Nanosecond rapid freezing of liquid benzene under shock compression studied by time-resolved coherent anti-Stokes Raman spectroscopy

Nanosecond time-resolved coherent anti-Stokes Raman spectroscopy is used to investigate the shock-induced liquid-solid phase transition and crystallization of liquid benzene. Temporal evolution of the Raman shift of the ring-breathing and C-H stretching modes is investigated. A metastable supercompressed state and a liquid-solid phase transition are observed under shock compression. Time-resolved Raman spectra reveal that the liquid state is initially a metastable state and rapidly transforms to the solid state within 25 ns under shock compression at 4.2 GPa.     

Atomistic molecular dynamics simulations of shock compressed quartz

Atomistic non-equilibrium molecular dynamics simulations of shock wave compression of quartz have been performed using the so-called BKS semi-empirical potential of van Beest, Kramer, and van Santen [Phys. Rev. B 43, 5068 (1991)] to construct the Hugoniot of quartz. Our scheme mimics the real world experimental set up by using a flyer-plate impactor to initiate the shock wave and is the first shock wave simulation that uses a geometry optimised system of a polar slab in a three-dimensional system employing periodic boundary conditions. Our scheme also includes the relaxation of the surface dipole in the polar quartz slab which is an essential pre-requisite to a stable simulation. The original BKS potential is unsuited to shock wave calculations and so we propose a simple modification. With this modification, we find that our calculated Hugoniot is in good agreement with experimental shock wave data up to 25 GPa, but significantly diverges beyond this point. We conclude that our modified BKS potential is suitable for quartz under representative pressure conditions of the Earth core, but unsuitable for high-pressure shock wave simulations. We also find that the BKS potential incorrectly prefers the β-quartz phase over the α-quartz phase at zero-temperature, and that there is a β → α phase-transition at 6 GPa.     

Nanosecond freezing of water under multiple shock wave compression: optical transmission and imaging measurements

Water samples were subjected to multiple shock wave compressions, generating peak pressures of 1-5 GPa on nanosecond time scales. This loading process approximates isentropic compression and leads to temperatures where the ice VII phase is more stable than the liquid phase above 2 GPa. Time resolved optical transmission and imaging measurements were performed to determine the solidification rate under such conditions. Freezing occurred faster at higher pressures as water was compressed further into the ice VII phase, in agreement with classical micleation theory. Water consistently froze when in contact with a silica window, whereas no solidification occurred in the presence of sapphire windows. The transition was determined to be a surface initiated process--freezing began via heterogeneous nucleation at the water/window interface and propagated over thicknesses greater than 0.01 mm. The first optical images of freezing on nanosecond time scales were obtained. These images demonstrate heterogeneous nucleation and irregular solid growth over 0.01-0.10 mm lateral length scales and are consistent with latent heat emission during the transformation. The combination of optical transmission and imaging measurements presented here provide the first consistent evidence for freezing on short time scales.     

Waterlike glass polyamorphism in a monoatomic isotropic Jagla model

We perform discrete-event molecular dynamics simulations of a system of particles interacting with a spherically-symmetric (isotropic) two-scale Jagla pair potential characterized by a hard inner core, a linear repulsion at intermediate separations, and a weak attractive interaction at larger separations. This model system has been extensively studied due to its ability to reproduce many thermodynamic, dynamic, and structural anomalies of liquid water. The model is also interesting because: (i) it is very simple, being composed of isotropically interacting particles, (ii) it exhibits polyamorphism in the liquid phase, and (iii) its slow crystallization kinetics facilitate the study of glassy states. There is interest in the degree to which the known polyamorphism in glassy water may have parallels in liquid water. Motivated by parallels between the properties of the Jagla potential and those of water in the liquid state, we study the metastable phase diagram in the glass state. Specifically, we perform the computational analog of the protocols followed in the experimental studies of glassy water. We find that the Jagla potential calculations reproduce three key experimental features of glassy water: (i) the crystal-to-high-density amorphous solid (HDA) transformation upon isothermal compression, (ii) the low-density amorphous solid (LDA)-to-HDA transformation upon isothermal compression, and (iii) the HDA-to-very-high-density amorphous solid (VHDA) transformation upon isobaric annealing at high pressure. In addition, the HDA-to-LDA transformation upon isobaric heating, observed in water experiments, can only be reproduced in the Jagla model if a free surface is introduced in the simulation box. The HDA configurations obtained in cases (i) and (ii) are structurally indistinguishable, suggesting that both processes result in the same glass. With the present parametrization, the evolution of density with pressure or temperature is remarkably similar to the corresponding experimental measurements on water. Our simulations also suggest that the Jagla potential may reproduce features of the HDA-VHDA transformations observed in glassy water upon compression and decompression. Snapshots of the system during the HDA-VHDA and HDA-LDA transformations reveal a clear segregation between LDA and HDA but not between HDA and VHDA, consistent with the possibility that LDA and HDA are separated by a first order transformation as found experimentally, whereas HDA and VHDA are not. Our results demonstrate that a system of particles with simple isotropic pair interactions, a Jagla potential with two characteristic length scales, can present polyamorphism in the glass state as well as reproducing many of the distinguishing properties of liquid water. While most isotropic pair potential models crystallize readily on simulation time scales at the low temperatures investigated here, the Jagla potential is an exception, and is therefore a promising model system for the study of glass phenomenology.     

A portable total reflection X-ray fluorescence spectrometer with a diamond-like carbon coated X-ray reflector

A diamond-like carbon (DLC) coated quartz glass sample holder is used in a portable total reflection X-ray fluorescence (TXRF) spectrometer. A spot area of a water sample on the DLC sample holder becomes smaller than that on a quartz glass sample holder usually used in TXRF analysis because DLC is more hydrophobic. Therefore, the use of the DLC sample holder enhances fluorescent X-rays reaching a detector compared with the use of a quartz glass sample holder, leading to improvement in detection sensitivity. A detection limit of 28 pg is achieved for Cr in a river water sample when using the DLC sample holder.     

Infra-red imaging of bulk water and water-solid interfaces under stable and metastable conditions

Superheated water has been studied by infrared spectroscopy to examine whether the special ability of liquid water to undergo such a metastable state corresponds to the development of peculiar inter-molecular networking under tension. As the best technique to superheat water is to trap the liquid inside micro-cavities in solids (the so-called "fluid inclusions"), the role of the water-solid interfaces to stabilize the adjoining liquid is also explored with the same infra-red micro-spectroscopy tool. The key signal is the intra-molecular OH stretching band, sensitive to the networking in the probed material. The sample of choice is liquid water occluded inside a quartz cavity of micrometric size, synthesized in laboratory from pure quartz and milli-Q water. The stretching band of the superheated water shows no significant spectral difference from that of a bulk "normal" water, which means that the molecular properties of the superheating liquid are quite similar to those of the stable bulk liquid. Liquid water is readily "superheatable" but retains its "normality" under these special conditions. Additionally, this result establishes a firm ground to justify that the properties of the former are predicted extrapolating the usual (though empirical) equation of state of the latter. The infra-red signals of the water-solid interfaces are more complex. The water-solid interfaces blue-shift the signal, affecting differently the three sub-bands of the OH-stretching. This effect was unexpected since the micro-IR spectroscopy probes volume beyond what is classically assigned for the interfacial properties. In addition, the interfacial signature is clearer under superheating than under the saturation conditions, which offers an interesting (and unexpected) way to interpret the special stability of the occluded metastable water. These encouraging results give confidence on the potentialities of the high-resolution micro-spectroscopy to get insights into the molecular basis of macroscopic properties.     

Mechanism of densification in silica glass under pressure as revealed by a bottom-up pairwise effective interaction model

A new short-range pairwise numerical potential for silica is presented. The potential is derived from a single ab initio molecular dynamics (AIMD) simulation of molten silica using the force-matching method with the forces being represented numerically by piecewise functions (splines). The AIMD simulation is performed using the Born-Oppenheimer method with the generalized gradient approximation (BLYP) for the XC energy functional. The new effective potential includes a soft-repulsive shoulder to describe the interactions of oxygen ions at short separations. The new potential, despite being short-ranged and derived from single-phase data, exhibits a good transferability to silica crystalline polymorphs and amorphous silica. The importance of the O-O soft-repulsive shoulder interaction on glass densification under cold and shock compressions is assessed from MD simulations of silica glass under room and shock Hugoniot conditions, respectively. Results from these simulations indicate that the appearance of oxygen complexes (primarily pairs) interacting through soft-repulsive shoulder potential occurs at 8-10 GPa, and under cold compression conditions becomes notable at 40 GPa, essentially coinciding with the transition to a Si sixfold coordination state. An analysis of changes in system structure in compressed and shocked states reveals that the O ions interacting through the soft-repulsive shoulder potential in denser states of silica glass may create a mechanical multi-stability under elevated pressures and thus to contribute to the observed anomalous densification.     

An effective method for evaluating the image-sticking effect of TFT-LCDs by interpretative modelling of optical measurements

The conventional method of evaluating the image-sticking effect of a LCD module is inspection by sight, because the residual optical difference between two stressing areas is small and viewing angle-dependent, so that it is difficult to obtain a significant optical difference value by instrumental measurement. We propose an effective method for evaluating the image-sticking effect of a TFT-LCD module by directly measuring its time evolution of transmission with the TFT glass turned off after a period of pattern stress. In this way, the liquid crystal system under charge equilibrium in constant-charge mode shows a dramatically amplified optical difference. Further, we interpret the measured results by a modelling that combines the calculation of liquid crystal director orientation and ionic charge distribution. It is supposed that there are four time constants that dominate the overall sticking phenomenon and belong to four transient processes: adsorption of ions, desorption of free ions, desorption of stuck ions, and TFT leakage. The modelling shows good accordance between measured and simulated results when fitting parameters are properly chosen.     

An effective method for evaluating the image-sticking effect of TFT-LCDs by interpretative modelling of optical measurements

The conventional method of evaluating the image-sticking effect of a LCD module is inspection by sight, because the residual optical difference between two stressing areas is small and viewing angle-dependent, so that it is difficult to obtain a significant optical difference value by instrumental measurement. We propose an effective method for evaluating the image-sticking effect of a TFT-LCD module by directly measuring its time evolution of transmission with the TFT glass turned off after a period of pattern stress. In this way, the liquid crystal system under charge equilibrium in constant-charge mode shows a dramatically amplified optical difference. Further, we interpret the measured results by a modelling that combines the calculation of liquid crystal director orientation and ionic charge distribution. It is supposed that there are four time constants that dominate the overall sticking phenomenon and belong to four transient processes: adsorption of ions, desorption of free ions, desorption of stuck ions, and TFT leakage. The modelling shows good accordance between measured and simulated results when fitting parameters are properly chosen.     

STUDIES ON LANGMUIR-BLODGETT FILM OF METAL COMPLEXES(Ⅰ)-PREPARATION AND CHARACTERIZATION OF THE LB FILM OF N-HEXADECYL PYRIDINIUM TETRAKIS(1-PHENYL-3-METHYL-4-BENZOYL-PYRAZOL-5-ONE)EUROPIUM,C_5H_5NC_(16)H_(33)Eu(PMBP)_4

The LB film of the title complex was prepared by dropping a benzene solution of the title complex on the surfaceof water subphase at 25±1℃.The film was deposited in Z type on various hydrophilic pretreated substrates ofquartz,CaF_2 and electronic conductive glass for different purposes.The π-A curve of the film shows that thecross section per molecule is 125 ~2,which indicates that the alkyl chain of the molecule is basically perpendiculalto the surface of the substrate.UV,IR spectra and transmission electronic microscopy of the film were also obtained.     

The surface energy of hydrophilic and hydrophobic adsorbents

Water vapor adsorption and heats of water wetting are studied for hydrophilic quartz, hydrophobic-hydrophilic talc, and hydrophobized Silochrom samples. Water contact angles on the materials under examination are found. The surface thermodynamic parameters of the sorbents are calculated from the data obtained. It is shown that boundary water layers on hydrophilic quartz surface are ordered to a higher extent, while those on hydrophobic basal surfaces of talc particles and hydrophobic surfaces of modified Silochrom samples are ordered to a lower extent relative to liquid water. An empirical equation relating the surface pressure of water films adsorbed on hydrophilic high-energy surfaces with the surface free energy of the latter is proposed. The values of surface free energy are estimated from this equation for a number of important hydrophilic adsorbents.     

Consolidated silica glass from nanoparticles

A dense silica glass was prepared by consolidating a highly dispersed silicic acid powder (particle size <10 nm) with the Spark Plasma Sintering (SPS) technique. The glass was characterized by ellipsometry, transmission electron microscopy (TEM), infrared reflectance and transmittance spectroscopy, as well as by Raman, UV-Vis-NIR and solid-state nuclear magnetic resonance (NMR) spectroscopy. The prototypic sample showed a transmittance of about 63% compared to silica glass in the UV-Vis spectral range. Based on the results of infrared transmittance spectroscopy this lower transparency is due to the comparably high water content, which is about 40 times higher than that in silica glass. ¹H magic-angle spinning (MAS) NMR confirmed an increase in hydroxyl groups in the sample prepared by SPS relative to that of the conventional SiO₂ reference glass. Aside from the comparably high water content, we conclude from the similarity of the IR-reflectance and the ²⁹Si MAS NMR spectra of the SPS sample and the corresponding spectra of the conventionally prepared silica glass, that the short- and medium-range order is virtually the same in both materials. Raman spectroscopy, however, suggests that the number of three- and four-membered rings is significantly smaller in the SPS sample compared to the conventionally prepared sample. Based on these results we conclude that it is possible to prepare glasses by compacting amorphous powders by the SPS process. The SPS process may therefore enable the preparation of glasses with compositions inaccessible by conventional methods.     

A method for trace element determination of single Daphnia specimens using total reflection X-ray fluorescence spectrometry

Two new preparation techniques for total-reflection X-ray fluorescence (TXRF) element determination of single freshwater crustacean specimens (dry weight: 3–40 μg ind⁻¹) have been developed and tested using Daphnia pulex from a deep, oligotrophic freshwater lake located in southern Chile. Dry method: Specimens were washed with 0.2 μm filtered lake water and frozen in liquid nitrogen. The freeze-dried Daphnia specimens were weighed using an ultra-fine microbalance and placed on quartz glass carriers for TXRF analysis. Wet method: Specimens were washed with 0.2 μm filtered lake water and placed on quartz glass carriers for TXRF analysis and dried in air. The dry weight was determined using the previously established body length–dry weight relationship. Method validation for both the dry and the wet preparation method in combination with TXRF spectrometry for the element determination in small single freshwater crustaceans showed that both methods can be used for routine investigations. There were no significant differences between the dry and the wet methods concerning the elements Ca, K, Fe, Zn, Br, P, Cu, but the determination of Mn, S and Sr revealed significant differences between the two methods. It seems that the dry method yields more precise results, but the wet method is easier to handle in the field when samples cannot be fixed with liquid nitrogen.     

Emergence of a new feature in the high pressure-high temperature relaxation spectrum of tri-propylene glycol

We investigated dielectric relaxation of a tri-propylene glycol system under high compression. By increasing temperature and pressure we observed that a new relaxation process emerges from the low frequency tail of the structural peak. This new peak starts to be visible at about 0.5 GPa and becomes clearly evident at 1.7 GPa. However, this additional peak merges again with the structural one as the glass transition is approached, since it has a weaker temperature dependence. This finding enriches the relaxation scenario of molecular glass formers confirming that the application of very high hydrostatic pressure can favor the detection of new relaxation or otherwise unresolved processes in supercooled liquid systems.     

Methodologies for the characterisation of glass fibre orientation and distribution in large components moulded from sheet molding compounds (SMC)

Sheet Moulding Compounds (SMC) made of unsaturated polyester resin and other additives, reinforced with glass fibres, have emerged as a substitute for steel automotive outer panels. For a better understanding of the compression moulding of SMC, it is necessary to characterise the flow of material and particularly of the glass fibres. The aim of this work is to develop methodologies for characterising local mass fraction and orientation of short glass fibres in compression moulded composite components such as SMC. Pyrolysis, photographs by transmission of visible light and X-ray photographs analysed with homemade software for characterising the orientation give valuable and interesting information concerning the flow of fibres.     

Phenomenon of influence of natural disasters (hurricanes and earthquakes) on long-range order in liquids. Risks and chances

The work showed a phenomenon of influence of seismic and resonance shock waves on the long-range order in a liquid. On examples of damage of ion pair solvated clusters in aqueous solutions of NaCl (3.5 wt%), HCl (2 wt%), AgNO₃ (1.7 wt%) and molecular bunches (clusters) in distilled water placed to laboratory chemical reactor far distant from the epicenters of earthquakes the relations between incoming shock and seismic waves and instability of cluster and supracluster long range organization (molecular bunches assocoates) in a liquid is demonstrated. Understanding of risks for chemical industry both in respect of quality and chemical processes instability, and in respect of loose control over chemical technology is considered. Examples of changes in internal organization of solutions in the period of strong hurricane in Europe at February 17, 2007, strong earthquake in Japan at March 25, 2007 and a series of earthquakes at April 4 to 9, 2007 are given and the phenomenon is explained. The risks for chemical industry and the chances of practical using the phenomenon are considered. The clusters in liquids show different responses to the processes in the disaster epicenter, and their responses can be used for understanding chemical processes in Earth crust and in the centers of hurricanes and for strategy of disposing and protecting chemical facilities.     

Fluorescent diazapyrenium films and their response to dopamine

Experimental protocols for the preparation of 2,7-diazapyrenium films on glass, quartz, and silica in one or two steps have been developed. The one-step procedures involve the adsorption of preformed 2,7-diazapyrenium dications with trimethoxysilane appendages to the hydroxylated substrates. The two-step procedures consist in the formation of interfacial polysiloxanes with pendent chloromethyl groups and their subsequent coupling to monoalkylated 2,7-diazapyrene derivatives. For the modification of the glass slides, the silane building blocks have been copolymerized with Si(OEt)4. The transmission absorption spectra of the coated glass and quartz slides all reveal the characteristic bands of the 2,7-diazapyrenium chromophores. Combustion analyses confirm the adsorption of the 2,7-diazapyrenium dications on the silica particles. A comparison of the surface coverages of all films indicates that the one-step procedures are significantly more efficient than their two-step counterparts. Furthermore, the copolymerization of the silane building blocks with Si(OEt)4 translates into an increase in 2,7-diazapyrenium surface coverage of approximately 1 order of magnitude. The emission and excitation spectra of all modified substrates reveal the characteristic bands of the 2,7-diazapyrenium fluorophores. The fluorescence quantum yield, however, decreases as the surface coverage increases. Presumably, interactions between adjacent fluorophores encourage nonradiative deactivation pathways. With the exception of the glass slides modified in two steps, all films respond to the presence of dopamine, in aqueous environments at neutral pH, with pronounced decreases in emission intensity. The association of the 2,7-diazapyrenium acceptors and dopamine donors at the solid/liquid interface is responsible for fluorescence quenching. The glass slides and silica particles modified in one step are the most sensitive substrates and respond to sub-millimolar concentrations of dopamine with large changes in emission intensity. Furthermore, their fluorescence is not affected by relatively large concentrations of ascorbic acid, which is the main interferent in conventional dopamine detection protocols. Thus, these results demonstrate that the supramolecular association of 2,7-diazapyrenium dications and pi-electron rich substrates can be reproduced successfully at solid/liquid interfaces and suggest that the unique properties of 2,7-diazapyrenium films might lead to dopamine-sensing schemes based on fluorescence measurements.     

Thick silicate glass film by an interfacial polymerization

A silicate glass film of 2–20 µm in thickness has been formed on a fused quartz substrate by a sol-gel process using an interfacial polymerization technique. A partially hydrolyzed silicon alkoxide was dissolved in hexane and brought into contact with ammonia water in a cylindrical Teflon container. A silica gel film formed at the interface between the two immiscible liquids by the polycondensation of the partially hydrolyzed silicon alkoxide was gently placed on a substrate at the bottom of the container, by draining the liquid. The crack free gel film was dried in an ambient atmosphere and dip-coated with boron ethoxide, followed by sintering in an oven at 1250°C for 1 h. The glass film thus obtained was highly transparent and 2–20 µm in thickness depending on the concentration of the precursor solution and the pH of ammonia water.