Evidence of deeply supercooled liquid water in interaction with LiCl

The properties of water above the glass transition temperature are highly controversial. By using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the presence of deeply supercooled water is manifested by dissolution of LiCl in the pure amorphous water films heated at 140-155 K and the formation of aqueous LiCl solutions. Two phases of deeply supercooled water, that lead to the dilute and concentrated LiCl solutions, are clearly identified. The former is short-lived and merges into the latter, whereas the latter is basically identical to normal liquid water as far as the solubility of LiCl is concerned.     

Liquid-liquid phase transitions in supercooled water studied by computer simulations of various water models

Liquid-liquid and liquid-vapor coexistence regions of various water models were determined by Monte Carlo (MC) simulations of isotherms of density fluctuation-restricted systems and by Gibbs ensemble MC simulations. All studied water models show multiple liquid-liquid phase transitions in the supercooled region: we observe two transitions of the TIP4P, TIP5P, and SPCE models and three transitions of the ST2 model. The location of these phase transitions with respect to the liquid-vapor coexistence curve and the glass temperature is highly sensitive to the water model and its implementation. We suggest that the apparent thermodynamic singularity of real liquid water in the supercooled region at about 228 K is caused by an approach to the spinodal of the first (lowest density) liquid-liquid phase transition. The well-known density maximum of liquid water at 277 K is related to the second liquid-liquid phase transition, which is located at positive pressures with a critical point close to the maximum. A possible order parameter and the universality class of liquid-liquid phase transitions in one-component fluids are discussed.     

Interaction of water with LiCl, LiBr, and LiI in the deeply supercooled region

The hydration mechanism of lithium halides was studied using time-of-flight secondary ion mass spectrometry as a function of temperature. The lithium halides embedded in thin films of amorphous solid water segregate to the surface at temperatures higher than 135-140 K, with efficiency increasing in the order of LiCl, LiBr, and LiI. A monolayer of LiCl and LiI adsorbed on the surface of amorphous solid water tends to diffuse into the bulk at 160 K. The infrared absorption band revealed that the aqueous lithium-halide solutions and crystals are formed simultaneously at 160 K; these phenomena are explicable as a consequence of the evolution of supercooled liquid water. The strong surfactant effect is inferred to arise from hydration of a contact ion pair having hydrophilic (lithium) and hydrophobic (halide) moieties. Furthermore, bulk diffusion of lithium halides might result from the formation of a solvent-separated ion pair in supercooled liquid water. The presence of two liquid phases of water with different local structures is probably responsible for the formation of these two hydrates, consistent with the calculated result reported by Jungwirth and Tobias[J. Phys. Chem. B 106, 6361 (2002)].     

Fragile-to-strong liquid transition in deeply supercooled confined water

Confining water in lab synthesized nanoporous silica matrices MCM-41-S with pore diameters of 18 and 14 A, we have been able to study the molecular dynamics of water in deeply supercooled states, down to 200 K. Using quasielastic neutron scattering and analyzing the data with the relaxing cage model, we determined the temperature variation of the average translational relaxation time and its Q-dependence. We find a clear evidence of an abrupt change of the relaxation time behavior at T approximately equal to 225 K, which we interpreted as the predicted fragile-to-strong liquid-liquid transition.     

Slow dynamics of supercooled m-toluidine investigated by mechanical spectroscopy

Dynamics of supercooled m-toluidine close to the glass transition have been investigated by dynamic shear modulus measurements and stress relaxation experiments. The viscoelastic response of this material follows time-temperature-superposition in the temperature range investigated. Comparison with results at ultrasonic frequencies suggests the existence of a secondary relaxation. A change of the temperature dependent viscosity from a Vogel-Fulcher-Tammann behavior to another regime at low temperatures is also found. Compared to most inorganic glass formers, the viscosity of m-toluidine at the glass transition is approximately two orders of magnitude lower. The shear relaxation times are characterized by the same temperature dependence as the viscosity. They are in reasonable agreement with the results of previous ultrasonic measurements. The conclusions of the present work agree with recent results obtained by high resolution dielectric spectroscopy.     

Two liquid phases of water in the deeply supercooled region and their roles in crystallization and formation of LiCl solution

The properties of supercooled liquid water and the mechanism of crystallization in it were investigated using time-of-flight secondary ion mass spectrometry and reflection absorption infrared spectroscopy. The self-diffusion of the water molecules commences at 136 K, and then the liquid-liquid phase transition occurs at 160-165 K. The latter is evidenced not only by the occurrence of fluidity but also by the formation of a LiCl solution. The infrared absorption band also changes drastically above 160 K due to crystallization of water (on the Au film) and the formation of LiCl solution (on the LiCl film). The immediate crystallization and dissolution of LiCl are thought to be characteristic of normal water that is created in a deeply supercooled region, indicating that viscous liquid water (T > 136 K) is transformed into supercooled liquid water at around 160 K. The crystallization kinetics is different between these two phases because the former (latter) involves nuclear growth (spontaneous nucleation). Without nuclei, crystallization is quenched below 160 K in the present experiment. It is suggested that the viscous liquid phase coexists at the surface or grain boundaries of metastable ice Ic.     

Effect of confinement on the liquid-liquid phase transition of supercooled water

We report on an observation of the phase transition between two liquid phases of supercooled confined water in simulations. The temperature of the liquid-liquid transition of water at zero pressure slightly decreases due to confinement in the hydrophobic pore. The hydrophilic confinement affects this temperature in the opposite direction and shifts the critical point of the liquid-liquid transition to a higher pressure. As a result, in a strongly hydrophilic pore the liquid-liquid phase transition becomes continuous at zero pressure, indicating the shift of its critical point from negative to a positive pressure. These findings indicate that experimental studies of water confined in the pores of various hydrophobicity/hydrophilicity may clarify the location of the liquid-liquid critical point of bulk water.     

Liquid-liquid interfaces: In isolation and in interaction

Although liquid-liquid interfaces are as important as liquid-vapor interfaces in many fields, including biology and technology, they have received much less attention in terms of systematic experimental studies. Many techniques are, in principle, relevant to both types of interface; likewise similar theories can often be developed for both. The basic physical chemistry of isolated interfaces, i.e. interfaces between two bulk liquids in mutual contact, is introduced first in this review. The interfacial tension, the forces acting at interfaces (i.e. van der Waals, Coulombic and steric forces), and the thermodynamic treatment of such systems are each considered, and the experimental techniques and some of the more important results are summarized. Next, the problem of three-phase contact (in which two or three of the phases are liquid) is introduced, and the concept of wetting and spreading considered. This leads to a discussion of systems in which two bulk phases (either, or both, of which are liquids) are separated by a liquid film; the mutual interaction of the two interfaces now becomes relevant. The stability of such systems is discussed in terms of the various forces acting within the systems, plus any external forces, such as gravity. The thermodynamics of liquid films is briefly introduced, and some discussion of the magnitude of the two interfacial tensions given. Finally, it is shown that the factors governing the formation and stability of liquid droplets and emulsion systems are directly related to the consideration of the earlier sections.     

The oxygen content in supercooled water

Summary The oxygen content in liquid water has been measured in the temperature range between 0°C and –7°C. The measurements have been carried out with an amperometric needle sensor in glass-capillaries with an inner diameter of 1.7 mm. It has been obtained that the oxygen content in water is rapidly increasing as the temperature is lowered below 0°C. At –5°C the concentration of oxygen in water at constant partial pressure of oxygen is by 13% higher than that at +3°C. The increase of oxygen content seems to be related to the unusual temperature dependence of heat capacity, density and isothermal compressibility of supercooled water.Herrn Professor Ulrich Wannagat in alter Verbundenheit zum 70. Geburtstag gewidmet.     

Liquid-liquid phase transition of protein aqueous solutions isothermally induced by protein cross-linking

We experimentally demonstrated that liquid-liquid phase separation (LLPS) of protein aqueous solutions can be induced by isothermal protein oligomerization. This phenomenon is analogous to LLPS induced by the polymerization of small organic molecules in solution. Specifically, using glutaraldehyde for protein cross-linking, we observed the formation of protein-rich liquid droplets for bovine serum albumin and chicken egg lysozyme at 25 degrees C. These droplets evolved into cross-linked protein microspheres. If the aqueous solutions of the protein monomer do not show LLPS at temperatures lower than the oligomerization temperature, protein-rich droplets are not observed. We experimentally linked the formation of these droplets to the increase of LLPS temperature during protein oligomerization. When macroscopic aggregation competes with LLPS, a rationale choice of pH, polyethylene glycol, and salt concentrations can be used to favor LLPS relative to aggregation. Although glutaraldehyde has been extensively used to cross-link protein molecules, to our knowledge, its use in homogeneous aqueous solutions to induce LLPS has not been previously described. This work contributes to the fundamental understanding of both phase transitions of protein solutions and the morphology of protein condensed phases. It also provides guidance for the development of new methods based on mild experimental conditions for the preparation of protein-based materials.     

Structural study of low concentration LiCl aqueous solutions in the liquid, supercooled, and hyperquenched glassy states

Neutron diffraction experiments on a solution of LiCl in water (R = 40) at ambient conditions and in the supercooled and hyperquenched states are reported and analyzed within the empirical potential structure refinement framework. Evidence for the modifications of the microscopic structure of the solvent in the presence of such a small amount of salt is found at all investigated thermodynamic states. On the other hand, it is evident that the structure of the hyperquenched salty sample is similar to that of pure low density amorphous water, although all the peaks of the radial distribution functions are broader in the present case. Changes upon supercooling or hyperquenching of the ion's hydration shells and contacts are of limited size and evidence for segregation phenomena at these states does not clearly show up, although the presence of water separated contacts between ion of the same sign is intriguing.     

Phase transition sequence of betaine arsenate investigated by infrared reflectivity

The ac-polarized infrared reflectivity spectra of betaine ortho-arsenic acid single crystals have been measured throughout the ferroelastic–ferroelectric phase transition observed near T_c2 = 120 K. The monoclinic symmetry of the system was explicitly taken into account and a three-polarization technique used for the first time to investigate in detail the critical behaviour of the B_u polar phonons. The results show that near the THz frequency range, the usual approximation of considering the system as pseudo-orthorhombic fails, giving rise to errors in the determination of the optical parameters. The obtained spectroscopic data indicate that the phase diagram and the physical mechanism involved in the stabilization of ferroelectricity in betaine arsenate (BA) are more complex than the prevalent view of a simple ordering process in bistable hydrogen bonds.     

微流控液液萃取-液液波导集成化分析系统

利用溴化1-丁基-3-甲基咪唑离子液体/碳酸钠溶液双水相体系,实现了多相层流液液萃取.以具有较高折射率的离子液体为液芯,较低折射率的盐溶液为包层,实现了液液波导吸光度检测.据此建立了一种液液萃取与液液波导检测集成化的微流控分析系统.该系统对甲酚红试样的萃取率在93%以上,对甲酚红试样检测的线性范围为0.01~0.40 mg/m L,相对标准偏差为3.4%(n=11),检出限为3.8μg/m L(3σ).该系统将萃取分离与液液波导长光程吸光度检测集成在一起,为拓展吸光度检测在微流控系统中的应用提供了新思路.     

Dynamics of supercooled water in various mesopore sizes

Double-quantum-filtered NMR and T(1) inversion-recovery spectroscopy were employed to exploit the temperature-dependent dynamics of D(2)O confined in MCM-41. Samples with three pore sizes of 1.58, 2.03, and 2.34 nm and two D(2)O contents were investigated. The reorientation correlation times of confined D(2)O in variously sized pores exhibit different temperature dependencies. The results reveal that the D(2)O molecules at fast motion site remain mobile below approximately 225 K and a liquid-liquid phase transition occurs around this temperature for all samples studied. This temperature is thought to be unreachable for supercooled D(2)O. Particularly, in 20 wt % D(2)O loaded samples with pore diameters of 1.58 and 2.03 nm, the reorientational correlation times of D(2)O at fast motion site exhibit Arrhenius behavior between 225 and 290 K, while other samples show power law dependency. Thus, a liquid phase of the fragile type in bigger pores changes to the strong type in samples with smaller pores.     

Structural transformations of supercooled water in nanopores, studied by microwave radiation

It is shown that the state of supercooled water in nanoporous materials can be studied by measuring the attenuation of microwave radiation. By analyzing variations in the intensity of radiation transmitted through a moistened medium during the supercooling of water in the range of ?37 to ?190°C, the temperatures at which structural transformations take place can be determined. Using the example of KSKG silica gel with a mean pore size of 8 nm, it is shown that at a moisture of 3?C18%, water is found in the liquid state up to a temperature of ?130°C, at which the transition to glass occurs.     

Multi-reference configuration interaction calculations on the systems Xe 2 + and Xe 3 +

Potential curves for the ground (²Σ _u ⁺ ) and the three lowest excited states of the Xe ₂ ⁺ dimer ion (²Π _g ,²Π _u ,²Σ _g ⁺ ) have been calculated using pseudopotentials in MRD-CI (multi-reference single anddouble excitationconfigurationinteraction) calculations. Spin-orbit interaction — leading to the six states 1.(1/2) _u , 1.(3/2) _g , 1.(3/2) _u , 1.(1/2) _g , 2.(1/2) _u , 2.(1/2) _g — has been taken into account using a semiempirical technique [1]. Subsequently, starting with a relaxed Xe ₂ ⁺ ion in its ground state, the potential energy surface for the system Xe-Xe ₂ ⁺ was studied. We found that the collinear approach of the Xe atom leads to the most stable geometry. This is a linear symmetric molecule with bond lengths of 6.38 bohr. In the bestT-shaped structure, the Xe atom is 7.83 bohr away from the midpoint of the Xe ₂ ⁺ (r=6.1 bohr) dimer. The calculated binding energy of 0.25 eV for the equilibrium structure of the Xe ₃ ⁺ molecule (i.e. the linear symmetric geometry), is in very good agreement with experimental results of 0.27 ± 0.02 eV [2].     

Experimental transition probability for theE1 intercombination transition in Be-like Xe50+

The 2s^{2 1}S₀ — 2s2p³P°₁ intercombination transition in Be-like Xe⁵⁰⁺ has been observed and the intensity decay with time has been measured using a foil-excited fast ion beam. The transition wavelength value is found to be λ = (9.81±0.05) nm and the upper level lifetime to be τ = (0.47±0.05) ns. Both values agree with recent theoretical predictions.     

The phase transition and reorientational fluctuations in pyridinium iodide crystal investigated by raman scattering

The order-disorder character of the transition in pyridinium iodide at 247 K is apparent from the relaxation of the zone-centre selection rules in the Raman spectra. Divergence of the librational modes bandwidth suggests that fluctuations in the out-of-plane orientation of the pyridinium ions exist in both the low- and high-temperature phases     

Phase transition sequence in ferroelectric Aurivillius compounds investigated by single crystal X-ray diffraction

The investigation of the phase transition sequence in SrBi₂Ta₂O₉ (SBT) and SrBi₂Nb₂O₉ (SBN) is reported using single-crystal X-ray diffraction. By monitoring specific reflections as a function of temperature, sensitive either to the superstructure formation or to polar displacements, it was possible to check the existence or not of an intermediate phase. This latter was confirmed in SBT, but within experimental accuracy could not be detected in SBN.