Capillary equilibrium and stability in liquids under microgravity

The conditions governing capillary equilibrium and stability of a fluid interface are stated. A distinction is drawn between hydrostatic (or Laplace) and diffusional (or Kelvin) equilibria, which is often of practical importance in the behaviour of real liquids. In the light of these principles, the fluid physics experiments proposed for the first Spacelab payload are discussed, with particular reference to the rotational stability of a fluid cylinder in microgravity and to processes used to grow large single crystals of pure materials.     

Observation and tuning of hypersonic bandgaps in colloidal crystals

Composite materials with periodic variations of density and/or sound velocities, so-called phononic crystals, can exhibit bandgaps where propagation of acoustic waves is forbidden. Phononic crystals are the elastic analogue of the well-established photonic crystals and show potential for manipulating the flow of elastic energy. So far, the experimental realization of phononic crystals has been restricted to macroscopic systems with sonic or ultrasonic bandgaps in the sub-MHz frequency range. In this work, using high-resolution Brillouin spectroscopy we report the first observation of a hypersonic bandgap in face-centred-cubic colloidal crystals formed by self-assembly of polystyrene nanoparticles with subsequent fluid infiltration. Depending on the particle size and the sound velocity in the infiltrated fluid, the frequency and the width of the gap can be tuned. Promising technological applications of hypersonic crystals, ranging from tunable filters and heat management to acousto-optical devices, are anticipated.     

Application of the similarity method to a study of hygrothermal equilibrium in capillary-porous colloidal materials

A method is shown of constructing a universal Sorption (desorption) isotherm for hygroscopically similar capillary-porous materials. It is shown to be feasible to ascertain the similarity of hygroscopic properties on the basis of a limited number of test points.     

Studying equilibrium thermophysical properties of simple liquids based on a four-parameter oscillating interaction potentia

The equilibrium thermodynamic properties of a system with a four-parameter oscillating interaction potential which can be reduced to an oscillating potential with a single varying parameter is studied in the context of the statistical approach. The appearance of a phase transition of the first kind in the system is established. The relations between the geometric characteristics of potential with coordinates of critical points are obtained. The temperature dependences of some thermophysical properties on the phase equilibrium line and in the supercritical region are found. Thermodynamic parameters that depend on temperature and density are represented as functions of a constituting parameter connected with the interaction potential. The results of calculations are compared with the measurement data.     

Measurement of transport properties of liquids with equilibrium and nonequilibrium Rayleigh scattering

We have developed an experimental arrangement for measuring Rayleigh scattering in liquids and liquid mixtures that are either in thermal equilibrium or in thermal nonequilibrium states. As an illustrative example we report experimental values for the thermal dilfusivity, the mass diffusion coefficient, the Rayleigh-factor ratio, and the Suret coefficient of an equimolar mixture of liquid toluene andn-hexane.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994 Boulder Colorado U S A     

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation. Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the Frenkel-Kontorova model, which considers a monolayer of interacting particles on a periodic substrate potential. In addition to the well-known stick-slip motion, such models also predict the formation of kinks and antikinks, which greatly reduce the friction between the monolayer and the substrate. Here, we report the direct observation of kinks and antikinks in a two-dimensional colloidal crystal that is driven across different types of ordered substrate. We show that the frictional properties only depend on the number and density of such excitations, which propagate through the monolayer along the direction of the applied force. In addition, we also observe kinks on quasicrystalline surfaces, which demonstrates that they are not limited to periodic substrates but occur under more general conditions.     

Characterization of aqueous lead removal by phosphatic clay: equilibrium and kinetic studies

Immobilization of heavy metals from contaminated environments is an emerging field of interest from both resource conservation and environmental remediation points of view. This study investigated the feasibility of using phosphatic clay, a waste by-product of the phosphate mining industry, as an effective sorbent for Pb from aqueous effluents. The major parameters controlling aqueous Pb removal, viz. initial metal ion concentrations, solution pH, sorbent amounts, ionic strength and presence of both inorganic and organic ligands were evaluated using batch experiments. Results demonstrated that aqueous Pb removal efficiency of phosphatic clay is controlled mainly by dissolution of phosphatic clay associated fluoroapatite [Ca(10)(PO(4))(5)CaCO(3)(F,Cl,OH)(2)], followed by subsequent precipitation of geochemically stable pyromorphite [Pb(10)(PO(4))(6)(F,Cl,OH)(2)], which was confirmed by both X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. Lead removal efficiency of phosphatic clay increased with increasing pH, sorbent amount and decreasing ionic strength. It also depends on the nature of complexing ligands. Formation of insoluble calcium oxalate and lead oxalate in the presence of oxalic acid explained high uptake of Pb by phosphatic clay from aqueous solution. However, Pb sorption kinetics onto phosphatic clay were biphasic, with initially fast reactions followed by slow and continuous Pb removal reactions. The slow reactions may include surface sorption, co-precipitation and diffusion. The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.     

Evaporation kinetics of volatile liquids and release kinetics of water from a smectite clay: Comparison between experiments and finite element calculations

Numerical calculations of the evaporation kinetics of bulk volatile liquids and of water from smectite clay granules are compared with experimental results. The weight loss of the volatiles is analyzed by thermogravimetry and differential calorimetry. Under the thermodynamic conditions of the experiments, finite element calculations are in good agreement with the experimental data, and an approximate semi-analytical model is developed in order to explain the dependence of the rate of evaporation on the temperature, the chemical species and the carrier gas flow rate. The initial rate of evaporation of water from the clay granule is close to that for bulk water. Its decrease with time is determined mainly by changes in the gas/condensed phase partition given by the equilibrium desorption isotherm, with little limitations due to internal diffusion effects for the present experimental conditions. Its temperature dependence could also be approximately described by an Arrhenius-type equation derived from the semi-analytical model. Further analysis of the experimental measurements reveals steps in the heat of vaporization of water as a function of water concentration, that could be related to the equilibrium desorption isotherm.     

The effect of clay treatment on remediation of diethylketone contaminated wastewater: uptake, equilibrium and kinetic studies

In this study we evaluated the efficiency of red muds (RM, a bauxite residue) to immobilize the arsenic present in a polluted sub-acidic soil (UP-soil; total As 2428 mg kg(-1)) and to influence some chemical, biochemical and microbiological properties after 2 years since RM addition. The RM addition caused a pH increase, a striking decrease of total organic carbon and a significant increase of water-soluble C, N and P. The analysis of As mobility through sequential extraction showed a reduction of the water-soluble arsenic in the RM-soil compared to the UP-soil (3.44% and 5.59% of the total As respectively) and a remarkable increase of the residual (non extractable) arsenic fraction in the RM-soil (>300% compared to UP-soil). RM addition increased significantly the microbial abundance and the activity of selected enzymes (dehydrogenase, urease) with respect to UP-soil while had a major influence on the structure of soil microbial communities as evaluated by the Biolog Community Level Physiological Profile. The reduced As mobility, together with an increase of C, N and P labile-pool (likely originating from a "de-structuring effect" of RM on the soil organic matter) were identified as the key factors affecting the biological activity in the RM-treated soil.     

Direct electron transfer of cytochrome P450 2B4 at electrodes modified with nonionic detergent and colloidal clay nanoparticles

A method for construction of biosensors with membranous cytochrome P450 isoenzymes was developed based on clay/detergent/protein mixed films. Thin films of sodium montmorillonite colloid with incorporated cytochrome P450 2B4 (CYP2B4) with nonionic detergent were prepared on glassy carbon electrodes. The modified electrodes were electrochemically characterized, and bioelectrocatalytic reactions were followed. CYP2B4 can be reduced fast on clay-modified glassy carbon electrodes in the presence of the nonionic detergent Tween 80. In anaerobic solutions, reversible oxidation and reduction is obtained with a formal potential between -0.292 and -0.305 V vs Ag/AgCl 1 M KCl depending on the preparation of the biosensor. In air-saturated solution, bioelectrocatalytic reduction currents can be obtained with the CYP2B4-modified electrode on addition of typical substrates such as aminopyrine and benzphetamine. This reaction was suppressed when methyrapone, an inhibitor of P450 reactions, was present. Measurement of product formation also indicates the bioelectrocatalysis by CYP2B4.     

The drying of clay minerals and mixed clay minerals

In natural plastic clays used on ceramic compositions, the presence of certain minerals is frequently observed in the mineralogical composition. In this study, the drying ability of five different clay minerals was examined. All experiments were conducted under steady-state drying conditions. The sorption isotherm of the samples was determined by measurement of the mass of water absorbed at a fixed temperature versus the relative partial water pressure. The shrinkage of pastes was measured under the same experimental conditions. From the experimental data the heat of water sorption was calculated using a model which comes from the interpretation of a sorption reaction. The specific behaviour of the five clay minerals studied was observed; this can explain the behaviour of common plastic clays during the drying process. In particular, some investigations were conducted on mixed minerals. The results should support the possibility of obtaining a correlation between the heat of water sorption of certain clay raw materials and their mineralogical composition.     

Motion of viscoelastic liquids in a porous medium

Nonlinear effects occurring in filtration of viscoelastic liquids are considered. The qualitative differences between one-dimensional and planar cases and between motion in homogeneous and inhomogeneous porous media are demonstrated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 5, pp. 751–756, May, 1987.     

Kinetics of temperature field in a three-layered colloidal body

The net method is used to obtain the numerical solution of the problem of the kinetics of the temperature field in a three-layered colloidal body in the presence of phase transformations. The obtained results are compared with experimental data.     

Observation of interactions between hydrophilic ionic liquid and water on wet agar gels by FE-SEM and its mechanism

In the present study, an attempt is made to understand the mechanism of field emission electron microscopy (FE-SEM) observation of wet agar gel using a typical hydrophilic ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate; [BMIM][BF₄]. The IL interaction with water molecules within agar gel during sample preparation condition for FE-SEM observation was investigated using Raman spectroscopy. Results showed that water molecules within agar gel form weak hydrogen bond such as BF₄⁻?HOH?BF₄⁻ by interaction with BF₄⁻ of IL, and, it remained stable even under vacuum condition at 60 °C, 24 h. This interaction was found to be helpful for IL displacement of the water molecules within agar gel. From this study, it was found that the exact morphology of gel materials in FE-SEM condition can be observed by optimization of water concentrations of IL and gel mixtures. Thus, using IL, agar gel or any other material under wet condition can be observed without drying in FE-SEM chamber, and, present result gives an insight to the mechanism of FE-SEM observation of agar gel using IL without any conducting coating.     

Initial phases of the collapse of an empty cavity in a liquid

This paper relates to the collapse of an empty spherical cavity in a liquid. The analysis is mainly theoretical, the object being to study the effects of liquid compressibility on the initial phases of the motion of the cavity. A method, similar to the Rayleigh-Janzen theory of subsonic aerodynamics, is described whereby the motion of the cavity can be systematically computed as it collapses from an initial radius R₀ down to a stage when the collapse Mach number approaches unity. Instead of the usual differential equation, a parameter $\text{R}\text{R}\text{?}\text{.R}{}^2$ describes the cavity motion. Results obtained are in excellent agreement with those obtained from numerical computations. Distributions of fluid properties behind the cavity are obtained at different stages of the collapse. These results, apart from demonstrating the effects of liquid compressibility, also indicate the existence of high-intensity pressure fields in the surrounding flow field even at these subsonic speeds. A general feature of the present theory is that it offers a method by means of which the subsonic phase of the collapse can be linked with the supersonic phase.     

Direct Observation of sp-d exchange interactions in colloidal Mn2+- and Co2+-doped CdSe quantum dots

The defining attribute of a diluted magnetic semiconductor (DMS) is the existence of dopant-carrier magnetic exchange interactions. In this letter, we report the first direct observation of such exchange interactions in colloidal doped CdSe nanocrystals. Doped CdSe quantum dots were synthesized by thermal decomposition of (Me4N)2[Cd4(SePh)10] in the presence of TMCl2 (TM2+ = Mn2+ or Co2+) in hexadecylamine and were characterized by several analytical and spectroscopic techniques. Using magnetic circular dichroism spectroscopy, successful doping and the existence of giant excitonic Zeeman splittings in both Mn2+- and Co2+-doped wurtzite CdSe quantum dots are demonstrated unambiguously.