Kinetics Of Phase Separation Research Articles

Investigation of Li0.6FePO4 Phase Separation Kinetics Starting from Solid Solution

The major contribution of lithium ion batteries towards sustainable energy originates in their use as energy vectors. In this context, lithium iron phosphate represents a safe, stable and environmental benign cathode material. The phase transition process during charge and discharge leads to questions regarding reactions rates, as the deintercalation/intercalation process via a phase transition mechanism is expected to strongly affect ionic and electronic transport. In order to study intrinsic properties of partially lithiated lithium iron phosphate, this study reports on factors that affect the transformation of the metastable Li0.6FePO4 solid solution prepared using both physical and chemical means. The stability of the solid solution was examined using a series of diverse experimental conditions. Crystal structure effects were examined via X-ray diffraction (XRD) while more localized changes were revealed by attenuated total reflectance infrared spectroscopy (ATR-IR). Specifically, the internal vibrations of the phosphate group were used with the aim of detecting lithium rich and lithium poor phases. These two techniques corroborate to distinguish the metastable solid solution phase relative to the olivine and heterosite phases which emerge over time. Particles morphologies and size distribution were analysed by field-emission gun scanning electron microscopy (FEG-SEM) and dynamic light scattering (DLS) respectively. In addition, lithium content was confirmed by flame emission spectrometry (AES). The developed techniques and results relative to the solid solution metastability will serve as the basis for upcoming kinetics studies. These studies will rely on imposing a uniform reaction environment on the entire particle population, in contrast to kinetics derived from electrochemical analysis using composite electrodes.

Solid State Viscoelastic Properties, Morphological and Melt Rheological Studies on PLA/TPU/POSS Nanocomposites

ABSTRACTEffects of trifluoropropyl-substituted polyhedral oligomeric Silsesquioxane (POSS), on the morphological, rheological and dynamic mechanical properties of a series of poly(lactic acid)(PLA)/thermoplastic polyurethane (TPU) blends were explored, thoroughly. Microscopic techniques including scanning electron microscope (SEM) and transmission electron microscope (TEM) utilized in conjunction with viscosity measurements to explain morphological dissimilarities between different samples. A remarkable morphological refinement was observed upon addition of POSS into the 50/50 PLA/TPU blend. This morphological change was detected by means of frequency sweep rheological experiments, where the shoulder-like plateau appears as a result of increase in the contribution from the interfacial component of elasticity in the enhancement of storage modulus. Based on the results of the dynamic time sweep small amplitude oscillatory shear (SAOS) experiments, a scaling relation was proposed to quantify the kinetics of phase separation and the associate time evolution of elasticity. It turned out that POSS particles can slow down the rate of morphological coarsening up to the 50%. Using dynamic mechanical thermal analysis (DMTA) and rheological experiments, the differences in the rate of undergoing dynamics in all the length scales, starting from segmental up to the chain level, were compared for various compositions and the discrepancies were fully described based on the dissimilarities in the entanglement densities, combinatorial effects of soft and hard segments of TPU, lubricating role of POSS particles, crystallinity, and morphological characteristics of samples.

Effect of organically modified clay on the morphology, rheology and viscoelasticity of epoxy –thermoplastic nanocomposites

The effect of cloisite 20A clay on rheology and dynamic mechanical properties of epoxy and poly-(styrene-co-acrylonitrile) (SAN) blend system cured with diamino-diphenyl sulphone (DDS) was investigated. The effect of modified clay (cloisite 20A) on two different compositions of initially miscible epoxy/SAN system has been investigated based on the differences in the mechanism of phase separation during curing. The dynamics of phase separation was followed by optical microscopy coupled with a heating stage. The developed microstructures obtained after complete curing were examined by scanning electron microscopy (SEM) after preferential etching of SAN phase with dichloroethane. The processing parameters occurring during the curing reaction was analyzed by dynamic in-situ rheometry. The viscoelastic properties of fully cured blends and composites were further determined by dynamic mechanical analysis (DMA). Localization of filler among the blend phases was established from dynamic mechanical analysis.

Study of single airborne particle using laser-trapped submicron position-resolved temporal Raman spectroscopy

Study of various molecules located in different positions and of their temporal reactions within a microsized particle in its natural phase is essential to deeper understanding the functions of these molecules. Here, we measured the temporal Raman spectra in different submicron positions of a laser-trapped droplet composed of diethyl phthalate and glycerol. Results demonstrated the micro-cavity enhanced effects, the morphology change, dynamics of phase-separation, and evaporation of the mixed droplet. This method offers a powerful tool to monitor various chemical reactions in different positions within a single cell, spore, or particle in life science and atmospheric science.

Direct test of the Gaussian auxiliary field ansatz in nonconserved order parameter phase ordering dynamics.

The assumption that the local order parameter is related to an underlying spatially smooth auxiliary field, u(r[over ⃗],t), is a common feature in theoretical approaches to non-conserved order parameter phase separation dynamics. In particular, the ansatz that u(r[over ⃗],t) is a Gaussian random field leads to predictions for the decay of the autocorrelation function which are consistent with observations, but distinct from predictions using alternative theoretical approaches. In this paper, the auxiliary field is obtained directly from simulations of the time-dependent Ginzburg-Landau equation in two and three dimensions. The results show that u(r[over ⃗],t) is equivalent to the distance to the nearest interface. In two dimensions, the probability distribution, P(u), is well approximated as Gaussian except for small values of u/L(t), where L(t) is the characteristic length-scale of the patterns. The behavior of P(u) in three dimensions is more complicated; the non-Gaussian region for small u/L(t) is much larger than that in two dimensions but the tails of P(u) begin to approach a Gaussian form at intermediate times. However, at later times, the tails of the probability distribution appear to decay faster than a Gaussian distribution.

Time-dependent phase separation of amorphous solid dispersions: Implications for accelerated stability studies

Freshly prepared amorphous solid dispersions (ASDs) may not be in an equilibrium mixed state, as high-temperatures and/or solvents are generally used during their preparation. In this study, tolbutamide (TLB) and acetaminophen (AAP) were transformed into ASDs using hydroxypropylmethylcellulose acetate succinate, Eudragit E100 (E100), Soluplus, and Kollidon VA64 using the melt-quench method to observe their phase stability at 5, 25, 40, and 60 °C. Time-dependent phase separation was observed for all the drug and excipient combinations under all investigated storage conditions. The phase separation of the E100/TLB and Soluplus/TLB ASDs was faster under high-temperature storage conditions, whereas the opposite trend was observed with the other ASDs. In the above-mentioned stability studies, phase separation kinetics of the E100/TLB and Soluplus/TLB ASDs appeared to be dominated by molecular mobility due to the low glass transition temperature (Tg) of both the drug and polymer, whereas departure from equilibrium was a dominating factor for the other ASDs. The Tg of the mixed phase just after preparation could be used as an indicator for predicting phase separation after long-term storage, as the mixing ratio calculated from the Tg was in agreement with that after storage for certain ASDs.

Electrochemical Oscillation in Li-Ion Batteries

Summary Two-phase reactions are prevalent in Li-ion batteries, whereas the underlying dynamics of phase separation in a real electrode still remain elusive, since numerous electrode particles constitute a formidably complex system for existing experimental techniques. Here we present an intriguing oscillatory phenomenon in the typical phase-separating electrode material Li 4 Ti 5 O 12 . During galvanostatic processes, the voltage oscillates due to the discrete nature of multi-particle phase-separating reactions, and the subtle oscillatory signals allow us to evaluate the fraction of actively phase-separating particles in real time. Through the analysis of oscillatory phenomena, we unveil the dependence of the active fraction on the depth of charge/discharge, cycling current, and working temperature, considerably deepening our understanding of the multi-particle phase-separation reaction. Moreover, it is the first time that electrochemical oscillations have been identified in rechargeable battery systems, opening up a new frontier for both theoretical and experimental researchers.

Nanorods with Different Surface Properties in Directing the Compatibilization Behavior and the Morphological Transition of Immiscible Polymer Blends in Both Shear and Shear-Free Conditions

To explore the mechanism of how the nanorod surface properties regulate the compatibilization behavior and the morphology transition in demixing polymer blends, we perform dissipative particle dynamics simulations and study the impact of three typical nanorods on the phase separation kinetics and structure as well as their location and arrangement under both shear-free and shear conditions with the variation of nanorod–polymer affinity parameters. Depending on the dispersion and location of nanorods, blends in the quiescent case either undergo full phase separation and generate bulky two-phase morphology, or experience microphase separation and form BμE-like structure, or proceed viscoelastic phase separation and take the kinetically trapped cocontinuous network morphology, whereas shear flow can either accelerate domain coarsening or strongly impact the phase behavior through shear-induced bulk phase separation or shear-induced ordering transition. Particularly, the shear-induced lamellar phase in Janus ...

Effect of phase separation kinetics on the homogenization kinetics of solid solution of 4He in 3He

New features of the kinetics of phase separation and the subsequent homogenization of solid solutions of 4He in 3He are observed at temperatures of 0.1–0.5 K. Separation was initiated by rapid cooling of a uniform solution, as well as by cooling it in small temperature steps. Information on the kinetics of the phase transitions was obtained using precision measurements of the pressure of the solid helium at constant volume. The homogenization kinetics are found to depend substantially on the kinetics of the preceding separation. The time constants for homogenization in the separation region are smaller by more than a factor of 5 with rapid cooling, than with slow cooling. These results are consistent with a model of homogeneous nucleation.

A Physical Model for Three‐Phase Compaction in Silicic Magma Reservoirs

AbstractWe develop a model for phase separation in magma reservoirs containing a mixture of silicate melt, crystals, and fluids (exsolved volatiles). The interplay between the three phases controls the dynamics of phase separation and consequently the chemical and physical evolution of magma reservoirs. The model we propose is based on the two‐phase damage theory approach of Bercovici et al. (2001, https://doi.org/10.1029/2000JB900430) and Bercovici and Ricard (2003, https://doi.org/10.1046/j.1365-246X.2003.01854.x) because it offers the leverage of considering interface (in the macroscopic limit) between phases that can deform depending on the mechanical work and phase changes taking place locally in the magma. Damage models also offer the advantage that pressure is defined uniquely to each phase and does not need to be equal among phases, which will enable us to consider, in future studies, the large capillary pressure at which fluids are mobilized in mature, crystal‐rich, magma bodies. In this first analysis of three‐phase compaction, we solve the three‐phase compaction equations numerically for a simple 1‐D problem where we focus on the effect of fluids on the efficiency of melt‐crystal separation considering the competition between viscous and buoyancy stresses only. We contrast three sets of simulations to explore the behavior of three‐phase compaction, a melt‐crystal reference compaction scenario (two‐phase compaction), a three‐phase scenario without phase changes, and finally a three‐phase scenario with a parameterized second boiling (crystallization‐induced exsolution). The simulations show a dramatic difference between two‐phase (melt crystals) and three‐phase (melt‐crystals‐exsolved volatiles) compaction‐driven phase separation. We find that the presence of a lighter, significantly less viscous fluid hinders melt‐crystal separation.

Correlation effects in the quench-induced phase separation dynamics of a two species ultracold quantum gas

We explore the quench dynamics of a binary Bose–Einstein condensate crossing the miscibility–immiscibility threshold and vice versa, both within and in particular beyond the mean-field approximation. Increasing the interspecies repulsion leads to the filamentation of the density of each species, involving shorter wavenumbers and longer spatial scales in the many-body (MB) approach. These filaments appear to be strongly correlated and exhibit domain-wall structures. Following the reverse quench process multiple dark–antidark solitary waves are spontaneously generated and subsequently found to decay in the MB scenario. We simulate single-shot images to connect our findings to possible experimental realizations. Finally, the growth rate of the variance of a sample of single-shots probes the degree of entanglement inherent in the system.

Mesoscopic simulation and characterization of the morphological evolution in phase separating fluid mixtures

In this article, we use a mesoscopic model discretized with Smoothed Dissipative Particle Dynamics to study the formation of morphology behind a moving precipitation front in a phase separating fluid mixture. In contrast to previous models we include thermodynamically consistent thermal fluctuations of the mass fraction in a binary mixture. The model is validated by phase separation dynamics and probability distribution functions of the thermal fluctuations. Variation of the velocity of the precipitation front and initial composition in 2D and 3D leads to diverse morphology. We characterize these morphology using a time- and space-dependent mapping procedure using the variables of the model of Doi & Ohta to identify different orientations of the evolving porous structure.

Aqueous food-grade and cosmetic-grade surfactant systems for the continuous countercurrent cloud point extraction

Abstract Nonionic surfactant aqueous two-phase systems represent an alternative extracting media to conventional organic solvents by ensuring a mild process temperature in an aqueous environment. However, their large-scale implementation is limited due to the challenging stripping of the target substances from the surfactant. In this study, we demonstrate the application of aqueous food-grade and cosmetic-grade surfactant systems as extraction media for solutes of natural origin. We suggest that no separation of surfactant and target product (or only rough separation is sufficient) is needed in this case due to the application of both substances in the final food or cosmetic formulation. To this purpose, sixteen potential commercial surfactants applied in food or in the personal care industry were investigated for their cloud point temperature and their phase separation kinetics. Among those, the aqueous surfactant systems containing Silwet L-7230 (poly[dimethylsiloxane-co-methyl(3-hydroxypropyl)siloxane]-graft-poly(ethylene/propylene glycol) and ROKAnol NL5 (C9–11, branched and linear, ethoxylated alcohol) separated in two phases rapidly at temperatures below 50 °C. Therefore, the liquid-liquid equilibria of the mixtures Silwet L-7230/water and ROKAnol NL5/water were determined, exhibiting lower critical solution temperatures (LCSTs) of 37.3 °C and 33.5 °C, respectively. Additionally, the mixtures were investigated for their capacity to extract the model solute cinnamic acid ((2E)-3-phenylprop-2-enoic acid, CA). Batch separations with 10 logP CA = 0.9 for ROKAnol NL5 and 10 logP CA = 1.6 for Silwet L-7230 were achieved, proving the potential of these surfactants for the extraction of hydrophobic compounds. To further design a stable liquid-liquid extraction process, the density and viscosity of the surfactant-water mixtures were measured. The density differences between the micellar and aqueous phases was found to be sufficient for continuous extraction, whereby the system with ROKAnol NL5 consisted of an upper surfactant-rich phase and a lower surfactant-lean phase, and vice versa for the Silwet L-7230 system. The formation of a liquid crystalline structure with high viscosity was observed in the Silwet L-7230 micellar phase. Based on these investigations, the corresponding processes were designed and finally, for the first time, the food-grade Silwet L-7230 and the cosmetic-grade ROKAnol NL5 surfactant systems could be successfully implemented in the batch (yield = 77% and 80%) and in the continuous (yield = 96% and 100%) cloud point extraction of cinnamic acid.

Designing Highly Thermostable Lysozyme–Copolymer Conjugates: Focus on Effect of Polymer Concentration

Designing biomaterials capable of functioning in harsh environments is vital for a range of applications. Using molecular dynamics simulations, we show that conjugating lysozymes with a copolymer [poly(GMA- stat-OEGMA)] comprising glycidyl methacrylate (GMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) results in a dramatic increase of stability of these enzymes at high temperatures provided that the concentration of the copolymer in the close vicinity of the enzyme exceeds a critical value. In our simulations, we use triads containing the same ratio of GMA to OEGMA units as in our recent experiments (N. S. Yadavalli et al., ACS Catalysis, 2017, 7, 8675). We focus on the dynamics of the conjugate at high temperatures and on its structural stability as a function of the copolymer/water content in the vicinity of the enzyme. We show that the dynamics of phase separation in the water-copolymer mixture surrounding the enzyme is critical for the structural stability of the enzyme. Specifically, restricting water access promotes the structural stability of the lysozyme at high temperatures. We identified critical water concentration below which we observe a robust stabilization; the phase separation is no longer observed at this low fraction of water so that the water domains promoting unfolding are no longer formed in the vicinity of the enzyme. This understanding provides a basis for future studies on designing a range of enzyme-copolymer conjugates with improved stability.

Mathematical modeling and computational simulation of phase separation in ternary mixtures

In this study, a phase field model for ternary partially miscible mixture is derived by extending an existing model for binary mixture. Particularly, a fourth-order free energy function for binary mixture is extended to a ternary model in such a way that the ternary model is dynamically and algebraically consistent with the binary model. The ternary model is employed to study the phase separation dynamics of ternary mixtures under initial still conditions. The scaling of domain size growth, d∝τ1/3, is always obeyed, which appears at the late stage of the phase separation. The scaling law can appear relatively earlier if one phase is totally spreading between two other phases.

Advances in Quantitative Analysis of Intracellular Protein Phase Separation Kinetics and its Modulation by Cellular Interactions

Advances in Quantitative Analysis of Intracellular Protein Phase Separation Kinetics and its Modulation by Cellular Interactions

Hydrodynamics of binary-fluid mixtures —An augmented Multiparticle Collison Dynamics approach

The Multiparticle Collision Dynamics technique (MPC) for hydrodynamics simulations is generalized to binary-fluid mixtures and multiphase flows, by coupling the particle-based fluid dynamics to a Ginzburg-Landau free-energy functional for phase-separating binary fluids. To describe fluids with a non-ideal equation of state, an additional density-dependent term is introduced. The new approach is verified by applying it to thermodynamics near the critical demixing point, and interface fluctuations of droplets. The interfacial tension obtained from the analysis of the capillary-wave spectrum agrees well with the results based on the Laplace-Young equation. Phase separation dynamics follows the Lifshitz-Slyozov law.

Synthesis, surface properties and temperature dependence of phase separation of DSPE chains in ethanol solutions

The surface properties, phase separation processes and kinetics of a DSPE/ethanol solution were investigated.

Theories of binary fluid mixtures: from phase-separation kinetics to active emulsions

Binary fluid mixtures are examples of complex fluids whose microstructure and flow are strongly coupled. For pairs of simple fluids, the microstructure consists of droplets or bicontinuous demixed domains and the physics is controlled by the interfaces between these domains. At continuum level, the structure is defined by a composition field whose gradients – which are steep near interfaces – drive its diffusive current. These gradients also cause thermodynamic stresses which can drive fluid flow. Fluid flow in turn advects the composition field, while thermal noise creates additional random fluxes that allow the system to explore its configuration space and move towards the Boltzmann distribution. This article introduces continuum models of binary fluids, first covering some well-studied areas such as the thermodynamics and kinetics of phase separation, and emulsion stability. We then address cases where one of the fluid components has anisotropic structure at mesoscopic scales creating nematic (or polar) liquid-crystalline order; this can be described through an additional tensor (or vector) order parameter field. We conclude by outlining a thriving area of current research, namely active emulsions, in which one of the binary components consists of living or synthetic material that is continuously converting chemical energy into mechanical work. Such activity can be modelled with judicious additional terms in the equations of motion for simple or liquid-crystalline binary fluids. Throughout, the emphasis of the article is on presenting the theoretical tools needed to address a wide range of physical phenomena. Examples include the kinetics of fluid–fluid demixing from an initially uniform state; the result of imposing a steady macroscopic shear flow on this demixing process; and the diffusive coarsening, Brownian motion and coalescence of emulsion droplets. We discuss strategies to create long-lived emulsions by adding trapped species, solid particles, or surfactants; to address the latter, we outline the theory of bending energy for interfacial films. In emulsions where one of the components is liquid-crystalline, ‘anchoring’ terms can create preferential orientation tangential or normal to the fluid–fluid interface. These allow droplets of an isotropic fluid in a liquid crystal (orvice versa) to support a variety of topological defects, which we describe, altering their interactions and stability. Addition of active terms to the equations of motion for binary simple fluids creates a model of ‘motility-induced’ phase separation, where demixing stems from self-propulsion of particles rather than their interaction forces, altering the relation between interfacial structure and fluid stress. Coupling activity to binary liquid crystal dynamics creates models of active liquid-crystalline emulsion droplets. Such droplets show various modes of locomotion, some of which strikingly resemble the swimming or crawling motions of biological cells.

Effects of substrate temperature and deposition rate on the phase separated morphology of co-sputtered, Cu-Mo thin films

We report on the evolution of phase-separated morphologies in co-sputtered Cu-Mo films as a result of varying substrate temperature and deposition rate during deposition. A transition from vertically-oriented concentration modulations to laterally-oriented modulations followed by randomly-oriented modulations was observed in the Cu-Mo films because of changing substrate temperature at constant deposition rate. A refinement of the Cu-Mo domains was observed at increasing deposition rate at a constant substrate temperature. A coarsening of phase-separated domains was also observed with increasing substrate temperature. The phase separation kinetics that controlled film morphology were limited by the surface interdiffusion of each species as the film grew in thickness. Control over the surface interdiffusion length was achieved by altering the deposition temperature and material flux.