Variation of surface unevenness of anomalous composite polymer particles produced by the stepwise heterocoagulation of small particles onto large particle by heat treatment

Variation of surface unevenness of anomalous composite polymer particles produced by the stepwise heterocoagulation, which we had suggested in previous articles, of small cationic polymer particles onto large anionic polymer particle (LP) by heat treatment was examined with transmission and scanning electron microscopes. When the anomalous polymer emulsion was kept at higher temperature than the glass transition temperature ofLP, the particle surfaces were continuously changed from uneven to smooth state with the treatment time.Part CXLII of the series of Studies on Suspension and Emulsion     

Influence of surfactant on gas bubble stability

Gas-bubble stability is achieved either by a reduction in the Laplace pressure or by a reduction in the permeability of the gas-liquid interface. Although insoluble surfactants have been shown definitively in many studies to lower the permeability of the gas-liquid interface and hence increase the resistance to interfacial mass transfer, remarkably little work has been done on the effects of soluble surfactants. An experimental system was developed to measure the effect of the soluble surfactant dodecyl trimethylammonium bromide on the desorption and absorption of carbon dioxide gas through a quiescent planar interface. The desorption experiments conformed to the model of non-steady-state molecular diffusion. The absorption experiments, however, produced an unexpected mass transfer mechanism, with surface renewal, probably because of instability in the density gradient formed by the carbon dioxide. In general, the soluble surfactant produced no measurable reduction in the rate of interfacial mass transfer for desorption or absorption. This finding is consistent with the conclusion of Caskey and Barlage that soluble surfactants produce a significantly lower resistance to interfacial mass transfer than do insoluble surfactants. The dynamic adsorption and desorption of the surfactant molecules at the gas-liquid interface creates short-term vacancies, which presumably permit the unrestricted transfer of the gas molecules through the interface. This surfactant exchange does not occur for insoluble surfactants. Gas bubbles formed in the presence of a high concentration of soluble surfactant were observed to dissolve completely, while those formed in the presence of the insoluble surfactant stearic acid did not dissolve easily, and persisted for very long periods. The interfacial concentration of stearic acid rises during bubble dissolution, as it is insoluble, and must eventually achieve full monolayer coverage and a state of compression, lowering the permeability of the interface. Thus, insoluble surfactants or hydrophobic impurities from solid surfaces may account for increased bubble stability.     

Influence of the ionic strength in the heterocoagulation process between bare and surfactant-coated latexes

A novel and useful process of heterocoagulation between bare and surfactant-coated latexes is studied. Basically, this process consists of the heterocoagulation of two identical latexes, i.e. of the same size and with charges of the same sign, but distinguished by the degree of coverage by a nonionic surfactant (Triton X-100). The different critical coagulation concentrations (ccc) of this type of sample permitted us to analyze the influence of the ionic strength in the heterocoagulation process between both colloidal samples. Different ratios (2:1, 1:1 and 1:2) of the bare and surfactant-coated latexes were used during the experiments. In all cases, the heterocoagulation rate constants were lower than the homocoagulation rate constant in diffusion conditions; however, for an ionic strength higher than the ccc of both systems, similar values were found for the rate constants. Received: 18 January 1999 Accepted in revised form: 14 April 1999     

Holographic generation of bubble gratings at liquid—glass interfaces and the dynamics of bubbles on surfaces

Intense diffraction from a periodic array of microscopic bubbles is reported. The bubbles are generated by 100 ps, 1.06 μm pulses from a Nd:YAG laser which are crossed at a liquid—dielectric interface. The time dependence of the diffraction yields information on surface bubble expansion, contraction, and migration. The mechanism for the production of the bubble gratings is described.     

Raspberry-like polymer/silica core-corona composite by self-assemble heterocoagulation based on a hydrogen-bonding interaction

Raspberry-like poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine)/silica (poly(EGDMA-co-VPy)/SiO₂) core-corona composite was prepared by a self-assemble heterocoagulation based on a hydrogen-bonding interaction between the pyridyl group of poly(EGDMA-co-VPy) core and the active hydroxyl group of silica corona. The raspberry-like composite was stable near the neutral environment with pH ranging from 5.0 to 8.0. The effects of the solvent and the mass ratio of silica to polymer microsphere on the coverage of the silica corona on poly(EGDMA-co-VPy) core were investigated in detail. The resultant core-corona heterocoagulates were characterized with scanning electron microscope and the nature of the interaction between the polymer core particle and silica corona particle was identified as hydrogen bonding with Fourier Transform Infrared spectroscopy.     

Solid particle in the boundary layer of a rising bubble

The hydrodynamic interaction of a solid particle and the boundary layer around a rising bubble is analyzed in the before-contact state (BCS) of a flotation act. The lagging of the particle behind the basic outer flow is accounted for. The forces acting on the particle are qualitatively examined. A new term is introduced in the force balance — the migration force. An expression for the collision efficiency is proposed that concerns a particle already entrained in the bubbles boundary layer.     

Ensemble modeling of very small ZnO nanoparticles

The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface.     

Dynamic aspects of small bubble and hydrophilic solid encounters

The capture of solid particles suspended in aqueous solution by rising gas bubbles involves hydrodynamic and physicochemical processes that are central to colloid science. Of the collision, attachment and aggregate stability aspects to the bubble-particle interaction, the crucial attachment process is least understood. This is especially true of hydrophilic solids. We review the current literature regarding each component of the bubble-particle attachment process, from the free-rise of a small, clean single bubble, to the collision, film drainage and interactions which dominate the attachment rate. There is a particular focus on recent studies which employ single, very small bubbles as analysis probes, enabling the dynamic bubble-hydrophilic particle interaction to be investigated, avoiding complications which arise from fluid inertia, deformation of the liquid-vapour interface and the possibility of surfactant contamination.     

Influence of particle hydrophobicity on particle-assisted wetting

The surface properties of silica particles significantly influence their efficiency in particle-assisted wetting. A series of small particles of controlled surface hydrophobicity was mixed with a nonvolatile oil. These mixtures were applied onto a water surface; the structures formed were subsequently solidified by photopolymerization and observed using scanning electron microscopy. For the most hydrophilic particles, only lenses of pure oil formed, with the particles being submerged into the aqueous phase. The most hydrophobic particles help to form patches of stable homogeneous mixed layers composed of oil and particles. In these cases the particles adhere to the air-oil as well as to the oil-water interfaces. For particles with intermediate hydrophobicity, lenses and patches of mixed layers were observed. These three different observations verify that the hydrophobicity of the particle surface determines the wetting behavior of the oil at the water surface.     

Force of a gas bubble on a foreign particle in front of a freezing interface

We monitored the formation and development of a single gas bubble on the surface of a spherical particle of size 1.676 mm under unidirectional freezing and thawing (4.6-5.0 microm/s) and for the first time quantitatively estimated the force exerted on this particle by measuring the deformation of an attached elastic stick. The bubble would nucleate and grow on the particle surface closest to the ice front, while the force curve for a freezing-thawing cycle presented a hysteresis characteristic. This force was much greater than in the case without a bubble, and hence it dominated the engulfment process in the present freezing tests. The bubble force increased with increasing bubble size and was shown to be mainly attributable to the elastic force by the deformed bubble shape. Comments were made on the need to incorporate the role of bubbles in predicting the critical velocity to freeze a suspension with high dissolved gas content.     

Effect of surface mobility on the particle sliding along a bubble or a solid sphere

The sliding velocity of glass beads on a spherical surface, made either of an air bubble or of a glass sphere held stationary, is measured to investigate the effect of surface mobility on the particle sliding velocity. The sliding process is recorded with a digital camera and analyzed frame by frame. The sliding glass bead was found to accelerate with increasing angular position on the collector's surface. It reaches a maximum velocity at an angular position of about 100 degrees and then, under certain conditions, the glass bead leaves the surface of the collector. The sliding velocity of the glass bead depends strongly on the surface mobility of a bubble, decreasing with decreasing surface mobility. By a mobile surface we mean one which cannot set up resistive forces to an applied stress on the surface. The sliding velocity on a rigid surface, such as a glass sphere, is much lower than that on a mobile bubble surface. The sliding velocity can be described through a modified Stokes equation. A numerical factor in the modified Stokes equation is determined by fitting the experimental data and is found to increase with decreasing surface mobility. Hydrophobic glass beads sliding on a hydrophobic glass sphere were found to stick at the point of impact without sliding if the initial angular position of the impact is less than some specific angle, which is defined as the critical sticking angle. The sticking of the glass beads can be attributed to the capillary contracting force created by the formation of a cavity due to spontaneous receding of the nonwetting liquid from the contact zone. The relationship between the critical sticking angle and the particle size is established based on the Yushchenko [J. Colloid Interface Sci. 96 (1983) 307] analysis.     

Recovery of thorium-Arsenazo III complex from very dilute solutions by a bubble extraction apparatus

Summary A procedure is proposed for the removal and determination of Arsenazo III complexes from very dilute solutions by ion-pairing with a cationic surfactant. The method is discussed with reference to the system Th-Arsenazo III-tetradecyldimethylbenzylammonium chloride by analyzing the influence of critical parameters such as ionic strength and collector concentration. When applied to natural waters with moderate ionic strength (0.15 mol/l) the procedure allows a fast and quantitative determination of 1–20 g Th from sample volumes as large as 12 l with preconcentration factors reaching up to about 1000.     

Micro air bubble manipulation by electrowetting on dielectric (EWOD): transporting, splitting, merging and eliminating of bubbles

This paper describes various manipulations of micro air bubbles using electrowetting on dielectric (EWOD): transporting, splitting, merging and eliminating. First, in order to understand the response of bubbles to EWOD, the contact angle modulation is measured in a capped air bubble and confirmed to be in good agreement with the Lippmann-Young equation until saturation. Based on the contact angle measurement, testing devices for the bubble manipulations are designed and fabricated. Sequential activations of patterned electrodes generate continuous bubble transportations. Bubble splitting is successfully realized by activating a single electrode positioned in the middle of bubble base. However, it is found that there are criteria that make splitting possible only in certain conditions. For successful splitting, smaller channel gap, larger bubble size, wider splitting electrode and/or larger contact angle changes by EWOD are preferred. These criteria are verified by a series of experiments as well as a static analysis. Bubble merging is achieved by moving bubbles towards each other in two different channel configurations: (1) channel I, where bubbles are in contact with the bottom channel plate only, and (2) channel II, where bubbles in contact with the top as well as bottom channel plates. Furthermore, eliminating a bubble to the ambient air is accomplished. All the bubble manipulation techniques may provide a versatile integrated platform not only to manipulate micro objects by utilizing micro bubbles as micro carriers, but also to enable a discrete bubble-based gas analysis system.     

浆态床反应器中相含率及粒径分布的研究

以空气－水－石英砂体系为对象，研究了费托合成浆态床反应器中表观气速、平均淤浆浓度、床层轴向位置等因素对气含率、固体浓度轴向分布和粒径分布的影响，并通过实验得出了气含率与操作变量之间的关联式。     

Effective spring description of a bubble or a droplet interacting with a particle

It is shown that the interaction of a particle with a liquid drop or a gas bubble may be quantitatively described over the whole distance regime by treating the fluid interface as a Hookean spring. An algorithm suitable for analyzing atomic force microscopy data suitable for a calculator or a spread-sheet is given and applied to data for oil drops.     

Adsorption and heterocoagulation of nonionic surfactants and latex particles on cement hydrates

The adsorption of nonionic surfactants of the alkyl-phenol-poly(ethylene oxide) family and of acrylic latex particles on several anhydrous (but hydrating) or fully hydrated mineral phases of Portland cement was studied. No or negligible adsorption of the surfactant was observed. This was assigned to the ionized character of the surface silanol groups in calcium-silicate-hydrates and to the strongly ionic character of the OH groups in calcium hydroxide and in the calcium-sulfoaluminate-hydrates, which prevents the formation of surface-ethoxy hydrogen bonds. In contrast, provided they are properly stabilized by the surfactant, the latex particles form a loose monolayer on the surface of hydrating tricalcium silicate particles. The attractive interaction between the positive mineral surface and the negative latex surface appears to be the driving force for adsorption. In line with this, adsorption is reduced by sulfate anions, which adsorb specifically onto the silicate surface. Compared to tricalcium silicate, portlandite and gypsum interact only marginally with the latex particles. Our results show that the stability of the nonionic surfactant/latex/cement systems is essentially controlled by the latex colloidal stability and the latex-cement interactions, the surfactant having little direct interaction, if any, with the mineral surfaces.     

Influence of interaction between poly(methyl methacrylate) and clay on the properties of nanocomposites prepared by a heterocoagulation method

To have a better insight into the effect of interaction between polymer matrix and clay on the properties of nanocomposite, poly(methyl methacrylate)/clay nanocomposites were prepared by a heterocoagulation method. Using a reactive cationic emulsifier, methacryloyloxyethyltrimethyl ammonium chloride (METAC), a strong polymer–clay interaction was obtained with the advantage of keeping a consistent polymer matrix property. X‐ray diffraction and transmission electronic microscopy indicated an exfoliated structure in nanocomposites. The glass transition temperature (T_g) of the nanocomposites was measured by DSC and DMA. The DMA results showed that with a strong interaction, PMMA–METAC nanocomposite showed a 20 °C enhancement in glass transition temperature (T_g), whereas a slight increase in T_g was observed for PMMA–cetyl trimethylammonium bromide (CTAB)/clay nanocomposite with a weak interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 733–738, 2010     

Technique for the performance of preliminary tests on a small particle

Summary Simple apparatus is described for the efficient performance of heating and solubility tests with a small particle.

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Zusammenfassung Ein einfaches Röhrchen eignet sich für die Ausführung von Erhitzungs- und Löslichkeitsproben mit einem sehr kleinen Körnchen des Untersuchungs-materials.

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Résumé On décrit un appareil simple pour la réalisation effective des essais de chauffage et de solubilité sur de petits échantillons.