Shift Of Phase Boundary Research Articles

Shear‐induced Apparent Shift of Phase Boundary of Binary Polymer Blends

The combined influence of the thermodynamical and hydrodynamic effects of shear was tentatively considered for the first time, in the modeling of the shear-induced phase behavior of binary polymer blends in this paper. In this model, the original two-fluid model proposed by Onuki [1,2] was modified by replacing the quiescent thermodynamical term with the one defined in the frame of extended irreversible thermodynamics (EIT). [3-5] The stress term of the polymer blend was determined by using the mixing rule of Double Reptation [6,7] along with the Graessley's [8] functions to make the mpdel applicable in both linear and weak non-linear regions. Then the apparent shift of phase boundary of a model blend system was computed by using this theory. It's found that this modified theory can predict both the miscibility gap and anisotropical phase separation of the polymer blend, while the two different previous theories, that is the pure thermodynamical one and hydrodynamic one, could only predict one but not both of them. For example, this modified two-fluid model predicts that the miscibility gap can be observable not only in vorticity direction but also in the velocity gradient direction.

1161. ジルコニウム-酸素-水素3元系計算状態図

In the present study, the phase diagrams for zirconium-oxygen-hydrogen ternary system were assessed between 573.15K and 1, 473.15K by means of CALPHAD technique. The calculated ternary isothermal section of zirconiumoxygen-hydrogen system at 973.15K was in good agreement with the experimental diagram. The calculated and experimental Sieverts' constants also accorded well. Isothermal sections of the other temperatures were also obtained, and drastic shifts of phase boundaries were prospected. From the zirconium (with hydrogen)-oxygen pseudo binary phase diagrams, it was predicted that dissolved hydrogen let the oxygen content for prior-β phase increase, and that the zirconium based fuel cladding became less ductile by the addition of hydrogen.

Effect of β-muricholic acid on the prevention and dissolution of cholesterol gallstones in C57L/J mice

This study investigated whether beta-muricholic acid, a natural trihydroxy hydrophilic bile acid of rodents, acts as a biliary cholesterol-desaturating agent to prevent cholesterol gallstones and if it facilitates the dissolution of gallstones compared with ursodeoxycholic acid (UDCA). For gallstone prevention study, gallstone-susceptible male C57L mice were fed 8 weeks with a lithogenic diet (2% cholesterol and 0.5% cholic acid) with or without 0.5% UDCA or beta-muricholic acid. For gallstone dissolution study, additional groups of mice that have formed gallstones were fed chow with or without 0.5% beta-muricholic acid or UDCA for 8 weeks. One hundred percent of mice fed the lithogenic diet formed cholesterol gallstones. Addition of beta-muricholic acid and UDCA decreased gallstone prevalence to 20% and 50% through significantly reducing biliary secretion rate, saturation index, and intestinal absorption of cholesterol, as well as inducing phase boundary shift and an enlarged Region E that prevented the transition of cholesterol from its liquid crystalline phase to solid crystals and stones. Eight weeks of beta-muricholic acid and UDCA administration produced complete gallstone dissolution rates of 100% and 60% compared with the chow (10%). We conclude that beta-muricholic acid is more effective than UDCA in treating or preventing diet-induced or experimental cholesterol gallstones in mice.

Universal phase boundary shifts for corner wetting and filling.

The phase boundaries for corner wetting (filling) in square and diagonal lattice Ising models are exactly determined and show a universal shift relative to wetting near the bulk criticality. More generally, scaling theory predicts that the filling phase boundary shift for wedges and cones is determined by a universal scaling function R(d)(psi) depending only on the opening angle 2psi. R(d)(psi) is determined exactly in d = 2 and approximately in higher dimensions using nonclassical local functional and mean-field theory. Detailed numerical transfer matrix studies of the magnetization profile in finite-size Ising squares support the conjectured connection between filling and the strong-fluctuation regime of wetting.

Shifting of Fatty Acid Monolayer Phases Due to Ionization of the Headgroups

Monolayers of simple fatty acids exhibit a rich polymorphism with at least seven solid phases. The reason for such a variety of phases is not known yet and therefore is the object of the current investigation. In the present work the pH of the subphase is varied between 2 and 10.5 and the influence of the degree of dissociation on phase transition pressures and temperatures of arachidic acid monolayers is investigated in detail in the range from 2 to 45 °C by means of Brewster-angle microscopy and surface pressure−area isotherms. The shift of phase boundaries is ascribed to the change in the steric, electrostatic, and bonding interactions between the lipid headgroups. The impressive correlation between the L2/Ov nearest neighbor to next nearest neighbor (NN/NNN) transition pressure and the position correlation length as functions of the pH value suggests that the L2/Ov NN/NNN transition in fatty acid monolayers is strongly influenced or even originates in headgroup bonding interactions. The influence of h...

Perturbative polydispersity: Phase equilibria of near-monodisperse systems

The conditions of multiphase equilibrium are solved for generic polydisperse systems. The case of multiple polydispersity is treated, where several properties (e.g., size, charge, shape) simultaneously vary from one particle to another. By developing a perturbative expansion in the width of the distribution of constituent species, it is possible to calculate the effects of polydispersity alone, avoiding difficulties associated with the underlying many-body problem. Explicit formulas are derived in detail, for the partitioning of species at coexistence and for the shift of phase boundaries due to polydispersity. Convective fractionation is quantified, whereby one property (e.g., charge) is partitioned between phases due to a driving force on another. To demonstrate the ease of use and versatility of the formulas, they are applied to models of a chemically polydisperse polymer blend, and of fluid–fluid coexistence in polydisperse colloid–polymer mixtures. In each case, the regime of coexistence is shown to be enlarged by polydispersity.

The phase diagrams of mixtures of EVAL and PEG in relation to membrane formation

The phase diagrams of various ethylene–vinyl alcohol (EVAL) copolymer with different hydroxyl (OH) group contents and poly(ethylene glycol) (PEG) with different molecular weights (ranging from 200 to 600) are determined. It is found experimentally that both the liquid–liquid (L–L) phase boundaries and the crystallization curves are shifted to higher temperature when the OH group contents in EVAL increase. On the other hand, only the L–L phase boundaries shift to higher temperature when the molecular weights of PEG increase. These phenomena are interpreted by using solubility parameters ( δ d, δ p) to estimate the Flory–Huggins interaction parameters, χ ∗, of the mixtures. By extrapolating the L–L bi-phasic curves from cloud points of temperature ( T cloud), the experimental interaction parameters χ are obtained, which are linearly correlated to the theoretically estimated interaction parameters, χ ∗.

Modification of the phase stability of polymer blends by fillers

We investigate the influence of filler particles on the phase stability of a model blend of polystyrene (PS) and polybutadiene (PB). The upper critical solution temperature cloud point curve of a PS:PB blend is “destabilized” (upward shift of cloud point temperature) by the addition of untreated fumed silica filler particles. Preliminary cloud point measurements on surface-functionalized fumed silica particles were also performed. A small downward shift of the cloud point temperature was observed by functionalizing the filler particles with grafted polystyrene chains, while grafting with a silane coupling agent resulted in a large apparent “stabilization” effect or a decrease of the cloud point temperature. (Further measurements on surface-functionalized filler particles over a range of polymer compositions are required to determine the filler concentration dependence of the shift of the blend critical temperature.) Surface treatments were selected to demonstrate that modifying the filler particle surface chemistry can alter the blend phase boundary. These phase boundary shifts have significance in commercial blends containing dispersions of filler particles.

On the preservation of mantle information in ultramafic nodules: glass inclusions within minerals versus interstitial glasses

This study questions the assumption that silicate melts preserved as glass inclusions in minerals and as interstitial films or pockets in mantle xenoliths have identical chemical compositions to one another and are both suitable for inferring deep mantle melt compositions. Theoretical models of the elastic behavior of melt inclusions indicate that only limited decompression of the inclusion takes place during ascent of the host xenolith, whereas the pressure of an interstitial melt follows the external pressure. Consequences of such behavior are considered using simple model systems, such as the alkali-bearing system forsterite–nepheline–SiO 2. With decreasing pressure, phase boundaries shift to silica normative compositions. Consequently, reequilibration of small-degree melts of peridotite, which are characterized by olivine–nepheline normative compositions at moderate pressure, yield quartz normative compositions at a lower pressure. Also, melt inclusions are simpler systems, i.e. the trapped melts are in contact with a single mineral phase, in contrast with interstitial glasses. We show here that experimental heating of the inclusions restores the original melt composition of melt inclusions prior to cooling, which is not possible for interstitial glasses. Data obtained for rehomogenized glass inclusions and interstitial glasses associated in the same xenoliths from intraplate ocean islands and subduction zones confirm the model predictions. In intraplate nodules, the highly silicic, alkali-rich melts preserved as glass inclusions inside minerals are olivine–nepheline normative and represent high-pressure (1 GPa) near-solidus melts in equilibrium with a peridotitic assemblage. In contrast, the silica-normative composition of the interstitial glasses records their last pressure of equilibration, i.e., shallow-level conditions. In subduction zone settings, exsolution of the oversaturated H 2O-rich volatile phase and decompression cause conflicting effects on the composition of the melts trapped in xenoliths. The composition of glass inclusions is characterized by higher levels of volatile elements, mainly H 2O, and by a higher quartz norm than interstitial glasses. This is consistent with the hypothesis that the glass inclusions represent quenched melts from H 2O-saturated peridotite or amphibolite/eclogite systems, whereas the composition of the interstitial glasses indicates reequilibration at low pressure, probably induced by the H 2O-rich volatile loss

Phase diagrams of mixtures of flexible polymers and nematic liquid crystals in a field

The Flory-Huggins theory of flexible polymers mixtures [P. J. Flory, Principles of Polymer Chemistry (Cornell University Press, Ithaca, 1953)] and the Lebwohl-Lasher model of nematogens [G. Lasher, Phys. Rev. A 5, 1350 (1972); P. A. Lebwohl and G. Lasher, ibid. 6, 426 (1972)] are combined to understand the phase behaviors of mixtures of flexible polymers (coils) and small molecular liquid crystals in an external magnetic field. It is found that, due to the field-induced ordering, the phase boundaries shift upwards and the paranematic spinodal regions are narrowed near the paranematic-nematic transition lines; however, the nematic spinodal regions are enlarged.

Structures in the System CaTiO3/SrTiO3

At room temperature the sequence of phases with increasing amounts of strontium in the system CaTiO3/SrTiO3is orthorhombic (Pnma), orthorhombic (Bmmb), tetragonal (I4/mcm), and cubic (Pm3m). All phase boundaries shift toward smaller strontium contents with increase of temperature. Volume changes resulting from phase transformations are small for all compositions. Shape changes are greatest (∼0.3%) for theBmmb/I4/mcmtransition, but would probably be accommodated by microtwinning and so are unlikely to affect the mechanical integrity of a specimen.

Effect of cooling rate and front velocity on solidification micro structure selection in Al-3.5wt.%Fe-0 to 8.5wt.%Si alloys

The aim of this work was to study the effect of solidification conditions on microstructure selection in Al-3.5Fe-0 to 8.5Si (wt.%) alloys cooled under non-equilibrium conditions. The alloys studied were Al-3.5Fe, Al-3.5Fe-1Si, Al-3.5Fe-2,8Si, Al-3.5Fe-7Si and Al-3.5Fe-8.5Si (wt.%), which were solidified by wedge chill casting and Bridgman directional solidification. Wedge casting gave cooling rates in the range 10 0–10 3 K −1, whilst Bridgman solidification was carried out at front velocities between 10 −2 and 2 mm s −1, and a temperature gradient of about 15 K mm −1. For the first three alloy compositions, the first phase to appear for the slower cooled regimes was the equilibrium primary phase of Al 13Fe 4. Material which solidified in wedge castings at cooling rates greater than about 150 K s −1 did so without formation of primary intermetallic and had microstructures of α-Al dendrites with interdendritic eutectic. Primary intermetallic was also suppressed in the Bridgman solidified material at front velocities greater than approximately 1 mm s −1. The as-solidified microstructure of the alloy containing 8.5 wt.% Si at lower cooling rates in the wedge and at all front velocities in Bridgman solidified material contained primary β-AlFeSi intermetallic in preference to the expected a-type AlFeSi ternary intermetallic, suggesting a shift in the liquidus surface phase boundaries.

The structure and phase transitions in polymer blends, diblock copolymers and liquid crystalline polymers: The Landau‐Ginzburg approach

AbstractThe polymer systems are discussed in the framework of the Landau‐Ginzburg model. The model is derived from the mesoscopic Edwards Hamiltonian via the conditional partition function. We discuss flexible, semiflexible and rigid polymers. The following systems are studied: polymer blends, flexible diblock and multi‐block copolymer melts, random copolymer melts, ring polymers, rigid‐flexible diblock copolymer melts, mixtures of copolymers and homopolymers and mixtures of liquid crystalline polymers. Three methods are used to study the systems: mean‐field model, self consistent one‐loop approximation and self consistent field theory. The following problems are studied and discussed: the phase diagrams, scattering intensities and correlation functions, single chain statistics and behavior of single chains close to critical points, fluctuations induced shift of phase boundaries. In particular we shall discuss shrinking of the polymer chains close to the critical point in polymer blends, size of the Ginzburg region in polymer blends and shift of the critical temperature. In the rigid‐flexible diblock copolymers we shall discuss the density nematic order parameter correlation function. The correlation functions in this system are found to oscillate with the characteristic period equal to the length of the rigid part of the diblock copolymer. The density and nematic order parameter measured along the given direction are anticorrelated. In the flexible diblock copolymer system we shall discuss various phases including the double diamond and gyroid structures. The single chain statistics in the disordered phase of a flexible diblock copolymer system is shown to deviate from the Gaussian statistics due to fluctuations. In the one loop approximation one shows that the diblock copolymer chain is stretched in the point where two incompatible blocks meet but also that each block shrinks close to the microphase separation transition. The stretching outweights shrinking and the net result is the increase of the radius of gyration above the Gaussian value. Certain properties of homopolymer/copolymer systems are discussed. Diblock copolymers solubilize two incompatible homopolymers by forming a monolayer interface between them. The interface has a positive saddle splay modulus which means that the interfaces in the disordered phase should be characterized by a negative Gaussian curvature. We also show that in such a mixture the Lifshitz tricritical point is encountered. The properties of this unusual point are presented. The Lifshitz, equimaxima and disorder lines are shown to provide a useful tool for studying local ordering in polymer mixtures. In the liquid crystalline mixtures the isotropic nematic phase transition is discussed. We concentrate on static, equilibrium properties of the polymer systems.

Phase diagrams of bcc alloys at low temperatures with ballistic atom movements.

Kinetic Monte Carlo simulations were used to determine the steady states of equiatomic bcc alloys with first- and second-nearest-neighbor (1NN and 2NN) effective pair interactions. Atom movements occurred with a vacancy mechanism, and were of two types: thermal and ballistic. The phase diagram in the space spanned by the 1NN and 2NN interaction strengths was determined for thermal atom movements alone, and with some ballistic atom movements. With increasing temperature, the region of B32 phase receded against the adjacent regions of B2 order and unmixed states. With some ballistic atom movements, however, the region of B32 order encroached on the adjacent regions of B2 order and unmixed state. The shifts in phase boundaries are attributed to differences in how the internal energies of the different phases are affected by ballistic atom movements. Local fluctuations in the internal energy density in the presence of ballistic atom movements caused two-phase regions in the phase diagram.

Polarizations andp-T-phase diagram of bccd: Interpretation in terms of frustrated Ising models

Abstract The observed (pressure, temperature)-phase diagram of betaine-calciumchloride-dihydrate—which exhibits a multitude of phases—and the polarizations of these phases are discussed in terms of the ANNNI model with an improved matching to the crystal structure and of the Ising version of Chen & Walker's model. The experimentally observed shifts of the main phase boundaries under uniaxial pressure and upon substituting part of the Cl ions by Br are explained.

Coexistence Curve of Dilute Polymer Solution in a Mixed Solvent Having Critical Demixing Point

The coexistence curves of dilute solutions of Poly(vinyl methyl ether) (PVME) in a solvent mixture methanol/cyclohexane which has a critical demixing point were measured. We found that in the methanol-rich region the presence of a small amount of PVME does not cause any appreciable change in the phase boundary of binary methanol/cyclohexane mixture, whereas in the cyclohexane-rich region it gives rise to a marked shift of phase boundary toward higher temperature region. It is shown that this characteristic phase behavior can be well explained qualitatively on the basis of Flory–Huggins solution theory, together with the interaction parameters deduced from small angle neutron and X-ray scattering experiments, as due to the smallness of the interaction parameter, χ13, between methanol and PVME. The smallness of χ13 can be interpreted as a manifestation of the association of methanol molecules.

Zagami: Product of a two-stage magmatic history

Large specimens of the Zagami shergottite show highly varied grain sizes and mineral abundances on a cm scale and preferred alignment of pyroxene laths. We document the presence of whitlockite and of melt veins and pockets of shock origin. Pyroxene crystals have homogeneous Mg-rich pigeonite and augite cores, overgrown by Fe-rich, zoned pyroxene (mostly pigeonite) rims. Amphibole-bearing magmatic (melt) inclusions occur exclusively in the cores. We conclude that Zagami experienced a twostage crystallization history. The first stage occurred in a deep-seated, slowly cooling magma chamber. There, the homogeneous Mg-rich cores of the pyroxenes crystallized during relatively slow cooling. The deep-seated origin of the cores is also indicated by the presence of amphibole within them, which requires pressures of formation equivalent to crystallization at depths > 7.5 km on Mars. Modest abundance of homogeneous Mg-rich cores (15–20% ) indicates that crystal settling did not play a significant role in this part of the magma chamber. During the second stage, the Mg-rich pyroxenes were entrained into a magma that either intruded to the near-surface and cooled in a relatively thin dike or sill, or extruded to the surface and crystallized in a lava flow > 10 m thick, again without indications for crystal settling. This scenario is suggested by estimates of cooling rates of 0.1–0.5°C/h, based on sizes of the plagioclase (maskelynite) crystals, and of ∼0.02°C/h, based on the width of pyroxene exsolution lamellae ( brearley, 1991). Irregular shapes of the Mg-rich cores result from resorption and possible solid-state diffusion, and the shapes and sizes of the pyroxenes after crystallization of Fe-rich pigeonite rims onto the cores were strongly controlled by the shapes and sizes of the cores. The finer-grained areas of the rock inherited smaller and more numerous Mg-rich pyroxene cores from the first stage than did the coarser-grained areas. Crystallization of both augite and pigeonite cores at depth, but mostly pigeonite rims in the nearsurface environment, may be the result of a phase-boundary shift and expansion of the pigeonite stability field at lower pressures. The estimated depth of the magma chamber for Zagami of >7.5 km and thickness of the putative lava flow of > 10 m are consistent with calculations and observations of volcanic constructs and flows in the Tharsis region of Mars.

Reconstitution of transferrin receptor in mixed lipid vesicles. An example of the role of elastic and electrostatic forces for protein/lipid assembly

We studied the interaction of transferrin receptors (of cell line Molt-4) with mixed model membranes as a function of lipid chain length (phospholipids with C14:0 and C18:1 hydrocarbon chains) and of the surface charge of the membrane using mixtures of C14:0 lecithin (DMPC) with C14:0 phosphatidylglycerol (DMPG) and C14:0 phosphatidylserine (DMPS). Spontaneous self-assembly of receptors and lipids was achieved by freeze-thaw cycles of a codispersion of mixed vesicles and receptors in buffer and subsequent separation of receptor-loaded and receptor-free vesicles by density gradient centrifugation. Information on specific lipid/protein interaction mechanisms was obtained by evaluation of protein-induced shifts of phase boundaries of lipid mixtures by calorimetry and by FTIR spectroscopy of partially deuterated lipid mixtures. The important role (1) of minimizing the elastic forces caused by the mismatch of the lengths of hydrophobic cores of the protein (lp) and the bilayer (lL) and (2) of the electrostatic coupling of protein head groups with the charged membrane/water interface for the lipid/protein self-assembly is established. The electrostatic interaction energy per receptor is about 10(3) kBT (by coupling to about 1000 charged lipids) which is sufficient to overcompensate the elastic energy associated with a mismatch of lp - lL approximately 1.0 nm. The maximum receptor concentration incorporated was measured as a function of membrane surface charge and lipid chain length. The maximum receptor molar fraction varied from xpmax = 5 x 10(-5) for DMPC to xpmax = 4 x 10(-4) for 1:1 DMPC/DMPG; moreover xpmax is higher for DMPS than for DMPG as charged component. For the long-chain lipids, xpmax is higher for a 9:1 DEPE/DEPC mixture [(4.2-9) x 10(-4)] than for pure DEPC (ca. 3.5 x 10(-4)). By decomposition of reconstituted receptors with proteases, we demonstrated the homogeneous orientation of the receptor with its extracellular head group pointing to the convex side of the vesicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of constrained equilibrium thermodynamics to irradiated alloy systems

Equilibrium thermodynamics are applied to systems with an excess of point defects to calculate the relative stability of phases. It is possible to model systems with supersaturation levels of vacancies and interstitials, such as those found under irradiation. The calculations reveal the extent to which phase compositional boundaries could shift when one phase or both in a two phase system contain an excess of point defects. Phase boundary shifts in the Ni-Si, Fe-Ni, Ni-Cr, and Fe-Cr systems are examined as a function of the number of excess defects in each phase. It is also found that the critical temperature of the sigma phase in the Fe-Cr system and the fcc-bcc transition in the Fe-Ni are sensitive to excess defect concentrations. These results may apply to local irradiation-induced phase transformations in the presence of solute segregation.

Antiferro-Quadrupolar Ordering in CeB6

The existence of an antiferro-quadrupolar ordering in the intermediate temperature region in CeB 6 is suggested by a model calculation. CeB 6 has two transition temperatures, T m =3.3 K and T N =2.3 K, enabling us to define three phases I, II and III in the sequence of decreasing temperature. The phase II shows unusual properties: A weak antiferromagnetism is induced and enhanced by the external magnetic field in the phase II, making the I-II phase boundary shift to the high-temperature side with increasing field. These properties can be explained by the present model based on the combined effect of the crystal field and the antiferro-quadrupolar interaction among 4f electrons on Ce 3+ ions. The molecular-field approximation with the two-sublattice model is used. Detailed comparison is made with experiment for various thermal and magnetic quantities.