layer at the bottom side where it contacts the interlayer surface. The formation mechanism of the sponge-like porous structure was studied and it was found that the progressive enrichment of methanol during the evaporation process is favorable for absorbing water vapor from the air into the solution, which is responsible for phase separation. In addition, a water-miscible mixture of solvent and nonsolvent, which can delay the liquid-liquid demixing process, is essential for the formation of the sponge-like porous structure.

A Concentration-Dependent Liquid Phase Separation Can Cause Toxicity upon Increased Protein Expression.

SummaryMultiple human diseases are associated with a liquid-to-solid phase transition resulting in the formation of amyloid fibers or protein aggregates. Here, we present an alternative mechanism for cellular toxicity based on a concentration-dependent liquid-liquid demixing. Analyzing proteins that are toxic when their concentration is increased in yeast reveals that they share physicochemical properties with proteins that participate in physiological liquid-liquid demixing in the cell. Increasing the concentration of one of these proteins indeed results in the formation of cytoplasmic foci with liquid properties. Demixing occurs at the onset of toxicity and titrates proteins and mRNAs from the cytoplasm. Focus formation is reversible, and resumption of growth occurs as the foci dissolve as protein concentration falls. Preventing demixing abolishes the dosage sensitivity of the protein. We propose that triggering inappropriate liquid phase separation may be an important cause of dosage sensitivity and a determinant of human disease.

Lysozyme Solubility and Conformation in Neat Ionic Liquids and Their Mixtures with Water

The room temperature solubility of a number of model proteins is assessed for a diverse set of neat ionic liquids (ILs). For two soluble protein-IL pairs, lysozyme in [C2MIM][EtSO4] (1-ethyl-3-methylimidazolium ethylsulfate) and in [C2,4,4,4P][Et2PO4] (tributyl(ethyl)phosphonium diethylphosphate), protein solubility and structure at various temperatures are probed by dynamic light scattering (assessing dissolved molecular size), turbidimetry (reflecting degree of solubility), and Fourier transform infrared spectroscopy (uncovering helical secondary structure). As compared to aqueous environments, [C2,4,4,4P][Et2PO4] thermally stabilizes protein size and secondary structure while [C2MIM][EtSO4] does the opposite. Lysozyme denatured in [C2MIM][EtSO4] does not aggregate, presumably due to an absence of hydrophobic interactions, and the denaturation appears thermally reversible. Both ILs at room temperature are miscible with water in all proportions, but to create the corresponding ternary mixtures with protein, the order of mixing is important. Mixed to avoid additions of water to IL-dissolved protein, stable solutions are obtained with [C2MIM][EtSO4] at all solvent compositions. When water is added to IL-rich solutions, liquid-liquid demixing is noted.

Processing and characterization of polyethersulfone wet-spun nanocomposite fibres containing multiwalled carbon nanotubes

Novel semi-conductive fibres from multiwalled carbon nanotubes (MWCNT) based-polyethersulfone (PES) have been produced by wet spinning insight of incorporation in composite matrix. N-methyl-2-pyrrolidone (NMP) was chosen as dispersing medium for MWCNT by sonication and as solvent for PES. MWCNT reinforced-PES fibres were spun into water coagulation bath with an observed instantaneous liquid-liquid demixing. After washing and drying steps, fibres are either directly characterized or annealed at 250°C during 15min and 24h prior to characterization. Scanning electron microscope (SEM) micrographs performed in each configuration disclose presence of macrovoids, pores and empty spaces inside fibres before thermal annealing whereas after thermal annealing, fibres display a cohesive and continuous morphology. A significant mechanical properties improvement of the wet-spun fibres is noticed by rising annealing time. Transmission electron microscope (TEM) investigations have also been carried out and reveal a two phases microstructure in unannealed fibres with a separation between a PES-rich continuous phase and NMP-rich nodules containing exclusively MWCNT. TEM images suggest also thermal annealing process allows solvent evaporation, MWCNT aggregation and a conductive nanofillers network formation in PES nanocomposite fibres. Electrical measurement in unannealed fibres indicate a deficiency of conductive character between 0.25 and 2wt.% MWCNT whereas a lowering electrical percolation threshold is achieved in fibres by increasing annealing time, around 1.5 and 1wt.% MWCNT for respectively a 15min and 24h thermal annealing. Influence of MWCNT sonication duration on electrical conductivity is also examined showing a gradually reduction of fibres' electrical conductivity by dispersion time increasing until losing their semi-conductive state. A dispersion analysis let suppose that a whole MWCNT agglomerates network is split in smaller but denser clusters which are dispersed and taken away from each other during sonication, which causes the conductive path rupture.

Physical Principles that Govern the Sequence-Encoded Phase Behavior of Intrinsically Disordered Block-Copolymeric Proteins

Many intrinsically disordered proteins (IDPs) and sequences with long disordered regions undergo reversible phase transitions such as liquid-liquid demixing or sol-gel transitions to form dense liquids or gel-like phases. Such phases underlie the formation of membraneless compartments within cells. Block-copolymeric disordered regions appear to be necessary and sufficient to drive phase separation in many systems. The interfacial tension between well-mixed and dense phases can be modulated in different ways: It can be diminished at high salt concentrations, regulated by post-translational modifications such as Ser / Thr phosphorylation, and altered by interactions with RNA molecules. These observations suggest that sequence-encoded electrostatic interactions provide at least part of the driving force for phase separation of IDPs with blocks that are enriched in charged residues.Our goal is to uncover the physical principles that govern the sequence-encoded driving forces for reversible phase transitions of block copolymeric IDPs. Here, we focus specifically on charge-mediated interactions by considering the phase behavior of block-copolymeric polyampholytes and polyelectrolytes. The physics of electrostatically driven phase separation, known as complex coacervation, has been explored in polymer chemistry for synthetic polyelectrolytes. Through a novel combination of lattice-based coarse grain simulations, off-lattice coarse-grain simulations driven by machine learning, atomistic simulations, and theoretical insights, we are uncovering a physical framework for sequence-encoded complex coacervation of polyampholytic and polyelectrolytic IDPs. Our focus is on the collective interplay among charge patterning, charge density, chain-length, and the influence of charged versus uncharged residues on the phase behavior, fluidity, and structures adopted by disordered proteins in dense phases. Our findings should enable the systematic design of IDPs with desired phase behavior and proteome-level identification and understanding of how specific types of sequences drive intracellular phase transitions.

Aqueous biphasic systems composed of ionic liquids and polypropylene glycol: insights into their liquid-liquid demixing mechanisms.

Novel ternary phase diagrams of aqueous biphasic systems (ABSs) composed of polypropylene glycol with an average molecular weight of 400 g mol(-1) (PPG-400) and a vast number of ionic liquids (ILs) were determined. The large array of selected ILs allowed us to evaluate their tuneable structural features, namely the effect of the anion nature, cation core and cation alkyl side chain length on the phase behaviour. Additional evidence on the molecular-level mechanisms which rule the phase splitting was obtained by (1)H NMR (Nuclear Magnetic Resonance) spectroscopy and by COSMO-RS (Conductor-like Screening Model for Real Solvents). Some systems, for which the IL-PPG-400 pairs are completely miscible, revealed to be of type "0". All data collected suggest that the formation of PPG-IL-based ABSs is controlled by the interactions established between the IL and PPG, contrarily to previous reports where a "salting-out" phenomenon exerted by the IL over the polymer in aqueous media was proposed as the dominant effect in ABS formation. The influence of temperature on the liquid-liquid demixing was also evaluated. In general, an increase in temperature favours the formation of an ABS in agreement with the lower critical solution temperature (LCST) phase behaviour usually observed in polymer-IL binary mixtures. Partition results of a dye (chloroanilic acid, in its neutral form) further confirm the possibility of tailoring the phases' polarities of IL-PPG-based ABSs.

Preparation of hydrophilic PVDF/PPTA blend membranes by in situ polycondensation and its application in the treatment of landfill leachate

High modulus poly(p-phenylene terephtalamide) (PPTA) reinforced composites are of great scientific interests. But the thermodynamic difference makes the polymer pairs incompatible and endows the composites with inferior physical-chemical properties. In this study, hydrophilic poly(vinylidene fluoride) (PVDF)/poly(p-phenylene terephtalamide) (PPTA) blend membrane with improved hydrophilicity and mechanical strength was prepared through in situ polycondensation of p-phenylene diamine (PPD) and terephthaloyl chloride (TPC) in PVDF solution and subsequent immersion precipitation phase inversion process. The effects of PPTA concentration in polymer dopes on membrane formation process, structure, morphology and performance were systematically investigated. The results showed that thermodynamically, PPTA acted as a demixing enhancer which accelerated the phase inversion process. Dynamically, liquid-liquid phase separation was still in control of membrane formation process especially in the later period, whereas the addition of PPTA mainly promoted the early emergence of the liquid-liquid demixing. The surface hydrophilicity, ant-fouling properties and mechanical strength were significantly improved when PPTA content was 17wt%. When PPTA content increased to 26wt%, membrane bursting pressure increased to nearly 0.6MPa which was 1.5 times higher than that of PVDF membrane. The resultant PVDF/PPTA blend membrane exhibited an improved antifouling property than that of PVDF membrane when applied in the MBR in the treatment of landfill leachate and also showed a relatively high removal rate of chemical oxygen demand (COD) and chrom.

PVDF hollow fiber formation via modified NIPS method: Evolution elucidation of phase separation mechanism, structure and properties of membrane with coagulation strength varied

In this work, hollow fiber membrane was prepared from poly(vinylidene fluoride) (PVDF)/triethyl phosphate (TEP)/water systems by modified non-solvent induced phase separation technique (mNIPS), which was characterized in the process with relative high polymer content of 30 wt% in spinning dope. The ternary phase diagram and precipitation rate were determined to elucidate the various membrane formation mechanisms, and the membranes morphologies were observed by field emission scanning electronic microscopy (FESEM). It was indicated that the phase separation mechanism was found to heavily depend on the bath strength. Although the solid-liquid demixing process initiated the precipitation process, by changing the bath gradually from pure water to 40% TEP, the liquid-liquid demixing occurred earlier and earlier. Accordingly the top surface morphologies evolved from a dense skin (asymmetric membrane) to a totally porous morphology (symmetric membrane). In addition, the permeability, maximum stress at break, medium pore size and porosity of hollow fiber membranes were also investigated. In conclusion, the successful application of modified non-solvent induced phase separation (mNIPS) may provide an effective route to improve the membrane structure modulation.

Morphology evolution of poly(vinylidene fluoride) membranes during supercritical CO2 assisted phase inversion

A supercritical carbon dioxide (ScCO2) assisted phase inversion was developed to produce microporous poly(vinylidene fluoride) (PVDF) membranes whose morphology characteristics arise from both liquid-liquid demixing and solid-liquid demixing (crystallization). This result was confirmed by Fourier transform infrared spectroscopy (FTIR), from which both α and β crystals were found. As revealed by contact angle experiment, the PVDF membranes prepared via ScCO2 assisted phase inversion were more hydrophobic compared with the control membrane produced via conventional immersion-precipitation technique. In particular, the sample with 15 wt% PVDF prepared at 45 °C and 13 MPa exhibited a contact angle of 142°, which was mainly caused by the multilevel micro- and nano-structure. The effects of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and lithium chloride (LiCl) on the structures and crystal form were investigated. PVP promoted the formation of α phase crystal form, while PEG boosts the evolution of β phase. LiCl restrained the crystallization degree of PVDF membrane under ScCO2.

Phase Behavior and Ternary Diagram Construction for Membrane Forming Polycarbonate Solutions

Cloud points at different polymer concentrations were obtained by the simple titration method and compared with the numerically calculated theoretical binodal curves for Polycarbonate/Dimethylacetamide/Water (PC/DMAc/Water) and Polycarbonate/N-Methyl-2-pyrrolidone/Water (PC/NMP/Water). The interaction parameters for solvent polymer and nonsolvent polymer were obtained from Hansen's solubility parameters. The cloud points determined were found to be in close agreement with the theoretical binodal curve calculated. Coagulation values for different solvents such as Dichloromethane (DCM), Dimethylacetamide (DMAc), N-Methyl-2-pyrrolidone (NMP) and Tetrahydrofuran (THF) were also determined and the results were plotted in a ternary diagram to realize the effect of interaction parameters on the coagulation values. The higher the mutual affinity of solvent to polymer (low χ23), the faster is the liquid-liquid demixing rate to occur. For DCM solvent, fastest demixing rate was exhibited and lowest for the THF.

Calculation on phase diagrams of polyetherimide/N,N-dimethylacetamide/H2O-BuOH casting system and their relevance to membrane performances

The ternary phase diagrams of polyetherimide (PEI)/N,N-dimethylacetamide (DMAc) with H2O and BuOH as non-solvent were simulated using solubility parameter and Flory-Huggins theory. The phase diagrams show that 5.5% H2O/BuOH system containing 5% BuOH and 0.5% H2O, or 6.5% H2O/BuOH system containing 6.2% BuOH and 0.3% H2O is required to induce liquid-liquid demixing for 20 wt-% PEI/DMAc casting solution. Therefore, BuOH can enhance the phase separation of the PEI casting solution and hereby induce higher porosity of the membrane, and the diffusion of BuOH into the water coagulation bath causes larger pore size easily compared with DMAc. Our predictions that the membrane pure water flux first increases then decreases, and the rejection ratio of bovine serum albumin decreases with the increasing concentration of BuOH were validated by the experiments using the prepared membranes.

Effect of Cellulose Acetate Phthalate (CAP) on Characteristics and Morphology of Polysulfone/Cellulose Acetate Phthalate (PSf/CAP) Blend Membranes

Polysulfone (PSf) membrane is catogorized as hydrophobic membrane that easily fouled during membrane operation process. The presence of second hydrophilic polymer which added into membrane casting solutions plays a crucial role in adjusting the membrane properties. This hydrophilic polymer was employed in hydrophobic polymer membranes in order to improve hydrophilicity and performance as well as formed antifouling ultrafiltration (UF) membranes. In this study, a hydrophilic polymer, cellulose acetate phthalate (CAP) was added into polysulfone (PSf) membrane casting solutions by blending technique to produce PSf/CAP blend membranes. Flat sheet asymmetric PSf/CAP blend membranes were prepared by wet phase inversion method. The results revealed that an increase in CAP increased the hydrophilicity properties of PSf/CAP blend membranes compared to pure PSf membrane. The significant changes in size and numbers of microvoids and macrovoids in the morphological structures of PSf/CAP blend membranes were due to CAP promote the instantaneous liquid-liquid demixing during phase inversion process.

Coarse Grain Models Highlight the Importance of Flexible Disordered Linkers as Determinants of the Phase Behavior in Polyvalent Proteins

Micron-sized, non-membrane bound cellular bodies can form as the result of collective, heterotypic interactions. These bodies form as the result of micron-scale phase separation akin to liquid-liquid demixing, microscale gelation, or a convolution of these processes. Recent efforts have focused on various biophysical aspects of the phase behavior of macromolecules. This interest is catalyzed by the recognized functional importance of various cellular bodies that result from micron-scale phase transitions.Li et al. have quantified the effects of polyvalent interactions between macromolecules. For the case of binary interactions between a polymer of SH3 domains and a polymer of proline-rich modules (PRMs), valence refers to the numbers of SH3 domains and PRMs within the respective polymers. Within each polymer, flexible linkers connect the interacting units (SH3 domains and PRMs). Here, we probe the effects of linker properties including lengths, flexibility, and asymmetry of properties between the proteins as determinants of the concentration dependence of phase transitions. Our approach utilizes a lattice-based model that belongs to the same universality class as a three-dimensional Ising model.We find that that the critical concentration for phase transition is inversely correlated with both the lengths and random-coil-like character of intrinsically disordered linkers. Our observations imply the entropic penalty associated with loop closure promotes the growth of a network. We also show, in consistency with published experiments, that asymmetry in linker lengths of the interacting proteins will manifest itself as asymmetries in details of the concentration dependencies within the phase diagrams of two-component systems. Our results provide a physical rationale for selection against compact disordered linkers that connect interacting modules.1. Li, P. et al., (2012) Nature, 483: 336-340.

Phase Separation of Multi-Valent Signaling Proteins

Cells are organized on length scales from Angstroms to microns. However, the mechanisms by which Angstrom-scale molecular properties are translated to micron-scale macroscopic properties are not well understood. We have shown that interactions between multivalent proteins and multivalent ligands can cause liquid-liquid demixing phase transitions, resulting in formation of micron-sized liquid droplets in aqueous solution and micron-sized puncta on membranes. These transitions appear to occur concomitantly with sol-gel transitions to form large, dynamic polymers within the droplets/puncta. I will discuss how such transitions may control the spatial organization and biochemical activity of actin regulatory signaling pathways, and contribute to formation of PML nuclear bodies in the mammalian nucleus. Our data suggest a general mechanism by which cells may achieve micron-scale organization based on interactions between multivalent macromolecules.

Predicting Morphologies of Solution Processed Polymer:Fullerene Blends

The performance of solution processed polymer:fullerene thin film photovoltaic cells is largely determined by the nanoscopic and mesoscopic morphology of these blends that is formed during the drying of the layer. Although blend morphologies have been studied in detail using a variety of microscopic, spectroscopic, and scattering techniques and a large degree of control has been obtained, the current understanding of the processes involved is limited. Hence, predicting the optimized processing conditions and the corresponding device performance remains a challenge. We present an experimental and modeling study on blends of a small band gap diketopyrrolopyrrole-quinquethiophene alternating copolymer (PDPP5T) and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) cast from chloroform solution. The model uses the homogeneous Flory-Huggins free energy of the multicomponent blend and accounts for interfacial interactions between (locally) separated phases, based on physical properties of the polymer, fullerene, and solvent. We show that the spinodal liquid-liquid demixing that occurs during drying is responsible for the observed morphologies. The model predicts an increasing feature size and decreasing fullerene concentration in the polymer matrix with increasing drying time in accordance with experimental observations and device performance. The results represent a first step toward a predictive model for morphology formation.

Thermo-reversible gelation of atactic poly(methyl methacrylate) in poly(ethylene glycol) oligomers

The temperature-concentration behavior of physical gel by atactic poly(methyl methacrylate) (aPMMA) in poly(ethylene glycol) oligomer (PEG400) was investigated. A liquid-liquid demixing interferes with a glass transition during cooling. The combination of demixing and T g leads to the formation of amorphous gels at low temperature. We suggest that the gelation of aPMMA/PEG400 is a glassy gel, in which short-range attractive depletion interaction in the polymer/oligomer system was the driving force at molecular level.

Aqueous biphasic systems composed of ionic liquids and sodium carbonate as enhanced routes for the extraction of tetracycline

Aqueous biphasic systems (ABS) using ionic liquids (ILs) offer an alternative approach for the extraction, recovery, and purification of biomolecules through their partitioning between two aqueous liquid phases. In this work, the ability of a wide range of ILs to form ABS with aqueous solutions of Na2 CO3 was evaluated. The ABS formed by IL + water + Na2 CO3 were determined at 25°C, and the respective solubility curves, tie-lines, and tie-line lengths are reported. The studied ILs share the common chloride anion, allowing the IL cation core, the cation isomerism, the presence of functionalized groups, and alkyl side chain length effects to be evaluated. An increase in the cation side alkyl chain length leads to a higher ability for liquid-liquid demixing whereas different positional isomers and the presence of an allyl group have no major influence in the phase diagrams behavior. Quaternary phosphonium- and ammonium-based fluids are more able to form an ABS when compared with imidazolium-, pyridinium-, pyrrolidinium-, and piperidium-based ILs. Moreover, the presence of an aromatic cation core has no major contribution to the formation of ABS when compared to the respective nonaromatic counterparts. Finally, to appraise on the systems applicability in downstream processing, selected systems were used for the partitioning of tetracyclines (neutral and salt forms) - a class of antibiotics produced by bacteria fermentation. Single-step extraction efficiencies for the IL-rich phase were always higher than 99% and confirm the great potential of ILs to be applied in the biotechnological field.