Phase Coexistence in a Dynamic Phase Diagram

Metastability and phase coexistence are important concepts in colloidal science. Typically, the phase diagram of colloidal systems is considered at the equilibrium without the presence of an external field. However, several studies have reported phase transition under mechanical deformation. The reason behind phase coexistence under shear flow is not fully understood. Here, multilamellar vesicle (MLV)‐to‐sponge (L₃) and MLV‐to‐L_α transitions upon increasing temperature are detected using flow small‐angle neutron scattering techniques. Coexistence of L_α and MLV phases at 40 °C under shear flow is detected by using flow NMR spectroscopy. The unusual rheological behavior observed by studying the lamellar phase of a non‐ionic surfactant is explained using ²H NMR and diffusion flow NMR spectroscopy with the coexistence of planar lamellar–multilamellar vesicles. Moreover, a dynamic phase diagram over a wide range of temperatures is proposed.     

Diffusion,elasticity, and shear flow in self-assembled block copolymers: A molecular dynamics study

Self-assembled ordered structures composed of block copolymers are simulated by molecular dynamics under stress-free conditions and under shear. We address several methodological points. The system must be allowed to adjust its size to accommodate natural periods of self-assembled structures. In addition, these structures need to be capable of rotating freely under shear. An examination of the diffusion of polymer molecules in the lamellar phase reveals subdiffusion along translationally invariant directions between the ballistic and diffusive regime. The diffused distance d increases with time t as d ∝ t^1/3. We also examine the possibility of mapping structures such as cylindrical phases onto particle–field types of models. Using measurements of the wavevector-dependent dynamic matrix, we show that this cannot be done with only two-body potentials. We then examine the molecular origin of shear alignment of lamellar phases. Lamellae oriented parallel to the shear direction become unstable at high shear rates when the major axis of the tensor of gyration of individual polymers forms an average angle of 45° with the lamellae. This instability can be understood in analogy to similar transitions in liquid crystals. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 970–982, 2005     

Charge‐Transfer Phase Transition of a Cyanide‐Bridged FeII/FeIII Coordination Polymer

Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge‐transfer phase transitions have not been reported for the simplest FeFe cyanide‐bridged systems. A mixed‐valence Fe^II/Fe^III cyanide‐bridged coordination polymer, {[Fe(Tp)(CN)₃]₂Fe(bpe)?5 H₂O}_n, which demonstrates a thermally induced charge‐transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high‐spin state of the whole system does not change to a low‐spin state. This result is in contrast to FeCo cyanide‐bridged systems that exhibit charge‐transfer‐induced spin transitions.     

Oscillatory shear‐induced alignment of ketjen black conductive particles in polylactic acid and its effect on the electrical anisotropy

This study aligned Ketjen black (KB) particles along one preferred direction in a polylactic acid (PLA) matrix using an oscillatory shear flow and investigated the effect of aligned KB on the electrical anisotropy. Under the oscillatory shear, the KB particles are aligned along the flow direction in the PLA matrix, resulting in an oriented conductive network. When the concentration of KB is in the range of 0.88–1.56 vol %, the electrical volume resistivity along the flow direction (ρ_∥) decreases to ～3 × 10⁴ Ω m and that perpendicular to the flow direction (ρ_⊥) remains at ～1 × 10¹⁰ Ω m, showing an extremely large electrical anisotropy, and the ρ_⊥/ρ_∥ value is 3–4 orders of magnitude higher than that of previously reported carbon‐nanotube‐based electrical anisotropic composites. This strong anisotropy is attributed to the preferential alignment of KB particles with lower percolation threshold for conductive path along the flow direction. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 369–373     

Rheo‐optical studies of the effect of shear flow on the structure of elastomer blends

The effect of shear flow on the structure of a phase‐separated, near‐critical blend of 50/50 (w/w) poly(styrene‐ran‐butadiene) and polybutadiene was studied with two different custom‐built rheo‐optical instruments that combined polymer melt flow and small‐angle light scattering (SALS). The deformation of the phase domains during shear flow was nonaffine, and the SALS patterns evolved from a spinodal ring (SR) pattern to a squashed SR with two high‐intensity lobes, to an H‐pattern, to a butterfly pattern with a dark streak along the equator, and finally to a steady‐state, elliptical pattern. The SALS patterns were explained in terms of a network model, in which the strands of the network first orient in the flow direction, then extend in this direction, and finally break up into droplets aligned in the flow direction. According to this picture, the strands in the vorticity direction do not deform until relatively high strains, after which the periodicity of the network begins to disappear. Supporting this model was the observation that the transitions between the different SALS patterns corresponded to inflections and/or maxima in the shear stress or first normal stress difference. Increasing the shear rate changed the kinetics of the structure evolution and reduced the size of the phase‐separated droplets in the steady state. No evidence was obtained for flow‐induced miscibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1725–1738, 2004     

Quantitative Investigation on Structural Evolution of Co-continuous Phase under Shear Flow

Components of co-continuous phase can form an interpenetrating network structure, which has great potential to synergistically improve the mechanical properties of the blends, and to impart the functional blends superior electrical conductivity and permeability. In this work, the effects of shear rates (50–5000 s^?1) at different temperatures on the phase morphology, phase size and lamellar crystallites of biodegradable co-continuous polybutylene terephthalate (PBAT)/polybutylene succinate (PBS) blend are quantitatively investigated. The results show that the above features of the PBAT/PBS have a strong dependence on the shear flow and thermal field. The co-continuous phase of the blend is well maintained at 130 °C. Interestingly, this phase structure transforms into a “sea-island” structure at 160 °C, which gradually recovers to a co-continuous phase when the shear rate increases from 1000 s^?1 to 5000 s^?1. The phase size decreases with the increase of shear rate both at 130 °C and 160 °C due to the refinement and deformation of phase structures caused by strong shear stress. Unexpectedly, a unique phenomenon is observed that the shear-induced lamellar crystallites are oriented perpendicular to shear direction in the range of 500–5000 s^?1 at 130 °C, while the orientation of lamellar crystallites at 160 °C is along the shear direction within the whole range of shear rates. The degree of orientation for the PBAT/PBS blend crystals increases first and then decreases at both temperatures above. In addition, the range of shear rate has reached the level in the industrial processing. Therefore, this work has important guiding significance for the regulation of the co-continuous phase structure and the performance for the blend in the practical processing.

     

Atmospheric Chemistry of α‐Diketones: Kinetics of C5 and C6 Compounds with Cl Atoms and OH Radicals

Carbonyls play an important role in atmospheric chemistry due to their formation in the photooxidation of biogenic and anthropogenic volatile organic compounds and their high atmospheric reactivity. The Cl‐initiated kinetics of two α‐diketones (2,3‐pentanedione (PTD) and 2,3‐hexanedione (HEX)) have been determined as well as the OH + HEX rate constant using atmospheric simulation chamber experiments and the relative rate method. Up to three different reference compounds were used to assess robust results. The following rate constants (in cm³ molecule⁻¹ s⁻¹) have been obtained at 298 K: k (Cl + PTD) = (1.6 ± 0.2) × 10⁻¹¹, k (Cl + HEX) = (8.8 ± 0.4) × 10⁻¹¹, and k (OH + HEX) = (3.6 ± 0.7) × 10⁻¹² with a global uncertainty of 30%. The present determinations of Cl‐ and OH‐ reaction rate constants for HEX constitute first measurements. Using the present measurements, a recently improved structure–activity relationship for Cl + ketone reactions has been updated by introducing an F (–COCO–) factor of 8.33 × 10⁻⁴. Atmospheric lifetime calculations indicate that chlorine‐initiated oxidation may be a significant α‐diketone sink in the marine‐boundary layer or in places where high Cl concentrations may be found.     

Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system

In this study, we investigate structural transitions of tetraethylene glycol monohexadecyl ether (C(16)E(4)) in D(2)O as a function of shear flow and temperature. Via a combination of rheology, rheo-small-angle neutron scattering and rheo-small-angle light scattering, we probe the structural evolution of the system with respect to shear and temperature. Multi-lamellar vesicles, planar lamellae, and a sponge phase were found to compete as a function of shear rate and temperature, with the sponge phase involving the formation of a new transient lamellar phase with a larger spacing, coexisting with the preceding lamellar phase within a narrow temperature-time range. The shear flow behavior of C(16)E(4) is also found to deviate from other nonionic surfactants with shorter alkyl chains (C(10)E(3) and C(12)E(4)), resembling to the C(16)E(7) case, of longer chain.     

Kossel diagrams of blue phases

CB15/E9 mixtures submitted to an electric field exhibit a tetragonal phase BPX, having a D¹⁰ ₄(I4₁22) symmetry and two hexagonal phases BPH^3d and BPH^2d The Kossel diagram technique allows us (a) to confirm the hexagonal symmetry of BPH^3d and to determine precisely its space group D² ₆ (P6₂22) and (b) to study the field-induced phase transitions between BP II, BPX and BPH^3d. We show that the BP II → BPH^3d transition is a continuous deformation involving a dilatation in the field direction and a shear perpendicular to this direction. The BP II → BPX and BPX → BPH^3d transitions are discontinuous.     

The self-organization properties of <Emphasis Type="Italic">n</Emphasis>-dodecylammonium α-glutamate/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>5</Subscript>H<Subscript>11</Subscript>OH/water system

A biocompatible surfactant-n-dodecylammonium α-glutamate (GDA) with biodegradable and biocompatible properties was synthesized, and the phase behavior and the structural properties of GDA/n-pentanol/water system was studied by small-angle X-ray diffraction, electron spin resonance, and freeze-fracture transmission electron microscopy (FF-TEM). In the ternary phase diagram of GDA/n-pentanol/water system, there exist three isotropic regions—O/W, bicontinuous, and W/O structures, and two anisotropic regions—hexagonal liquid crystal (HEX), and lamellar liquid crystal (LLC) regions. UV irradiation causes the decrease in the interlayer space, d, of lamellar liquid crystal and in the radius, r, of column aggregates of hexagonal liquid crystal, but it has little effect on the structure of O/W and W/O microemulsions.     

Synthesis,Crystal Structure and Density Functional Studies on 1N‐Phenyl‐3‐(2,4‐Dichlorophenyl)‐5‐(4‐Chlorophenyl)‐2‐Pyrazoline

1N‐Phenyl‐3‐(2,4‐dichlorophenyl)‐5‐(4‐chlorophenyl)‐2‐pyrazoline has been synthesized and characterized by elemental analysis, IR, UV‐Vis and X‐ray single crystal diffraction. Density functional calculations have been carried out for the title compound by using the B3LYP method with a 6‐311G** basis set. The calculated results show that the predicted geometry can reproduce well the structural parameters. The electronic absorption spectra calculated in the gas phase are better than those calculated in EtOH solvent to model the experimental electronic spectra. Natural Bond Orbital (NBO) analyses suggest that the above electronic transitions are mainly assigned to π → π* transitions. On the basis of vibrational analyses, the thermodynamic properties of the compound at different temperatures have been calculated, revealing the correlations between C⁰_{p, m}, S⁰_m, H⁰_m and temperature.     

On the role of intermolecular interactions on structural and spin-crossover properties of 2D coordination networks [Fe(bbtr)3]A2 (bbtr=1,4-bis(1,2,3-triazol-1-yl)butane; A=ClO4(-), BF4(-))

A series of complexes [M(bbtr)₃]A₂ (M=Fe^II, Zn^II; bbtr=1,4‐bis(1,2,3‐triazol‐1‐yl)butane; A=ClO₄^?, BF₄^?) and [Fe_xZn_1?x(bbtr)₃](ClO₄)₂ (0<x<1) dilute systems was synthesized and characterized. Earlier studies on [Fe(bbtr)₃](ClO₄)₂ ( 1?ClO₄ ), which crystallizes in space group P$\bar 3A series of complexes [M(bbtr)(3)]A(2) (M=Fe(II), Zn(II); bbtr=1,4-bis(1,2,3-triazol-1-yl)butane; A=ClO(4)(-), BF(4)(-)) and [Fe(x)Zn(1-x)(bbtr)(3)](ClO(4))(2) (0相似文献   

Lamellar thickening in nascent poly(acrylonitrile) upon annealing

No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm⁻¹ ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (t_a) and the temperature (T_a). Depending on t_a, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (t_a = 0.5–3 min, depending on T_a), rapidly increased in stage II (t_a = 0.5–8 min), and stayed at a constant value characteristic for each T_a at yet longer t_a's in stage III. The lamellar thickness characteristic for T_a increased rapidly with increasing T_a at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (T_m = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the T_m is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000     

Characterization of G‐Quadruplex/Hairpin Transitions of RNAs by 19F NMR Spectroscopy

2′‐O‐[(4‐Trifluoromethyl‐triazol‐1‐yl)methyl] reporter groups have been incorporated into guanosine‐rich RNA models (including a known bistable Qd/Hp RNA and two G‐rich regions of mRNA of human prion protein, PrP) and applied for the ¹⁹F NMR spectroscopic characterization of plausible G‐quadruplex/hairpin (Qd/Hp) transitions in these RNA structures. For the synthesis of the CF₃‐labeled RNAs, phosphoramidite building blocks of 2′‐O‐[(4‐CF₃‐triazol‐1‐yl)methyl] nucleosides (cytidine, adenosine, and guanosine) were prepared and used as an integral part of the standard solid‐phase RNA synthesis. The obtained ¹⁹F NMR spectra supported the usual characterization data (obtained by UV‐ and CD‐melting profiles and by ¹H NMR spectra of the imino regions) and additionally gave more detailed information on the Qd/Hp transitions. The molar fractions of the secondary structural species (Qd, Hp) upon thermal denaturation and under varying ionic conditions could be determined from the intensities and shifts of the ¹⁹F NMR signals. For a well‐behaved Qd/Hp transition, thermodynamic parameters could be extracted.     

Structure of a Lamellar Phase Formed by Non-ionic Surfactant and Water: Effects of shear flow

We have investigated effects of shear flow on the structure of lamellar phase in hepta(oxyethylene glycol)—n—hexadecylether—water system using small-angle neutron scattering (SANS) under shear flow at the shear rates (

剪切场作用下环形二嵌段共聚物微相形态变化的耗散粒子动力学研究

采用耗散粒子动力学(Dissipative particle dynamics, DPD)方法研究了在剪切场作用下, 环形二嵌段共聚物微观相分离过程中的形态变化. 在层状(lamellae, LAM)体系中发生了微相的平行重取向和平行-垂直转变以及剪切导致的波动不稳定现象. 对于穿孔层状(Perforated lamellae, PL)体系, 强剪切导致了穿孔层状-柱状(Hexagonal cylinder, HEX)微相转变. 在剪切场作用下, 柱状体系中同样也有平行重取向发生. 可以用相区破坏-相区重生的两步机理描述微相的平行重取向、平行-垂直转变以及PL-HEX转变现象. 在球状相(Body centered cubic, BCC)体系中发现了剪切诱导相融合.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

Selective synthesis of poly(p‐oxybenzoyl) by fractional polycondensation: Enhancement of selectivity by shearing

The influence of shear flow, especially the timing for the application of shearing, was examined to enhance the selectivity for the preparation of poly(p‐oxybenzoyl) (Pp‐OB) by using hydrodynamically induced phase separation during polymerization of 4‐(4‐acetoxybenzoyloxy)benzoic acid (p‐ABAD) and m‐acetoxybenzoic acid (m‐ABA). The polymers containing few m‐oxybenzoyl (m‐OB) moieties were obtained as precipitates even at high content of m‐OB moiety in feed (χ_f) under shear flow. The content of m‐OB moiety in the precipitates (χ_p) prepared under shearing throughout the polymerization at the shear rate (γ) of 489 s^?1 was 6.3 mol % even at χ_f of 60 mol %. Especially, the Pp‐OB was obtained as the precipitates at χ_f of less than 50 mol %. The timing of the application of the shearing influenced the selectivity significantly, and the shearing just after the precipitation of the oligomers started was quite efficient to enhance the selectivity more. The χ_p of the precipitates prepared with shearing at γ of 489 s^?1 just after the precipitation was only 3.9 mol % even at χ_f of 60 mol %. The shear flow reduced the difference in the reactivity between p‐ABAD and m‐ABA, resulting in the decrease in the selectivity with regard to the formation of p‐oxybenzoyl homo‐oligomer. However, the shear flow enhanced the difference in the miscibility between homo‐oligomers and co‐oligomers. This change in the miscibility by shear flow brought about the more rapid precipitation of homo‐oligomers, leading to the enhancement of the selectivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

The nature of multiple melting transitions in cis-polyisoprene

The multiple melting transitions previously reported for cis-polyisoprene have been related to different morphological species observed in thin films using transmission electron microscopy. Two distinct types of spherulitic lamellar crystal have been identified which have characteristic growth rates, lamellar thicknesses, and fold planes. In addition to the α-lamellar crystals, which grow in prestrained films with the a axis perpendicular to the stretch direction, a second type of lamellar crystal was identified with the b axis perpendicular to the stretch direction: β-lamellae. From an analysis of the kinetics of growth and the variation of lamellar thicknesses with crystallization temperature, values of the side and surface free energies of the two types of lamellar crystal have been calculated.