Electron mobility in supercritical pentanes as a function of density and temperature

The excess electron mobility in supercritical n-, iso- and neopentane was measured isothermally as a function of density. The density-normalized mobility μN in all three isomers goes through a minimum at a density below the respective critical densities, and the mobility is quite temperature-dependent in this region, then goes through a minimum. The μN behavior around the minimum in n-pentane is well accounted for by the Cohen-Lekner model with the structure factor S(K) estimated from the speed of sound, while that in iso- and neopentane is not.     

Halogen bonding: a new interaction for liquid crystal formation

It is shown for the first time that liquid crystal behavior can be induced through halogen bonding. Thus, mixing the nonmesomorphic components 4-alkoxystilbazole with pentafluoroiodobenzene leads to a 1:1 halogen-bonded complex whose integrity is shown by X-ray single-crystal analysis and which shows thermotropic smectic A and nematic phases.     

Drift mechanism for the formation of metallic wires in liquid helium

A drift mechanism of formation of wires in liquid helium from metal laser ablation products has been suggested. The latter are usually ionized and are attracted to any surface due to the electric image force. This is responsible for that the drift of microparticles prevail over diffusion. The formation of anisometric structures (wires) under the drift conditions is a well-known phenomenon [9], not related to the properties of superfluid helium.     

Development of a new polarizable potential model of hydrogen fluoride and comparison with other effective models in liquid and supercritical states

Development of a new polarizable potential of hydrogen fluoride through the reparametrization of the JV-P model is presented: The length of the H-F bond has been shortened and the other parameters of the model have been readjusted accordingly. The structural, thermodynamic, and liquid-vapor equilibrium properties of the new model are compared with those of other effective potential models of HF as well as with experimental data in a broad range of thermodynamic states, from near-freezing to supercritical conditions. It is found that although the reparametrization does not change the structural properties of the HF model noticeably at the level of the pair correlations, it improves the reproduction of the thermodynamic properties of hydrogen fluoride over the entire range of existence of a thermodynamically stable liquid phase and also that of the vapor-liquid coexistence curve. However, the new model, which still overestimates the close-contact separation of the HF molecules, underestimates the density of the coexisting liquid phase and overestimates the saturation pressure, probably due to the too steep repulsion of the potential function.     

Molecular volume calculation using AM1 semi-empirical method toward diffusion coefficients and electrophoretic mobility estimates in aqueous solution

Diffusion coefficients and electrophoretic mobility are two important physicochemical parameters used in mass transport phenomenon studies. The volume of the solute is required to determine or estimate these parameters. Classical methods, such as the LeBas method are commonly used. However, although valid, this method may represent a boring and time-consuming task, depending on the nature and number of compounds to be calculated. In this study, the volumes of a series of neutral and charged substances of the main functional groups present in organic molecules, amino acids, drugs and diverse compounds, such as cytosine and glucose, were calculated according to the LeBas method (V_M) and the AM1 semi-empirical method, V_W(AM1). The latter showed to be statistically coincident with the former. Employed as a pure value or corrected by the LeBas molar volume, the AM1 molecular volume was also demonstrated to estimate the diffusion coefficients in infinite aqueous dilution within an acceptable average error, according to the Othmer–Thakar, Wilke–Chang and Hayduk–Laudie methods, as well as the electrophoretic mobility of charged substances, such as carboxylates and protonated amines. According to these results, the AM1 method was seen to be statistically valid to calculate molecular volume. Many advantages in the construction of most diverse structures were noted, as well as a reduction in time and an increase in the quality of the information, when run on molecular modeling software.     

Zero-field mobilities in helium: highly accurate values for use in ion mobility spectrometry

The zero-field mobilities of 46 atomic ions in helium are calculated as functions of the gas temperature in an ion mobility spectrometer. The calculations are based on highly accurate, ab initio potential energy curves obtained in the last few years. In general, they start from a small value at low temperature, rise steadily to a maximum at some specific temperature, T _max , and then decline at higher temperatures. The ratio of T _max to the dissociation energy (well depth) of the ion-neutral interaction potential is shown to be approximation the same for all singly-charged ions and a few multiply-charged ions.     

Generation of discharges in dynamic foam for oxidants formation using various types of electrodes

An innovatory apparatus for the discharge generation in foaming conditions was constructed. The main goal of the research was to obtain various kinds of oxidants, useful in Advanced Oxidation Processes (AOP) in one compact reactor, potentially even in the treated medium. Such an application of dynamic foam, created without the addition of surfactant has not been investigated as yet. To find the optimum conditions for the efficient foam generation and the discharge development and moreover, to assure the presence of oxidants in sufficient concentrations several electrode materials and electrode set-ups were tested. The experiments were done in the metal plate-to-metal plate, metal plate-to-dielectric plate, needles-to-metal plate and needles-to-dielectric plate electrodes’ set-ups. The discharge gap space ranged from 4 mm in the case of plate-to-plate electrodes to 7 mm in the case of needles-to-plate electrodes. Generally, the highest oxidants’ concentrations at the highest comparable gas flow rate were obtained in the needles-to-dielectric plate arrangement, where 521 and 875 ppm of gaseous ozone, 0.36 and 0.5 mg dm⁻³ of dissolved ozone and 59 and 62 mg dm⁻³ of hydrogen peroxide were obtained at 14 kV of applied voltage and at 5 dm³ min⁻¹ of the substrate gas flow in air and oxygen, respectively. The presence of OH radicals was confirmed by the spectroscopic measurements. The larger gap size was more advantageous from the foam formation point of view and the dielectric layer assured more uniform spatial discharge development between the electrodes.     

Analysis of testosterone in human urine using molecularly imprinted solid-phase extraction and corona discharge ion mobility spectrometry

Analysis of testosterone was accomplished using corona discharge ion mobility spectrometry. Molecular imprinted polymer was used for the extraction and pre-concentration of testosterone. Analytical parameters including precision, dynamic range and detection limit were obtained. The linear dynamic range was from 10 to 250 ng/mL and the limit of detection was 0.9 ng/mL. The proposed method was used for analysis of testosterone in urine samples. A urine sample from a 3-year-old girl was used as the blank. The RSD was below 10%. The obtained results from the method were also compared with the standard method for analysis of testosterone using SPE-HPLC analysis. The results demonstrate the accuracy of the method.     

Dielectric constant and density dependence of the structure of supercritical carbon dioxide using a new modified empirical potential model: a Monte Carlo simulation study

Two modified versions of the Elementary Physical Model (EPM) [J. Phys. Chem. 1995, 99, 12021] for supercritical carbon dioxide have been proposed in this work and their validities are affirmed by computing the thermodynamic properties and dielectric constant up to 910 kg/m3 with use of canonical ensemble Monte Carlo simulation. Simulations performed for 500 molecules with the EPM2-M model reproduce the experimental data accurately at all thermodynamic states. The structural analyses demonstrate that the aggregation is strong at low density while the coordination number is large at high density. In addition, a detailed study on the radial and angular correlation functions reveals that the T-shaped geometry is dominate while a variety of other structures still appear in the first coordination shell. Furthermore, the angular correlation functions show that the probability of a molecule being oriented toward the convex side of another molecule is equal to that pointing toward the concave side since the molecular nonlinearity of carbon dioxide is only marginal. As the distance between two molecules increases, the preferred orientations disappear quickly and all the results are in good agreement with the prior ab initio calculation [J. Chem. Phys. 2004, 120, 9694].     

Selectivity assessment of a sequential extraction procedure for metal mobility characterization using model phases

This study considers the selectivity of the extractants used in a sequential extraction scheme for metals mobility assessment by analyzing individual mineral phases previously coprecipitated or sorbed with trace metals. The scheme evaluated was a modification of the Tessier et al. [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844] sequential procedure proposed by the authors. The phases studied were calcite, amorphous iron oxide, hausmannite, humic acid, kaolinite and illite. Selective extractions were obtained for As, Cr, Cu, Ni, Pb and Zn in metal-coprecipitated phases whereas NH(2)OH-HCl was not selective for the extraction of Hg and Cd coprecipitated in hausmannite and amorphous iron oxide, respectively. Otherwise, Cd, Hg, Ni and Zn sorbed on the different phases were released with MgCl(2) and NaOAc/HOAc, but stronger reagents were needed to release As, Cr, Cu and Pb.     

The influence of crystal formation on segmental mobility in polymers: hints from a statistical mechanical relaxation model

A statistical mechanical model is used to analyze literature data regarding the restricted segmental dynamics of a number of crystallized polymers, as observed by means of broadband dielectric spectroscopy. A relationship between well defined physical quantities and the width parameter in the Havriliak–Negami representation of symmetric processes is established. It is found that, for materials crystallized from an isotropic amorphous state, the segmental relaxation process is associated to conformational changes within cooperatively rearranging regions of ~1 nm diameter. In case of chain orientation, the dimension of the rearranging regions along the chain direction increases up to 3–5 nm. It is argued that the average size of the rearranging regions may influence the thickness of the amorphous interlamellar layers in the stacks. It is also found in all cases that, at the end of the crystallization process, the average fluctuation component of the chemical potential within the confined amorphous regions, $\overline{\Delta\mu}A statistical mechanical model is used to analyze literature data regarding the restricted segmental dynamics of a number of crystallized polymers, as observed by means of broadband dielectric spectroscopy. A relationship between well defined physical quantities and the width parameter in the Havriliak–Negami representation of symmetric processes is established. It is found that, for materials crystallized from an isotropic amorphous state, the segmental relaxation process is associated to conformational changes within cooperatively rearranging regions of ~1 nm diameter. In case of chain orientation, the dimension of the rearranging regions along the chain direction increases up to 3–5 nm. It is argued that the average size of the rearranging regions may influence the thickness of the amorphous interlamellar layers in the stacks. It is also found in all cases that, at the end of the crystallization process, the average fluctuation component of the chemical potential within the confined amorphous regions, [`(Dm)]\overline{\Delta\mu}, is of the same order of the chemical potential drop Δμ <sub>cryst</sub> associated to crystallization from the undercooled, relaxed melt. Except in one among the cases considered, it is found that [`(Dm)] ? - Dm_cryst\overline{\Delta\mu}\approx - \Delta\mu_{\rm cryst}, which is a hint towards the formalization of a thermodynamic criterion for crystallization arrest.     

A general theory for the formation of a new phase. Static cavitation in a nonvolatile liquid

The rate of formation of cavities in a nonvolatile liquid subjected to negative pressure is calculated. The pressure is assumed to be sufficiently moderate, so that the critical bubble (hole) can be treated macroscopically. If this condition is satisfied one may apply the Zel'dovich saddle-point method. However, in distinction from that method, the present paper makes use of a construction of Gibbs grand canonical ensemble, which allows one to avoid the ambiguities that appear in the calculation of the microscopic initial stage of formation of the hole and yields a more accurate value of the kinetic (preexponential) factor. A more accurate value of the work required to form a critical hole, the value which occurs in the exponent, is obtained by taking into account the dependence of the surface tension of the hole on the curvature of the surface. For this purpose we use an expansion of the surface tension in powers of the curvature of the surface of the hole. Since the surface tension occurs in the exponent of the expression for the probability or rate of cavitation, it is necessary to retain the expansion terms which are linear or quadratic in the curvature, whereas the correction factors to the cavitation rate, due to higher-order terms tend to unity as the expansion of the liquid decreases, in contradistinction from the first terms. It is important that for large expansions, and hence for small curvatures of the surface of the critical hole, the series for the surface tension diverges.     

Electron interaction with nitromethane embedded in helium droplets: attachment and ionization measurements

Results of a detailed study on electron interactions with nitromethane (CH(3)NO(2)) embedded in helium nanodroplets are reported. Anionic and cationic products formed are analysed by mass spectrometry. When the doped helium droplets are irradiated with low-energy electrons of about 2 eV kinetic energy, exclusively parent cluster anions (CH(3)NO(2))(n)(-) are formed. At 8.5 eV, three anion cluster series are observed, i.e., (CH(3)NO(2))(n)(-), [(CH(3)NO(2))(n)-H](-), and (CH(3)NO(2))(n)NO(2)(-), the latter being the most abundant. The results obtained for anions are compared with previous electron attachment studies with bare nitromethane and nitromethane condensed on a surface. The cation chemistry (induced by electron ionization of the helium matrix at 70 eV and subsequent charge transfer from He(+) to the dopant cluster) is dominated by production of methylated and protonated nitromethane clusters, (CH(3)NO(2))(n)CH(3)(+) and (CH(3)NO(2))(n)H(+).     

A rapid and effective synthesis of propylene carbonate using a supercritical CO2-ionic liquid system

The synthesis of propylene carbonate from propylene oxide and carbon dioxide under supercritical conditions in the presence of 1-octyl-3-methylimidazolium tetrafluoroborate was achieved in nearly 100% yield and 100% selectivity within 5 minutes, whose TOF value is 77 times larger than those so far reported.     

Planarity selectivity in supercritical fluid and liquid chromatography using octadecylsilane-modified silicas with carbon dioxide

Summary The influence of column temperature and pressure on the planarity selectivity of encapsulated and polymeric octadecylsilane-modified silicas was examined using carbon dioxide mobile phase in supercritical fluid and liquid chromatography. The use of liquid carbon dioxide was found to enhance remarkably the molecular planarity recognition capability of the polymeric stationary phase compared with supercritical conditions. The influence of pressure and temperature on selectivity was seen to be significant with the polymeric phase but less with the encapsulated. It seems that pressure and temperature change the morphology of the polymeric phase to a greater extent than the encapsulated one.     

A new method for computing surface tension using a drop of liquid

In the simulation of a liquid drop it is expensive to calculate the excess pressure and obtain the surface tension by the Laplace formula. We use the Kelvin formula which only requires the vapour density, or at most the virial pressure. Some results are given for a Lennard-Jones 12-6 fluid.