Temperature-induced Structural Transformation Research Articles

PH- and temperature-dual responsive polymer emulsion for rapid release of drag reducer

Slick water fracturing fluid is widely used in major oil fields due to its low cost and high drag reduction. Polyacrylamide emulsions drag reducers play a decisive role in slick water fracturing. The dissolution rate of polymer emulsions drag reducers was increased by adding hydrophilic surfactants, but the stability of the emulsions is poor, which limits its wide application. In order to solve the contradiction between the stability of polymer emulsion and rapid release of drag reducer. Here, a P(AA-AM-AMPS) polymer emulsion drag reducer with dual stimulation response of pH and temperature was designed. Surfactant (D400/OA) with dual responses to pH and temperature is synthesized by using oleic acid (HOA) and polyether amine 400 (D400). D400/OA shows a remarkable pH- and temperature-responsive behavior due to the pH- and temperature-induced structural transformation of D400/OA. Interestingly, D400/OA-stabilized monomer emulsion exhibits an obvious pH- and temperature-induced structural transformation. Meanwhile, The D400/OA-stabilized monomer emulsion has remarkable stability, which benefits the inverse emulsion polymerization of P(AM-AA-AMPS) polymer. The obtained P(AM-AA-AMPS) polymer emulsion maintain stability whose particle size nearly unchanged by storing for 15 days. Interestingly, P(AM-AA-AMPS) polymer emulsion can be released completely by changing the pH or temperature of the aqueous solution. The apparent viscosity of P(AM-AA-AMPS) polymer, in either the alkaline (pH=10.31) solution of 25±2 °C or neutral (pH=7) solution of 70±2 °C, respectively required 40 s and 8 min to reached a maximum value of 96 mPa·s. The release rate of P(AM-AA-AMPS) polymer emulsion is further enhanced under the dual responsive of temperature (70±2 ℃) and pH (10.31) and it takes only 20 s, In addition, the drag reduction rate of P(AM-AA-AMPS) polymer emulsion is 72 % when completely released under the dual responsive of temperature and pH, showing a remarkable drag reduction property. The D400/OA-stabilized P(AM-AA-AMPS) polymer emulsion are expected to meet the demand for the production enhancement of the oil and gas reservoirs.

Strong renormalization of Ba vibrations in thermoelectric type-IX clathrate Ba24Ge100

We report a combined experimental and theoretical study of the lattice dynamics of the type IX clathrate ${\mathrm{Ba}}_{24}{\mathrm{Ge}}_{100}$ by inelastic neutron scattering (INS) experiments and density functional theory (DFT) calculations. We observe low-energy optical modes at $\ensuremath{\sim}2--3\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ due to the motion of the heavy Ba atoms along the high-symmetry axis and the largest dimension of the open Ge@20 cages present in the compound. Even though the phonon participation ratio indicates that these low-energy modes are localized, their $Q$ dependence shows that the dynamics of the Ba guests are correlated. We observe a strong change in the spectral weight of these modes when the compound undergoes a temperature-induced structural transformation in the temperature range 190--230 K. In the high-temperature phase, the low-energy optical modes show high intensities in the INS data and frequencies rather insensitive to temperature changes up to \ensuremath{\sim}550 K. In the low-temperature structural modification, the low-energy mode intensities are strongly depleted and apparently shifted to higher energies; this behavior is in line with an off-centering of the Ba atoms at low temperatures. Our DFT calculations successfully approximate the essential features in the dynamics of the high-temperature ${\mathrm{Ba}}_{24}{\mathrm{Ge}}_{100}$ structure.

Temperature-sensitive properties of occluded hydration centers in direct hexagonal (HI) mesophases

Temperature-induced structural transformations of a direct hexagonal mesophase were investigated by SAXS, rheology, DSC, and NMR. The investigated mesophase region consists of two distinct direct hexagonal structures. The primary structure, detected at lower water content (33.0–39.0 wt%, 25 °C), is oriented as a bidiscontinuous assembly; it is composed of "occluded hydration centers" (OHCs) and direct surfactant-oil aggregates. The secondary structure, detected at higher water content (39.5–42.5 wt% water, 25 °C), is composed of an unbound water continuous phase and direct surfactant-oil aggregates.The OHCs within the bidiscontinuous mesophase were found to enhance the mesophase's order (correlation length (ξ)) and storage modulus (G′). The content of the unbound water occluded within the OHCs is temperature dependent, due to the ethoxylates’ water binding properties. At temperatures below 18 °C, the water in the bidiscontinuous mesophase (<39.0 wt% water) remains bound, resulting in a decreased mesophase order (correlation length (ξ)) and storage modulus (G′). Elevated temperatures increase the unbound water content, causing the unbound water domains to swell. Above the critical swelling point, the unbound water domains interlink to form a continuous phase, reducing the systems’ range order (ξ) and the storage modulus (G′).Better understanding the temperature dependence of the direct hexagonal mesophase enables mapping of the critical factors affecting the controlled delivery vehicles for non-bioavailable drugs.

Stability and mechanical properties of molybdenum carbides and the Ti–Mo–C solid solutions: A first-principles study

First-principles calculations were carried out to study the hypothetical MoC, Mo2C, Mo3C2 and random MoCx, x = 1.0, 0.875, 0.75 and 0.5 phases, and those that were experimentally verified, as well as the random cubic and hexagonal TiC–MoC and cubic and orthorhombic Ti2C–Mo2C solid solutions (alloys). The electronic and phonon structures, formation energy, elastic constants and moduli, hardness, Debye temperature, fracture toughness and stress-strain relation for these structures were calculated in order to understand the differences in phase stability; to explain their properties; and to predict possible new stable phases. The phase diagrams of the Mo–C system for three compositions, 67 at.% Mo + 33 at.% C, 60 at.% Mo + 40 at.% C and 50 at.% Mo + 50 at.% C, were built in the temperature range of 0–4000 K. First-principles molecular dynamics simulations and the group-theoretical analysis are used to identify the plausible mechanisms of the temperature-induced structural transformations in the α-, γ- and γ’-phases of MoC. The composition dependence of the mechanical characteristics of the solid solutions was found to have an extremal character, and in particular a maximum hardness for the cubic Ti0.75Mo0.25C (27.2 GPa) and orthorhombic Ti0.5Mo1.5C (14.6 GPa) alloys. The theoretical phase stability diagrams for the Mo–C system and Ti–Mo–C alloys contain not only the structures experimentally observed but also hypothetical phases, and the available experimental properties were reproduced and explained.

Lithium Borates from the Glass to the Melt: A Temperature-Induced Structural Transformation Viewed from the Boron and Oxygen Atoms.

A multiedge study of the local structure of lithium borate glasses and melts has been carried out using X-ray Raman scattering (XRS) as a function of temperature. Thanks to a wide range of compositions, from pure B2O3 up to the metaborate composition, we are able to finely interpret the modifications of the local environment of both the boron and oxygen atoms in terms of boron coordination number, formation of nonbridging oxygens (NBOs), and polymerization degree of the borate framework as a function of temperature and composition. A temperature-induced [4]B to [3]B conversion is observed above the glass transition temperature (Tg) from the glass to the melt from the triborate composition up to the metaborate composition. Two distinct melt structures are reported: a well-polymerized borate network-with few NBOs-below the triborate composition and a depolymerized borate network above the diborate composition with a rapid increase of the number of NBOs when Li2O is added. These two structurally distinct melts allow explaining the two dynamic regimes observed for lithium ion diffusion.

Temperature-induced structural transformations accompanied by changes in magnetic properties of two copper coordination polymers

Two ferromagnetic copper compounds have been synthesized under different temperature, which represented the rare example of structural transformations resulting from the coordination modes of organic ligands supported by magnetic results.

Temperature-Induced Reversible and Irreversible Transitions between Metastable Perovskite Phases in the BiFe1−yScyO3 Solid Solutions

The antipolar orthorhombic Pnma phase with the 2 a p × 4 a p × 2 2 a p superstructure (ap ~4 Å is the pseudocubic perovskite unit-cell parameter) is observed in many perovskite compositions derived from BiFeO3. Temperature-induced structural transformations in metastable perovskite solid solutions with the Pnma structure corresponding to the range of 0.30 ≤ y ≤ 0.60 of the (1−y)BiFeO3-yBiScO3 quasi binary system were studied using temperature X-ray and neutron powder diffraction. These compositions cannot be prepared in bulk form at ambient pressure but can be stabilized in the Pnma phase by means of quenching after synthesis under high pressure. The compositions were investigated in situ between 1.5 K and the temperature of the stability limit of their metastable phases (about 870–920 K). It has been found that heating the as-prepared compositions with the Pnma phase leads to formation of the rhombohedral R3c phase ( 2 a p × 2 a p × 2 3 a p ), which, on cooling down to room temperature, either remains or transforms into a polar orthorhombic Ima2 phase ( 2 a p × 2 a p × 2 a p ). The observed phase transformations in the BiFe1−yScyO3 perovskite series on heating and on cooling are considered in terms of geometrical factors.

LEEM study of high-temperature oxygen structures on W(110) and their transformations

High-temperature reorganization of the adsorbed oxygen on the W(110) surface was investigated using low-energy electron diffraction (LEED) and low-energy electron microscopy (LEEM). Using these two techniques, we have resolved two out of three high-temperature tungsten oxide phases reported in the literature. We verified the structural properties of oxygen adsorbed on tungsten by comparing bright- and dark-field LEEM images. In particular, we determined the relationship between atomic steps and the occurrence of a specific structural domain in different phases. Finally, we described the temperature-induced structural transformation that was directly observed, both in real and reciprocal space, for two oxygen surface phases formed on W(110). By careful examination, it was proven that under specific circumstances, this transition can be conducted in both directions, and it is possible to halt it at any stage.

A Copper-Nitroxide Adduct Exhibiting Separate Single Crystal-to-Single Crystal Polymerization-Depolymerization and Spin Crossover Transitions.

A complex cascade of solid-state processes initiated by variation of temperature was found for the heterospin complex [Cu(hfac)2L(Me/Et)] formed in the reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)2] with stable nitronyl nitroxide 2-(1-methyl-3-ethyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L(Me/Et)). The cooling of the compound below 260 K initiated a solid-state chemical reaction, which led to a depolymerization of chains and formation of a pair heterospin complex [Cu(hfac)2L(Me/Et)2][[Cu(hfac)2]3L(Me/Et)2]. Further decrease in temperature below 144 K led to a spin transition accompanied by a drastic decrease in the effective magnetic moment from 2.52 to 2.24 μB. When the compound was heated, the order of effects was reversed: at first, the magnetic moment abruptly increased, and then the molecular fragments of the pair cluster united into polymer chains. Two hysteresis loops correspond to this cascade of temperature-induced structural transformations on the experimental dependence μeff(T): one at high (T↑ = 283 K and T↓ = 260 K) and the other at low (T↑ = 161 K, T↓ = 144 K) temperature. The spin transitions were also recorded for the [[Cu(hfac)2]3L(Bu/Et)2] and [[Cu(hfac)2]5L(Bu/Et)4] molecular complexes, which are models of the trinuclear fragment of the {[Cu(hfac)2]3L(Me/Et)2} pair cluster.

Pressure-induced structural change in liquid Ge0.15Te0.85 alloy

X-ray diffraction has been measured up to 2.4 GPa for liquid Ge0.15Te0.85 alloy using synchrotron radiations. Static structure factor S(Q) and pair distribution function g(r) were obtained. At 0.5 GPa, S(Q) shows different temperature dependence below and above 700 K. With increasing temperature above 700 K the increasing rate of the height ratio between the first and second peaks in S(Q) becomes moderated. This finding suggests a temperature-induced structural transformation occurs at 700K. At 1.8 GPa and 2.4 GPa such anomalous behaviour was not observed in the temperature region from the melting temperature to 850 K. The boundary between the low-temperature and the high-temperature phases has a negative slope. The Clausius-Clapeyron equation suggests the high-temperature phase has larger entropy than the low-temperature one.

Constant pressure–temperature molecular dynamics on a torus

A model of many-body system on the surface of a torus is employed to conduct isothermal–isobaric molecular dynamics. Six independent variables, which are three radius and three angles determining the orientations of the curvatures describe the flexibility of the surface, eliminating the size and the shape of the cell from dynamics. The isotropic and flexible cell motion equations are derived with the help of an approach analogous to the Nosé–Hoover one. Simulations for a temperature-induced structural transformation of a model helium lattice under isotropic applied pressure are used to illustrate the new method. Results of calculations with the usage of time-reversible integrator are compared with the results of the Martyna–Tobias–Klein algorithm.

Temperature- or Guest-Induced Drastic Single-Crystal-to-Single-Crystal Transformations of a Nanoporous Coordination Polymer

Aside from a temperature-induced structural transformation, a new nanoporous coordination polymer [Ag6Cl(atz)4].OH.6H2O (Hatz = 3-amino-1,2,4,-triazole) comprised of interpenetrated Ag3(atz)2 coordination nets exhibits a single-crystal-to-single-crystal transformation of a 5-fold to 6-fold net interpenetration change triggered by guest desorption/absorption.

Relationship between electronic and crystal structure in Cu–Ni–Co–Mn–O spinels: Part A: Temperature-induced structural transformation

Local atomic and crystal structures around Cu and Mn atoms in Mn 1.68Cu 0.6Ni 0.48Co 0.24O 4 spinel samples fabricated by metal–organic decomposition synthesis at different annealing temperatures were investigated by X-ray absorption fine structure analysis. There are two distinct copper cations, Cu 1+ and Cu 2+, both of which maintain tetrahedral coordination. The bond-length distances are Cu 1+–O = 2.00 Å and Cu 2+–O = 1.80 Å. The manganese cations are for the most part octahedral. The spinels prepared at low temperature (600 °C) contain smaller (Mn 4+–O = 1.88 Å) undistorted MnO 6 octahedrons corresponding to Mn 4+ valence, whereas the manganese octahedrons in high-temperature materials (800 °C and higher) were larger and had a pronounced tetragonal distortion pertaining to Mn 3+ oxidation state (Mn 3+–O = 1.93 Å and 2.11 Å). By rising the fabrication temperatures, relative concentration of the species of Mn 4+ and Mn 3+ varies as a result of the reaction represented by Cu 1+ + Mn 4+ ⇒ Cu 2+ + Mn 3+, implying irreversible temperature-induced structural transformation. Atomic coordinates in the low-temperature phase are similar to those found in the ideal cubic spinel with oxygen parameter u = 0.27, whereas local environments of the Cu and Mn atom correspond to the tetragonal CuMn 2O 4 phase (space group I4 1/ amd). Unlike in CuMn 2O 4, orientation of the lattice distortions is random, however, the long-range cubic spinel structure is retained at all time.

Temperature-induced structural transformations of layered titanosilicate JDF-L1

Layered titanosilicate JDF-L1 is synthesised in a Na 2O:TiO 2:SiO 2:H 2O system applying a rapid procedure and without using organic additives in the synthesis mixture. The thermal evolution of the JDF-L1 structure is studied by thermogravimetric-differential thermal analysis, powder X-ray diffraction and Raman spectroscopy. It is shown that on heating JDF-L1 undergoes a sequence of structural rearrangements causing formation of noncrystalline alkali titanate–titanosilicate phases, defect-rich microcrystalline silica and crystalline titanosilicate narsarsukite, the latter becoming the dominant phase at high temperatures.

CHARACTERISTIC OF TEMPERATURE-INDUCED CHANGE ON THE STRUCTURE OF LIQUID Al AND Sn

Based on the analysis of the X-ray diffraction data of liquid Al and Sn, temperature-induced structural transformations are found for liquid Al in the range of 1050—1250℃ and for liquid Sn near 800 and 1200℃. The nearest neighbor distance r1 of Al and Sn decreases with the increase of temperature. The structure of liquid Sn is similar to α-Sn on the short-range order length scale. The physical meaning of the correlation radius rc is discussed.

The magnetic balance and its application to studying the magnetic mineralogy of igneous rocks.

A magnetic balance operating between -196°C and 800°C with magnetic fields up to 1.2MAm-1 is described. The typical noise level of the instrument corresponds to a sample dipole moment of 1.6×10-7 Am2 (the moment of 1.7μg of magnetite magnetized to saturation at room temperature or about 200μg of typical basaltic rock). Small samples may be used which leads to consistency between the calibration figure for both ferrimagnetic and paramagnetic minerals coexisting in the same sample and also allows rapid temperature change. An important feature is a programmable temperature-time regime. Above room temperature heating rates between 2°/min and 100°/min can be selected, and the influence that heating rate can have on the form of the thermomagnetic curve is demonstrated.The magnetic balance operating in high field is the principal instrument for Curie point temperature determination. However, the balance has much wider application than this one task. The balance is a powerful tool in magnetochemistry or in monitoring temperature-induced structural transformations. We present here results which, for the first time, show the temperature dependence of the inversion process by which the cation-deficient magnetic minerals in submarine basalts transform to other magnetic phases. It may be that inversion proceeds at a slow rate under submarine conditions. Such inversion, which is accompanied by a change in saturation magnetization and grain size, will inevitably affect the intensity of remanent magnetization and magnetic susceptibility of the submarine crust.