Phase Separation In Binary Mixtures Research Articles

Decay Dynamics of a Single Spherical Domain in Near-Critical Phase-Separated Conditions.

Domain decay is at the heart of the so-called evaporation-condensation Ostwald-ripening regime of phase ordering kinetics, where the growth of large domains occurs at the expense of smaller ones, which are expected to "evaporate." We experimentally investigate such decay dynamics at the level of a single spherical domain picked from one phase in coexistence and brought into the other phase by an optomechanical approach, in a near-critical phase-separated binary liquid mixture. We observe that the decay dynamics is generally not compatible with the theoretically expected surface-tension decay laws for conserved order parameters. Using a mean-field description, we quantitatively explain this apparent disagreement by the gradient of solute concentrations induced by gravity close to a critical point. Finally, we determine the conditions for which buoyancy becomes negligible compared to capillarity and perform dedicated experiments that retrieve the predicted surface-tension induced decay exponent. The surface-tension driven decay dynamics of conserved order parameter systems in the presence and the absence of gravity, is thus established at the level of a single domain.

Liquid–liquid phase separation in binary mixtures of quaternary alkylammonium chlorides with carboxylic acids

We reported the phase separation measurements of mixtures obtained from choline, tetramethylammonium and tetraethylammonium chlorides with methacrylic (MAA), butyric (BA) and isobutyric (IBA) acids as solvents. Liquid-liquid equilibrium (LLE) experiments were performed under atmospheric pressure in a temperature range of 287–403 K using cloud-point method and the data were correlated with the Non-Random Two Liquid (NRTL) solution model. The density, the viscosity, the Kamlet-Taft and the solvent polarity (ET(30)) parameters were measured for coexisting liquid phases. The applicability of the obtained binary biphasic system in extraction process, particularly purification of MAA from a phenolic inhibitor, was demonstrated.

Hydrogen bond structure and associated dynamics in micro-heterogeneous and in phase separated alcohol-water binary mixtures: A THz spectroscopic investigation

Despite being a simple and widely studied solution, a correlation between the structure and dynamics of the hydrogen bond (HBond) network in alcohol-water binary mixtures remains highly debatable. The present work combined Terahertz time domain spectroscopy (TTDS) and Terahertz-Fourier transform infrared (THz-FTIR) spectroscopy covering a wide frequency window of 0.3–18 THz, which probes most of the intermolecular roto-vibrational modes of water, to extract an extensive idea on such aspect of the binary mixtures. This study demonstrates a unified picture of the solute concentration-dependent HBond network structure and its associated dynamics in alcohol-water binary mixtures considering micro- and macro-scale (for partially water-soluble alcohols) phases present inside the systems. The work extensively took into account both the factors of hydrophobic chain length and macroscopic self-aggregation of alcohols to present a comprehensive view of HBonded intermolecular networks in binary mixtures. We found a balance between the local homo-molecular and cross-molecular solvation which leads to a micro/macro scale self-aggregation for various alcohol-water mixtures.

Hydrodynamic effects in kinetics of phase separation in binary fluids: Critical versus off-critical compositions.

Via hydrodynamics-preserving molecular dynamics simulations we study growth phenomena in a phase-separating symmetric binary mixture model. We quench high-temperature homogeneous configurations to state points inside the miscibility gap, for various mixture compositions. For compositions at the symmetric or critical value we capture the rapid linear viscous hydrodynamic growth due to advective transport of material through tubelike interconnected domains. For state points very close to any of the branches of the coexistence curve, the growth in the system, following nucleation of disconnected droplets of the minority species, occurs via a coalescence mechanism. Using state-of-the-art techniques, we have identified that these droplets, between collisions, exhibit diffusive motion. The value of the exponent for the power-law growth, related to this diffusive coalescence mechanism, has been estimated. While the exponent nicely agrees with that for the growth via the well-known Lifshitz-Slyozov particle diffusion mechanism, the amplitude is stronger. For the intermediate compositions we observe initial rapid growth that matches the expectations for viscous or inertial hydrodynamic pictures. However, at later times these types of growth cross over to the exponent that is decided by the diffusive coalescence mechanism.

Structural correlations and phase separation in binary mixtures of charged and neutral colloids.

Structural correlations between colloids in a binary mixture of charged and neutral spheres are calculated using computer simulations of the primitive model with explicit microions. For aqueous suspensions in a solvent of large dielectric constant, the traditional Derjaguin-Landau-Vervey-Overbeek (DLVO) theory of linear screening, supplemented with hard core interactions, reproduces the structural correlations obtained in the full primitive model quantitatively. However, for lower dielectric contrast, the increasing Coulomb coupling between the counterions and charged colloids results in strong deviations. We find a fluid-fluid phase separation into two regions either rich in charged or rich in neutral colloids, which is not reproduced by DLVO theory. Our results are verifiable in scattering or real-space experiments on charged-neutral mixtures of colloids or nanoparticles.

Controlling cluster size in 2D phase-separating binary mixtures with specific interactions.

By varying the concentration of molecules in the cytoplasm or on the membrane, cells can induce the formation of condensates and liquid droplets, similar to phase separation. Their thermodynamics, much studied, depends on the mutual interactions between microscopic constituents. Here, we focus on the kinetics and size control of 2D clusters, forming on membranes. Using molecular dynamics of patchy colloids, we model a system of two species of proteins, giving origin to specific heterotypic bonds. We find that concentrations, together with valence and bond strength, control both the size and the growth time rate of the clusters. In particular, if one species is in large excess, it gradually saturates the binding sites of the other species; the system then becomes kinetically arrested and cluster coarsening slows down or stops, thus yielding effective size selection. This phenomenology is observed both in solid and fluid clusters, which feature additional generic homotypic interactions and are reminiscent of the ones observed on biological membranes.

Numerical Approximations for the Solutions of Fourth Order Time Fractional Evolution Problems Using a Novel Spline Technique

Developing mathematical models of fractional order for physical phenomena and constructing numerical solutions for these models are crucial issues in mathematics, physics, and engineering. Higher order temporal fractional evolution problems (EPs) with Caputo’s derivative (CD) are numerically solved using a sextic polynomial spline technique (SPST). These equations are frequently applied in a wide variety of real-world applications, such as strain gradient elasticity, phase separation in binary mixtures, and modelling of thin beams and plates, all of which are key parts of mechanical engineering. The SPST can be used for space discretization, whereas the backward Euler formula can be used for time discretization. For the temporal discretization, the method’s convergence and stability are assessed. To show the accuracy and applicability of the proposed technique, numerical simulations are employed.

Competition between clustering and phase separation in binary mixtures containing SALR particles.

We investigate by Monte Carlo simulations a mixture of particles with competing interactions (hard-sphere two-Yukawa, HSTY) and hard spheres (HS), with same diameters σ and a square-well (SW) cross attraction. In a recent study [G. Munaò et al., J. Phys. Chem. B, 2022, 126, 2027-2039], we have analysed situations-in terms of relative concentration and attraction strength-where HS promote the formation of clusters involving particles of both species under thermodynamic conditions that would not allow for clustering of the pure HSTY fluid. Here, we focus on the role played by the range of cross attraction in determining the equilibrium structure of the mixture, starting from a homogeneous low-density state. When the width of the well exceeds approximately σ, clustering takes place in the system, with aggregates characterised by various sizes and shapes. Only for low HSTY concentrations (less than 10%) a single big cluster appears, anticipating the behaviour observed for a wider well, around 1.2σ. In the latter case, a spherical cluster encompassing almost all particles is the stable structure at equilibrium. We interpret this outcome as a macrophase, liquid-vapour separation where the spherical cluster is just the form taken at low density by the liquid phase inside the vapour phase: indeed, when the density takes larger values, periodic boundary conditions select liquid-vapour interfaces with other non-spherical shapes, similarly as found for a finite sample of simple fluid going through the liquid-vapour coexistence region. For still higher densities we document the existence of a solid phase characterized by the alternation of bilayers filled with particles of one species and bilayers of the other species, giving the solid a peculiar wafer structure.

Size conservation emerges spontaneously in biomolecular condensates formed by scaffolds and surfactant clients

Biomolecular condensates are liquid-like membraneless compartments that contribute to the spatiotemporal organization of proteins, RNA, and other biomolecules inside cells. Some membraneless compartments, such as nucleoli, are dispersed as different condensates that do not grow beyond a certain size, or do not present coalescence over time. In this work, using a minimal protein model, we show that phase separation of binary mixtures of scaffolds and low-valency clients that can act as surfactants—i.e., that significantly reduce the droplet surface tension—can yield either a single drop or multiple droplets that conserve their sizes on long timescales (herein ‘multidroplet size-conserved’ scenario’), depending on the scaffold to client ratio. Our simulations demonstrate that protein connectivity and condensate surface tension regulate the balance between these two scenarios. The multidroplet size-conserved scenario spontaneously arises at increasing surfactant-to-scaffold concentrations, when the interfacial penalty for creating small liquid droplets is sufficiently reduced by the surfactant proteins that are preferentially located at the interface. In contrast, low surfactant-to-scaffold concentrations enable continuous growth and fusion of droplets without restrictions. Overall, our work proposes one thermodynamic mechanism to help rationalize how size-conserved coexisting condensates can persist inside cells—shedding light on the roles of protein connectivity, binding affinity, and droplet composition in this process.

Addition to “Phase-Separating Binary Polymer Mixtures: The Degeneracy of the Virial Coefficients and Their Extraction from Phase Diagrams”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionAddition to “Phase-Separating Binary Polymer Mixtures: The Degeneracy of the Virial Coefficients and Their Extraction from Phase Diagrams”Arjen BotArjen BotMore by Arjen Bothttps://orcid.org/0000-0002-2065-8964, Belinda P. C. DewiBelinda P. C. DewiMore by Belinda P. C. Dewihttps://orcid.org/0000-0003-0340-3131, and Paul Venema*Paul VenemaMore by Paul VenemaCite this: ACS Omega 2021, 6, 30, 20086–20087Publication Date (Web):July 23, 2021Publication History Received25 June 2021Published online23 July 2021Published inissue 3 August 2021https://doi.org/10.1021/acsomega.1c03331Copyright © 2021 American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoiceCC: Creative CommonsBY: Credit must be given to the creatorNC: Only noncommercial uses of the work are permittedND: No derivatives or adaptations of the work are permittedArticle Views428Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (513 KB) Get e-Alerts Get e-Alerts

Control of Phase Morphology of Binary Polymer Grafted Nanoparticle Blend Films via Direct Immersion Annealing.

While the phase separation of binary mixtures of chemically different polymer-grafted nanoparticles (PGNPs) is observed to superficially resemble conventional polymer blends, the presence of a "soft" polymer-grafted layer on the inorganic core of these nanoparticles qualitatively alters the phase separation kinetics of these "nanoblends" from the typical pattern of behavior seen in polymer blends and other simple fluids. We investigate this system using a direct immersion annealing method (DIA) that allows for a facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient "aging" time. In particular, by switching the DIA solvent composition from a selective one (which increases the interaction parameter according to Timmerman's rule) to an overall good solvent for both PGNP components, we can achieve rapid switchability between phase-separated and homogeneous states. Despite a relatively low and non-classical power-law coarsening exponent, the overall phase separation process is completed on a time scale on the order of a few minutes. Moreover, the roughness of the PGNP blend film saturates at a scale that is proportional to the in-plane phase separation pattern scale, as observed in previous blend and block copolymer film studies. The relatively low magnitude of the coarsening exponent n is attributed to a suppression of hydrodynamic interactions between the PGNPs. The DIA method provides a significant opportunity to control the phase separation morphology of PGNP blends by solution processing, and this method is expected to be quite useful in creating advanced materials.

Ground-State Properties and Phase Separation of Binary Mixtures in Mesoscopic Ring Lattices.

We investigated the spatial phase separation of the two components forming a bosonic mixture distributed in a four-well lattice with a ring geometry. We studied the ground state of this system, described by means of a binary Bose–Hubbard Hamiltonian, by implementing a well-known coherent-state picture which allowed us to find the semi-classical equations determining the distribution of boson components in the ring lattice. Their fully analytic solutions, in the limit of large boson numbers, provide the boson populations at each well as a function of the interspecies interaction and of other significant model parameters, while allowing to reconstruct the non-trivial architecture of the ground-state four-well phase diagram. The comparison with the L-well () phase diagrams highlights how increasing the number of wells considerably modifies the phase diagram structure and the transition mechanism from the full-mixing to the full-demixing phase controlled by the interspecies interaction. Despite the fact that the phase diagrams for share various general properties, we show that, unlike attractive binary mixtures, repulsive mixtures do not feature a transition mechanism which can be extended to an arbitrary lattice of size L.

Prediction of hypothetical solubility of drugs in phase separated miscible binary solvent mixtures using an interpolation technique

Solubility is one of the most important thermodynamic properties in drug discovery, and a major parameter to be considered in pharmaceutics in order to achieve suitable formulations for the desired pharmacological response. It is also an impotant issue in drug re-crystalization and drug extraction using liquid–liquid phase separation. So, the knowledge of solubility in the neat and mixed solvents at various temperatures is neccesary in many pharmaceutical/chemical areas. However, the experimental measurement of this property in all mixture compositions and temperatures is not possible; for example, due to phase separation. In the current study, the applicability of the Jouyban-Acree based models will be investigated for prediction of solubility data in such a solvent mixture using an interpolation technique that provides hypothetical solubility data for these troubled fractions.

Metastable dynamics for a hyperbolic variant of the mass conserving Allen–Cahn equation in one space dimension

In this paper, we consider some hyperbolic variants of the mass conserving Allen–Cahn equation, which is a nonlocal reaction-diffusion equation, introduced (as a simpler alternative to the Cahn–Hilliard equation) to describe phase separation in binary mixtures. In particular, we focus our attention on the metastable dynamics of solutions to the equation in a bounded interval of the real line with homogeneous Neumann boundary conditions. It is shown that the evolution of profiles with N+1 transition layers is very slow in time and we derive a system of ODEs, which describes the exponentially slow motion of the layers. A comparison with the classical Allen–Cahn and Cahn–Hilliard equations and theirs hyperbolic variations is also performed.

Phase separation of binary mixtures induced by soft centrifugal fields.

We use the model system ethanol-dodecane to demonstrate that giant critical fluctuations induced by easily accessible weak centrifugal fields as low as 2000g can be observed above the miscibility gap of a binary liquid mixture. Moreover, several degrees above the phase transition, i.e. in the one-phase region, strong gradients of ethanol concentration occur upon centrifugation. In this case, the standard interpretation of sedimentation equilibrium in the analytical ultracentrifuge (AUC) yields an apparent molar mass of ethanol three orders of magnitude higher than the real value. Notably, these composition gradients have no influence on the distribution gradient of solutes such as dyes like Nile red. The thick opaque interphase formed upon centrifugation does not appear as the commonly observed sharp meniscus, but as a turbidity zone, similar to critical opalescence. This layer is a few millimeters thick and separates two fluids with low compositional gradients. All these effects can be qualitatively understood and explained using the Flory-Huggins solution model coupled to classical density functional theory (DFT). In this domain hetero-phase fluctuations can be triggered by gravity even far from the critical point. Taking into account Jean Perrin's approach to external fields in colloids, a self-consistent definition of the Flory effective volume and an explicit calculation of the total free energy per unit volume is possible.

Sheared phase-separating binary mixtures with surface diffusion

The phase-separation process of a binary mixture with order-parameter-dependent mobility under shear flow is numerically studied. The ordering is characterized by an alternate stretching and bursting of domains which produce oscillations in the physical observables. The amplitude of such modulations reduce in time when the mobility vanishes in the bulk phase, disfavoring the growth of bubbles coming from bursted domains. We propose two equations for the typical sizes Rx and Ry of domains finding the long-time behaviors Rx ∼ t5/4 and Ry ∼ t1/4 in the flow and shear directions, respectively, in the case of surface diffusion. A reduction of the excess viscosity with increasing shear rate is observed in simulations.

Phase Separation in the Advective Cahn–Hilliard Equation

The Cahn--Hilliard equation is a classic model of phase separation in binary mixtures that exhibits spontaneous coarsening of the phases. We study the Cahn--Hilliard equation with an imposed advection term in order to model the stirring and eventual mixing of the phases. The main result is that if the imposed advection is sufficiently mixing then no phase separation occurs, and the solution instead converges exponentially to a homogeneous mixed state. The mixing effectiveness of the imposed drift is quantified in terms of the dissipation time of the associated advection-hyperdiffusion equation, and we produce examples of velocity fields with a small dissipation time. We also study the relationship between this quantity and the dissipation time of the standard advection-diffusion equation.

Liquid–Liquid Interface Can Promote Micro-Scale Thermal Marangoni Convection in Liquid Binary Mixtures

Liquid–liquid phase separation, a physical transition in which a homogeneous solution spontaneously demixes into two coexisting liquid phases, has been a key topic in the thermodynamics of two-component systems and may find applications in separation, drug delivery, and protein crystallization. Here we applied a microscale temperature gradient using optothermal heating of a gold nanoparticle to overcome the experimental difficulties inherent in homogeneous heating: We aimed at highlighting precise structural development by avoiding randomly nucleating/growing microdomains. In response to laser illumination, a single gold nanoparticle immersed in a binary mixture of aqueous 2,6-dimethylpyridine (lutidine) and N-isopropylpropionamide (NiPPA) was clearly sensitive to the phase transition of the surrounding liquid as demonstrated by light-scattering signals: spectral red-shifts and bright-spot images. The local phase separation encapsulating the gold nanoparticle resulted in immediate formation and growth of an organic-rich droplet which was confirmed by Raman spectroscopy. Remarkably, the droplet was stable under a nonequilibrium steady-state heating condition because of strong thermal confinement. Microdroplet growth was ascribed to thermocapillary flow induced by a newly formed liquid–liquid interface around the hot gold nanoparticle. On the basis of a tracer experiment and numerical simulation, it is deduced that the transport of solute to the high-temperature area is driven by this thermocapillary flow. This study enhances our understanding of phase separation in binary mixtures induced by microscale temperature confinement.

Morphology formation in binary mixtures upon gradual destabilisation.

Spontaneous liquid-liquid phase separation is commonly understood in terms of phenomenological mean-field theories. These theories correctly predict the structural features of the fluid at sufficiently long time scales and wavelengths. However, these conditions are not met in various examples in biology and materials science where the mixture is slowly destabilised, and phase separation is strongly affected by critical thermal fluctuations. We propose a mechanism of pretransitional structuring of a mixture that approaches the miscibility gap and predict scaling relations that describe how the characteristic feature size of the emerging morphology decreases with an increasing quench rate. These predictions quantitatively agree with our kinetic Monte Carlo and molecular dynamics simulations of a phase-separating binary mixture, as well as with previously reported experimental observations. We discuss how these predictions are affected by non-conserved order parameters (e.g., due to chemical reactions or alignment of liquid-crystalline molecules), hydrodynamics and active transport.

Optical diagnostics of dusty plasmas

Particle-containing (complex or dusty) plasmas offer and require the development of sophisticated diagnostic techniques to measure their properties such as particle motion, particle density, particle size and demixing properties. Here, an overview of selected optical diagnostic techniques for dusty plasmas and some recent applications are given. As examples, angle-resolved optical tomography reveals the spatially resolved particle density in dense dust systems as well as the size distribution of particles trapped in the plasma. Phase separation of binary mixtures of dust particles can be studied by exploiting the fluorescence of dyed particles. There, the dynamics of the demixing process can be measured in terms of an effective diffusion coefficient. Finally, three-dimensional trajectories of particles are determined from stereoscopy allowing to study the motion of hundreds of particles in a restricted volume.