Kinetics Of Phase Separation Research Articles

Non-thermal processing of inulin-enriched soursop whey beverage using supercritical carbon dioxide technology

The effects of supercritical CO2 technology on the non-thermal processing of soursop (Annona muricata L.) whey beverage enriched with inulin, a prebiotic carbohydrate, were analyzed. The functional dairy beverage was processed employing different supercritical process conditions: 35 and 55 °C, 10 and 20 MPa, and a CO2 volume ratio of 20 and 50%. Physicochemical properties (pH, soluble solids, ζ-potential), microstructural characteristics (microstructure, particle size distribution), rheological behavior, color parameters and phase separation kinetics were evaluated. Our results demonstrated that this emerging technology did not promote physicochemical and color changes in the prebiotic whey beverage processed. The temperature and CO2 volume ratio showed a significant effect on rheological behavior, microstructure, and kinetic stability, while pressure influenced only the beverage's microstructure. Supercritical CO2 technology can be used as a promising non-thermal treatment for the production of dairy beverages, however, the combination with another homogenization technique may improve the beverage kinetic stability.

Interfacial aggregation of Janus rods in binary polymer blends and their effect on phase separation.

Janus particles interfacially self-assemble into different structures when incorporated into multiphase systems. Dissipative particle dynamics simulations are employed herein to investigate the interplay between aggregation mechanisms and phase separation in polymer blends. Shorter rods with a standing configuration become increasingly "caged" or trapped in larger aggregates as weight fraction increases, which is reflected in the way that their diffusion is coupled to their aggregation rates. Janus rods of higher aspect ratios that are tilted at the interface aggregate side-by-side and are able to hinder phase separation kinetics. This is due to a combination of individual Janus rod conformations at the interface, their intrinsic aggregation mechanisms, aggregate fractal dimension, and aggregation rates, and can also be traced back to the scaling of the diffusion coefficient of aggregates with their size. Findings presented provide insight into the mechanisms governing two dimensionally growing colloidal aggregates at fluid interfaces, more specifically, those associated with Janus particles, and shed light on the potential of these systems in paving the way for designing new functional materials.

Analytical and numerical simulations for the kinetics of phase separation in iron (Fe–Cr–X (X=Mo, Cu)) based on ternary alloys

In this paper, we investigate the physical behavior of the basic elements that related to phase decomposition in ternary alloys of (Fe–Cr–Mo) and (Fe–Cr–Cu) according to analytical and approximate simulation. We study the dynamic of the separation phase for the ternary alloys of iron. The dynamical process of this separation has been described in a mathematical model called the Cahn–Hilliard equation. The minor element behavior in the process has been described by the Cahn–Hilliard equation. It describes the process of phase separation for two components of a binary fluid in ternary alloys of (Fe–Cr–Mo) and (Fe–Cr–Cu). We implement a modified auxiliary equation method and the cubic B-spline scheme on this mathematical model to show the dynamical process of phase separation and the concentration of one of two components in a system. We try obtaining the solitary and approximate solutions of this model to show the relation between the components in this phase. We discuss our solutions in view of a Stefan, Thomas-Windle, and Navier–Stokes models. Whereas, these models describe the motion of viscous fluid substance.

Interrupted Motility Induced Phase Separation in Aligning Active Colloids.

Switching on high activity in a relatively dense system of active Janus colloids, we observe fast clustering, followed by cluster aggregation towards full phase separation. The phase separation process is however interrupted when large enough clusters start breaking apart. Following the cluster size distribution as a function of time, we identify three successive dynamical regimes. Tracking both the particle positions and orientations, we characterize the structural ordering and alignment in the growing clusters and thereby unveil the mechanisms at play in these regimes. In particular, we identify how alignment between the neighboring particles is responsible for the interruption of the full phase separation. Our large scale quantification of the phase separation kinetics in active colloids points towards the new physics observed when both alignment and short-range repulsions are present.

Morphology, dynamics, and order development in a thermoplastic polyurethane with melt blended POSS

ABSTRACTA top‐down approach is applied for the production of polyurethane (PU)–polyhedral oligomeric silsesquioxane (POSS) nanocomposites, namely melt blending. As opposed to the typical chemical incorporation during synthesis, a POSS moiety with two hydroxyl groups is melt blended into a commercial thermoplastic polyurethane with mass fraction up to 2 wt %. POSS disperses in the matrix in submicrometer‐sized crystals, as well as in length scale of few tens of nanometers, in the bulk. Phase separation of the produced composites was studied by both standard dynamic and isothermal annealing experiments. In an approach rare in the literature, the dynamics of phase separation is discussed based on isothermal differential scanning calorimetry curves recorded during annealing. The blended‐in nanoparticles affect the micromorphology in a complicated manner, dependent on the intrinsically complex phase separation mechanism of PU. At higher temperatures, POSS slows down the phase separation, whereas at lower ones, it enhances and accelerates it. POSS decreases the mechanical modulus of the final material, presumably as a result of changes in the microphase separation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1133–1142

Enabling sustainable green close-loop membrane lithium extraction by acid and solvent resistant poly (ether ether ketone) membrane

Membrane extraction (ME) for separating lithium ions from salt-lake brine is a green process comparing to conventional liquid-liquid extraction. Previous research has identified suitable organic extractant and membrane materials for extracting lithium from salt-lake brine. However, stripping solution, a concentrated hydrochloride acid (HCl), dissolves current solvent resistant membrane. We presents here a novel application of acid and solvent resistant poly (ether ether ketone) (PEEK) membrane for membrane stripping. PEEK membranes were prepared via immersion precipitation using a mixture solvent consisting of methanesulphonic acid (MSA) and sulfuric acid (SA). A linear cloud point curve of PEEK/MSA/SA/H2O quaternary system was determined and the phase separation kinetics was analyzed. Competition of solid-liquid and liquid-liquid demixing was proposed as the mechanism for the morphology change varying with PEEK concentration. Increase of PEEK concentration lead to high crystallinity in membrane, but comparably high mass transfer resistance; this lead to similar trend in the water permeability, lithium ion diffusion and stripping fluxes as well. Successful stripping of lithium ions from lithium-loaded extractant using 7 mol/L HCl solution was demonstrated. The resistance of PEEK membrane in HCl solution and organic extractant (tributyl phosphate (TBP)/kerosene) was demonstrated by monitoring the weight change and mechanical strength of PEEK membrane. Long-term stable stripping performance for 504 h further confirmed the stability of PEEK membrane. An extraction-stripping close-loop is thus available by combining with the solvent resistant nanoporous poly (ethylene vinyl alcohol, EVAL) in extraction and PEEK membrane in the stripping steps. Besides lithium extraction, the membrane based extraction/stripping process is suitable for a wider ion separation and purification.

Incorporation of Alkali Lignin in Polyacrylonitrile: Phase Separation, Coagulation, and Cyclization Kinetics.

In this study, we systematically investigated the phase separation behaviors of polyacrylonitrile (PAN)/alkali lignin (AL)/dimethyl sulfoxide (DMSO) systems and found that the addition of AL causes phase separation and the systems form sea (PAN)/island (AL) types of structures. Interestingly, the AL-rich domains are very stable even after a long time of storage up to 15 days. Additionally, how the phase separation affected the solution rheology, the coagulation process and PAN cyclization were explored. The addition of AL in PAN/DMSO solutions changes the solution viscosity and gelation behaviors. Also, the existence of AL-rich domains accelerates the coagulation rate of the PAN solution in water. Because AL degrades at a lower temperature than PAN, it reduces the PAN cyclization temperature but leads to a higher cyclization activation energy, which could be caused by their different initiation mechanisms. These results would be useful to understand how the addition of AL affects the PAN solution structures, solution rheology, solution coagulation behaviors, and PAN stabilization reactions.

Quenched Li0.6FePO4 As a Vehicle for Studying Phase Separation Kinetics in Li-Ion Battery Materials

Olivine-type cathodes have asserted their ability to store energy efficiently in wide range of applications. Still, the phase transition process during charge and discharge raises questions regarding reactions rates, as the deintercallation/intercalation process via a phase transition mechanism is expected to affect ionic and electronic transport. In this study, the metastability of LixFePO4 solid solution is used to study the kinetics of the phase transition. Factors that affect the transformation of the metastable Li0.6FePO4 are reported, including preparation conditions and surface effects. Crystal structure dynamics were examined via X-ray diffraction (XRD) while more localized changes were revealed by attenuated total reflectance infrared spectroscopy (ATR-IR). These two techniques corroborate to distinguish the metastable solid solution phase relative to phase separation which emerges over time. Specifically, Reitveld refinement was used with the aim of detecting lithium rich and lithium poor phases as a function of time, resulting in a phase transition kinetic profile. In addition, lithium content was confirmed by flame emission spectrometry (AES). Recent results show how the phase separation is affected by the Li-ion battery chemistry as well as physical conditions. Importantly, surface effects were identified as crucial aspects in the kinetics of phase separation. The developed techniques serve as an experimental tool towards understanding Li0.6FePO4 solid solution.

Phase separation in binary fluid mixtures with symmetric and asymmetric Schmidt numbers: A DPD study.

We investigate the effect of the Schmidt number (Sc) on phase separation dynamics of two immiscible fluids in a two-dimensional periodic box using dissipative particle dynamics. The range of Sc investigated spans liquid-liquid separation processes. Phase separation is characterized by a domain size r(t), which typically follows a power law tβ in time t, where β is a characteristic exponent corresponding to the coarsening mechanism at play. The phase separation dynamics is studied for strongly (deep quench) separating mixtures. We consider cases of critical (ϕ ∼ 0.5) and off-critical (ϕ < 0.5) mixtures of fluids A and B for both ScA = ScB and ScA ≠ ScB. In all cases, the growth dynamics slow down with the increasing Schmidt number of either fluid. We observe the power law exponent β = 0.5 for symmetric (ScA = ScB) critical mixtures and β = 0.33 for all other cases. However, for off-critical mixtures, the exponent is 0.33 irrespective of the Schmidt number ratio of the two fluids. We explain these results from an analysis of the competition between diffusive effects vis-á-vis dynamical forces.

Conservation-Dissipation Formalism for soft matter physics: I. Augmentation to Doi's variational approach

In the first paper of this series, we prove that by choosing the proper variational function and variables, the variational approach proposed by Doi in soft matter physics is equivalent to the Conservation-Dissipation Formalism. To illustrate the correspondence between these two theories, several novel examples in soft matter physics, including the particle diffusion in dilute solutions, polymer phase separation dynamics and nematic liquid crystal flows, are carefully examined. Based on our work, a deep connection among the generalized Gibbs relation, the second law of thermodynamics and the variational principle in non-equilibrium thermodynamics is revealed.

Pore scale study of amphiphilic fluids flow using the Lattice Boltzmann model

We study ternary amphiphilic fluid flow at pore scale using a “bottom-up” Lattice Boltzmann (LB) model. The model introduces a dipole to capture the amphiphilic structure of surfactant molecules, and characterizes microscopic fluid interactions at the kinetic level. We first verify the established model by three examples, i.e., interfacial tension test, phase separation, and droplet dynamics in shear flow. The numerical results show that surfactants reduce the interfacial tension (IFT), and are able to emulsify the amphiphilic fluids, and the contours of the droplets are quantitatively in agreement with the results of level set method. Then we study the droplet dynamics in a confined environment. The surfactants make the droplet easy to deform and break up in shear flow, but inhibit coalescence due to the Marangoni stress. Moreover, there are four typical patterns for droplet collisions, i.e. coalescence, breakup after coalescence, brushing past, and brushing back. Furthermore, we improve the model by considering the wettability reversal effect caused by surfactant adsorption onto walls, and find that surfactants can decrease the critical Bond number for oil detaching from walls by 90%. Finally, we simulate the surfactant-enhanced aquifer remediation (SEAR) or enhanced oil recovery (EOR) process in a 2D porous medium. Surfactants improve the oil recovery in all wetting conditions, but the surfactant loss due to adsorption onto walls diminishes the effect of IFT reduction.

Plectoneme dynamics and statistics in braided polymers.

Braids composed of two interwoven polymer chains exhibit a "buckling" transition whose origin has been explained through the onset of plectonemic structures. Here we study, by a combination of simulation and analytics, the dynamics of plectoneme formation and their statistics in steady state. The introduction of an order parameter-the plectonemic fraction-allows us to map out the phase boundary between the straight-braid phase and the plectonemic one. We then monitor the formation and the growth of plectonemes, observing events typical of phase separation kinetics for liquid-gas systems (fusion, fission, and one-dimensional Ostwald ripening) but also of DNA supercoiling dynamics (plectonemic hopping). Finally, we propose a stochastic field theory for the coupled dynamics of twist and local writhe which explains the phenomenology found with Brownian dynamics simulations as well as the power laws underlying the coarsening of plectonemes.

Time–temperature superposition principle for the kinetic analysis of destabilization of pharmaceutical emulsions

The time–temperature superposition principle (TTSP) was applied to the destabilization kinetics of a pharmaceutical emulsion. The final goal of this study is to predict precisely the emulsion stability after long-term storage from the short-period accelerated test using TTSP. As the model emulsion, a cream preparation that is clinically used for the treatment of pruritus associated with chronic kidney disease was tested. After storage at high temperatures ranging from 30 to 45 °C for designated periods, the emulsion state was monitored using magnetic resonance imaging, and then the phase separation behaviors observed were analyzed according to the Arrhenius approach applying TTSP. The Arrhenius plot showed a biphasic change around 35 °C, indicating that the separation behaviors of the sample were substantially changed between the lower (30–35 °C) and higher (35–45 °C) temperature ranges. This study also monitored the coalescence behavior using a backscattered light measurement. The experiment verified that the destabilization was initiated by coalescence of oil droplets and then it eventually led to obvious phase separation via creaming. Furthermore, we note the coalescence kinetics agreed well with the phase separation kinetics. Therefore, in the case of the sample emulsion, the coalescence behavior has a dominant influence on the destabilization process. This study offers a profound insight into the destabilization process of pharmaceutical emulsions and demonstrates the promising applicability of TTSP to pharmaceutical research.

Three-stage phase separation kinetics in a model liquid binary mixture: A computational study

We study microscopic aspects of initial phase separation through atomistic molecular dynamics simulation of a structure breaking liquid binary mixture. We find that the phase separation kinetics in a fluid binary mixture model system can indeed be unusual. It can be fast, with a crossover from a pronounced exponential to non-exponential and non-linear dynamics. An important outcome of this work is the quantification of time scales involved in phase separation kinetics at an early stage. The initial exponential phase separation is complete within ∼100 ps. The initial phase separation involves aggregation of small droplets that form rapidly after the quench. This is followed by segregation that gives rise to pattern formation with multiple bands of segregated species. During this initial phase, a particle is found to have moved only about ∼5 molecular diameters. The next stage is slower and characterized by break-up and disappearance of small islands of species trapped inside the domains of other species of the binary mixture. The phase separation in this second stage is highly non-exponential and power-law-like. We identify a new feature in the very late stage of phase separation kinetics that seems to have eluded previous attention, the smoothing of the rugged interface between the two species. This is opposite to the roughening transition one finds on the surface of solids in contact with its vapor phase. The present atomistic simulation provides a molecular picture in terms of molecular motions and displacements.

Dynamic transition of dendrite orientation in the diffusive spinodal decomposition of binary mixtures under a thermal gradient

While the spinodal decomposition of mixtures in unbounded systems has been largely investigated, little is known about phase separation constrained within a slab. In this study, spinodal decomposition of a very viscous regular binary mixture bounded within two walls cooled at different temperatures is simulated by using the diffuse interface model in 2D. Under a temperature gradient, phase separation starts from the cooler wall forming dendritic structures growing anisotropically with time. Two remarkably different dynamics are identified depending on whether heat propagates slower or faster than mass. For small thermal conductivity (i.e., small Lewis number), dendrites grow parallelly to the temperature gradient, keeping such an alignment until the steady-state. On the other hand, for large Lewis number, during the early stages phase separation proceeds within stripes oriented along iso-temperature lines, i.e., with dendrites aligned perpendicularly to the temperature gradient, which, however, gradually shift their orientation parallel to the temperature gradient as the steady-state is approached. Such a dynamic transition of dendrite orientation upon a temperature gradient when heat propagates faster than mass is found to hold also for non-equimolar mixtures and for different species thermal conductivities. These results shed light on the dynamics of phase separation in constrained systems and anisotropic conditions.

Pattern formation of skin cancers: Effects of cancer proliferation and hydrodynamic interactions.

We study pattern formation of skin cancers by means of numerical simulation of a binary system consisting of cancer and healthy cells. We extend the conventional model H for macrophase separations by considering a logistic growth of cancer cells and also a mechanical friction between dermis and epidermis. Importantly, our model exhibits a microphase separation due to the proliferation of cancer cells. By numerically solving the time evolution equations of the cancer composition and its velocity, we show that the phase separation kinetics strongly depends on the cell proliferation rate as well as on the strength of hydrodynamic interactions. A steady-state diagram of cancer patterns is established in terms of these two dynamical parameters and some of the patterns correspond to clinically observed cancer patterns. Furthermore, we examine in detail the time evolution of the average composition of cancer cells and the characteristic length of the microstructures. Our results demonstrate that different sequence of cancer patterns can be obtained by changing the proliferation rate and/or hydrodynamic interactions.

Liquid phase separation in undercooled Cu-Co alloys under the influence of static magnetic fields.

Undercooling of Cu-based alloys often induces metastable liquid phase separation followed by rapid solidification of separated liquids. The rapid solidification can help freeze in the morphology of a higher-melting liquid and eases difficulties in studies of liquid phase separation kinetics. In the present work, the influence of static magnetic fields on liquid phase separation in bulk Cu84Co16 composition was investigated. Inductively melted samples were glass-fluxed, undercooled and solidified under uniform and non-uniform magnetic fields generated by a superconducting magnet. Solidification microstructure of the phase-separated samples was examined using an optical microscope. The imposition of the magnetic fields, both uniform and non-uniform, altered the morphology, segregation pattern and size distribution of Co-rich droplets due to liquid phase separation. The imposition of the non-uniform magnetic fields with positive and negative gradients brought about segregation of the Co-rich droplets at the top and the bottom side of the samples, respectively. Such influence of the static magnetic fields is interpreted by assuming intensification of convective flow and Kelvin force-controlled migration of the Co-rich droplets. This article is part of the theme issue 'Heterogeneous materials: metastable and non-ergodic internal structures'.

Phase Separation Dynamics of a Binary Fluid with a Closed-Loop Phase Diagram

We perform molecular dynamics simulations of the phase separation processes of a binary quadrupolar fluid that shows a closed-loop phase diagram with two types of critical points. These simulations...

Universality of miscible–immiscible phase separation dynamics in two-component Bose–Einstein condensates

We investigate the non-equilibrium dynamics across the miscible–immiscible phase separation in a binary mixture of Bose–Einstein condensates. The excitation spectra reveal that the Landau critical velocity vanishes at the critical point, where the superfluidity spontaneously breaks down. We analytically extract the dynamical critical exponent z = 2 and static correlation length critical exponent v = 1/2 from the Landau critical velocity. Moreover, by simulating the real-time dynamics across the critical point, we find the average domain number and the average bifurcation delay show universal scaling laws with respect to the quench time. We then numerically extract the static correlation length critical exponent v = 1/2 and the dynamical critical exponent z = 2 according to Kibble–Zurek mechanism. The scaling exponents (v = 1/2, z = 2) in the phase separation driven by quenching the atom–atom interaction are different from the ones (v = 1/2, z = 1) in the phase separation driven by quenching the Rabi coupling strength (2009 Phys. Rev. Lett. 102 070401; 2011 Phys. Rev. Lett. 107 230402). Our study explores the connections between the spontaneous superfluidity breakdown and the spontaneous defect formation in the phase separation dynamics.

Phase-Separation Kinetics in Protein-Salt Mixtures with Compositionally Tuned Interactions.

Liquid-liquid phase separation (LLPS) in protein systems is relevant for many phenomena, from protein condensation diseases to subcellular organization to possible pathways toward protein crystallization. Understanding and controlling LLPS in proteins is therefore highly relevant for various areas of (biological) soft matter research. Solutions of the protein bovine serum albumin (BSA) have been shown to have a lower critical solution temperature-LLPS (LCST-LLPS) induceable by multivalent salts. Importantly, the nature of the multivalent cation used influences the LCST-LLPS in such systems. Here, we present a systematic ultrasmall-angle X-ray scattering investigation of the kinetics of LCST-LLPS of BSA in the presence of different mixtures of HoCl3 and LaCl3, resulting in different effective interprotein attraction strengths. We monitor the characteristic length scales ξ( t, Tfin) after inducing LLPS by subjecting the respective systems to temperature jumps in their liquid-liquid coexistence regions. With increasing interprotein attraction and increasing Tfin, we observe an increasing deviation from the growth law of ξ ∼ t1/3 and an increased trend toward arrest. We thus establish a multidimensional method to tune phase transitions in our systems. Our findings help shed light on general questions regarding LLPS and the tunability of its kinetics in both proteins and colloidal systems.