Transport properties of supercooled confined water

This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature T_h. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.     

Melting of microinclusions close packed in an elastic matrix

A novel representation is proposed of the liquid state in a microcavity, the collective nature of that state being taken into account. In this case a microinclusion undergoing melting is described as a single two-level system. The phase transition of melting in a close-packed system of such inclusions embedded in an elastic medium is described rigorously within the framework of the self-consistent approach. When an additional intermediate premelting state is taken into account, the curve of the steady-state phase transition with a critical point that happens on the phase diagram can be transformed in different ways, depending on the values of the specific parameters. In the simplest case shortening of the straight line takes place; bending is also possible. There is a region of the parameters where the critical line is split. In the latter case the existence of the triple point is also possible. The results obtained are in agreement with the experimental data.     

Optical and resonant X-ray diffraction studies confirm a SmC*FI2-SmC* liquid crystal phase sequence reversal

Employing both null transmission ellipsometry and resonant x-ray diffraction, we confirmed the SmC*FI2-SmC* phase sequence reversal in one liquid crystal compound and specially prepared binary mixtures. This phase sequence reversal was predicted by two recent theoretical advances. Moreover, the temperature range for the SmC*FI2 phase increases significantly in the mixture suggesting that such a phase sequence may exist in other compounds.     

Dielectric properties of LC mixture with induced antiferroelectric phase

Mixture of two liquid crystalline components exhibits the antiferroelectric phase in a broad temperature range at room temperatures, though the two components separately do not show an antiferroelectric phase in a temperature range applied. The dielectric spectroscopy technique combined with measurements of the selective light reflection was used for identification and characterization of the phases and subphases existing in the mixture. In the SmC*_A phase, the low frequency mode characteristic of antiferroelectric phase has been detected. In the broad temperature range between SmC*_A and SmA* phases, no relaxation mode has been detected. The soft mode registered near the phase transition to SmA* phase follows the Curie-Weiss law.     

二元混合溶液闪点行为的激光拉曼光谱研究

本文以乙醇-甲酰胺,乙腈-甲酰胺,乙醇-环己酮,乙腈-环己酮四种混合溶液为研究对象,采用激光拉曼光谱对四种溶液体系的闪点行为进行讨论和研究。通过测定四种溶液体系的拉曼光谱和闪点,结合溶液拉曼光谱的特征峰强度比和拉曼位移的变化,探索四种溶液闪点的变化规律。试验结果表明,随着溶液浓度的增大,溶质的拉曼特征峰强线性增加,混合溶液的闪点降低。采用三次多项式分别对四种溶液体系的闪点与拉曼特征峰、溶液浓度的关系进行拟合,拟合结果良好。混合溶液的闪点随拉曼特征峰强比、溶液浓度的变化趋势相同。该试验方法将有助于从分子结构角度分析混合溶液的闪点变化规律,同时该方法可用于混合溶液闪点的实时在线检测。     

Effect of liquid phase on the triple point pressure of argon

We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value ofτ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔP _h), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.     

Quantum critical end point for the Kondo volume collapse model

The Kondo volume collapse describes valence transitions in f-electron metals and is characterized by a line of first order transitions in the pressure-temperature phase plane terminated at critical end points. We analyze the quantum critical end point, when the lower end point is tuned to T=0, and determine the specific heat, thermal expansion, and compressibility. We find that the inclusion of quantum critical fluctuations leads to a novel bifurcation of the first order phase line. Finally, we show that critical strain fluctuations can cause both, superconductivity and non-Fermi liquid behavior near the critical point.     

Critical Behavior of Liquid 3He

We investigate the liquid–gas second-order phase transition in liquid ³He using the variational calculations based on the cluster expansion of the energy functional. We also compute the critical point exponents of liquid ³He that are in agreement with experimental data.     

Carbon phase diagram from ab initio molecular dynamics

We compute the free energy of solid and liquid diamond from first-principles electronic structure theory using efficient thermodynamic integration techniques. Our calculated melting curve is in excellent agreement with the experimental estimate of the graphite-diamond-liquid triple point and is consistent with shock wave experiments. We predict the phase diagram of diamond at pressures and temperatures that are difficult to access experimentally. We confirm early speculations on the presence of a reentrant point in the diamond melting line but find no evidence for a first order liquid-liquid phase transition near the reentrant point.     

Dielectric and electro-optical studies of a nickel-ferrite-nanoparticle- doped ferroelectric liquid crystal mixture

Effect of magnetic nanoparticles (nickel ferrite) doping on the dielectric and electro-optical properties of a ferroelectric liquid crystal mixture has been studied. In a doped ferroelectric liquid crystal mixture, dispersion of a small amount (0.25 wt.%) of nickel ferrite nanoparticles decreases the polarization and improves the response time compared to an undoped mixture. The significant changes in the polarization and response time are explained on the basis of dipole–dipole interaction and anchoring phenomena. Dielectric permittivity also increases with increasing the temperature of the SmC* phase and shows a reduction in dielectric loss in a doped sample. A Goldstone mode is clearly observed at ～200 and ～500 Hz in an undoped and a doped sample, respectively.     

Melting of 2D Monatomic Solids: Lennard-Jones System

The Lennard-Jones interaction has been introduced into the Collins mix lattice of 2D liquids. By means of rigoroue calculation of the total potential and the free area, the Gibbs functions for 2D liquid and solid have been derived. The melting line obtained from the phase transition equation agrees quite well with the result of recent computer simulation experiments. The obtained reduced temperature of the triple point T_c^* = 0.438 agrees with the data measured in experiments of some inert gas monolayers adsorbed on graphite as well as in computer simulation experiments.     

Theory of the vortex matter transformations in high-Tc superconductor YBCO

Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.     

Quantum critical phase and Lifshitz transition in an extended periodic Anderson model

We study the quantum phase transition in f-electron systems as a quantum Lifshitz transition driven by selective-Mott localization in a realistic extended Anderson lattice model. Using dynamical mean-field theory (DMFT), we find that a quantum critical phase with anomalous ω/T scaling separates a heavy Landau-Fermi liquid from ordered phase(s). This non-Fermi liquid state arises from a lattice orthogonality catastrophe originating from orbital-selective Mott localization. Fermi surface reconstruction occurs via the interplay between and penetration of the Green function zeros to the poles, leading to violation of Luttinger's theorem in the strange metal. We show how this naturally leads to scale-invariant responses in transport. Thus, our work represents a specific DMFT realization of the hidden-FL and FL* theories, and holds promise for the study of 'strange' metal phases in quantum matter.     

Electro-optic and dielectric studies of silica nanoparticle doped ferroelectric liquid crystal in SmC* phase

We present the results based on the electro-optic and dielectric properties of silica nanoparticle (SNP) doped ferroelectric liquid crystal (FLC) in SmC* phase. Switching time, spontaneous polarization and rotational viscosity decreases with increase in the silica concentration. An improvement in switching time after doping the silica nanoparticle is due to enhancement in anchoring energy exist between silica nanoparticle and ferroelectric liquid crystal. We noticed that the dielectric permittivity and dielectric strength decreases with increasing the concentration of silica nanoparticle in SmC* phase. Relaxation frequency increases with increasing the silica concentration and temperature in SmC* and decreases as we approaches towards transition temperature.     

Mixturelike behavior near a liquid-liquid phase transition in simulations of supercooled water

In simulations of a waterlike model (ST2) that exhibits a liquid-liquid phase transition, we test for the occurrence of a thermodynamic region in which the liquid can be modeled as a two-component mixture. We assign each molecule to one of two species based on the distance to its fifth-nearest neighbor, and evaluate the concentration of each species over a wide range of temperature and density. Our concentration data compare well with mixture-model predictions in a region between the liquid-liquid critical temperature and the temperature of maximum density. Fits of the model to the data in this region yield accurate estimates for the location of the critical point. We also show that the liquid outside the region of density anomalies is poorly modeled as a simple mixture.     

Spin glass behavior upon diluting frustrated magnets and spin liquids: a Bethe-Peierls treatment

A Bethe-Peierls treatment to dilution in frustrated magnets and spin liquids is given. A spin glass phase is present at low temperatures and close to the percolation point as soon as frustration takes a finite value in the dilute magnet model; the spin glass phase is reentrant inside the ferromagnetic phase. An extension of the model is given, in which the spin glass/ferromagnet phase boundary is shown not to reenter inside the ferromagnetic phase asymptotically close to the tricritical point whereas it has a turning point at lower temperatures. We conjecture similar phase diagrams to exist in finite dimensional models not constraint by a Nishimori's line. We increase frustration to study the effect of dilution in a spin liquid state. This provides a “minimal” ordering by disorder from an Ising paramagnet to an Ising spin glass. Received 9 April 1999 and Received in final form 27 September 1999     

Reversible phase transition of colloids in a binary liquid solvent

We report fluid-fluid and fluid-solid phase transitions of charge-stabilized polystyrene particles suspended in a binary liquid mixture of 3-methylpyridine and water. These thermally reversible phase transitions occur in the homogeneous phase of the binary liquid mixture below the coexistence temperature of the two liquids. Close density matching of the particles and the solvent allows us to follow the phase behavior until complete coexistence of macroscopic phases with temperature as the control parameter. We use small angle x-ray scattering to characterize these phases as colloidal gas, liquid, fcc crystal, and glass.     

Quantitative theory of thermal fluctuations and disorder in the vortex matter

A metastable supercooled homogeneous vortex liquid state exists down to zero fluctuation temperature in systems of mutually repelling objects. The zero temperature liquid state therefore serves as a (pseudo) ‘fixed point’ controlling the properties of vortex liquid below and even around the melting point. Based on this picture, a quantitative theory of vortex melting and glass transition in Type II superconductors in the framework of Ginzburg-Landau approach is presented. The melting line location is determined and magnetization and specific heat jumps are calculated. The point-like disorder shifts the line downwards and joins the order-disorder transition line. On the other hand, the disorder induces irreversible effects via replica symmetry breaking. The irreversibility line can be calculated within the Gaussian variational method. Therefore, the generic phase diagram contains four phases divided by the irreversibility line and melting line: liquid, solid, vortex glass and Bragg glass. We compare various experimental results with the theoretical formula.