Thermodynamics and transport properties of monatomic systems from the MSK potential

Shukla, K.P., Luckas, M., Ameling W. and Lucas, K., 1986. Thermodynamics and transport properties of monatomic systems from the MSK potential. Fluid Phase Equilibria, 28: 217–231.The MSK potential has been used to correlate and extrapolate the thermodynamic and transport properties of various monatomic systems. The statistical mechanical equations in the dilute gas range were solved in the standard way. In the liquid range, hard-sphere perturbation theory and comoputer simulations were used, taking non-additive three-body forces and quantum effects into account. Very satisfactory results are obtained for pure systems and mixtures over the whole density range, lending support to the potential function, its particular parameters and the combination rules for the unlike interactions.     

A particle-hole model for light scattering by simple fluids

The intensity, I, of depolarized light scattered by simple fluids is calculated by modeling the fluid as a dilute gas of dielectric spheres at low density and as a dilute gas of spherical holes in a dielectric continuum at high density. It is shown that a pair of spheres has more inherent scattering power than a pair of holes. Thus, at liquid density, I is smaller than would be predicted by using gas-phase scattering theory plus liquid-state statistics, as has generally been done in the past; the implications of our result for existing theories are discussed.     

Stabilization of methane hydrate by pressurization with He or N2 gas

The behavior of methane hydrate was investigated after it was pressurized with helium or nitrogen gas in a test system by monitoring the gas compositions. The results obtained indicate that even when the partial pressure of methane gas in such a system is lower than the equilibrium pressure at a certain temperature, the dissociation rate of methane hydrate is greatly depressed by pressurization with helium or nitrogen gas. This phenomenon is only observed when the total pressure of methane and helium (or nitrogen) gas in the system is greater than the equilibrium pressure required to stabilize methane hydrate with just methane gas. The following model has been proposed to explain the observed phenomenon: (1) Gas bubbles develop at the hydrate surface during hydrate dissociation, and there is a pressure balance between the methane gas inside the gas bubbles and the external pressurizing gas (methane and helium or nitrogen), as transmitted through the water film; as a result the methane gas in the gas bubbles stabilizes the hydrate surface covered with bubbles when the total gas pressure is greater than the equilibrium pressure of the methane hydrate at that temperature; this situation persists until the gas in the bubbles becomes sufficiently dilute in methane or until the surface becomes bubble-free. (2) In case of direct contact of methane hydrate with water, the water surrounding the hydrate is supersaturated with methane released upon hydrate dissociation; consequently, methane hydrate is stabilized when the hydrostatic pressure is above the equilibrium pressure of methane hydrate at a certain temperature, again until the dissolved gas at the surface becomes sufficiently dilute in methane. In essence, the phenomenon is due to the presence of a nonequilibrium state where there is a chemical potential gradient from the solid hydrate particles to the bulk solution that exists as long as solid hydrate remains.     

Calculations of the frequency dependences of viscosity coefficients and elastic moduli for solutions of electrolytes over broad ranges of thermodynamic parameter variations

The dynamic equations obtained earlier for the coefficients of bulk η_V(ω) and shear η_S(ω) viscosities and bulk K(ω) and shear μ(ω) elastic moduli were used to calculate these values for a certain model of solution structure in the approximation of the theory of osmotic solution properties. The interparticle interaction potential was written as the sum of the potential of hard spheres and Coulomb attraction. The corresponding thermodynamic parameter values for the density ρ, temperature, concentration C, and adiabatic bulk modulus K _S were taken from experimental works. The results of numerical calculations of the viscoelastic properties of solutions over broad ranges of thermodynamic parameter and frequency variations were plotted and tabulated. The calculation results are compared with the available experimental data. The theoretical viscoelastic properties of solutions of electrolytes were in satisfactory agreement with the published experimental data and the results of numerical experiments for classic liquids.     

Terrestrial and microgravity studies with nanoconductor networks: basic principles and applications of “huge molecule Van der Waals gases”

Conducting nanocrystals (“nanoconductors”) are metal, semimetal or semiconductor particles with individual sizes s ≈ 10 nm. If allowed to assemble freely, they form black low-density aggregates (“blacks”) with relative volume filling f of a few percent. Matrix-free networks are prepared by evaporation of the bulk material and subsequent particle nucleation and growth in the presence of a high-purity low-pressure noble gas. Each nanoconductor consisting of some 10⁴ atoms, Van der Waals coupling between the particles is strongly enhanced making the networks suitable model systems for hypothetical huge molecule Van der Waals gases. For an isotropic charge distribution that is typical of metallic electron densities, the VdW interaction is expected to be particularly genuine in nanoconductors. Owing to the small particle sizes (s ≈ 10 nm) and filling factors (f < 0.05), the contacts between the particles are both nanostructures and weak coupling devices. This makes nanoconductors intriguing objects for modern microelectronics whose preparation does not require lithographic methods. The networks can be kept under well-defined conditions: matrix-free in high vacuum or in a gas. Being aerosols, blacks constitute matter in an unusual form: as ill-condensed tenuous structures they can be given almost any shape like a liquid. On the other hand, they may change their mean density like a gas by filling variable volumes under suitable conditions. Moreover, blacks exemplify a class of extremely dilute conductors and electron tunneling systems. Their electrical and thermal conductivities may be manipulated towards very small values by reducing the degree of network aggregation. Previous experiments have shown that the dielectric properties of blacks crucially depend on the spatial distribution of the nanocrystals. We therefore propose to extend the dilution of non-supported blacks beyond the limit of self-aggregation under terrestrial conditions. Microgravity (μg) is a promising tool for studies of reversible aggregation and separation and to establish the properties of blacks in a “phase diagram”. Electromagnetic radiation, sound, and dielectric screening offer themselves to influence the spatial structure of blacks in vacuum or in the presence of a suitable gaseous or liquid matrix. These influences help to establish specific differences in dielectric or elastic behaviour between the aggregated and separated state of blacks and to explore their potential applications e.g. as detectors, sensors, and thermoelectric converters. The comparative studies are expected to yield valuable information on dielectric and elastic properties of the individual nanocrystals and of the Van der Waals-induced aggregates in the regime of low filling factors. The planned experiments cross-link a number of topical fields of basic and applied research such as soft matter, fractal structures, nanoporous materials, tunneling structures, quantum dots, Coulomb blockade effects, ultra-low capacity devices, point contacts, catalysts, effective medium model systems, Anderson dielectrics, and steric stabilization. Moreover, chemically different (including non-metallic) nanocrystal components maybe mixed for applications as quantum dot alloys with more degrees of freedom for the design of hitherto unpredictable properties.     

Dynamooptical and electrooptical properties of poly(methylphenylsiloxane) in solution and bulk

The dynamooptical, electrooptical, and hydrodynamic properties of a low-molecular-mass poly(methylphenylsiloxane) containing 33% phenyl radicals (with respect to the total amount of side groups) in dilute solutions and in bulk are studied. The size of macromolecules, as well as the molecular mass of the polymer, its shear optical coefficients Δn/Δτ = (0.29 ± 0.3) × 10^?10 (in decalin) and (0.43 ± 0.03) × 10^?10 cm s²/g (in bulk), and the specific Kerr constants K = (2.30 ± 0.02) × 10^?12 (in benzene), (2.23 ± 0.02) × 10^?12 (in decalin), and (2.24 ± 0.09) × 10^?12 cm⁵/[g (300 V)²] (in bulk), are estimated and compared with the corresponding characteristics of poly(dimethylsiloxane). The effect of solvents on the intramolecular mobility, optical anisotropy, and dipole structure of polymer macromolecules is considered.     

Electrochemical behaviour of mono- and oligonucleotides I. Effects of charge and configuration of adenine mononucleotides on their adsorption at the mercury—solution interface

A systematic study of the adsorption and interfacial behaviour of the adenine mono-nucleotides (5′-AMP, 3′-AMP, cyclic 3′,5′-AMP, 5′-ADP and 5′-ATP) and adenosine for comparison at the HMDE has been carried out at pH 3.4 to 3.5. Thus, the N(1) of the adenine moiety is protonated to a major extent.The adsorption was followed by single sweep voltammetry (measurement of the time integral of the reduction peak of the adsorbed adenine moiety) and by a.c. voltammetry (out-of-phase component of the a.c. response being proportional to the differential double layer capacity). In this paper the situation corresponding to a “dilute” adsorption layer existing at low bulk concentrations is studied for various degrees of coverage. The potential dependence of the coverage is of bell shaped type with an extended maximum region around the potential of electrocapillary maximum (E_ecm) of the blank. For the same bulk concentration the coverage decreases in the series AMP, ADP, ATP, i.e. with increasing negative charge of the nucleotide, and at the same time the potential range of adsorption narrows. Among the monophosphates the coverage decreases in the series 3′-AMP, 5′-AMP, cyclic 3′,5′-AMP. The variations are connected with the varying charge of the mononucleotides and with the possibilities for interactions with adjacent molecules in the adsorption layer.At elevated bulk concentrations above a threshold value a substantial increase in coverage occurs around E_ecm as due to strong interactions between the adsorbed base moieties a rather compact film is formed.     

N-substitution of polybenzimidazoles: Synthesis and evaluation of physical properties

Series of N-substituted polybenzimidazoles (PBI) were synthesized using selective alkyl groups with varying bulk and flexibility, viz., methyl, n-butyl, methylene trimethylsilane and 4-tert-butylbenzyl. PBI-I based on 3,3′-diaminobenzidine (DAB) and isophthalic acid and PBI-BuI based on DAB and 5-tert-butyl isophthalic acid were chosen for N-substitution. Structural characterizations of substituted polymers by FT-IR and ¹H NMR revealed elimination of hydrogen bonding. Evaluation of their physical properties revealed that N-substitution rendered better solvent solubility in common organic solvents, more open polymer matrix, but reduced thermal properties in comparison to their respective parent PBI. 4-tert-butylbenzyl, methylene trimethylsilane or n-butyl group substituted polymers were soluble even in chlorinated solvents (CHCl₃ and TCE). Substantial variations in gas permeability of inert gases, He and Ar and attractive P_He/P_Ar selectivity, especially after methyl group substitution depicted potential of these materials for gas separation.     

Electronic,elastic and thermal properties of lutetium intermetallic compounds

The electronic, structural, elastic, thermal and mechanical properties of Lutetium intermetallic compounds LuX (X = Mg, Cu, Ag, Au, Zn, Cd and Hg) have been studied using ab-initio full potential linear augmented plane wave (FP-LAPW) with the generalized gradient approximation (GGA) in their non magnetic phase. The ground state properties such as lattice constant, bulk modulus, pressure derivatives of bulk modulus are reported in CsCl-(B₂ phase) structure. We also report the band structure and density of states at equilibrium lattice constant. The calculated band structures indicate that these intermetallics are metallic in nature. The second order elastic constants of these compounds are also predicted for the first time. The ductility of these compounds is determined by calculating the bulk to shear ratio B/G_H.     

Benzoylation of polyphenylene oxide: Characterization and gas permeability investigations

Benzoylation of polyphenylene oxide (PPO) was carried out with aromatic acid chlorides bearing specific groups at para-position (H, methyl, Br, Cl and nitro), which differ in their polarity and bulk. The reaction conditions were optimized individually to get the high degree of substitution. These materials were characterized for thermal as well as other physical properties that are known to affect the gas permeation. In a series investigated, the nitrobenzoyl substitution on PPO resulted in the highest increase in glass transition temperature and the lowest thermal stability. An estimation of the packing density parameters—fractional free volume by density measurement and the d-spacing by X-ray diffraction analysis showed an increase in the packing density. The gas permeability was found to decrease in all the cases of benzoylation. The helium and oxygen based selectivities were increased, while CO₂ based selectivities were decreased. The unusual trend observed in the gas permeation properties is explained on the basis of nature of substituent and the degree of substitution.     

Transient finite element analysis of electric double layer using Nernst-Planck-Poisson equations with a modified Stern layer

A finite element implementation of the transient nonlinear Nernst-Planck-Poisson (NPP) and Nernst-Planck-Poisson-modified Stern (NPPMS) models is presented. The NPPMS model uses multipoint constraints to account for finite ion size, resulting in realistic ion concentrations even at high surface potential. The Poisson-Boltzmann equation is used to provide a limited check of the transient models for low surface potential and dilute bulk solutions. The effects of the surface potential and bulk molarity on the electric potential and ion concentrations as functions of space and time are studied. The ability of the models to predict realistic energy storage capacity is investigated. The predicted energy is much more sensitive to surface potential than to bulk solution molarity.     

Liquid membrane extraction of Cephalosporin-C from fermentation broth

The extraction of Cephalosporin-C (CPC) from dilute fermentation broth of Cephalosporium acremonium was studied in a bulk liquid membrane as well as in an emulsion liquid membrane system. Aliquat-336 was used as the extracting agent to provide facilitated transport of CPC via liquid–liquid ion exchange mechanism. By maintaining an appropriate pH gradient in the feed and receiving phases, facilitated uphill transport could be achieved in the bulk liquid membrane system. The culture broth contains CPC and deacetyl CPC (DCPC) which are structurally almost similar, but CPC is more hydrophobic in nature. Selective separation of CPC could be achieved in a suitably formulated liquid membrane system. A simple mass transfer model predicts the permeation rate in the bulk liquid membrane. The permeation process in an emulsion liquid membrane appears to be controlled by the aqueous boundary layer resistance and diffusion in the emulsion globule. This is perhaps the first demonstration of the liquid membrane as an effective technique for selective extraction of CPC from fermentation broth of Cephalosporium acremonium.     

Synthesis and properties of N-carbazole end-capped conjugated molecules

A series of novel N-carbazole end-capped π-conjugated molecules were synthesized by a divergent approach with the use of bromination, Suzuki cross-coupling, and Ullmann reactions and their physical properties were investigated. In dilute solution, UV-vis absorption spectra displayed bathochromic shift with respect to their conjugated backbones, and photoluminescence spectra showed emission maxima in the blue region. Thermal analysis revealed that they are thermally stable semi-crystalline and amorphous materials. All molecules exhibited good electrochemical stability with high-lying HOMO energy levels and have potential applications as hole-transporting and light-emitting layers in organic light-emitting diodes or as host materials for electrophosphorescent applications.     

Interactions in water-alcohol mixtures studied by NMR and infrared spectroscopy

By using low temperatures and largely deuterated solvents, the rate of OH proton exchange for aqueous solutions of alcohols is reduced sufficiently to give separate NMR signals from water and alcohol OH protons. The limiting shifts for dilute alcohols in water are down-field of both the water resonance and those of the pure alcohols. This contrasts with the limiting shift for water in the alcohols, which is to high field of the bulk water resonance. The resonance shifts initially to low fields as [ROH] increases, the rate of shift being greatest for t-butyl alcohol. For dilute aqueous solutions, all the alcohols reduce the total concentration of free OH groups, as judged by the overtone infrared spectra. Some of these results are interpreted in terms of a scavenging of free OH groups by the excess lone-pairs of the alcohol molecules. An extra, temperature dependent, down-field shift in the water proton resonance induced by t-butyl alcohol is assigned to a clathrate cage effect.     

Concentration and separation of actinides from urine using a supported bifunctional organophosphorus extractant

A method has been developed to isolate quantitatively the actinide elements (as a group) from urine samples and to produce near massless electrodeposits suitable for high-resolution α-spectrometry. The actinides are concentrated from the bulk urine sample by coprecipitation with calcium phosphate. The precipitate is then ashed, dissolved in dilute nitric acid and passed through a column of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in tributyl phosphate (TBP) supported on an inert substrate (Amberlite XAD-7) which absorbs the actinides. The actinides are stripped from the column with dilute ammonium hydrogenoxalate, electrodeposited on a stainless-steel disk and counted on an α-spectrometer. Recoveries of added tracers are uniformly high (? 90%) so that samples can be routinely run without yield monitors, permitting an α peak anywhere in the spectrum to be detected with few interferences. Detection limits are influenced only by the available sample size, counting time and counter backgrounds.     

The effect of solute—membrane affinity on cyclic hydrocarbon—water transport in pressure-driven membrane separation processes

Experimental results for the pressure-driven membrane separation of cyclic hydrocarbons (1,3-cyclohexadiene, cyclohexene, and cyclohexane) from dilute binary aqueous solution using asymmetric cellulose acetate membranes are reported here. In these experiments, total solution fluxes are significantly lower than pure water fluxes at the same applied pressure; this flux reduction is attributed to strong solute—membrane affinity rather than to the osmotic pressure of either the bulk retentate or the boundary layer. An empirical parameter, Z, is used to describe flux reduction. A theoretically based friction parameter, B, is derived assuming the membrane can be represented as an ideal, finely porous membrane; this parameter indicates the influence of solute—membrane affinity on flow through the pores of the membrane. Both the empirical parameter Z and the theoretically based parameter B relate flux reduction to concentrations in the system. Both Z and B increase as solute—membrane affinity increases and decrease as membrane pore size increases. It is concluded that both the empirical flux reduction parameter, Z, and the theoretically based friction parameter, B, indicate the same system properties: solute—membrane affinity and membrane pore size.     

Transport Properties of Simple Fluids from the Soft‐Core Double Yukawa Potential

The present work is concerned with checking a new and simple pair potential function (soft‐core double Yukawa potential) for noble gases by calculation of the transport properties. The viscosity, thermal conductivity and self diffusion coefficient in dilute gas limit in the temperature range of 298‐1400 K are calculated and agreement with the measurements is, in general, within the experimental error. A comparison of the calculated and experimental values of the viscosity, thermal conductivity and the diffusion coefficients yields an average absolute deviation of 0.5%, 1.5% and 1.2%, respectively. Also, the calculated transport properties from this potential have been compared with those calculations via the accurate experimental potential and also the corresponding state.     

An atomic force microscopy investigation on self-assembled peptide nucleic acid structures on gold(111) surface

We studied interaction of hydrophilic polymer chain and hydrophilic silica nanoparticles in a dilute aqueous system using an idealized model system comprised of a well characterized polyvinyl alcohol of 100 Å R_g and hard spherical LUDOX® silica of 80 Å radii. Interaction among the polymer chains forming polymer clusters with collective polymer structure factor induced by the polymer-mediated potentials of mean force between the nanoparticles, was observed. However, Gaussian nature of individual polymer chain remains unaltered. The dilute system of polymer with low silica volume fraction has the scattering form which was appropriately modeled as the sum of the individual profiles of spherical silica particles and polymer cluster of interchain packing. With increasing silica volume fraction in the dilute solution, the spatial range parameter between the particles is reduced; hence there is a net increase in the mean potential force and consequently to stronger interaction between the silica and polymer. In the dilute systems of high silica with low polymer volume fraction, the polymer chain apparently attracted closer to the silica and concurrently absorbed to the silica hard surface and their scattering data were excellently fit with a model form factor as comprising of one unit forming the core of the spherical silica particles and the interacting polymer as the corona. This result of severe change in polymer interchain conformation in a dilute system corroborated with reduced polymer viscosity observed.