Improved Dispersion Stability Research Articles

ChemInform Abstract: Polymer‐Coated Magnetic Carbonyl Iron Microparticles and Their Magnetorheological Characteristics

AbstractReview: 49 refs.

Improved Dispersion Stability of Surface-fluorinated TiO2 Particles

Abstract Fluorinated TiO2 (F-TiO2) particles with good dispersion stability were synthesized at a temperature lower than 100 °C using fluorine gas. The average particle sizes and ζ potentials of F-TiO2 particles were around seven times smaller and 1.4 times larger, respectively, than those (2200 nm and −19.35 mV) of untreated TiO2 particles in water. However, the existence of TiOF2 prepared at a temperature higher than 100 °C might negatively affect the dispersion stability of TiO2. To prepare the fluorinated TiO2 without TiOF2, it is essential for optimizing the beneficial effects of surface fluorination against the dispersion stability of TiO2.

Fabrication and Ink-Jet Patterning of Copper Nanoparticles with Improved Dispersion Stability

Copper (Cu) nanoparticles as the metal nanoparticles in the conductive ink were synthesized using electrochemical reaction. This method is characterized as the synthesis process without any metal salts and the post-treatment of washing and drying. It means that it does not need to consider about oxidized and agglomerated metal nanoparticles during the extra treatments. The Cu nanoparticles were synthesized in the various conditions of electrolyte to investigate the mechanism of the synthesis reaction of Cu nanoparticles. And also, the synthesized Cu nanoparticles were controlled the dispersion stability with the addition of dispersion agent such as PVP and Dextran. Finally, it was achieved the ink-jet printed Cu patterns using the synthesized Cu nanoparticles, and examined the morphology of the patterns.

Surface Modification of Carbon Nanotube by Poly(ethylene glycol) for the Preparation of Poly(vinyl alcohol) Nanocomposite

Herein, PEGylated multi-walled carbon nanotube (MWNT) was prepared for the successive fabrication of poly(vinyl alcohol) PVA/MWNT nanocomposite film by solution casting. The surface modified MWNT showed a good colloidal stability in a polar solvent, i.e., water. Also, the PEGylated MWNT had an improved dispersion stability in aqueous PVA solution. The mixture of PEGylated MWNT and PVA dissolved in water was film casted and the dispersion uniformity and corresponding improvement of electrical conductivity were investigated. The electrical conductivity of PVA/modified MWNT composite film was three-fold higher than that of PVA/pristine MWNT composite film due to the much improved distribution uniformity of modified MWNT in PVA matrix.

Polymer-coated magnetic carbonyl iron microparticles and their magnetorheological characteristics

We review core/shell structured magnetic carbonyl iron (CI)/polymer hybrid particles fabricated with various polymeric systems and their magnetorheological (MR) characteristics when dispersed in non-magnetic suspending medium. Their morphology and magnetization properties are compared with those from different fabrication methodologies. Rheological characteristics of the MR fluids, exhibiting improved dispersion stability compared to the pure CI based MR fluid, are presented along with their potential engineering applications.

Miniemulsion polymerization of styrene in the presence of graphite nanosheets

Miniemulsion polymerization of styrene was performed in the presence of carbon nanosheets. As a result, PS particles were introduced onto the surface of graphite nanosheets by the miniemulsion polymerization. The formation of SDS surface micelles is influenced by the concentration of graphite nanosheets. Therefore, the composites show three different surface morphologies of graphite nanosheets surfaces; (1) the surface attached with PS particles, (2) the surface covered with PS thin film, and (3) the bare exposed surface. The crosslinked PS particles strongly stick to the surface of graphite nanosheets and the graphite nanosheet/ crosslinked PS composites show much improved dispersion stability in toluene.

The simple and facile methods to improve dispersion stability of nanoparticles: Different chain length alkylcarboxylate mixtures

The dispersion stability of the Ag nanoparticles with a mixed surfactant of alkylcarboxylates was quantitatively examined, compared with those of the Ag nanoparticles with a single molecule surfactant of alkylcarboxylates. The nanoparticles with a mixed surfactants have far-improved dispersion stability compared with those with normal alkylcarboxylates. The surface roughness of the surfactant layer might be responsible for the improved dispersion stability through the enhanced solvent–surfactant interaction and the decrease in inter-particle surfactant interactions.

Magnetorheological carbonyl iron particles doubly wrapped with polymer and carbon nanotube

To improve magnetorheological (MR) characteristics of carbonyl iron (CI) microparticles, we introduce two-step CI coating procedures with poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotube (MWNT) for the first time. Core(CI)-shell(PMMA) (CI-PM) structured composite magnetic microbeads were synthesized by dispersion polymerization first, showing improved dispersion stability and sedimentation quality. However, its magnetic strength was decreased compared with that of pristine CI-based MR fluid. To enhance its magnetic strength, the core-shell type CI-PM particles were wrapped with MWNT via ultrasonication. Rheological properties of their MR fluid were measured by a rotational rheometer with a magnetic field supplier. The CI-PMMA-MWNT (CI-PM-NT) particles were found to show better flow and dynamic rheological properties compared to those from CI-PM particles while density of the CI-PM-NT particles was not much different from that of CI-PM, implying that sedimentation stability of the CI-PM-NT particles was also being kept.

Chemical modification of carbon black by a simple non-liquid-phase approach

Chemical modification is the most popular and efficacious approach to improve dispersion stability for commercial carbon blacks in organic media. Even though this method has been used successfully in liquid systems, there have been few reports of chemical modification of carbon black in non-liquid-phase systems. In the present work, a simple non-liquid-phase approach to preparing modified carbon black with high dispersibility and stability in polar organic media from an industrial carbon black, N220, is reported. The treatment was carried out in a rheology mixer by blending carbon black with a low-molecular-weight organic compound, 3,9-bis-{1,1-dimethyl-2[ β-(3- tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80), under proper conditions. The modified carbon black had a smaller particle size than the original carbon black, as proven by dynamic light scattering and transmission electron microscopy, and it could be dispersed facilely in acetone to form a stable suspension. Time-of-flight secondary ion mass spectroscopy was used to detect the chemical presence of AO-80 fragments on the surface of the modified carbon black and consequently the modification mechanism.

Improvement of dispersion stability and characterization of upconversion nanophosphors covalently modified with PEG as a fluorescence bioimaging probe.

Upconverting (UC) phosphors (UCPs) are ceramic materials doped with rare earth ions. These materials can absorb and upconvert infrared (IR) radiation to emit visible light by the stepwise excitation among discrete energy levels of the rare earth ions. UCPs are potentially useful reagents for use in bioimaging since the use of low energy photons avoids photo-toxicity. The use of UCP nanoparticles as bioimaging probes requires surface modifications in an effort to improve dispersion stability in aqueous milieu. In this study, we covalently attached poly(ethylene glycol) (PEG) to the surface of Er-doped Y2O3 nanoparticles and firstly demonstrated that PEG covalently bound to the Y2O3 surface markedly improved dispersion stability in water. UC emission of PEG-modified Er–Y2O3 nanoparticles excited with IR light was successfully observed. We also showed that PEG-modified Er–Y2O3 nanoparticles exhibit no cell-toxicity. These observations lend strong support to the potential use of PEG-modified UCP nanoparticles as bioimaging tools.

Tuning solution polymer properties by binary -solvent mixtures.

The solubility of polymers can be significantly altered by the use of solvent mixtures. The solvent composition also effects the self-assembly properties of amphiphilic copolymers. In addition, water-ethanol mixtures are known to exhibit abnormal physicochemical properties due to the presence of hydration shells around the ethanol molecules, while at the same time both solvents have very low toxicity. However, the solution properties of amphiphilic copolymers in water-ethanol mixtures have been scarcely studied. Here we show that the solution polymer properties of amphiphilic copoly(2-oxazoline)s can be significantly altered in binary water-ethanol mixtures resulting in increased solubility, tuneable lower critical solution temperatures as well as polymer-solvent combinations with both a LCST followed by an UCST and improved dispersion stability. Surprisingly, it was found that polymers insoluble in both ethanol and water could be dissolved in water-ethanol mixtures, opening the way to novel formulations for drug delivery or personal care applications. Our results represent a straightforward method for tuning solution polymer properties without the synthetic efforts that are generally required to change the copolymer composition and properties.

Effect of Surfactant on Preparation of Poly(4-Vinylphenol)/Titanium Dioxide Composite for a Gate Insulator of Organic Thin Film Transistors

Composite materials of poly(4-vinylphenol) (PVP) and titanium dioxide (TiO2) nanoparticles were fabricated via a spin coating process in order to enhance dielectric properties for a gate insulator application of the OTFT in this study. In order to improve dispersion stability of the TiO2 nanoparticles in the polymeric solution during the process, a surfactant was also adopted onto the solution mixture. The dispersion property was observed by measuring sedimentation time of TiO2 particles in the polymeric solution, and the effect of surfactant on the surface morphology of the dielectric layer was further analyzed by using atomic force microscopy. Dielectric properties of the PVP-TiO2 composite and performance of OTFTs with the PVP-TiO2 composite insulator are presented, along with their effects on device performance with pentacene layer as a semiconductor.

Synthesis of polystyrene brush on multiwalled carbon nanotubes treated with KMnO4 in the presence of a phase‐transfer catalyst

AbstractMultiwalled carbon nanotubes (MWNTs) were effectively functionalized with KMnO4 in the presence of a phase‐transfer catalyst at room temperature. The hydroxyl functionalized MWNTs were reacted with a vinyl‐group carrying silane‐coupling agent and the terminal vinyl groups were used to fabricate polystyrene (PS) brushes by solution polymerization. Finally, PS‐encapsulated MWNTs were obtained. The synthesis results were verified from FT‐Raman, thermal gravimetric analysis, energy dispersive X‐ray analysis, and transmission electron microscope. PS‐encapsulated MWNTs had much improved dispersion stability in hydrophobic medium, toluene since grafted hydrophobic PS interacts with media and has improved compatibility. This functionalization technique would provide a facile route to prepare various polymer brushes on the surface of MWNTs to improve the dispersion of MWNTs for potential applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4413–4420, 2007

Characterization of Sub-Micron Perovskite Suspensions Formed Through Cavitation Processing

The size distribution within and electrokinetic properties of aqueous perovskite (LaCoO3) suspensions, have been characterized as a function of processing conditions. Submicron–sized perovskite particles have been obtained using a cavitation technique in which the suspension is passed through a series of small orifices under extreme driving pressure drops. When no additives were used, the zeta potential of the particles was found to be positive over the entire pH range studied. Use of an acrylic copolymer surfactant with multiple negatively charged sites during the cavitation processing was found to improve dispersion stability. The observed variations in zeta potential and particle size for the suspensions are explained in terms of electrostatic interactions between particles, the tendency for the surfactant to adsorb onto the particles, and the degree of steric stabilization provided by the surfactant.

Magnetorheological characteristics of nanoparticle-added carbonyl iron system

Magnetorheological (MR) fluid, suspension of magnetic carbonyl iron (CI) and magnetic additives in mineral oil, were prepared. The novel core–shell structured additives, comprising monodisperse polystyrene (PS) spheres as cores and magnetite as shells, were fabricated by surfactant-free emulsion polymerization. This MR fluid with bimodal particles was suspended in mineral oil and their MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. MR properties of the bimodal MR fluid with magnetic additive exhibit similar magnetic and MR properties compared to MR fluid consisting of pristine CI, but with much improved dispersion stability.

Covalent attachment of poly(ethylene glycol) on multi-walled carbon nanotubes

A new 'graft-onto' method to attach poly(ethylene glycol) (PEG) onto multi-walled carbon nanotubes (MWNTs) has been developed. The method is based on the coupling reaction of radicals formed at the chain end of PEG onto the surface of MWNTs. The polymeric radicals are generated by atom (halogen) transfer reaction between chloroacetyl-terminated PEG and transition metal catalysts. The method allows direct covalent attachment of PEG to pristine MWNTs without pretreatment that could alter their original structure. The resulting PEG-grafted MWNTs showed improved dispersion stability in isopropanol and methanol.

Preparation of highly monodisperse poly(methyl methacrylate) particles incorporating fluorescent rhodamine 6G for colloidal crystals

Soap-free emulsion polymerization was extended to preparation of monodisperse poly(methyl methacrylate) (PMMA) particles incorporating rhodamine 6G (R6G) fluorescent molecules. The polymerization was conducted in the presence of an anionic monomer, p-styrenesulfonate (NaSS), which improved dispersion stability of the polymer particles. NaSS concentrations was ranged up to 2 mol/m3 H2O in the polymerization at 0.5 kmol/m3 H2O methyl methacrylate (MMA) monomer and 5 mol/m3 H2O potassium persulfate (KPS) initiator for R6G concentrations from 0.1 to 10 mol/m3-polymer. At R6G concentrations lower than 1.0 mol/m3-polymer, PMMA particles were highly monodisperse and incorporated most R6G molecules. The average sizes of PMMA particles were in a rage of 160–300 nm, and decreased with the concentration of NaSS. The high monodispersity of the particles enabled the fabrication of colloidal crystals of the particles with a vertical deposition method.

Calcium coagulation properties of hydrothermally processed soymilk

AbstractThe effects of hydrothermal cooking (HTC), a steam‐injection process otherwise known as jet cooking, on the calcium salt coagulation properties of soymilk were determined. Full‐fat soymilk was processed at five different conditions (traditional kettle cooking at 100°C for 5 min, HTC at 100°C for 20 s, HTC at 134°C for 26 s, HTC at 154°C for 31 s, and HTC at 162°C for 35 s) and coagulated at four calcium chloride concentrations (0.05, 0.10, 0.20, and 0.30%). Tofu yields and recoveries of dry matter and protein in the coagulated curd followed similar trends with increasing calcium chloride concentration, namely, an initial increase rising to a peak followed by a decrease. HTC‐processed soymilks, especially those processed at high temperature (162°C), gave lower tofu yields and lower recoveries of dry matter and protein in tofu. HTC‐processed soymilks, especially those processed at 134°C or higher, resulted in very soft, fragile, and adhesive tofu. The high calcium salt tolerance of HTC‐processed soymilk might be used to improve dispersion stability of calcium‐fortified soy‐based dairy analogs.

Preparation of carbon black dispersion with enhanced stability by aqueous copolymerization of a polymerizable surfactant

Radical copolymerization of the polymerizable surfactant, 1-nonylphenyloxy-2-deca(oxyethylene)-3-allyloxypropane ammonium sulfate (SE-10N) and acrylonitrile (AN) with potassium persulfate (KPS) in the presence of carbon black (CB) in water was investigated for the purpose of improving dispersion stability of aqueous carbon black dispersion. The aqueous dispersion with a high dispersion stability was obtained by the copolymerization at molar ratios of AN:SE-10N>5 in the feed. The dispersion stability was dependent on the conversion of SE-10N which could be related to the amount of SE-10N immobilized onto CB particles.

ＳＡＰとミクロフィブリル状セルロースの複合構造体に関する研究 （第２報） 水と有機溶媒との混合溶媒系に於けるＭＦＣおよびＢＣの分散安定性に関する研究

By uniformly dispersing microfibrillated cellulose (the “MFC”) or bacterial cellulose (the “BC”) in a solvent mixture of water and hydrophilic organic solvent, a dispersion system of low concentration and high viscosity can be obtained. If super absorbent polymer particles (the “SAP”) are dispersed in this system, the SAP can be dispersed stably at a high concentration by virtue of such viscosity effect. The authors have found that, by forming a sheet from such a dispersion slurry and removing the solvent component therefrom, a SAP/MFC composite or a SAP/BC composite can be obtained efficiently where the MFC or the BC acts as the bonding agent. The MFC or the BC retains water stably in its microfibril structure when it is dispersed in water. That is to say, the MFC or the BC exhibits a similar behavior as it is in a so-called hydrating condition. Their hydrating condition, however, may vary very much depending on the kinds or amounts of organic solvents added. This report summarizes the results of the dispersing concentrations of the MFC or the BC with respect to the dispersion stability of the MFC or the BC in the solvent systems of water and organic solvents. The conclusions obtained are as follows : (1) Both of the S-MFC and the BC can be dispersed stably in organic solvents and water mixture systems where the SAP does not swell or coagulate. As an indication of the dispersion stability, the volumes of phase separation were measured.(2) Three kinds of fine fibers in the form of microfibrillated fibers (the “MF”), namely, the S-MFC, diluted BC and refined BC, were compared in terms of the dispersion stability, and found in the order of refined BC, the BC and the S-MFC. Thus, it was found that different dispersion stabilities were given different of the MF. This was probably because of different hydration capabilities, that is to say, different viscosities or amounts of water retained when they are dispersed in water.(3) The MF shows a very high dependence of dispersion stability on its concentration in water dispersion systems or in organic solvents/water mixture systems.(4) The dispersion stabilities of solvent systems were investigated when the ratios of organic solvent to water varied. It was consequently found that there existed a critical stability concentration value (Y value), beyond which the dispersion was stable. The Y value differs with the kinds of the MF. Specifically, the Y value of the S-MFC was around 0.3%, that of the BC was around 0.25%, and the value of refined BC was around 0.05%(5) As it was considered that increasing dispersion stability by the addition of an organic solvent was because of the viscosity of the system, changes in viscosity with three kinds of the MF, namely, the S-MFC, the BC and the refined BC, dispersed in an ethanol/water system, which is a standard condition, were investigated. The viscosity of any one of the these three MFs was higher as dispersed in an ethanol/water system than in a water dispersion system. It was confirmed that the maximum viscosity existed at around 50/50 of the ethanol/water ratio. From these results it was concluded that improved dispersion stability in solvent mixture systems was attributable to the increase in viscosity of the system.(6) If propylene glycol (the “PG”) is used as the organic solvent, the viscosity of the PG and the interaction of MF as dispersed in a solvent mixture so act in concert as to increase the viscosity of the MF dispersed system as the PG concentration increases so that the dispersion gets to be more stabilized. From this fact, the PG/water =70/30 system together with the ethanol/water =60/40 system was selected as a standard dispersion medium to be considered in future studies.