Dispersed Drops Research Articles

Orientation specific deposition of mesoporous particles

We present a protocol for a facile orientation specific deposition of plate-like mesoporous SBA-15 silica particles onto a surface (mesopores oriented normal to surface). A drop of an aqueous dispersion of particles is placed on the surface and water vaporizes under controlled relative humidity. Three requirements are essential for uniform coverage: particle dispersion should not contain aggregates, a weak attraction between particles and surface is needed, and evaporation rate should be low. Aggregates are removed by stirring/sonication. Weak attraction is realized by introducing cationic groups to the surface. Insight into the mechanisms of the so-called coffee stain effect is also provided.

Low shear rheological behaviour of two-phase mesophase pitch

The low shear rate rheology of two phase mesophase pitches derived from coal tar pitch has been investigated. Particulate quinoline insolubles (QI) stabilised the mesophase spheres against coalescence. Viscosity measurements over the range 10–106Pas were made at appropriate temperature ranges. Increasing shear thinning behaviour was evident with increasing mesophase content. At low mesophase contents the dominant effect on the near Newtonian viscosity was temperature but at higher contents it was the shear rate; temperature dependence declined to near zero. The data indicated that agglomeration could be occurring at intermediate mesophase volume fractions, 0.2–0.3. The Krieger–Dougherty function and its emulsion analogue indicated that in this region the mesophase pitch emulsions actually behaved like ‘hard’ sphere systems and the effective volume fraction was estimated as a function of shear rate illustrating the change in extent of agglomeration. At the higher volume fractions approaching the maximum packing fraction, which could only be measured at higher temperatures, the shear thinning behaviour changed in character and it is considered that this is possibly due to shear induced deformation and breakup of dispersed drops in the shear field.

Effect of surface free energy to control the deposit morphology during evaporation of graphite/SDS dispersion drops

Uniform spherical cap shaped graphite/sodium dodecyl sulfate surfactant (SDS) micro-deposits were formed after the complete evaporation of aqueous graphite/SDS dispersion drops containing 2 and 4mM of SDS and 10, 20, 40, 60, 80 and 110mg/ml graphite micro-powder on hydrophobic surfaces such as Teflon-FEP and tridecafluorooctyltriethoxysilane coated glass slides. The shapes and sizes of the graphite/SDS micro-deposits were also investigated on polypropylene, polymethyl methacrylate, and polyvinyl alcohol surfaces. A good linear relationship was found between the surface free energy of the substrates and the diameters of the graphite/SDS deposits. The volumes and heights of the spherical cap shaped deposits can be controlled by varying the substrate surface free energy, concentration of graphite and SDS in the dispersion drop. SDS adsorption on graphite resulted in better surface packing of the microparticles on hydrophobic substrates. Effect of particle size on the deposit shape and size was also investigated by comparing SDS/graphite deposits formed from carbon microparticles with SDS/fullerene deposits formed from carbon nanoparticles. In addition, “stick-slip” motion of a (graphite+water) dispersion droplet on a polypropylene surface was investigated by the model proposed by Shanahan et al. and the potential energy barrier was calculated to be small for graphite microparticles on this surface.

Experimental Study of a Pulsed-Pressure-Swing-Adsorption Process with Very Small 5A Zeolite Particles for Oxygen Enrichment

The pressure drop characteristics, dynamic column breakthrough, and pulsed-pressure-swing-adsorption (PPSA) experiments in an adsorption column packed with very fine 5A zeolite particles of mixed size in the range 63–75 μm are presented. A multipurpose experimental setup was designed and constructed to perform these experiments. The pressure drop and axial dispersion were very high in the adsorption column. Darcy’s equation and the correlation by Langer et al. were recalibrated to account for the increased pressure drop and enhanced axial dispersion, respectively. With these recalibrated constituent models, the numerical process model, solved using COMSOL Multiphysics software, was able to correctly capture the measured experimental breakthrough and PPSA performance results. The principal conclusion from this study is that the high axial dispersion and pressure drop in a column packed with very fine 5A zeolite particles are due to the surface roughness and clustering of the particles and channeling in the...

Characterization of hydromechanical stress in aerated stirred tanks up to 40 m(3) scale by measurement of maximum stable drop size.

BackgroundTurbulence intensity, or hydromechanical stress, is a parameter that influences a broad range of processes in the fields of chemical engineering and biotechnology. Fermentation processes are often characterized by high agitation and aeration intensity resulting in high gas void fractions of up to 20% in large scale reactors. Very little experimental data on hydromechanical stress for such operating conditions exists because of the problems associated with measuring hydromechanical stress under aeration and intense agitation.ResultsAn indirect method to quantify hydromechanical stress for aerated operating conditions by the measurement of maximum stable drop size in a break-up controlled dispersion was applied to characterize hydromechanical stress in reactor scales of 50 L, 3 m3 and 40 m3 volume with a broad range of operating conditions and impeller geometries (Rushton turbines). Results for impellers within each scale for the ratio of maximum to specific energy dissipation rate ϕ based on measured values of maximum stable drop size for aerated operating conditions are qualitatively in agreement with results from literature correlations for unaerated operating conditions. Comparison of data in the different scales shows that there is a scale effect that results in higher values for ϕ in larger reactors. This behavior is not covered by the classic theory of turbulent drop dispersion but is in good agreement with the theory of turbulence intermittency. The data for all impeller configurations and all aeration rates for the three scales can be correlated within ±20% when calculated values for ϕ based on the measured values for dmax are used to calculate the maximum local energy dissipation rate. A correlation of the data for all scales and all impeller configurations in the form ϕ = 2.3∙(ϕunaerated)0.34∙(DR)0.543 is suggested that successfully models the influence of scale and impeller geometry on ϕ for aerated operating conditions.ConclusionsThe results show that besides the impeller geometry, also aeration and scale strongly influence hydromechanical stress. Incorporating these effects is beneficial for a successful scale up or scale down of this parameter. This can be done by applying the suggested correlation or by measuring hydromechanical stress with the experimental method used in this study.

CIRCUMNUCLEAR MOLECULAR GAS IN MEGAMASER DISK GALAXIES NGC 4388 AND NGC 1194

We explore the warm molecular and ionized gas in the centers of two megamaser disk galaxies using K-band spectroscopy. Our ultimate goal is to determine how gas is funneled onto the accretion disk, here traced by megamaser spots on sub-pc scales. We present NIR IFU data with a resolution of ~50 pc for two galaxies: NGC 4388 with VLT/SINFONI and NGC 1194 with Keck/OSIRIS+AO. The high spatial resolution and rich spectral diagnostics allow us to study both the stellar and gas kinematics as well as gas excitation on scales only an order of magnitude larger than the maser disk. We find a drop in the stellar velocity dispersion in the inner ~100 pc of NGC 4388, a common signature of a dynamically cold central component seen in many active nuclei. We also see evidence for non-circular gas motions in the molecular hydrogen on similar scales, with the gas kinematics on 100-pc scales aligned with the megamaser disk. In contrast, the high ionization lines and Br-gamma trace outflow along the 100 pc-scale jet. In NGC 1194, the continuum from the accreting black hole is very strong, making it difficult to measure robust two-dimensional kinematics, but the spatial distribution and line ratios of the molecular hydrogen and Br-gamma have consistent properties between the two galaxies.

Maximum stable drop size measurements indicate turbulence attenuation by aeration in a 3 m3 aerated stirred tank

In this study, break-up controlled drop dispersion experiments in a 3m3 pilot scale reactor with 1.2m inner diameter are presented that allow a correlation of the maximum local energy dissipation rate in stirred reactors with intense aeration. Experiments with two different setups of 6-bladed Rushton turbine impellers with diameters of d=0.41m (d/DR=0.34) and d=0.51m (d/DR=0.43) in a 3 impeller configuration were conducted. The results from experiments without aeration are well in agreement with the existing literature on drop dispersion. The results from experiments with aeration indicate a strong attenuation of turbulence intensity in stirred tank reactors by the presence of air. The ratio between maximum and volume-averaged energy dissipation rate was reduced by aeration by 64% for the d/DR=0.34 impeller and by 52% for the d/DR=0.43 impeller when compared with unaerated operating conditions on the basis of equal volumetric power input. The value of the aeration rate had no measurable effect in the range of aeration rates applied, which was between 0.1vvm (volume of gas/volume liquid/minute) and 1vvm.

Impact of pNIPAM Microgel Size on Its Ability To Stabilize Pickering Emulsions

We study the influence of the particle size on the ability of poly(N-isoprolylacrylamide) microgels to stabilize direct oil-in-water Pickering emulsions. The microgel size is varied from 250 to 760 nm, the cross-linking density being kept constant. The emulsion properties strongly depend on the stabilizer size: increasing the particle size induces an evolution from dispersed drops and fluid emulsions toward strongly adhesive drops and flocculated emulsions. In order to get insight into this dependency, we study how particles adsorb at the interface and we determine the extent of their deformation. We propose a correlation between microgel ability to deform and emulsion macroscopic behavior. Indeed, as the microgels size increases, their internal structure becomes more heterogeneous and so does the polymeric interfacial layer they form. The loss of a uniform dense layer favors bridging between neighboring drops, leading to flocculated and therefore less handleable emulsions.

Low-voltage electrohydrodynamic micropumping of emulsions

A novel low-voltage technique employing electrohydrodynamic (EHD) flow for micropumping oil-in-water emulsions through microchannels is presented. The concept of EHD flow reported at microscopic scale during colloidal aggregation is extended to larger scales, for actuation of bulk motion of emulsion. The experiments involve immersing two vertical parallel electrodes in an oil-in-water emulsion and applying AC fields (15–40Vp-p; 5–500Hz) across the electrodes. Liquid flow along the electrode gap is analyzed by microscopically tracking the motion of the suspended oil drops on the free surface. Experimental results confirm an EHD mechanism of flow through field distortions caused by the dispersed oil drops leading to tangential electric field on the charge polarization layer. Comparison of the scheme with conventional EOF scheme shows a drastic reduction in the actuation voltage required for attaining identical velocities. Additional advantage of EHD over EOF includes the independence of the actuation voltage on the microchannel length.

Triglyceride–water emulsions stabilised by starch-based nanoparticles

Emulsions stabilized solely by edible particles have attracted great interest very recently because of their potential application in the food and pharmaceutical fields. In this work, starch-based nanospheres are used as the particulate emulsifier for triglyceride–water emulsions. The effects of particle concentration, oil:water ratio and salt concentration on emulsion type and stability are investigated in detail. The linear relationship between the inverse average oil drop diameter and the particle concentration allows estimation of the coverage by particles of the curved oil–water interfaces. Confocal microscopy confirms that the nanospheres are mainly adsorbed at the liquid interface to form a dense film around the dispersed drops impeding coalescence. Moreover, catastrophic phase inversion from oil-in-water (O/W) to water-in-oil (W/O) emulsions is achieved by increasing the volume fraction of oil beyond 0.65. The stability to creaming of O/W emulsions increases approaching phase inversion, as does the stability to sedimentation of W/O emulsions. Finally, O/W emulsions are destabilized with respect to coalescence on adding salt.

Shape and diameter control of C60 fullerene micro-stains by evaporation of aqueous SDS–fullerene dispersion drops

The effect of the surface free energy of substrates such as glass slide, polymethyl methacrylate, polystyrene, polypropylene and Teflon-FEP was investigated on the shape and diameter of fullerene (C60) stains which were obtained by evaporation of aqueous sodium dodecyl sulfate/fullerene dispersion drops having different SDS/C60 fullerene compositions and different drop volumes. It was found that the surface free energy of the substrates was the most important parameter to control the shape and the diameters of the formed SDS/C60 fullerene deposits and a good linear relationship was obtained between the stain diameter and surface free energy of the substrates. Uniform circular fullerene/SDS deposits were obtained on polystyrene surfaces.

The effect of alkali and alkaline earth elements on cobalt based Fischer–Tropsch catalysts

A CoRe catalyst supported on γ-Al2O3 was impregnated with 25–20000ppm alkali or alkaline earth elements (Li, Na, K, and Ca). For samples containing less than 1000ppm impurities catalyst characterization showed that the dispersion as measured by H2-chemisorption was constant (∼7.9%) and that reduction temperatures increased slightly 5–15K according to temperature programmed reduction experiments. Microcalorimetric measurements with H2 and CO chemisorption did not reveal any significant change for the concentration up to 1000ppm sodium. However, the catalytic activity at 483K, 20bar and H2/CO=2.1 was 33–43% lower compared with the uncontaminated sample. For samples containing between 10000 and 20000ppm sodium a moderate drop in dispersion and an increase in heats of CO and H2 chemisorption were observed. These samples showed significantly decreased activity in CO hydrogenation in SSITKA experiments (1bar, 483K). Our results are in agreement with the idea that small amounts of alkali, below the level where they can be detected by chemisorption, are present on the surface on locations of particular importance for the catalytic activity.

The complex nature of the nuclear star cluster in FCC 277★

Recent observations have shown that compact nuclear star clusters (NSCs) are present in up to 80% of galaxies. However, detailed studies of their dynamical and chemical properties are confined mainly to spiral galaxy hosts, where they are more easily observed. In this paper we present our study of the NSC in FCC 277, a nucleated elliptical galaxy in the Fornax cluster. We use a combination of adaptive optics assisted near-infrared integral field spectroscopy, Hubble Space Telescope imaging, and literature long slit data. We show that while the NSC does not appear to rotate within our detection limit of ~6 km/s, rotation is detected at larger radii, where the isophotes appear to be disky, suggesting the presence of a nuclear disk. We also observe a distinct central velocity dispersion drop that is indicative of a dynamically cold rotating sub-system. Following the results of orbit-based dynamical modelling, co-rotating as well as counter-rotating stellar orbits are simultaneously needed to reproduce the observed kinematics. We find evidence for varying stellar populations, with the NSC and nuclear disk hosting younger and more metal rich stars than the main body of the galaxy. We argue that gas dissipation and some level of merging have likely played an important role in the formation of the nucleus of this intermediate-mass galaxy. This is in contrast to NSCs in low-mass early- type galaxies, which may have been formed primarily through the infall of star clusters.

New Dissolved Nitrogen Predispersed Solvent Extraction Method, 2: Selectivity

Dissolved Nitrogen Predispersed Solvent Extraction (DNPDSE) is a new method in which the two-phase mixture operation is based on bubble dispersion of the organic phase, instead of its drop dispersion into the aqueous phase. This substitution is intended to increase the two-phase contact area (to improve recovery of metal ions from the dilute solutions) and also to enhance the buoyancy force of organic phase (to improve separation of two phases). However, the performance mode of this method can increase the recovery of interfering elements, because of increased surface contact, entrainment, and precipitate flotation, and thus have an unfavorable effect on the selectivity of this method. Therefore, selectivity of this innovative method was compared with the conventional solvent extraction (SX) method. The results of experiments conducted on the dilute and dense copper, zinc, and iron synthetic solutions within the copper extraction pH values (1.2–2.1) showed a lack of zinc recovery (i.e., no effect on total selectivity) in both methods and increased iron recovery (i.e., effect on partial selectivity) only in the DNPDSE method. The results also showed that increased iron recovery was not just dependent on increased contact area of the two phases, and gel-like precipitates observed on the surface of organic phase indicated precipitation of Fe ions and their transfer onto the surface by bubble entrainment and precipitate flotation.

New Dissolved Nitrogen Predispersed Solvent Extraction Method, 1: Performance

The new Dissolved Nitrogen Predispersed Solvent Extraction (DNPDSE) method was invented for promoting the operational power and improving the equipment performance used in the conventional solvent extraction (SX) method, especially for dilute solutions. The main difference between this method and the SX method is in the mixing mode of aqueous and organic phases. The mixing operation in the SX method is performed with drop dispersion of one phase into another phase; however, in the DNPDSE method, it is carried out with bubble dispersion of organic phase into the aqueous phase. As a result, the performance of the method is improved due to the increase in the contact area of the two phases, thus enhancing in the buoyancy force of the organic phase. The performance comparison of the two methods in similar conditions showed that the copper recovery in the DNPDSE method compared with the SX method in dilute (128 mg Cu/L) and dense (2000 mg Cu/L) synthetic solutions was increased by 22% and 2.5% (on average), respectively.

Kinetics and Reactor Design for N2O Decomposition in the EnviNOx® Process

AbstractThe kinetics of N2O decomposition over a commercial iron zeolite catalyst was determined in an integral laboratory reactor. The formal kinetic equation developed permits a very good description of the observed rate as a function of temperature and the concentrations of N2O, NO and H2O. The influence of mass transfer phenomena on the reaction rate was investigated experimentally by using different catalyst particle sizes. A reactor model taking into account internal and external mass transfer resistances, axial dispersion and pressure drop was developed. Reactor simulations for different configurations revealed that random packings of catalyst extrudates must be placed in radial‐flow reactors to limit the pressure drop. Honeycomb monolith catalysts are attractive alternative geometries because they allow both better utilization of active material and the design of more compact reactors.

Evolution of dispersed drops during the mixing of mineral oil and water phases in a stirringtank

In this paper, a focused beam reflectance method is used to investigate the evolution of dispersed droplets at various dispersed volume fractions for an Exxsol D80 mineral oil–water dispersion in a stirring tank. Two types of inversion experiments are compared, the direct and continuous mixing of the oil–water phases. The number density of the chord lengths and distributions are identified as the main parameters for comparison. The drop coalescence is dominant slightly before inversion, at which point the measured mean square weighted (Sqr-wt) chord length increases significantly. The way of mixing will also influence the effect of drop coalescence and result in different inversion processes.

Direct observation of concentration profiles induced by drying of a 2D colloidal dispersion drop

We report experimental results on the drying of a colloidal dispersion drop in a circular thin cell. This confined geometry is well adapted to quantify concentration profiles inside the drop using fluorescence microscopy. Two stages have been identified in the drop evolution. In the first one the drop is shrinking such as if a pure drop, keeping axisymmetry. In the second one strong distortions occur and result in the appearance of a local depression at the drop surface. This process results in the spontaneous formation of a complex drop shape with both concave and convex interfaces. The influence of the interface concavity on the concentration profiles inside the drop and the drying kinetics are investigated. Particularly, concentration profiles are related to the nonuniform evaporation rate at the distorted drop surface.

Imaging internal flows in a drying sessile polymer dispersion drop using Spectral Radar Optical Coherence Tomography (SR-OCT)

In this work, we present the visualization of the internal flows in a drying sessile polymer dispersion drop on hydrophilic and hydrophobic surfaces with Spectral Radar Optical Coherence Tomography (SR-OCT). We have found that surface features such as the initial contact angle and pinning of the contact line, play a crucial role on the flow direction and final shape of the dried drop. Moreover, imaging through selection of vertical slices using optical coherence tomography offers a feasible alternative compared to imaging through selection of narrow horizontal slices using confocal microscopy for turbid, barely transparent fluids.

Geochemistry of zircons from ultrametapmorphic granitoids in junction zone of Aldan Shield and Dzhugdzhur-Stanovoi Fold Region

The geochemistry of zircons from autochthonous granite gneiss (Lc1) anatectic (Lc3–4) and injection (Lc5) leucosomes has been studied. Neoarchean prismatic zircon grains with cores that reveal oscillatory zoning and are overgrown by a couple of rims have been seen to occur in Lc3–4. The prismatic grains are occasionally modified into isometric grains with block structure by Paleoproterozoic secondary alteration, which is accompanied by the depletion in HREE, Y, Nb, U; enrichment in Ti, Li, LREE; increasing Th: U ratio and Ce anomaly; and decreasing Eu anomaly. The Paleoproterozoic alteration is related to the low-temperature amphibolite-facies metamorphism followed by partial melting. The Neoarchean prismatic zircons were formed under the conditions of high-temperature amphibolite-facies ultrametamorphism at a temperature of ∼700°C. Judging by the higher Ce/Ce* ratio, the metamorphic rounded zircons were formed at a higher oxygen fugacity as compared with ultrametamorphic zircons from Lc1 and Lc3–4. Specific variation trends of trace element concentrations in prismatic L1 and L3–4 zircons, occasionally with opposite directions, emphasize their different origin. The former are products of metasomatic granitization completed by selective melting with appearance of dispersed melt drops, while the latter are products of anatexis in the open system and by lit-par-lit migmatization. Prismatic zircons L5 are characterized by rhythmic zoning in the core surrounded by rims. The concordant U-Pb age of rims is 129 Ma; the 206Pb/238U age of cores varies from 2213 to 147 Ma. The appreciable enrichment (by a factor of 2–13) of zircons in all minor elements from the core to the rims is caused by the effect of residual postmagmatic fluid, which not only altered zircons, but also facilitated the recrystallization of granite into a pegmatoid variety.