Structural Changes In Liquid Research Articles

In situ high-pressure pair distribution function measurement of liquid and glass by using 100keV pink beam.

Understanding the pressure-induced structural changes in liquids and amorphous materials is fundamental in a wide range of scientific fields. However, experimental investigation of the structure of liquid and amorphous material under in situ high-pressure conditions is still limited due to the experimental difficulties. In particular, the range of the momentum transfer (Q) in the structure factor [S(Q)] measurement under high-pressure conditions has been limited at relatively low Q, which makes it difficult to conduct detailed structural analysis of liquid and amorphous material. Here, we show the in situ high-pressure pair distribution function measurement of liquid and glass by using the 100keV pink beam. Structures of liquids and glasses are measured under in situ high-pressure conditions in the Paris-Edinburgh press by high-energy x-ray diffraction measurement using a double-slit collimation setup with a point detector. The experiment enables us to measure S(Q) of GeO2 and SiO2 glasses and liquid Ge at a wide range of Q up to 20-29 Å-1 under in situ high-pressure and high-temperature conditions, which is almost two times larger than that of the conventional high-pressure angle-dispersive x-ray diffraction measurement. The high-pressure experimental S(Q) precisely determined at a wide range of Q opens the way to investigate detailed structural features of liquids and amorphous materials under in situ high-pressure and high-temperature conditions, as well as ambient pressure study.

An arrayed-window microfluidic device for observation of mixed nanoparticles with an X-ray free-electron laser

A microfluidic device was developed for coherent diffraction imaging using an X-ray free-electron laser (XFEL-CDI). Liquid samples, which are separately packed in reservoirs of the device, are mixed in a flow channel after an XFEL irradiation as a trigger. An XFEL-CDI experiment was conducted and images of gold nanoparticles in solution were obtained with a resolution of several nanometers from single-shot coherent diffraction patterns. We were able to capture the images of various structures of mixed nanoparticles in the flow channel, clearly demonstrating the function of the microfluidic device. The direct observation of structural changes in liquids will contribute to development of chemistry and biology.

Structural Water Stabilizes Protein Motifs in Liquid Protein Phase: The Folding Mechanism of Short β-Sheets Coupled to Phase Transition.

Macromolecular associates, such as membraneless organelles or lipid-protein assemblies, provide a hydrophobic environment, i.e., a liquid protein phase (LP), where folding preferences can be drastically altered. LP as well as the associated phase change from water (W) is an intriguing phenomenon related to numerous biological processes and also possesses potential in nanotechnological applications. However, the energetic effects of a hydrophobic yet water-containing environment on protein folding are poorly understood. Here, we focus on small β-sheets, the key motifs of proteins, undergoing structural changes in liquid–liquid phase separation (LLPS) and also model the mechanism of energy-coupled unfolding, e.g., in proteases, during W → LP transition. Due to the importance of the accurate description for hydrogen bonding patterns, the employed models were studied by using quantum mechanical calculations. The results demonstrate that unfolding is energetically less favored in LP by ~0.3–0.5 kcal·mol−1 per residue in which the difference further increased by the presence of explicit structural water molecules, where the folded state was preferred by ~1.2–2.3 kcal·mol−1 per residue relative to that in W. Energetics at the LP/W interfaces was also addressed by theoretical isodesmic reactions. While the models predict folded state preference in LP, the unfolding from LP to W renders the process highly favorable since the unfolded end state has >1 kcal·mol−1 per residue excess stabilization.

Structural changes in liquids at high pressures can be observed by shock compression

By shock compressing tin to extreme conditions, researchers studied how its liquid properties evolved -- a first step towards understanding the structure of molten materials surrounding planetary cores.

Abnormal viscosity changes in high-temperature metallic melts

The viscosity of high-temperature metallic melt, which is an important index for evaluating dynamics of liquid melt, is one of the basic physical properties. It not only influences the mold-filling capacity of melting metal in traditional casting techniques, but also exhibits more distinct influence on the fabrication of advanced material, such as metallic glass. According to the variation tendency of viscosity with temperature in alloy melt, the fragility of superheated melt could be obtained, which has proved to correlate with the ability of alloy to form glass. Besides, the viscosity of alloy well above the liquidus temperature also plays a key role in probing into the characteristic of liquid-liquid phase transition, the fragile-to-strong transition phenomenon, how the potential energy landscape evolves during cooling, etc. It has been generally accepted that the viscosity of metallic melt at high temperatures increases with temperature decreasing and could be fitted by an Arrhenius curve in the whole temperature range. However, recently more and more studies show that the viscosity of metallic melt cannot be fitted by only one Arrhenius curve. Instead, there exists at least one specific temperature below which the viscosity data begins to deviate from the Arrhenius curve at high temperature during cooling. These data could be described by another Arrhenius curve. In order to in depth understand this phenomenon, in this paper we summarize the viscosity data of different metallic melts in the literature. On the basis of introducing the method of detecting high-temperature melt viscosity, we discuss comprehensively the changing tendency of viscosity with temperature and the characteristics of abnormal viscosity changes in pure metal, binary and multivariate alloys well above the liquidus temperature. It is found that the abnormal viscosity changes generally occur in alloys that could form the types of intermetallic compounds. The abnormal viscosity change in metallic melt is accompanied with exothermic or endothermic effect, depending on alloy system, and reflects the existence of liquid-liquid transition well above the liquidus temperature. Besides, such an abnormal change of viscosity influences the ability to form metallic glass liquids. Although the abnormal dynamic change of metallic melt hints the existence of complexity of structural change in liquid during cooling, what is the key factor underlying this phenomenon remains a mystery. By combining the advanced experimental techniques such as high-energy X-ray diffraction and neutron scattering with the computer simulation method, this problem may be understood further. Besides, the relation between viscosity abnormity and the phase diagram is another problem that deserves to be noticed in the future.

Structural changes in supercooled Al2O3–Y2O3 liquids

Structural changes in liquids between Al2O3 and Y2O3 are investigated as a function of the composition and during supercooling using high energy X-ray diffraction (HEXRD) techniques combined with containerless aerodynamic levitation. Many-body molecular dynamics simulation techniques utilizing potential models that incorporate anion polarization effects are applied to study the same liquid systems. The X-ray scattering experiments indicate a change in liquid structure during supercooling around a composition 20% Y2O3 (AlY20) that occurs over a narrow temperature interval. We have associated this change in structure with the onset of a liquid-liquid phase transformation. Analysis of the MD simulated structures has allowed the structure changes to be interpreted in terms of Al(3+) and Y(3+) coordination environments and particularly the Y(3+)-Y(3+) structural correlations. We show that the incipient liquid-liquid phase transition behaviour is correlated with local density fluctuations that represent different coordination polyhedra surrounding oxygen ions. The difference in energy and volume associated with this sampling of high and low density basins in the underlying energy landscape is consistent with independent verifications of the volume and enthalpy differences between different amorphous forms. The differences in the high- and low-density configurations match the difference in diffraction patterns observed experimentally.

Density contrast between silicate melts and crystals in the deep mantle: An integrated view based on static-compression data

Mineral-physics data of SiO 2, MgSiO 3, and MgO under static compression, together with the physical theories of melting and structural changes in liquid, suggest that the density of silicate melts does not exceed that of crystalline assemblages with the same chemical composition at the pressure range of the deep mantle. Because drastic structural changes accompanied by the increase in the coordination number of silicon are completed in the shallow mantle, SiO 2 component becomes stiff and the compressibility of magnesium silicate melts decreases with SiO 2 content in the deep mantle while it increases with SiO 2 content in the shallow mantle. If the ideal mixing of melts with respect to volume is valid in the deep mantle, as is the case for the shallow mantle, the density contrast is significant in a composition range close to MgSiO 3. Therefore, magmas in a wide composition range would be buoyant in the deep mantle. Chemical compositions of magmas which are neutrally buoyant in the deep mantle have been estimated with a simplified model in (Mg,Fe)O–SiO 2 system.

High pressure effects on liquid viscosity and glass transition behaviour, polyamorphic phase transitions and structural properties of glasses and liquids

Since the pioneering work of Bridgman it has been known that pressure affects the glass transition of polymers and liquid state viscosities. Usually the Tg and viscosity both increase as a function of pressure as expected from ‘free volume’ theories. However, H2O provided a notable exception in that the viscosity passes through a minimum at low temperature. It was thought that this might be linked to the anomalous thermal expansion behavior. However further research on geologically important aluminosilicate liquids revealed that they could show anomalous viscosity decreases with increasing pressure and this behavior is given a structural interpretation as five-fold coordinated Si4+ and Al3+ species are formed. Also the existence of polyamorphism or density-driven liquid–liquid phase transitions in certain systems can lead to anomalies in the Tg or η vs. P relations. This may be the case for H2O, for example. Current research is focusing on investigating structural changes in liquids and glasses at high pressure as the rich variety of behavior is becoming recognized. Both experimental studies and computer simulations are important as the underlying phenomonology is linked to changes in the glass or liquid structure as a function of densification.

Pressure-Induced Structural Change in Liquids and Glasses

Recent development of strong synchrotron radiation sources enables us to study pressure-induced structural changes in liquids and glasses. These studies revealed that the structural changes in liquids and glasses are not monotonous and transformation sometimes occurs sharper than previously thought. Our studies on liquid phosphorus and silica glass are reviewed.

四配位共有結合性物質の液体の圧力誘起構造変化

We investigate pressure-induced structural changes in liquids of tetrahedrally bonded materials by synchrotron x-ray diffraction. The liquids show various structural changes, depending on their ionic characters in the chemical bonds. The liquids with a small ionic character, such as GaSb, InSb, and InAs, show continuous structural changes over a wide pressure region of about 20 GPa. In contrast, those with a large ionic character, such as CdTe and AgI, show drastic structural changes within a narrow pressure region of about 2 GPa. We discuss the effect of the ionicity on the pressure-induced structural changes in the liquids and compare the effect with that in the crystalline phases.

Photo-induced structural change in liquid sulphur

The structure of liquid sulphur at 400 K, below the polymerizationtemperature Tp = 432 K, is investigated by first-principlesmolecular-dynamics simulations. The calculated structure factor isin excellent agreement with the experimental data. To investigatethe microscopic mechanism of the photo-induced structural change inliquid sulphur below Tp, simulations are performedby exciting electrons in the valence band to the conduction band.It is found that a bond in one of the S8 rings is easily broken andconsequently the S8 ring turns out to be the S8 chain after anelectron excitation, in the same way as was seen for an isolated S8ring. After the electron excitation is stopped, the S8 chain doesnot reconstruct the S8 ring; instead a `tadpole' structure is formed.Since the tadpole structure persists for a long time, it isconsidered that the tadpole is one of possible structures for theexperimentally observed long-lived product in the relaxationprocess. We have shown that photo-induced polymerization occursin liquid sulphur when the S8 chains or the S8 tadpoles areclose to each other at their ends.

Accurate, sensitive, and fully automatic method to measure sound velocity and attenuation

An automatic high-precision ultrasonic system with the corresponding ultrasonic cell is described to measure simultaneously the speed of sound and the attenuation as a function of frequency. The technique is based on the pulse-echo method and is designed to detect small structural changes in liquids, when an external variable is changed. The precision of the technique is limited by the stability of the temperature, which was kept constant within ±0.5 mK. The method, which permits one to obtain the absolute value of the velocity as well as the attenuation with respect to the solvent, is fully automated for the whole variation of the external variable, which added to its fast response permits easy use in dynamic processes.

Environmental effects on molecules immersed in liquids

A methodology to study environmental effects is thoroughly discussed. It combines molecular quantum mechanics and classical statistical mechanics of molecular fluids. Pair distribution functions collecting statistical information appear quite naturally in the quantum equations describing a single molecule. As well as allowing the computation of any individual molecular property in a liquid phase, this approach satisfies a number of theoretical requirements (dependence on density and temperature, validity in the thermodynamic limit). In a sense, it can be regarded as a useful alternative to the well-known Monte Carlo averaging processes for calculating molecular properties. Numerical applications studying liquid carbon disulphide and liquid carbon tetrachloride at several state points are given. Results cover typical RHF information (CNDO/2) on molecules, and show the sensitivity of the presented methodology to structural changes in liquids.

Structural temperature coeficients of specific volume and viscosity of lead borate glass forming melts

The temperature coefficients of liquids depend not only on the changing intensity of thermal vibrations of atoms but also on the structural changes of liquid due to the change in temperature. The study of the glass transition regions permits to single out the structural part of the thermal coefficient of property of liquid. In this paper the results of systematic measurements of such structural thermal coefficients are presented and shortly discussed.

Compressional Relaxation in Liquids

A set of phenomenological equations, valid at all frequencies, is proposed for the rates of change of internal relaxation parameters describing molecular excitations and structural changes in liquid. An Onsager coupling is found to exist between the rate equations for the parameters and the pressure tensor, so that the diagonal terms of the pressure contain a linear sum of thermodynamic affinities governing the internal irreversible processes. These affinities can be eliminated from the pressure, using the rate equations, to give a complex compressional modulus, reducing to a bulk viscosity term at low frequencies and a contribution to the bulk modulus at very high frequencies. The bulk viscosity is calculated at 20°C for two nonassociated liquids, on the assumption of a single thermal and single structural relaxation time, with use of a “hole” model of structural relaxation based on a shear viscosity theory of Mooney. The acoustic absorption coefficient is computed from the bulk viscosity, yielding fair order-of-magnitude agreement with experiment in both cases.