Possibility Of Phase Separation Research Articles

Molecular dynamics study of the thermodynamic properties of triglyceride/methanol mixtures in the presence of cosolvent

Biodiesel is a renewable source of energy that has the potential to replace fossil fuel-based resources. It is produced via the transesterification reaction in which a triglyceride reacts with methanol in the presence of a catalyst. Cosolvents are usually added to the reactants in transesterification to improve the mutual solubility of methanol and triglycerides and to create a single phase. The commonly used cosolvents in transesterification include tetrahydrofuran (THF) and diethyl ether (DEE). Understanding the thermodynamic properties of this system is important in the selection of cosolvent. In this study, molecular dynamics simulations were used to study the mixing behavior between the components of ternary mixtures of triolein/methanol/THF and triolein/methanol/DEE via the application of Flory-Huggins theory of solutions. A simple approach to calculation of the Flory-Huggins interaction parameters is used in which the mixing energy is derived from averaged non-bonded pair interaction energies. Apart from pure triolein, these ternary systems resemble the experimentally studied ternary systems employing various plant-based oils. The binary interaction parameters, Gibbs Free energy and chemical potentials of the components were calculated to study the mixing behavior. Our results show that along the experimental phase boundary the binary interaction parameters remain relatively unchanged with a deviation observed at the highest volume fractions of triolein where the highest binary interactions were observed indicating the possibility of phase separation. The Gibbs energy of mixing for the systems changed from positive to negative as one moves from two phase to single phase part of the ternary system as expected and in agreement with experimental data. The chemical potentials of the ternary mixture components were calculated from the partial derivatives of the Gibbs free energy of mixing. The activities calculated from Flory-Huggins chemical potentials were compared to those calculated using the UNIFAC model. There is good agreement between the two, with both able to predict a single and biphasic mixture. However, disagreements are noted at low and high concentrations of triolein.

Impact of thermomechanical reprocessing on multilayer plastic packaging blend

Multilayer plastic packaging (MPP) has attracted extensive attention due to its functionality and inherent difficulty in reclamation. One primary concern is the performance of reprocessed MPP since it inherently consists of many dissimilar polymers. This study aims to assess the effect of multiple thermomechanical reprocessing cycles on the properties of a MPP blend. Low density polyethylene (LDPE)/maleic anhydride grafted linear LDPE (LLDPE-g-MA)/ethylene vinyl alcohol (EVOH) blend was manufactured and subjected to thermomechanical reprocessing, including thermal compounding, grinding, and injection molding for six cycles to characterize the impact of thermomechanical reprocessing on the blend's mechanical, morphological, thermal, and rheological properties. The tensile strength and modulus of the reprocessed blend remained consistent throughout six cycles. A pronounced decline in elongation at break was observed after four cycles of reprocessing. Toughness, as represented by the essential work of fracture, increased steadily up to three cycles of processing, followed by a decline in the following reprocessing cycles. The main property change is possibly caused by the gelling of the EVOH in the reprocessed blend, as demonstrated by larger EVOH agglomerates in the LDPE matrix. Differential scanning calorimetry results indicated that the degree of crystallization of the EVOH phase changed with increasing reprocessing cycles, suggesting EVOH degradation. Rheological behavior in the linear viscoelastic region indicated enhanced interfacial interaction between LDPE and EVOH due to the cross-linking of LLDPE-g-MA and rigid EVOH in the early reprocessing stages. After four cycles of reprocessing, decreases in storage and loss moduli were observed, indicating the possibility of phase separation caused by gelling of EVOH. Using polymer blending to reclaim LDPE-based EVOH multilayer is promising for up to four cycles of reprocessing as shown by mechanical, thermal, and rheological behaviors.

Flash-Thermal Shock Synthesis of High-Entropy Alloys Toward High-Performance Water Splitting.

High-entropy alloys (HEAs) provide unprecedented physicochemical properties over unary nanoparticles (NPs). According to the conventional alloying guideline (Hume-Rothery rule), however, only size-and-structure similar elements can be mixed, limiting the possible combinations of alloying elements. Recently, it has been reported that based on carbon thermal shocks (CTS) in a vacuum atmosphere at high temperature, ultrafast heating/cooling rates and high-entropy environment play a critical role in the synthesis of HEAs, ruling out the possibility of phase separation. Since the CTS requires conducting supports, the Joule-heating efficiencies rely on the carbon qualities, featuring difficulties in uniform heating along the large area. This work proposes a photo-thermal approach as an alternative and innovative synthetic method that is compatible with ambient air, large-area, remote process, and free of materials selection. Single flash irradiation on carbon nanofibers induced momentary high-temperature annealing (>1800°C within 20ms duration, and ramping/cooling rates >104 Ks-1 ) to successfully decorate HEA NPs up to nine elements with excellent compatibility for large-scale synthesis (6.0 × 6.0 cm2 of carbon nanofiber paper). To demonstrate their feasibility toward applications, senary HEA NPs (PtIrFeNiCoCe) are designed and screened, showing high activity (ηoverall = 777mV) and excellent stability (>5000 cycles) at the water splitting, including hydrogen evolution reactions and oxygen evolution reactions.

Fine Particles as Solute in Fine Particle (Dusty) Plasmas

Analysis has been made on a possibility of phase separation and critical point as a solution of fine particles in plasmas, extending the previous work which pointed out this as one of two such possibilities. Fine particles are treated as a solute in the solvent of weakly coupled plasmas of electrons and ions. Examples of phase diagram have been obtained and coexisting phases are shown to have fine particles which differ in densities by almost one order of magnitude.

Phase separation in aqueous systems for realizing virtually significant extractions

Polyvinylpyrrolidone (PVP) forms aqueous biphasic systems with tri-block co-polymers, surfactants and salts. The phase diagrams of PVP–salt and PVP–surfactant systems were constructed by a turbidometric titration method at 296 K. Density measurements of the phase forming solutions at this temperature also led to an attractive outcome of the formation of two tri-phasic systems among the components of our study (Na-tartrate + PVP + Triton-X-100 and Na-tartrate + PVP + PPG–PEG–PPG). We also constructed a spreadsheet reflecting the relationship between miscibility and the possibility of phase separation between the components, consisting of the seven phase forming solutions to open up different possibilities of ABS formation. Some completely new biphasic systems were obtained as well as the process of gel formation of a PVA solution in the presence of salt and polymer solutions was also observed. The applications of some of the developed ABSs are described for the recovery of an antibiotic drug, amoxicillin and a catalyst, molybdenum disulphide.

Gas/particle partitioning of n-alkanes, PAHs and oxygenated PAHs in urban Denver

In this study, a medium volume sampler equipped with quartz fiber filters (QFFs) and a polyurethane foam (PUF)/XAD-4/PUF sandwich (PXP) was used to collect semi-volatile organic compounds (SVOCs) in both gaseous and particle (PM2.5) phases. A backup QFF (bQFF) was used to evaluate possible sampling artifact of particulate organics due to vapor-phase adsorption. A series of n-alkanes (molecular weight: 170–562) and PAHs (128–300), and two oxy-PAHs (acenaphthenone, 168; fluorenone, 180) were measured. Breakthrough experiments demonstrated that the PXP could collect all gas-phase target compounds with high efficiency, even the low molecular weight (MW) species (e.g., naphthalene). Comparing species concentrations across different sampling matrices encountered at the Denver, Colorado field site, the light n-alkanes (MW < 282) and PAHs (MW < 192) were mostly distributed into the gas phase; while those heavy n-alkanes (MW > 324) and PAHs (MW > 202) were primarily in the particle phase (Average temperature, 12.5 ± 10.1 °C). Log values of measured gas/particle (G/P) partitioning coefficients (Kmp,OM) of selected SVOCs (docosane, tricosane, fluoranthene, pyrene, acenaphthenone and fluorenone) were linearly regressed to those of theoretically-based partitioning coefficients (Ktp,OM) for comparison. Prior to Kmp,OM calculation, the gas- and particle-phase concentrations of SVOCs were corrected following two different approaches based on bQFF measurements. The first approach assumed that the bQFF associated SVOCs were from the adsorption of gaseous SVOCs (positive artifact); the second approach assumed equal contributions from positive and negative (organics evaporated from top QFF and adsorbed by bQFF) artifacts. Under both corrections, significant correlations (p < 0.05) were observed between log Kmp,OM and log Ktp,OM for the six selected SVOCs, suggesting that the predicted G/P partitioning can reasonably capture the measured G/P partitioning behavior. The large deviations (1-2 orders of magnitudes) between Kmp,OM and Ktp,OM for acenaphthenone and fluorenone might be caused by the assumption of ideality (activity coefficient = 1) and the over prediction of vapor pressures (for Ktp,OM calculation). Negative correlations were observed between regression residuals of log Kmp,OM vs. log Ktp,OM and relative humidity, which might be attributed to the use of a constant activity coefficient and the possibility of phase separation.

Fischer–Tropsch Synthesis Over Cobalt Supported On Silica‐Incorporated Mesoporous Carbon

AbstractThe influence of carbon–silica hybrid supports on cobalt catalysts in Fischer–Tropsch synthesishas been investigated. Mesoporous carbon–silica hybrid supports were synthesized through a hydrogen‐bonding‐assisted self‐assembly route by loading different amounts of silica (0 to 45 %) as a framework composition with mesoporous carbon. These carbon and hybrid supports were then impregnated with 15 wt. % cobalt and the resulting catalysts were characterized by various physicochemical, gravimetric, and spectroscopic methods. The dispersion of silica in the framework of mesoporous carbon modified the surface chemistry and enhanced the wetting properties of the support. Hence, the dispersion and reducibility of cobalt over the hybrid supports increased compared to those of the carbon‐supported catalyst. However, above the optimum silica incorporation of 34 %, the possibility of phase separation and structural transformation of silica at the high carbonization temperature decreased the dispersion and reducibility of the supported Co catalysts. The carbon‐supported catalyst showed a quick drop in the activity during the initial stages of the reaction due to the migration of cobalt particles over the hydrophobic and inert support surface. On the contrary, carbon–silica hybrid supports inhibited the mobility of cobalt particles and produced a higher density of active Co0 sites, leading to a higher initial activity. Carbon–silica‐supported catalysts with a silica content of up to 34 % were found to exhibit excellent steady state Fischer–Tropsch synthesis activity and C5+ selectivity compared to only carbon and carbon–silica‐supported catalyst with &gt;34 % silica incorporation.

Organic particulate matter formation at varying relative humidity using surrogate secondary and primary organic compounds with activity corrections in the condensed phase obtained using a method based on the Wilson equation

Abstract. Secondary organic aerosol (SOA) formation in the atmosphere is currently often modeled using a multiple lumped "two-product" (N·2p) approach. The N·2p approach neglects: 1) variation of activity coefficient (ζi) values and mean molecular weight MW in the particulate matter (PM) phase; 2) water uptake into the PM; and 3) the possibility of phase separation in the PM. This study considers these effects by adopting an (N·2p)ζpMW,ζ approach (θ is a phase index). Specific chemical structures are assigned to 25 lumped SOA compounds and to 15 representative primary organic aerosol (POA) compounds to allow calculation of ζi and MW values. The SOA structure assignments are based on chamber-derived 2p gas/particle partition coefficient values coupled with known effects of structure on vapor pressure pL,io (atm). To facilitate adoption of the (N·2p)ζpMW,θ approach in large-scale models, this study also develops CP-Wilson.1 (Chang-Pankow-Wilson.1), a group-contribution ζi-prediction method that is more computationally economical than the UNIFAC model of Fredenslund et al. (1975). Group parameter values required by CP-Wilson.1 are obtained by fitting ζi values to predictions from UNIFAC. The (N·2p)ζpMW,θ approach is applied (using CP-Wilson.1) to several real α-pinene/O3 chamber cases for high reacted hydrocarbon levels (ΔHC≈400 to 1000 μg m−3) when relative humidity (RH) ≈50%. Good agreement between the chamber and predicted results is obtained using both the (N·2p)ζpMW,θ and N·2p approaches, indicating relatively small water effects under these conditions. However, for a hypothetical α-pinene/O3 case at ΔHC=30 μg m−3 and RH=50%, the (N·2p)ζpMW,θ approach predicts that water uptake will lead to an organic PM level that is more double that predicted by the N·2p approach. Adoption of the (N·2p)ζpMW,θ approach using reasonable lumped structures for SOA and POA compounds is recommended for ambient PM modeling.

Preparation and properties of bio‐nanoreinforced composites from biodegradable polymer matrix and cellulose whiskers

AbstractCrystalline cellulose was extracted from one of the cheapest source; grass by alkali, acid, and mechanical treatments. To evaluate the reinforcing effect of this filler, biodegradable polymer matrix, polylactic acid (PLA) was used and samples were prepared at different concentrations. The modified whiskers were also used as filler to examine the effect on mechanical properties. Crystallinity, thermal behavior, surface morphology and functional group variation was monitored through, XRD, TGA, SEM, and FTIR respectively. The properties were largely depending on the concentration of filler whereas; modification of hydroxyl groups did not exhibit remarkable change in mechanical properties. Thermal resistance was decreased in comparison of neat matrix and reduction in crystallinity was also observed for composites, regardless of filler nature. It was thought that the hydrophilicity of cellulose could be altered by modifying its hydroxyl groups, thereby promoting dispersion. However, the possibility of phase separation was increased, and the thermal stability of the composites gradually decreased with increasing filler load in the matrix. In the examined systems, it was observed that improvement of reinforcing capacity may not only depend on the chemical compatibility between matrixes but also some compositional and physical parameters may be responsible for variation in properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The carbon number-polarity grid: A means to manage the complexity of the mix of organic compounds when modeling atmospheric organic particulate matter

Current regional models for predicting atmospheric organic particulate matter (OPM) levels rely heavily on the computationally simple, lumped “two-product” (2p) approach for parameterizing the formation of secondary organic aerosol (SOA). At the other extreme, molecular kinetic models of SOA formation are available that use numerous complex reaction pathways to produce large numbers of potentially condensable organic oxidation products, but the complexities of those models currently limit implementation in large-scale air quality models. This study proposes use of a carbon number ( n C) vs. polarity grid (with concentration bins) for tracking the various OPM-relevant compounds and their time-dependent concentrations T i (μg m −3). The grid can be used when adding complexity to the 2p approach, or for managing and limiting the complexity of molecular kinetic models. For the former, an expanded n p + m P approach is proposed with n products and m possible types of very low volatility polymer ( P ) materials. For the latter, the grid limits system complexity by allowing compounds with similar structures to be lumped together in the same grid bin even when they are formed by different routes. With either an n p + m P approach or a molecular kinetic approach, the n C vs. polarity grid will allow consideration of the effects of variation in the activity coefficients ζ i of the partitioning compounds, variation in the mean molecular weight of the absorbing OPM phase, water uptake, and the possibility of phase separation in the OPM phase.

A model for phase separation in systems with orbital ordering

The possibility of phase separation in the substances with orbital ordering is analyzed. The additional charge carriers introduced due to doping favor the formation of nanosize inhomogeneities with the orbital structure different from that in the undoped material. The shapes and sizes of such inhomogeneities are determined.

Diverse approaches to the controlled generation of nanotextured surfaces

Abstract Smooth, chemically uniform surfaces are seldom found in nature. Mimicry of natural variegation is a powerful approach for controlling chemical affinity at the nanoscale. Molecular recognition is one of the fundamental concepts underlying the functioning of living cells, and it depends on a particular relationship between the nanoscale, i.e., molecular, variegations of two potentially interacting molecular partners. The primary subject matter of this paper is how to articially generate appropriate nanoscale texture at the surfaces of materials. Excluding "pick and place" chemistry, in which essentially a Maxwellian demon intervenes to place objects with atomic precision, and nowadays achievable through an adaptation of atomic force microscopy, on the grounds that it is too slow to be practicable for fabricating useful quantities of material, three approaches are explored in some detail: (i) "powder", i.e., mixing at least two individually monofunctional (with respect to the ultimate molecular recognition task) precursor components (possibly with secondary functionality enabling them to appropriately self-assemble on a substratum); (ii) mixing polymers with the possibility of phase separation and frustrated phase separation with block copolymers; and (iii) felting. The emphasis is on processes that create more or less irregular structures, rather than regular arrays. The final section deals with the metrology of nanotexture.

The role of static and dynamic characteristics of diglycerol esters and β-lactoglobulin mixed films foaming. 1. Dynamic phenomena at the air–water interface

In this work, we have studied dynamic surface pressure and surface dilatational characteristics of diglycerol esters (diglycerol monolaurate and diglycerol monostearate) and β-lactoglobulin mixed films adsorbed at the air–water interface. The concentrations of protein and lipid and the protein/lipid ratio in the aqueous bulk phase were studied as variables, while pH (7), ionic strength (0.05 M) and temperature (20 °C) were maintained constant. We have observed competitive adsorption from aqueous solutions of mixed emulsifiers ( β-lactoglobulin and diglycerol esters) and/or the displacement between emulsifiers at the air–water interface depending on the chemistry of the lipid and on the protein/lipid ratio. For the mixed systems a lag period was not observed, even for low concentrations of emulsifiers in solution. During the initial period the kinetics of adsorption of mixed emulsifiers at the air–water interface are controlled by a diffusion mechanism. At long-term adsorption the rate of penetration controls the adsorption of mixed emulsifiers at the interface, which increases with the lipid concentration in solution and is faster for diglycerol monostearate than for diglycerol monolaurate. From a rheological point of view, mixed films behave as viscoelastic (practically elastic) with a loss angle tangent higher than zero. The evolution of surface dilatational modulus ( E) with surface pressure ( π) for β-lactoglobulin–diglycerol ester mixed films reflects the amount of emulsifier adsorbed at the interface (giving high values of E at the higher π) and confirms the idea that the protein–lipid interactions at the air–water interface are somewhat weak, there even being the possibility of phase separation.

Carrier-density effects in many-polaron systems

Many-polaron systems with finite charge-carrier density are often encounteredexperimentally. However, until recently, no satisfactory theoretical description of thesesystems has been available even in the framework of simple models such as theone-dimensional spinless Holstein model considered here. In this work, previous resultsobtained using numerical as well as analytical approaches are reviewed from a unifiedperspective, focusing on spectral properties which reveal the nature of the quasiparticles inthe system. In the adiabatic regime and for intermediate electron–phonon coupling, acarrier-density driven crossover from a polaronic to a rather metallic system takes place.Further insight into the effects due to changes in density is gained by calculating thephonon spectral function, and the fermion–fermion and fermion–lattice correlationfunctions. Finally, we provide strong evidence against the possibility of phase separation.

Interfacial Properties of Diglycerol Esters and Caseinate Mixed Films at the Air−Water Interface

The surface pressure (π) at equilibrium (surface pressure isotherm) and surface dynamic properties (dynamic surface pressure and surface dilatational characteristics) of diglycerol ester (diglycerol-monocaprinate, diglycerol-monolaurate, diglycerol-monostearate, and diglycerol-monooleate) and protein (sodium caseinate) as emulsifiers, at different concentrations in the aqueous phase, were measured using tensiometry and a dynamic drop tensiometer, respectively. We have observed that (1) at equilibrium the value of critical micelle concentration (CMC) decreases and the maximum surface excess (Γmax) increases as the hydrocarbon chain increases because the hydrophobic character of the lipid also increases. The presence of a double bond in the hydrocarbon chain also increases the value of CMC and decreases those of Γmax. Caseinate presents higher adsorption efficiency but the surface activity is between those for lipids. The surface pressure isotherm of mixed systems is dependent on the emulsifier concentration and the protein/lipid ratio in the mixture. (2) The adsorption of pure emulsifiers at the air−water interface increases with emulsifier concentration in the aqueous phase via diffusion and penetration of the emulsifier at the interface. For mixed films, the rate of adsorption depends on the concentration and composition of the mixture. Competitive or cooperative phenomena were observed during the adsorption of both emulsifiers at the interface. (3) The surface dilatational characteristics of mixed films are viscoelastic. The surface dilatational modulus reflects the amount of emulsifier adsorbed at the interface and confirms the idea that the protein−lipid interactions at the air−water interface are somewhat weak, there even being the possibility of phase separation.

Phase separation in H2O:N2 mixture: Molecular dynamics simulations using atomistic force fields

A class II atomistic force field with Lennard-Jones 6-9 nonbond interactions is used to investigate equations of state (EOS) for important high explosive detonation products N(2) and H(2)O in the temperature range of 700-2500 K and pressure range of 0.1-10 GPa. A standard sixth order parameter-mixing scheme is then employed to study a 2:1 (molar) H(2)O:N(2) mixture, to investigate, in particular, the possibility of phase separation under detonation conditions. The simulations demonstrate several important results, including (i) the accuracy of computed EOS for both N(2) and H(2)O over the entire range of temperature and pressure considered, (ii) accurate mixing-demixing phase boundary as compared to experimental data, and (iii) the departure of mixing free energy from that predicted by ideal mixing law. The results provide comparison and guidance to state-of-the-art chemical kinetic models.

Superconducting properties of [formula omitted][formula omitted

The superconducting properties of the magnetic ( T M ≈ 130 K ) superconductors RuSr 2 RECu 2 O 8 ( RE = Eu , Gd ) ( T c , Eu ≈ 27.5 K , T c , Gd ≈ 46 K ) were investigated using resistance and AC-susceptibility measurements. T c , Eu showed a magnetic-field dependence up to 14 T which can be described by the empirical relation T c ( B ) = T c ( 0 ) [ 1 - B / B c ( 0 ) ] 1 / 2 , contrary to previous reports pointing out the possibility of phase separation in the ruthenocuprates. A plausible explanation of this discrepancy is based on the significance of the Ru 5 + / Ru 4 + ratio in the ruthenocuprates affecting the competition between antiferromagnetic superexchange and ferromagnetic double exchange in these compounds.

Origin of particle clustering in a simulated polymer nanocomposite and its impact on rheology

Many nanoparticles have short-range interactions relative to their size, and these interactions tend to be “patchy” since the interatomic spacing is comparable to the nanoparticle size. For a dispersion of such particles, it is not a priori obvious what mechanism will control the clustering of the nanoparticles, and how the clustering will be affected by tuning various control parameters. To gain insight into these questions, we perform molecular dynamics simulations of polyhedral nanoparticles in a dense bead–spring polymer melt under both quiescent and steady shear conditions. We explore the mechanism that controls nanoparticle clustering and find that the crossover from dispersed to clustered states is consistent with the predictions for equilibrium particle association or equilibrium polymerization, and that the crossover does not appear to match the expectations for first-order phase separation typical for binary mixtures in the region of the phase diagram where we can equilibrate the system. At the same time, we cannot rule out the possibility of phase separation at a lower temperature. Utilizing the existing framework for dynamic clustering transitions offers the possibility of more rationally controlling the dispersion and properties of nanocomposite materials. Finally, we examine how nanocomposite rheology depends on the state of equilibrium clustering. We find that the shear viscosity for dispersed configurations is larger than that for clustered configurations, in contrast to expectations based on macroscopic colloidal dispersions. We explain this result by the alteration of the polymer matrix properties in the vicinity of the nanoparticles. We also show that shear tends to disperse clustered nanoparticle configurations in our system, an effect particularly important for processing.

Statistical Theory of Elastic Constants of Cholesteric Liquid Crystals

A statistical theory of cholesteric liquid crystals composed of short rigid biaxial molecules is presented. It is derived in the thermodynamic limit at a small density and a small twist. The uniaxial (biaxial) cholesteric phase is regarded as a distorted form of the uniaxial (biaxial) nematic phase. The chirality of the interactions and the implementation of the inversion to the rotation matrix elements are discussed in detail. General microscopic expressions for the elastic constants are derived. The expressions involve the one-particle distribution function and the potential energy of two-body short-range interactions. It is shown that the elastic constants determine the twist of the phase. The stability condition for the cholesteric and nematic phases is presented. The theory is used to study unary and binary systems. The temperature and concentration dependence of the order parameters, the elastic constants and the twist of the phase are obtained. The possibility of phase separation is not investigated.

Exact bounds on the ground-state energy of the infinite-UHubbard model

We give upper and lower bounds for the ground-state energy of the infinite-$U$ Hubbard model. In two dimensions, using these bounds we are able to rule out the possibility of phase separation between the undoped-insulating state and a hole-rich state.