Inorganic Dispersion Research Articles

Colloid‐Electrospinning: Fabrication of Multicompartment Nanofibers by the Electrospinning of Organic or/and Inorganic Dispersions and Emulsions

Solution-, melt-, and co-axial electrospinning are well-known methods for producing nano- and microfibers. The electrospinning of colloids (or colloid-electrospinning) is a new field that offers the possibility to elaborate multicompartment nanomaterials. However, the presence of colloids in the electrospinning feed further complicates theoretical predictions in a system that is dependent on chemical, physical, and process parameters. Herein, we give a summary of recent important results and discuss the perspectives of electrospinning of colloids for the synthesis and characterization of multicompartment fibers.

Nano-structured cathodes based on La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ for solid oxide fuel cells

Lanthanum-based iron- and cobalt-containing perovskite is a promising cathode material because of its electrocatalytic activity at a relatively low operating temperature in solid oxide fuel cells (SOFCs), i.e., 700–800 °C. To enhance the electrocatalytic reduction of oxidants on La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF), nanocrystalline LSCF materials are successfully fabricated using a complexing method with chelants and inorganic nano dispersants. When inorganic dispersants are added to the synthesis process, the surface area of the LSCF powder increases from 18 to 88 m 2 g −1, which results in higher electrocatalytic activity of the cathode. The performance of a unit cell of a SOFC with nanocrystalline LSCF powders synthesized with nano dispersants is increased by 60%, from 0.7 to 1.2 W cm −2.

Preparation of albumin–ferrite superparamagnetic nanoparticles using reverse micelles

AbstractBACKGROUND: Micellar systems are widely applied as reactors to encapsulate inorganic nanoparticles in polymeric materials. However, only low inorganic contents and microscale dimensions are often achieved.RESULTS: The adsorption of albumin protein on ferrite nanoparticles permits to increase the stability of inorganic dispersions in water by inhibiting particle flocculation. Subsequent glutaraldehyde addition induces protein crosslinking and ferrite entrapment. Polymer–ferrite composite nanoparticles were obtained in this way. The magnetic albumin nanoparticles (25 nm mean diameter) obtained contain about 40 wt% of ferrite and show superparamagnetic behaviour. The composite powder was successfully functionalized with a model drug and the biological activity was evaluated.CONCLUSION: Using a reverse micelle approach, ferrite–albumin composite nanoparticles with a high inorganic content were obtained. The method permits the formulation of biocompatible magnetic particles of nanoscale dimensions. The exhibited superparamagnetic behaviour permits to hypothesize an application of the powder composite as a carrier in biomedical technologies. Copyright © 2009 Society of Chemical Industry

Tunable ultraviolet emission of ZnO quantum dots in transparent poly(methyl methacrylate)

We report experimental results on tuning ultraviolet (UV) emissions of colloidal ZnO quantum dots (QDs) with uniform size in poly(methyl methacrylate) (PMMA) through controlling their dispersion. Instead of using organic ligands, exfoliated nanoplatelets were utilized as an inorganic dispersant to achieve controlled aggregate sizes of ZnO QDs in PMMA. The polymer nanocomposites are highly transparent in the visible range and readily exhibit blueshifted UV luminescence as the aggregate size of ZnO QDs reduces. The mechanisms responsible for the observed dispersion-dependent UV emissions are also described. The above approach presents an alternative way to design inorganic/organic hybrids with desired physical properties.

Preparation and property of porous hydroxyapatite as an inorganic dispersant used in suspension polymerization

The porous hydroxyapatite (HAP) for suspension polymerization dispersant was prepared using calcium carbonate and phosphoric acid as raw materials. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET nitrogen adsorption. The results show that the prepared HAP has a porous structure, low particle density, large specific surface area, uniform particle size and does not agglomerate easily between the particles. The preparation conditions for the HAP were optimized as follows: solid content of calcium carbonate aqueous suspension 90 g/L, concentration of phosphoric acid 1.0 mol/L, reaction/aging temperature 50°C, and aging time 3 h. The HAP prepared under optimal preparation conditions has 106.8 m2·g−1 of specific surface area, which is about 1.5–1.8 times asmuch as that of Japanese HAP or commercial HAP. Its application result in the suspension polymerization of styrene show that the porous HAP dispersant has high surface activity, excellent suspension dispersibility and stability and can markedly improve the quality of polystyrene beads.

Effects of modified poly(methacrylic acid) copolymer on rheological properties of ceramic suspension and sintered ceramic strength

AbstractModified waterborne poly(methacrylic acid) (MPBMA) with hydrophilic and hydrophobic groups is prepared by reacting maleic anhydride/polyglycol, α‐olefine benzenesulfone, and methyl methacrylate. Using MPBMA as a ceramic dispersant, the effects of the MPBMA concentration on the rheological behavior of a ceramic suspension and the ceramic breaking strength are studied, and the reasons and its dispersing mechanism are analyzed. The results show that MPBMA can improve the suspension's rheological properties and enhance the ceramic strength. The optimum copolymer concentration is 0.20 wt % at pH 9–10. When adding 0.20 wt % MPBMA, the suspension's absolute ζ potential increases from 23.7 to 64.2 mV, and its zero shear viscosity decreases from 714.3 to 73.4 mPa s. At the same time, its thixotropy area reaches the minimum, and the suspension exhibits Newton flow behavior and good dispersivity. Compared with inorganic dispersant, the ceramic with added MPBMA has higher breaking strength, which is increased from 160 to 352 MPa. Scanning electron microscopy photographs show that the flocculate of particles is disintegrated and the particles scatter mutually. They also show that no aggregation phenomenon appears in the ceramic with MPBMA added and the pores distribute uniformly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2661–2667, 2006

Shear flocculation of celestite with anionic surfactants and effects of some inorganic dispersants

Shear flocculation characteristics of celestite (SrSO 4) mineral have been investigated using sodium dodecyl sulfate (SDS) and Aero 845 as anionic surfactants. The celestite suspension could be flocculated by SDS and Aero 845 in the broad pH range. However, these surfactants were slightly more effective on the celestite suspension at a pH of 7. The shear flocculation of celestite with SDS and Aero 845 increased rapidly with increasing surfactant concentration. However, it decreased at SDS concentrations higher than 45 mg/dm 3, and eventually stabilization of the suspension took place at concentration values above approximately 80 mg/dm 3. From the experiments carried out to determine the effects of stirring speed and flocculation time on the shear flocculation of celestite suspension, it was found that a stirring speed of 500 rpm and a flocculation time of 3 min were required to achieve the maximum aggregation degree of celestite particles. The effects of sodium silicate, sodium phosphate and sodium polyphosphate used as inorganic dispersants on the shear flocculation of celestite were also studied. Sodium silicate strongly prevented the shear flocculation of celestite with SDS. However, the dispersive effect of sodium silicate was low in the presence of Aero 845. In the case of sodium polyphosphate, a dispersive effect on the celestite suspension was not observed for both surfactants. On the contrary, the shear flocculation power values increased slowly in the presence of sodium polyphosphate. In addition, the similar phenomenon also took place for sodium phosphate in the presence of SDS.

無機微粒子のポリマー修飾，分散および機能化

無機微粒子のポリマー修飾，分散および機能化

Performance Evaluation of Dispersants Through Streaming Potential Measurements

Stability of 5% (w/v) colloidal alumina suspension was examined in the presence of three organic dispersants; Dispex N‐40, Darvan C, and tribasic ammonium citrate (TAC), and three inorganic dispersants; sodium tri‐polyphosphate, sodium silicate, and Calgon (sodium hexameta phosphate). The performance and the required dosage for the maximum dispersibility were evaluated by streaming potential measurement. It was shown that there is a critical concentration of each dispersant indicated by the attainment of the highest streaming potential for maximum stability conditions of the suspension. Dispersion quality of the suspension in the presence of dispersant Darvan C was investigated in detail using the sedimentation technique. It was observed that the magnitude of the charge developed on a particle surface at the dosage indicated by the inflection point is the minimum dosage required for the maximum stability of the suspension.

Unifying model for associative thickener influences on waterborne coatings: II. Competitive adsorption of nonionic surfactants and HEUR thickeners on titanium dioxide pretreated with inorganic stabilizers and organic oligomeric dispersants

Size exclusion chromatography in tandem with UV absorbance of the surfactant is used to separate and quantify the amount of nonionic surfactant and model hydrophobically modified ethoxylated urethane (HEUR) thickeners adsorbed on different organic oligomeric polyacid, metal oxide-treated TiO2 surfaces. The isoelectric point imposed on TiO2 by the metal oxide surface treatment determines the amount of organic dispersant adsorbed. The size of the α-olefin on the maleic acid dispersant is also important in the adsorption of the dispersant. The size of the α-olefin on the organic acid dispersant, in turn, determines the amount of surfactant and HEUR thickener adsorbed. The surfactant, unlike the HEUR thickener, exhibits a dependence on the metal oxide treatment in neutral media, independent in several aspects of the amount of organic dispersant adsorbed. The adsorption dependence of HEUR thickeners and nonionic surfactant on the hydrophobe size of the HEUR is discussed.

Optimisation of performance of dispersants in aqueous plasma dissociated zircon suspension

Plasma dissociated zircon (PDZ) is a unique product obtained during in-flight dissociation of zircon sand in a plasma reactor. In PDZ, submicron zirconia crystallites are intimately mixed with glassy silica. This paper describes the selection and optimisation of dispersants in controlling stability of an aqueous suspension of PDZ. It has been observed that inorganic dispersants and organic additives give clearly distinct behaviour. In both cases, optimum dispersant dosages can be obtained from the streaming potential characteristics. It is shown that there is a critical concentration of each dispersants, which gives the highest streaming-potential/surface charge and hence optimum performance. Studies showed that the isoelectric point of PDZ particulate is at pH 2.8. Additions of dispersant increase the charge in magnitude and modified the surface to have more negative charge in the pH range 2.8–9.4. An assessment of particle/additive interactions, overall stability, and optimised chemical additive required to obtain homogeneous, well-stabilized suspension can be derived from the streaming potential characteristics.

Long-range attraction between surfaces: existence and amplitude?

The possible occurrence of a long-range attraction between hydrophobic surfaces is fundamental for understanding the kinetics of protein folding or self-assembling structures, such as biological membranes, the stability of emulsions and inorganic dispersions. Direct force measurements have revealed the presence in water of a long-range attraction between macroscopic and hydrophobic surfaces. Nevertheless, the existence of this so-called ‘hydrophobic force’ for smaller objects is still under discussion. For macroscopic surfaces, it appears that electrostatic contributions due to surface heterogeneities and gas effects and/or bubble bridging have to be taken into account, but do they define an intrinsic ‘hydrophobic force’? For charged colloidal particles, theoretical predictions of electrostatic attraction and a phase separation when the counterions are multivalent, are partially confirmed by experiments, and recent experimental evidences of an attraction in a confined geometry put an exciting challenge for theoreticians.

Aggregation and Dispersion of Colloidal Suspensions by Inorganic Surfactants: Effect of Chemical Speciation and Molecular Conformation

Polyphosphates are widely used as inorganic dispersants, but the mechanism of the dispersing is not well understood. In this study, the colloidal properties of fine alumina suspensions in water were studied at different pH conditions in the presence of linear chain polymetaphosphates. The chemical speciation and molecular conformation were probed using liquid and solid state 31P and 27Al nuclear magnetic resonance spectroscopy. Three regimes have been found: (i) Neutral pHlong-chain metaphosphates are partially anchored to the alumina surface. The negatively charged metaphosphate molecules extend from the particle surface to the solution to provide an effective electrosteric repulsion force that acts to disperse the colloidal particles. (ii) Low pHthe alumina particle surfaces hydrolyze and the dissolved species react with the surfactant to form amorphous aluminum phosphate gels. The reaction product causes bridging flocculation of the suspension. (iii) High pHpartial dissolution of alumina produces tetrahedrally bonded hydroxyaluminate anions, which induces the long-chain polymetaphosphates to dissociate into phosphate anions. Under these conditions, the metaphosphate no longer exhibits dispersion properties. A fundamental understanding of the particle−surfactant interactions in terms of adsorption, chemical reaction, and molecular conformation will provide insights for the rational design of more effective inorganic dispersants.

Adsorption studies of associative interactions between thickener and pigment particles

Adsorption of a HEUR thickener and a HMHEC thickener have been studied on two titanium dioxide pigment grades with and without dispersant previously adsorbed. One of the pigments had an acidic surface, mainly silica, and the other a more basic alumina/zirconia surface. Both associative thickeners adsorbed on pigments having a partially hydrophobic ( α-olefinic—maleic acid co-polymer) dispersant preadsorbed on the surface. No adsorption takes place when sodium hexametaphosphate, a highly charged low molecular weight inorganic dispersant, was used. The α-olefinic—maleic acid co-polymer dispersant is shown to adsorb on a negatively charged silica surface. This is assigned to hydrogen bonding between unionised carboxylic groups from the dispersant and oxide ions on the pigment surface.

Svedberg — Discoverer of the protein macromolecules

AbstractThe(odor) Svedberg* (1884‐1971), Uppsala University, was the first professor of physical chemistry in Sweden. He started his research in 1904 as a colloid chemist. He prepared inorganic dispersions by electrical discharge through organic liquids, measured particle size and size distribution of colloids by diffusion and sedimentation rates and invented the ultracentrifuge for convection‐free sedimentation of colloidal particles. In 1924 Svedberg applied the ultracentrifuge for studies of haemoglobin in aqueous solution. Unexpectedly he found that the protein was not a gel of associated small molecules. It sedimented as macromolecules of uniform mass (68 000 dalton), i.e. is monodisperse.In subsequent work Svedberg found that other proteins like ovalbumin (from egg white) and haemocyanins from snails and other invertebrates also are monodisperse or contain a few uniform macromolecular components. After extensive studies of soluble protein molecules from a large number of animals and plants, Svedberg classified the species and could trace the relations for the species from the molecular mass of their protein macromolecules.Studies of soluble polysaccharides from bulbs also showed well defined macromolecules of masses that could be related to the various botanical species. Other native substances like cellulose, other wood polysaccharides and starch were found to be of high molecular mass but polydisperse.Svedberg's research in the 1920's and 1930's gave strong experimental support for Staudinger's macromolecular concept although Svedberg, at the time of his own important discoveries, was not influenced by Staudinger. Svedberg's discovery of the protein macromolecules and their uniform molecular mass initiated the macromolecular research in biochemistry.

Influence of polarity of polymer on inorganic particle dispersion in dielectric particle/polymer composite systems

AbstractThe influence of the polarity of polymers on the degree of dispersion of BaTiO3 particles in BaTiO3/polymer composite systems was investigated. The BaTiO3 polymer composite systems were prepared from BaTiO3 particles and low‐density polyethylene (LDPE) or ethylene vinyl acetate copolymer (EVA) with 7 and 15 wt % vinyl acetate. Scanning electron microscopy observation showed that BaTiO3 particles aggregated in the polymer matrices and dispersed more readily into the EVA matrix than into LDPE. The shift of the β‐peak temperature by ca. +5°C in the temperature dispersion of the loss modulus was observed for EVA–BaTiO3 composite systems in dynamic mechanical property measurement. On the other hand, the β‐peak temperature of the polymers filled with graphite particles, which have hydrophobic surfaces, was almost constant in a volume fraction region of 0–0.3. The ellipsoidal axes' ratios given by comparison of experimental dielectric constant values and theoretical ones using the Maxwell equation were 4.2, 3.6, and 3.1 for LDPE/BaTiO3, EVA(7%)/BaTiO3, and EVA(15%)/BaTiO3 composite systems, respectively. The axes' ratio decreased by the introduction of polar vinyl acetate groups into nonpolar LDPE. The results confirmed that the polarity of the polymers was one of the key factors governing the dispersibility of BaTiO3 particles in the polymer matrix. © 1995 John Wiley & Sons, Inc.

Pyrite depression during coal flotation Part I — Inorganic ions

This investigation is an exploratory study to evaluate a large number of potential pyrite depressants for use during coal flotation. Subsequently, the more promising reagents can be evaluated in detail. Several reagent categories (such as alkalis, lime, oxidizing agents, reducing agents, specific inorganic ions and dispersants) that were found to be effective pyrite depressants are discussed here. Other pyrite depressants will be discussed in Parts II and III.

Characterization Of The Binding of Inorganic Polymers To Oxide Surfaces By NMR and NMR/MAS Spectroscopy

ABSTRACTSolution and solid state Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectroscopy have been used to monitor the 31P signal of cyclic phosphazenes and associated linear polymers in solution and of these materials bound to alumina in stabilized dispersions. The differences between the simple solution experiments and the suspensions are being studied to determine the viability of NMR techniques to probe the chemical interactions between inorganic polymer dispersants and alumina particles. It has been observed in colloidal suspensions that the adsorption of phosphazenes onto an aluminum oxide surface causes a broadening of the 31P signal in solution NMR. This broadening is dependant on the amount of solid to polymer concentration, the amount of solids loading, the solvent polarity and the phosphazene substituent under investigation [1]. Conversely, the solid MAS experiments show a narrowing of the 31P signal upon adsorption of the phosphazene to alumina.

Converting to water-soluble organic varnishes makes environmental, economic, and processing sense

Types of water-based varnishes and their properties are described. They include inorganic solutions, inorganic dispersions, organic emulsions, organic dispersions, and organic solutions. The performance of these varnishes is examined. The three major types of organic water-soluble resins used as electrical insulating varnishes, namely alkyds, polyesters, and epoxies, are discussed, and guidelines for their use are given. It is shown that of all the water-based varnished available, water-soluble organic varnishes offer the best processing properties and lasting insulating value needed for the manufacture of electrical products. Inorganic solutions and dispersions, as well as organic emulsions and dispersions, all have drawbacks that preclude such use.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Chapter 14. Inorganic dispersion technology

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