Nature Of Phase Separation Research Articles

Exploration of micellization and phase separation nature of surfactants in metformin hydrochloride + additives media: An experimental and DFT study

The study explores the aggregation and phase separation of a newly synthesized cationic surfactant − octadecyltriethylammonium bromide (OTEAB) and triton X-100 (TX-100) respectively with/without metformin hydrochloride (MMH) drug in absence/presence of NaCl. The conductivity measurements were performed to investigate the aggregation of cationic OTEAB at temperatures between 298.15 and 323.15 K with a 5 K gap. The micelle development of OTEAB in pure state and with MMH drug has been assessed by determining the critical micelle concentration (CMC). The reduction of CMC of OTEAB has been detected owing to the introduction of the MMH drug. The CMC was further decreased in attendance of NaCl. The CMC values also demonstrate the dependency on the change of temperature in all situations investigated. The decrease of CP values of triton X-100 and MMH mixture in aqueous NaCl was attained with the augmentation of the concentration of NaCl. The negative and positive values of free energy of micellization (ΔGm0) and clouding (ΔGc0) indicate the spontaneous and nonspontaneous nature of the respective processes. The enthalpy (ΔHm0) and entropy(ΔSm0) changes of the micellization were negative (exothermic) and positive, respectively. The enthalpy (ΔHc0) and entropy(ΔSc0) changes of the clouding were negative (exothermic) and positive, respectively, at lesser and higher concentrations of NaCl. The values of ΔHm0/ΔHc0 and ΔSm0/ΔSc0 designated that both hydrophobic and electrostatic interaction are present as important forces among the components under investigation. The thermodynamics of transfer and the enthalpy-entropy compensation parameters for the two processes were also computed and explained appropriately. Herein, we have also performed the computational analysis to find out the optimized structures, HOMO-LUMO orbitals, and the band gaps of OTEAB, MMH, and OTEAB+MMH mixture.

Effect of electrolytes on the mechanism of clouding process and physico-chemical quantities of non-ionic surfactant and ciprofloxacin hydrochloride mixture

An investigation of the clouding behaviour of the aqueous solution of ciprofloxacin hydrochloride (CIPH) + Triton X-100 (TX-100) under different electrolytes media was performed by the phase-changing measurement method. The CP of the resultant mixture has been studied in aqueous solutions of some organic and inorganic salts (sodium carbonate (Na2CO3), sodium oxalate (NaOxa), sodium acetate (NaOAc) and magnesium sulphate (MgSO4)). The CP values of TX-100 (50 mmol kg−1) + CIPH (1 mmol kg−1) solution decreases in the presence of all electrolytes while the CP values satisfy the sequence: CP (aq. NaOAc) > CP (aq. MgSO4) > CP (aq. Na2CO3) > CP (aq. NaOxa). The decrease in the solubility of employed solution in the aq. electrolytes media was observed and obtained maximum solubility in aqueous NaOAc and minimum solubility in the aqueous NaOXa medium. The obtained positive Gibbs-free energy ( Δ G c 0 ) demonstrates the nonspontaneous nature of phase separation while the extent of nonspontaneity exhibits the reduction with enhancing electrolyte concentrations. The Δ H c 0 and Δ S c 0 values depict the existences of electrostatic and hydrophobic interactions between TX-100 and CIPH in aq. electrolytes solutions and the clouding process is enthalpy controlled. Entropy-enthalpy compensation variables were computed.

Physicochemical approaches reveal the impact of electrolytes and hydrotropic salt on micellization and phase separation behavior of polymer polyvinyl alcohol and surfactant mixture

The polymer-surfactant mixture has usages in numerous industries mainly in the production of daily used materials. Herein, the micellization and phase separation nature of the sodium dodecyl sulfate (SDS) and TX-100 along with a synthetic water-soluble polymer-polyvinyl alcohol (PVA) have been conducted using conductivity and cloud point (CP) measurement tools. In the case of micellization study of SDS + PVA mixture by conductivity method, the CMC values were obtained to be dependent on the categories and extent of additives as well as temperature variation. Both categories of studies were performed in aq. solutions of sodium chloride (NaCl), sodium acetate (NaOAc), and sodium benzoate (NaBenz) media. The CP values of TX 100 + PVA were decreased and enhanced in simple electrolytes and sodium benzoate media respectively. In all cases, the free energy changes of micellization (∆Gm0) and clouding (∆Gc0) were obtained as negative and positive respectively. The enthalpy (∆Hm0) and entropy (∆Sm0) changes for SDS + PVA system micellization was negative and positive respectively in aq. NaCl and NaBenz media, and in aq. NaOAc medium the ∆Hm0 values were found negative while ∆Sm0 were found negative except at the highest studied temperature (323.15 K). The enthalpy-entropy compensation of both processes was also assessed and described clearly.

Diffusion kinetics of vitamin B6 from phase-separated gelatin and agarose gels using blending law modelling

This study was conducted to understand the diffusion kinetics of vitamin B6 from composite gels of gelatin and agarose via blending law and diffusion modelling. Fourier-transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), confocal laser scanning microscopy (CLSM) and small-deformation dynamic oscillation in shear were used to analyse the structural properties of the composite gels. UV–vis spectroscopy was employed to study the diffusion kinetics of vitamin B6 from the gelatin-agarose gels. FTIR confirmed the absence of chemical interactions between gelatin and agarose in the mixture. XRD demonstrated that vitamin B6 was thoroughly hydrated in the polymeric mixture that balanced disordered polymer segments with structured junction zones. CLSM provided tangible evidence of the phase-separated nature of the two macromolecules, and blending law predicted the phase volume and their effective concentrations in the system. The diffusion of vitamin B6 from composite gels, prepared with estimated phase volumes and effective concentrations of the individual components according to rheological blending law, was measured with UV–vis spectroscopy. As far as we are aware, for the first time, rheological blending law was recast to provide the corresponding blending law for diffusion. Thus, theoretical diffusion coefficients were calculated and compared favourably with those from the experimental studies. Results argue for the presence of a blending law-based diffusion theory that can predict the diffusion kinetics of bioactive compounds in aqueous composite gels.

Multiscale Modeling of Protein-RNA Condensation in and Out of Equilibrium.

A vast number of intracellular membraneless bodies also known as biomolecular condensates form through a liquid-liquid phase separation (LLPS) of biomolecules. To date, phase separation has been identified as the main driving force for a membraneless organelles such as nucleoli, Cajal bodies, stress granules, and chromatin compartments. Recently, the protein-RNA condensation is receiving increased attention, because it is closely related to the biological function of cells such as transcription, translation, and RNA metabolism. Despite the multidisciplinary efforts put forth to study the biophysical properties of protein-RNA condensates, there are many fundamental unanswered questions regarding the mechanism of formation and regulation of protein-RNA condensates in eukaryotic cells. Major challenges in studying protein-RNA condensation stem from (i) the molecular heterogeneity and conformational flexibility of RNA and protein chains and (ii) the nonequilibrium nature of transcription and cellular environment. Computer simulations, bioinformatics, and mathematical models are uniquely positioned for shedding light on the microscopic nature of protein-RNA phase separation. To this end, there is an urgent need for innovative models with the right spatiotemporal resolution for confronting the experimental observables in a comprehensive and physics-based manner. In this chapter, we will summarize the currently emerging research efforts, which employ atomistic and coarse-grained molecular models and field theoretical models to understand equilibrium and nonequilibrium aspects of protein-RNA condensation.

Study on FeCr thin film for a spintronic material with negative spin polarization

Negative spin polarization materials generate a spin current whose spin direction is opposite to the magnetization direction. This characteristic is technologically important because it increases the freedom in the design of spintronic devices. In this paper, we studied FeCr from the viewpoints of band structure, atomic magnetic moments, and local atomic arrangement to explore its potentiality as a negative spin polarization material. First-principles calculations on the disordered FeCr alloy predicted a high negative spin polarization, which was attributed to the band matching of the minority spin. We experimentally fabricated Fe1-xCrx thin films in the Cr concentration (x) range from 0.2 to 0.4 by sputter deposition and demonstrated inverse magnetoresistance using current-perpendicular-to-plane giant magnetoresistance (GMR) devices, which provided evidence of negative spin polarization. The spin polarization of Fe0.7Cr0.3 estimated from the GMR device measurements was −0.28 and fell below the calculated value. Synchrotron X-ray magnetic circular dichroism measurements showed a ferrimagnetic configuration of the Fe and Cr magnetic moments. The Fe moment showed a large moment over a wide Cr concentration range, whereas the Cr moment decreased with the Cr concentration, which agreed with the calculation result. Synchrotron Mössbauer spectroscopy measurements indicated the inhomogeneity of the FeCr composition even in the as-deposited state. Fe-rich regions were formed after annealing, reflecting the phase separation nature of the Fe-Cr system. Inhomogeneity was not considered in the calculation and could be the origin of the smaller negative spin polarization observed in the experiment.

Role of Solvent Compatibility in the Phase Behavior of Binary Solutions of Weakly Associating Multivalent Polymers.

Condensate formation of biopolymer solutions, prominently those of various intrinsically disordered proteins (IDPs), is often driven by “sticky” interactions between associating residues, multivalently present along the polymer backbone. Using a ternary mean-field “stickers-and-spacers” model, we demonstrate that if sticker association is of the order of a few times the thermal energy, a delicate balance between specific binding and nonspecific polymer–solvent interactions gives rise to a particularly rich ternary phase behavior under physiological circumstances. For a generic system represented by a solution comprising multiassociative scaffold and client polymers, the difference in solvent compatibility between the polymers modulates the nature of isothermal liquid–liquid phase separation (LLPS) between associative and segregative. The calculations reveal regimes of dualistic phase behavior, where both types of LLPS occur within the same phase diagram, either associated with the presence of multiple miscibility gaps or a flip in the slope of the tie-lines belonging to a single coexistence region.

Probing phase separation in Nd1−xSrxMnO3 (x ≈ 0.4, 0.5) polycrystals through temperature dependent magnetic and Raman spectroscopy studies

The manuscript reports temperature-dependent magnetic transitions correlated to variations in the phonon modes in Nd1−xSrxMnO3. Synthesis of x = 0.4 & 0.5 compounds by the solid-state reaction method was followed by structural/microstructural and electronic characterizations. The crystal structure of both compositions is orthorhombic with Pbnm symmetry, as confirmed by x-ray diffraction. The XPS data confirm the mixed Mn valance with the desired stoichiometry. The phase-separated nature is manifested through the occurrence of various phases, e.g., spin-glass (SG), charge order (CO), ferromagnetic (FM), and paramagnetic (PM), as the temperature is varied from 20 to 300 K. The temperature-dependent Raman measurements reveal that although the material is structurally stable in the studied temperature range of 80–440 K, noticeable discontinuities in the phonon mode shifts were noticed. These phonon mode shifts are found to directly correspond to the magnetic transitions. The change in the frequency of the Raman modes with temperature, which causes the observed shift, could be attributed to various factors such as lattice expansion, anharmonic interactions, spin-phonon coupling, electron-phonon interaction, etc. Here, we have used spin-phonon coupling along with lattice expansion as well as anharmonic interactions to describe the behavior of modes in the FM regime and lattice expansion and anharmonic interaction in the PM phase.

Recyclable, self-healing, absorption-dominated and highly effective electromagnetic shielding elastomers based on bridged micro capacitance structures

It is a challenge for carbon based conductive polymer composites (CPC) to combine easiness of fabrication, high EMI shielding effectiveness (EMI SE), high absorptivity, high mechanical properties and self-healing property in one material. Here, a flexible, self-healing and recyclable EMI shielding material is fabricated based on a bridged micro capacitance structure spontaneously formed in ionomer/carbon fillers nanocomposites. The anionic groups in the ionomer phase-separate into aggregates and moreover drive the carbon fillers to align along the aggregates through the anion-π interaction, thereby forming the bridged micro capacitance structure. This structure leads to outstanding EMI SE of 64 dB and high absorption coefficient of 0.82. Meanwhile, the material is self-healable and recyclable due to the dynamic anion-π interaction and autonomous nature of phase separation. In particular, the healed or recycled material shows nearly 100% recovery of EMI SE. The structural design of bridged micro capacitance can be easily extended to other ionomers, leading to a novel class of CPC with significant promise in electronic fields.

Анализ фазовых равновесий в тройной системе Ge–P–Sn

На основании анализа характера фазовых равновесий в двойных системах, ограняющих диаграмму состояний тройной системы Ge – P – Sn, предложены теоретически возможные схемы ее фазового субсолидусного разграничения. Исследование методом рентгенофазового анализа образцов, принадлежащих политермическим сечениям Sn4P3-Ge, Sn4P3-GeP, показало, что разделение трехкомпонентной диаграммы состояния ниже солидуса осуществляется с помощью сечений Sn4P3-Ge, Sn4P3 -GeP и SnP3-GeP. Построенная по данным дифференциального термического анализа фазовая диаграмма сечения Sn4P3-Ge представляет диаграмму эвтектического типа с координатами эвтектической точки 800 К, 15 mol % Ge.
 
 
 REFERENCES
 
 Castellanos-Gomez A. Why all the fuss about 2D semiconductors? Nature Photonics, 2016, v. 10, pp. 202-204. https://doi.org/10.1038/nphoton.2016.53
 Hasan M. Z., Kane C. L. Colloquium: Topological insulators. Mod. Phys., 2010, v. 82, pp. 3045–3067. https://doi.org/10.1103/revmodphys.82.3045
 Piot P., Behrens C., Gerth C., Dohlus M., Lemery F., Mihalcea D., Stoltz P., Vogt M. Erratum: Generation and Characterization of Electron Bunches with Ramped Current Profi les in a Dual-Frequency Superconducting Linear Accelerator. Rev. Lett., 2012, v. 108, pp. 1–5. https://doi.org/10.1103/physrevlett.108.229902
 Dávila M. E., Xian L, Cahangirov S., Rubio A., Le Lay G. Germanene: a novel two-dimensional germanium allotrope akin to graphene and silicene . New J. Phys., 2014, v. 16, pp. 095002. https://doi.org/10.1088/1367-2630/16/9/095002
 Lalmi B., Oughaddou H., Enriquez H., Kara A., Vizzini S., Ealet B., Aufray B. Epitaxial growth of a silicene sheet. Phys. Lett., 2010, v. 97, pp. 223109. https://doi.org/10.1063/1.3524215
 Kara H., Enriquez H., Seitsonen Ari P., Lew Yan Voon L.C., Vizzini S., Aufray B., Oughaddou H. Corrigendum to “A review on silicene – New candidate for electronics”. Sci. Rep., 2012, v. 67, pp. 1–18. https://doi.org/10.1016/j.surfrep.2012.01.001
 Barreteau C, Michon B, Besnard C, Giannini E. High-pressure melt growth and transport properties of SiP, SiAs, GeP, and GeAs 2D layered semiconductors. Cryst Growth., 2016, v. 443, pp. 75–80. https://doi.org/10.1016/j.jcrysgro.2016.03.019
 Ugai Ya. A., Sokolov L.I., Goncharov E.G. P-T-X diagramma sostoyaniya sistemy GeP i termodinamika vzaimodeystviya komponentov [P-T-X GeP system state diagram and thermodynamics of componentinteraction] // Russian Journal of Inorganic Chemistry, 1978, v. 23(7), рр. 1907–1911. (in Russ.)
 Lee K., Synnestvedt S., Bellard M., Kovnir K. GeP and (Ge1−Sn )(P1−Ge ) (x≈0.12, y≈0.05): Synthesis, structure, and properties of two-dimensional layered tetrel phosphides. Solid State Chem., 2015, v. 224, pp. 62–70. https://doi.org/10.1016/j. jssc.2014.04.021
 Vivian A. C. Inst. Met, 1920, v. 23, pp. 325-336.
 Zavrazhnov A. Yu., Semenova G. V., Proskurina E. Yu., Sushkova T.P. Phase diagram of the Sn–P system. Thermal Analysis and Calorimetry, 2018, v. 134(1), pp. 475–481. https://doi.org/10.1007/s10973-018-7123-0
 Olesinski R. W., Abbaschian G. J. The Ge−Sn (Germanium−Tin) system. Bulletin of Alloy Phase Diagrams, 1984, v. 5(3), pp. 265–271. https://doi.org/10.1007/bf02868550
 Glazov V. M., Pavlova L. M. Khimicheskaya termodinamika i fazovyye ravnovesiya [Chemical thermodynamics and phase equilibria]. Moscow, Metallurgiya Publ, 1988, 560 p. (in Russ.)
 Emsley J. The elements: Second Edition. Oxford University Press, Oxford, 1991.
 Arita M. Kamo K. Measurement of Vapor Pressure of Phosphorus over Sn–P Alloys by Dew Point Method. Jpn. Inst. Met, 1985, v. 26(4), pp. 242–250. https://doi.org/10.2320/matertrans1960.26.242

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.

Consequences of phase separation on magnetotransport in dc magnetron sputtered Sm0.50Sr0.50MnO3 thin films on LSAT substrate

Single crystalline thin films of Sm0.50Sr0.50MnO3 (SSMO) (thickness ∼200 nm) were prepared on LSAT (100) single crystal substrates by dc magnetron sputtering. The X-ray diffraction θ‒2θ and ω-2θ scan reveals that these films (i) have very good crystallinity, (ii) are oriented along out-of-plane c-direction, and (iii) are under small tensile strain. Temperature and magnetic field dependent electrical transport of these films shows (i) sharp paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition, (ii) large enhancement in TIM when subjected to magnetic field, (iii) hysteretic variation in resistivity with magnetic field, and (iv) huge occurrence of magnetoresistance near PMI-FMM transition. The magnetic state in the FMM (T < TC) regime resembles cluster glass, which is formed by the presence of charge ordered-antiferromagnetic clusters in the ferromagnetic matrix. The results shown in the present study could be regarded as the consequence of strong nature of phase separation in these films due to competing FMM and AFM-COI phases in these films which is known to be the generic feature of low bandwidth manganites.

Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films

Single crystalline thin film (∼ 100 nm) of La0.18Pr0.40Ca0.42MnO3 is grown on (001) oriented LaAlO3 substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M|| and M⊥) measured at 10 K, viz., M||/M⊥ (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (TC) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (Mr||) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (Mr⊥) shows a nearly linear behaviour. The coercivity (HC) follows a law of the type \(H_{\mathrm {C}}\left (T \right )\mathrm {=}H_{\mathrm {C}}\mathrm {(0)(1-}{\text {AT}}^{b}\mathrm {)}\). The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both HC|| and HC⊥. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.

Spontaneous Separation in Trapped Fermi Gas with p-Wave Interactions: Due to the Mass-Imbalance

Based on density functional theory, the spontaneous separation in the mass-imbalanced Fermi–Fermi mixture is studied. The ground-state energy density functional is constructed with the effective contact interaction, with which the ground-state density profiles of the mixture are calculated under different conditions of mass-imbalance and coupling strength. The influence of mass-imbalance on the separation and the cloud size is analyzed. In addition, the system with both mass- and population-imbalance is also calculated and studied. Despite our rough treatment in the Thomas–Fermi approximation, it is hoped that the results may provide new clues to understand the nature of phase separation of a trapped ultracold gas in both theoretical and experimental researches in the future.

Electrical, magnetic and magnetocaloric properties of polycrystalline Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi)

We studied the effects of the partial substitution (10%) of praseodymium by samarium and bismuth, on the structural, magnetic, magnetocaloric and electrical properties of the Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) manganites prepared using the solid state reaction. Refinement of the X-ray diffraction patterns shows that all our samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Magnetic studies indicate that all the samples exhibit a ferromagnetic–paramagnetic transition with increasing temperature. Curie temperature TC decreases by substitution. M(H) curves indicate the presence of some antiferromagnetic domains in the substituted samples testifying the phase-separated nature of these samples. The magnetic entropy curves –ΔS(T) show a maximum in vicinity of TC. Important values of maximum of −ΔS are recorded for our compounds. For the parent compound, we found 4.59J/kgK for an applied magnetic field of 2T at TC=266K which raises the possibility of using this compound as a magnetic refrigerant. The temperature dependence of the electrical resistivity ρ(T) indicates that all compounds exhibit a metal-insulator transition with increasing temperature. Electrical study suggests the presence of a correlation between electrical and magnetic properties.

Synthesis and characterization of PEDOT aqueous dispersions with sulfonated polyfluorene as a template and doping agent

In this study, a sulfonated polyfluorene, poly-[9,9-bis(3-propylamide-2-methylpropyl sulfonic acid) fluorene]-co-(4,4′-diphenyl) (PFDBSO3H), was synthesized and characterized. The poly(3,4-ethylenedioxythiophene) (PEDOT) water dispersions with PFDBSO3H as a template were synthesized and investigated. Results showed that conductivity increment of PEDOT film was observed when the semiconductor, PFDBSO3H, was used as the template and doping agent, and square resistance of the PEDOT film decreased as the amount of PFDBSO3H increased in the template. This increase of conductivity of the PEDOT film was mainly attributed to the semiconductive nature of PFDBSO3H template and better phase separation between PFDBSO3H and poly(styrenesulfonate) (PSS). The PEDOT film with PFDBSO3H template showed good transparency in the 400–800-nm wavelength region and good electrochemical stability. However, a slight decrease in thermal stability was observed.

Intrinsic phase separation in low-temperature quenched arsenic trisulfide glass

The nature of intrinsic phase separation initiated under different homogenization routes is studied in arsenic trisulfide As2S3 glass using Raman scattering spectroscopy.It is shown that As2S3 glass prepared within conventional melt-quenching route is subjected to essential phase separation dependent on the homogenization of elemental constituents sealed in evacuated ampoules. Under condition of low-temperature homogenization at 450–550°С, chemical interaction due to limited solubility of liquid S in solid As results in structurally intrinsic As- and S-rich phases with high content of homoatomic As–As and S–S bonds, respectively, which are “wrong” from the point of As2S3 stoichiometry This process can be essentially facilitated with more rapid heating and greater amount of initial elemental ingredients taken for synthesis. During prolonged homogenization of this intrinsically-decomposed melt (such as lasting 2days in a rocking furnace), these products are partially separated giving main glassy phase enriched on As in the form of realgar- and dimorphite-type molecules, isolated As–As bonds in a glassy network and volatilized S-rich phase, which condenses on the walls of ampoules. If such melt is insufficiently homogenized as under 6-h heating at 500°C with only 2-h rocking, the coordination disordering is maintained in the ultimate glass. This provides that volatilized S-rich phase does not form, and all decomposition products are stabilized in glassy state as quasi-tetrahedral units and compensating homoatomic As–As bonds.

Structural and magnetic phase separation of complex half-doped manganites by the example of Sm0.32Pr0.18Sr0.5MnO3

High-resolution neutron powder diffraction is used to investigate the phase separation and microscopic nature of the magnetoresistance in complex half-doped manganites. Investigations are performed by the example of Sm0.32Pr0.18Sr0.5MnO3 exhibiting the colossal magnetoresistance effect. The structural transition from a high-temperature orthorhombic Pbnm phase to a mixed phase containing two (orthorhombic Pbnm and monoclinic P21/m) phases is revealed. A gradual decrease in the amount of the orthorhombic phase and, consequently, an increase in the amount of the monoclinic phase are observed with decreasing temperature. Redistribution of the two phases ceases below T ≈ 100 K. Low-temperature analysis of the magnetic contribution to the experimental neutron-diffraction patterns indicates that the magnetic ground state of the compound under study is phase-separated and corresponds to a mixed state involving three magnetic phases formed at different temperatures: a ferromagnetic phase, A- type antiferromagnetic, and CE- type charge ordered antiferromagnetic phases with charge-orbital ordering. Ferromagnetic ordering arises near room temperature in the orthorhombic Pbnm phase and manifests itself only until helium temperatures. The A- and CE-types antiferromagnetic states (T N ≈ 170 and 120 K, respectively) appear in the monoclinic crystallographic phase.

On the nature of phase separation of polymer solutions at high extension rates

ABSTRACTExperiments with stretching moderately concentrated polymer solutions have been carried out. Model experiments were carried out for poly(acrylonitrile) solutions in dimethyl siloxane. Just the choice of concentrated solutions allowed for a clear demonstration of a demixing effect with the formation of two separate phases—an oriented polymer fiber and solvent drops sitting on its surface. An original experimental device for following all subsequent stages in the demixing process was built. It combined two light beams, one transverse to the fiber and a second directed along (inside) the fiber, the latter played the role of an optical line. This gives a unique opportunity to observe processes occurring inside a fiber. The process of demixing starts from the volume phase separation across the whole cross section of a fiber at some critical deformation and the propagation of the front of demixing along the fiber. Then a solvent cylindrical skin appears which transforms into a system of separate droplets. New experimental data are discussed based on a comparison of the current different points of view on the phenomenon of deformation‐induced phase separation: thermodynamic shift of the equilibrium phase transition temperature, growth of stress‐induced concentration fluctuations in two‐component fluids, and mechanically pressing a solvent out from a polymer network. The general belief is that a rather specific (so‐called “beads‐on‐a‐string”) structure of a filament is realized in stretching dilute solutions: beads of a polymer solution connected by oriented polymer bridges forming a single object. The situation in stretching moderately concentrated solutions appears quite different: real phase separation was observed. So, the alternative phenomenon to the formation of the “beads‐on‐a‐string” structure has been experimentally proven. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 559–565

Influence of bridging atom on the vertical phase separation of low band gap bulk heterojunction solar cells

Vertical phase separation of the polymer and fullerene molecules in bulk heterojunction organic solar cells influences the exciton dissociation, charge carrier transport and collection. This work compares the vertical phase separation of poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b′]dithiophene-2,6-diyl]] (C-PCPDTBT):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) and poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b′]dithiophene-siloe2,6-diyl]] (Si-PCPDTBT):PC71BM blend films, using X-ray photoemission spectroscopy depth profiles. The difference between the two polymers is the bridging atom, which is carbon for C-PCPDTBT and silicon for Si-PCPDTBT. Si-PCPDTBT exhibits enhanced polymer chain packing and crystallinity. We believe this enhanced chain packing provides a driving force during film drying which alters the vertical morphology. The different nature of vertical phase separation plays a role in determining the increased device performance observed for Si-PCPDTBT:PC71BM solar cells. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)