Photo–induced processes in Ag and Eu β-diketonates incorporated into aerogel matrix of silicon dioxide by supercritical fluid impregnation

Samples of silicon dioxide aerogel with embedded Ag and Eu β-diketonate molecules are obtained by impregnation in supercritical carbon dioxide (SC-CO₂). The sample impregnated by Eu(tta)₃ molecules possesses photoluminescence properties. Moreover, adsorption of Eu(tta)₃ on the walls of the pores results in a strong broadening of the Stark components of its photoluminescence spectra. It is found that aerogel impregnation by AgFOD molecules followed by laser irradiation causes the formation of Ag nanoparticles in the sample volume as a result of AgFOD photolysis and subsequent diffusion self-assembly. The Ag nanoparticles assemble into filament structures due to self-organization as they focus laser radiation.     

Formation of porous matrices from lactide and ε-caprolactone copolymers in supercritical carbon dioxide medium

A series of lactide and ε-caprolactone copolymers containing 4–24 mol % of ε-caprolactone with 20- to 30-kDa molecular weights are synthesized. Based on them, porous materials are produced by foaming in supercritical carbon dioxide. The pore size was shown to decrease with increasing ε-caprolactone content in copolymer, while the porosity of the entire sample was not altered. The resulting pore size also decreases if 7 wt % polyethylene glycol is added to the initial monomer mixture. The Young’s modulus of the porous samples decreases with increasing ε-caprolactone content and when polyethylene glycol is added.     

Equation of state SAFT-CP for vapour–liquid equilibria and mutual solubility of carbon dioxide and water

ABSTRACT

The statistical associating fluid theory (SAFT) was proposed first in 1990, and has been extended to various forms for the calculation of thermodynamic properties of complex systems, such as oil reservoir fluids, polar systems, polymers, electrolytes, near-critical systems, interfacial phenomena, solids and even biomaterials. SAFT-CP (critical point) has been established for nonpolar fluids in 2001 with excellent expression of thermodynamic properties across critical points. It was extended later for polar and associating fluids with the addition of just a dipole–dipole interaction, which leads simple calculation procedure without an association term. In this article SAFT-CP is applied to carbon dioxide, water and their mixture. Vapour–liquid equilibria for pure components CO₂ and H₂O, CO₂ solubility in water and H₂O solubility in dense CO₂ are analysed. Expression of pure CO₂ properties is improved with the dipole–dipole interaction term used, while expression of pure water is a little bit improved with the non-spherical degree parameter less than 1.0. For the high asymmetry in polarity and association between CO₂ and H₂O molecules, the Stryjek–Vera combining rule is used with different temperature-dependent parameters. With the quadratic temperature-dependent parameters, the mutual solubilities in the system are calculated with good agreement with experimental ones over the wide range of temperature as 298–474 K and of pressure as 0.1–70 MPa.     

Equation of state and liquid–vapour equilibrium in a triangle-well fluid

The second-order thermodynamic perturbation theory formulation of Barker and Henderson is used to derive the equation of state of the triangle-well fluid. This is combined with the rational function approximation to the radial distribution function of the hard-sphere fluid. Results are obtained for the critical parameters and the liquid–vapour coexistence curve for various values of the range of the potential. A comparison with available simulation data is presented.     

Gasification and removal of carbon materials and redeposited boron–carbon layers exposed in an oxygen–ozone mixture

The results from experiments on measuring the rate of gasification for carbon and boron–carbon films and carbon fiber composite (CFC) exposed in oxygen–ozone mixtures are presented. The rate of gasification is 0.4–0.6 μm h^–1 (at temperatures of 220–250°C, a pressure of 0.3 atm, and an ozone concentration of 0.6 at %) for carbon films; plane CFC samples; gaps 1 and 2 mm wide with walls of stainless steel; and gaps 1 mm wide with walls of CFC. It is 15 μm h^–1 for plane CFC at a temperature of 250°C, a pressure of 1 atm, and an ozone concentration of 10 at %. The rate of gasification for boron–carbon films is from 3 to 30 nm h^–1 for B/C ratios of 2.1 to 0.8 (at 250°C, 1 atm, and ozone concentration of 10 at %).     

Synthesis,characterization and thermodynamic study of carbon dioxide adsorption on akaganéite

A mixture of akaganéite nanoparticles and sodium salts was synthesized and modified, first by washing, and then by Li exchange. The structural characterization of the produced materials was performed with: powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, thermo-gravimetric analysis, diffuse reflectance infrared Fourier transform spectrometry, Mössbauer spectroscopy and magnetization measurements. Additionally low pressure nitrogen and high pressure carbon dioxide adsorption experiments were performed. The sum of the characterization information made possible to conclude that the produced akaganéite phases crystallized in a structure exhibiting the symmetry of the I2/m space group, where the measured equivalent spherical diameter of the akaganéite crystallites yielded 9 nm, as well, the tested phases exhibited a standard behaviour under heating and displayed a superparamagnetic behaviour. Finally the high pressure carbon dioxide adsorption experiments demonstrated a pressure-responsive framework opening event due to a structural transformation of the adsorbent framework induced by the guest molecules. This fact opens new applications for akaganéite as a high pressure adsorbent.     

Simulation of solid–fluid mixture flow using moving particle methods

A new basic framework for solid–fluid mixture flow simulation was developed using moving particle methods. The interactions between solid and fluid were modeled by the finite volume particle (FVP) method. The distinct element method (DEM) together with a multi-time-step algorithm was introduced into the FVP method to calculate the effects of contact between solid bodies and between solid bodies and walls. The introduced DEM model was verified by experimental analyses for the collapse of multiple solid cylinder layers. The proposed algorithm using the optimized DEM model was then applied to a water dam breaking, involving multiple solid cylinder layers. A comparison between experiments and simulations demonstrated the DEM model introduced into the FVP method is effective in representing solid–fluid mixture flows reasonably well.     

Loci of extrema of thermodynamic response functions for the Lennard–Jones fluid

Lines of extrema along isotherms and isobars for the residual isochoric heat capacity, the residual isobaric heat capacity, the isobaric thermal expansivity, and the isothermal compressibility of the Lennard–Jones fluid have been studied from popular equations of state due to Johnson et al. [Mol. Phys. 78, 591 (1993)], Kolafa and Nezbeda [Fluid Phase Equilib. 100, 1 (1994)], and Mecke et al. [Int. J. Thermophys. 17, 391 (1996)]. On depicting such loci in the pressure–temperature plane, the characteristic behaviour of thermodynamic response functions in the ideal-gas limit (at high enough temperatures or low enough pressures), the close-packed-fluid limit (at low enough temperatures or high enough pressures) as well as in the liquid, critical, and supercritical regions is identified. The present analysis is informative itself, but it also stimulates further work in order to tackle more complicated cases of study including associated fluids.     

Formation of long-lived “colored” spiroantrooxazine isomers incorporated into fluoroplast F-42 matrix in a supercritical carbon dioxide medium

It has been demonstrated that formation of isomeric “colored” merocyanine forms B and B _x of indoline spiroantrooxazine (SAO) introduced into Fluoroplast F-42 matrix from supercritical carbon dioxide (SC-CO₂) depends on the volume concentration of toluene in the medium, which plays a role of an aromatic electron donor cosolvent. It also has been shown that observed dependencies of changes in the content of introduced photochrome forms, forming in the Fluoroplast F-42 matrix, can be described by a scheme which reflects the redistribution kinetics of SAO molecules between the medium (SC-CO₂) and the polymer. In this case, the “blue” form B is formed by SAO molecules solvated by toluene, which localize at specific fragments of the matrix and form triple SAO/F-42/toluene complexes. The “Red” form B _x is formed under the coordination of desolvated SAO molecules, which transfer into the matrix from the SC-CO₂ medium, near F-42 matrix fragments.     

Controlled drug release applications of the inclusion complex of peracetylated-β-cyclodextrin and water-soluble drugs formed in supercritical carbon dioxide

Supercritical carbon dioxide (scCO₂) processing was performed with mixtures of CO₂-soluble peracetylated-β-cyclodextrin (PAc-β-CD) heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin, and highly water-soluble drug molsidomine (MOL) to prepare inclusion complexes of MOL and PAc-β-CD. The MOL/PAc-β-CD inclusion complex was confirmed by differential scanning calorimetry, X-ray diffractometry, and ¹H NMR analyses. The complexes were further investigated for their potential use in controlled drug delivery applications. The in-vitro release of MOL from the peanut oil suspensions into aqueous phase was found to be significantly retarded by the complexation with PAc-β-CD, mainly due to the hydrophobic properties associated with the PAc-β-CD.     

Model of the unsteady two-phase three-component filtration of the oil–water–supercritical fluid system in a homogeneous porous medium

A mathematical model of the two-phase three-component filtration of the oil–water–supercritical fluid system in a porous medium is developed. The results of numerical simulations of the three-component two-phase filtration during oil displacement by supercritical CO₂ from a watered stratum are reported. In the region of oil displacement from watered stratum, there is a significant discrepancy between the experimental and simulation results because of the transient mode of filtration associated with the concurrent saturation of the oil and water with supercritical CO₂ under high pressure. In the region of two-phase filtration of the oil–water system and in the region of pumping of three or more pore volumes of supercritical CO₂, the deviation of the simulation results from the experimental data does not exceed 10%.     

Steady state fluorescence technique for studying phase transitions in PAAm–PNIPA mixture

The steady state fluorescence (SSF) technique was used to study the sol-gel phase transition during free radical crosslinking copolymerisation of various amounts of acrylamide (AAm) and N-isopropylacrylamide (NIPA) mixtures. N,N′-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator, respectively. Pyranine (8-hydroxypyrene-1, 3, 6-trisulfonic acid, trisodium salt, HPTS) was added as a fluoroprobe for monitoring the polymerisation. It was observed that pyranine molecules bind to AAm and NIPA chains upon the initiation of the polymerisation, thus the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol-gel phase transition, without disturbing the system mechanically, and to test the universality of the sol-gel transition as a function of polymer concentration ratios. Observations around the gel point of PAAm–PNIPA mixtures show that the gel fraction exponent β obeyed the percolation result.     

Partial and complete oxidation of brown coal in a supercritical water–oxygen fluid under conditions of counterflowing reactant streams

The oxidation of brown coal continuously fed as part of a coal–water slurry into a counterflowing stream of a supercritical water–oxygen fluid at a temperature difference along the reactor axis of 673–873 K and a pressure of 30 MPa has been studied. It has been found that, in the case of a partial combustion of coal (under conditions of O₂ deficiency), the yield of hydrogen-enriched products increases owing to heat evolution. Under conditions of excess O₂, coal undergoes complete oxidation. In this case, the heat evolved per unit volume of furnace space is about 1.0 MW/m³. It has been shown that the heat consumed for the implementation of the process using external sources can be partially or completely compensated for by heat evolution during homogeneous and heterogeneous combustion coupled with coal thermolysis.     

Fluid–fluid phase equilibria in disordered porous media. Nonadditive hard sphere mixture

We report a computer simulation and integral equation study of fluid–fluid phase equilibria of nonadditive hard sphere binary mixture adsorbed in disordered hard sphere matrix. The mixture exhibits phase separation with critical density ρ_c^f lower than its bulk counterpart. It is found that ρ_c^f decreases with increasing both porosity and nonadditivity parameter.     

Mössbauer study of the iron atom state in modified chromium dioxide

Powders of modified chromium dioxide produced by the hydrothermal method were studied using ⁵⁷Fe Mössbauer spectroscopy at a temperature of 298 K. The content of the modifier, i.e., ⁵⁷Fe compound, was varied from 2 to 10 mmol/mol Cr at a Sb content of 2.2 and 10 mmol/mol Cr. It was shown that, independently of concentrations, Fe³⁺ ions are distributed between three magnetic solid solutions (sextets): based on CrO₂ (bulk material and iron-enriched surface layer), based on Cr₂O₃, and surface β-CrOOH (doublet). In this case, chromium atoms were not substituted in the CrSbO₄ nucleation (12 nm in size) phase with an accuracy up to the Mössbauer factor. It was assumed that the powder coercivity, in addition to the size factor, is controlled by the iron concentration in the CrO₂ surface layer.     

Equations of state in the Brans–Dicke cosmology

We investigate the Brans–Dicke (BD) theory with the potential as cosmological model to explain the present accelerating universe. In this work, we consider the BD field as a perfect fluid with the energy density and pressure in the Jordan frame. Introducing the power-law potential and the interaction with the cold dark matter, we obtain the phantom divide which is confirmed by the native and effective equation of state. Also we can describe the metric f(R) gravity with an appropriate potential, which shows a future crossing of the phantom divide in viable f(R) gravity models when employing the native and effective equations of state.     

Ionization of molecules at the fluid–fluid phase transition in warm dense hydrogen

The problem of the fluid–fluid phase transition in warm dense hydrogen/deuterium has been studied experimentally and theoretically in the best laboratories in the last decade. However, the nature of the phase transition remains unclarified. In this paper we put forward the new idea that H₂ molecules are ionized at the phase transition to produce molecular H ₂ ⁺ and H ₃ ⁺ ions     

The Klein–Gordon equation in mixture models of tumour growth

A mixture model of tumour microenvironment is considered, which consists of a solid phase for the tumour cells, a liquid phase for the interstitial fluid, and a nutrient phase. The balance equations for the three phases take into account exchange of mass between tumour and nutrients, and exchange of drag forces between the constituents. Under rather natural assumptions, the determination of the nutrient density is reduced to the solution of a Klein–Gordon equation, with source term depending on mass injection from outside. A chain of decoupled equations for the remaining unknowns is then determined in terms of the nutrient density. Finally, the growth of tumour volume is investigated under the assumption of spherical symmetry.