Composition Of Dispersion Medium Research Articles

Microstructure formation mechanism of catalyst layer and its effect on fuel cell performance: Effect of dispersion medium composition

The design of the catalyst layer (CL) offers a feasible way to realize the commercialization of proton exchange membrane fuel cells (PEMFCs). An in-depth understanding of catalyst inks is critical to achieving the optimal CL structure and cell performance. In this work, the effects of the solvent evaporation process during ink drying on the formation of the CL microstructure are particularly considered to reveal the structure–property correlations among the catalyst ink, drying process, CL microstructure and fuel cell performance. An increase in the alcohol content of the catalyst ink increases the amount of free ionomers while allowing the ionomer backbone to be more stretched in the dispersion medium. The higher alcohol content contributes to rapid solvent evaporation and thus inhibits the formation of coffee rings; as a result, a more developed ionomer network with a denser pore structure is obtained. Therefore, the alcohol-rich electrode exhibits better proton conduction capability, but higher oxygen transport resistance. For complex fuel cell operating conditions, a catalyst ink formulation with 50 wt% alcohol content is preferred due to its proper ionomer and pore size distribution, providing satisfactory fuel cell performance.

Effect of the Composition of Dispersion Medium on the Structural Parameters of Resins and Asphaltenes in Low-Temperature Dewaxing of Oil

Effect of the Composition of Dispersion Medium on the Structural Parameters of Resins and Asphaltenes in Low-Temperature Dewaxing of Oil

Effect of the Composition of Dispersion Medium on the Structural Parameters of Resins and Asphaltenes in Low-Temperature Dewaxing of Oil

Effect of the Composition of Dispersion Medium on the Structural Parameters of Resins and Asphaltenes in Low-Temperature Dewaxing of Oil

Effect of Dispersion Medium Composition and Ionomer Concentration on the Microstructure and Rheology of Fe-N-C Platinum Group Metal-free Catalyst Inks for Polymer Electrolyte Membrane Fuel Cells.

We present an investigation of the microstructure and rheological behavior of catalyst inks consisting of Fe-N-C platinum group metal-free catalysts and a perfluorosulfonic acid ionomer in a dispersion medium (DM) of water and 1-propanol (nPA). The effects of the ionomer-to-catalyst (I/C) ratio and weight percentage of water (H2O %) in the DM on the ink microstructure were studied. Steady-shear and dynamic-oscillatory-shear rheology, in combination with synchrotron X-ray scattering, was utilized to understand interparticle interactions and the level of agglomeration of the inks. In the absence of the ionomer, the inks were significantly agglomerated, approaching a gel-like microstructure for catalyst concentrations as low as 2 wt %. The effect of H2O % in the DM on particle agglomeration was found to vary with particle concentration. In concentrated inks (≥2 wt % catalyst), increasing H2O % was found to increase agglomeration because of the hydrophobic nature of the catalysts. In dilute inks (<1 wt % catalyst), the trend was reversed with increasing H2O %, suggesting that electrostatic interactions are dominating the behavior. In inks with 5 wt % catalyst, the addition of an ionomer was found to significantly stabilize the catalyst against agglomeration. Maximum stability was observed at 0.35 I/C for all DM H2O % studied. At high ionomer concentrations (I/C > 0.35), interesting differences were observed between nPA-rich inks (H2O % ≤ 50%) and H2O-rich (82% H2O) inks. The nPA-rich inks remained predominantly stable-ink viscosity only weakly increased with I/C and the Newtonian behavior was maintained for I/C up to 0.9. In contrast, the H2O-rich inks exhibited a significant increase in viscoelasticity with increasing I/C, suggesting flocculation of the catalyst by the ionomer. These differences suggest that the nature of the interactions between the ionomer and catalyst is highly dependent on the H2O % in the DM.

Sodium Oleate as a Templating Agent for the Synthesis of Mesoporous SiO2 Containers: from Capsules to “Monolithic” Particles

The peculiarities of the synthesis of silica-based mesoporous container particles with the use of sodium oleate as a templating agent have been discussed. Sodium oleate is an anionic surfactant and an efficient corrosion inhibitor. It has been shown that the container particles obtained as a result of combining the stages of their synthesis and loading contain a very large amount of the inhibitor. The effect of dispersion medium composition and temperature on the structure of surfactant associates and, hence, the morphology of the obtained particles has been analyzed.

Agglomeration of titanium dioxide nanoparticles increases toxicological responses in vitro and in vivo

BackgroundThe terms agglomerates and aggregates are frequently used in the regulatory definition(s) of nanomaterials (NMs) and hence attract attention in view of their potential influence on health effects. However, the influence of nanoparticle (NP) agglomeration and aggregation on toxicity is poorly understood although it is strongly believed that smaller the size of the NPs greater the toxicity. A toxicologically relevant definition of NMs is therefore not yet available, which affects not only the risk assessment process but also hinders the regulation of nano-products. In this study, we assessed the influence of NP agglomeration on their toxicity/biological responses in vitro and in vivo.ResultsWe tested two TiO2 NPs with different primary sizes (17 and 117 nm) and prepared ad-hoc suspensions composed of small or large agglomerates with similar dispersion medium composition. For in vitro testing, human bronchial epithelial (HBE), colon epithelial (Caco2) and monocytic (THP-1) cell lines were exposed to these suspensions for 24 h and endpoints such as cytotoxicity, total glutathione, epithelial barrier integrity, inflammatory mediators and DNA damage were measured. Large agglomerates of 17 nm TiO2 induced stronger responses than small agglomerates for glutathione depletion, IL-8 and IL-1β increase, and DNA damage in THP-1, while no effect of agglomeration was observed with 117 nm TiO2.In vivo, C57BL/6JRj mice were exposed via oropharyngeal aspiration or oral gavage to TiO2 suspensions and, after 3 days, biological parameters including cytotoxicity, inflammatory cell recruitment, DNA damage and biopersistence were measured. Mainly, we observed that large agglomerates of 117 nm TiO2 induced higher pulmonary responses in aspirated mice and blood DNA damage in gavaged mice compared to small agglomerates.ConclusionAgglomeration of TiO2 NPs influences their toxicity/biological responses and, large agglomerates do not appear less active than small agglomerates. This study provides a deeper insight on the toxicological relevance of NP agglomerates and contributes to the establishment of a toxicologically relevant definition for NMs.

The Factors Determining Formation Dynamics and Structure of Ring-Shaped Deposits Resulting from Capillary Self-Assembly of Particles

The influence of different physicochemical parameters, such as particle concentration and size, droplet volume, dispersion medium composition, and substrate hydrophilicity, on the structure of deposits resulting from evaporating sessile droplets of colloidal dispersions has been studied. Parameters enabling one to targetedly control the structure of a deposit have been determined. The possibility of obtaining deposits having the shapes of thin rings and monolithic disks has been shown. The conditions have been found under which monolayer and multilayer deposits with ordered arrangement of particles are formed.

Detection and quantification of chitosan aggregates by pressure-assisted capillary zone electrophoresis

An approach to the detection and determination of chitosan aggregates in acetic acid solutions is proposed using pressure-assisted capillary zone electrophoresis. Processes of chitosan aggregation are studied depending on the composition of dispersion medium and storage time. The presence of several species of positively charged chitosan aggregates is revealed for the first time. Particle sizes in the range 20–2500 nm are determined by scanning electron microscopy and static and dynamic light scattering. The dependence of the shape of electropherograms on particle size distribution obtained under the same conditions is found. A trend to changing electrophoretic mobility depending on the size of the aggregate is observed, which enables the approximate evaluation of the polydispersity of chitosan solutions. Chitosan is used for the effective dynamic modification of capillaries, which does not require the introduction of a modifier into the background electrolyte.

Influence of dispersion medium composition on Fischer—Tropsch synthesis in three-phase system in the presence of iron-containing catalysts

The Fischer—Tropsch synthesis over iron-containing catalysts in a three-phase system with synthetic polymers of different compositions introduced into the dispersion medium has been studied. It has been found that these catalysts exhibit activity in the synthesis of liquid hydrocarbons from CO and H2. It has been revealed that the addition of synthetic polymers into the catalyst samples leads to the formation of smaller particles, the size of which depends on the employed polymer, and to an increase in the selectivity for the target product of the synthesis in the entire studied temperature range.

One‐pot synthesis of self‐stabilized and carboxyl‐functionalized fluorescent poly(methyl methacrylate) microspheres covalently dyed with tris(8‐hydroquinolinato)aluminium by dispersion polymerization

AbstractThe dispersion polymerization of methyl methacrylate (MMA) with fluorescent monomer tris[2‐((8‐hydroxyquinolin‐5‐yl)methoxy)ethyl methacrylate]aluminium (Al‐HQHEMA) was investigated to obtain fluorescent microspheres under varying conditions (such as composition of dispersion medium, and content of stabilizer polyvinylpyrrolidone (PVP) and Al‐HQHEMA) in methanol–water at 70 °C with 2,2′‐azoisobutyronitrile as the initiator. Fluorescent microspheres with particle size of 2.039 µm and uniformity of 0.171 were obtained under the following conditions: methanol–water, 7:3 (v/v); PVP, 15 wt% of MMA; Al‐HQHEMA solution, 1.5 mL. Maleic monoester of monomethoxyl poly(ethylene glycol) (Mal‐MPEG) was used as a comonomer to simultaneously incorporate carboxyl groups and PEG chains. With Mal‐MPEG, no aggregation was observed in the measurements of particle size and size distribution for the obtained microspheres after cleaning off PVP, indicating that self‐stabilized fluorescent microspheres were obtained. While without Mal‐MPEG, obvious aggregation was observed. The determination of surface carboxyl content using aqueous acid–base titration showed that most of the carboxyl groups of Mal‐MPEG were located on the surface of the microspheres. © 2015 Society of Chemical Industry

Photo‐Initiated Dispersion Polymerization of Copolymer Microspheres in a Closed System: Poly(MMA‐co‐MAA)

AbstractA simple closed system is introduced to construct copolymer microspheres with specific surface groups by low‐power UV irradiation. As an example, poly(MMA‐co‐MAA) microspheres with narrow size distribution were prepared by photo‐initiated dispersion polymerization. Sizes and size distributions of the microspheres were closely related to light intensity, composition of dispersion medium and the concentrations of initiators, stabilizers, and monomers. Many carboxyl groups could be moored on the spheres' surfaces, which enabled the construction of nanostructures on the surface. Many copolymer microspheres with different surface functional groups, such as –NH2, –SH, –OH, etc. could be directly prepared in an ordinary laboratory.magnified image

Nanostructured Pt-γ-Al2O3-CeO2 catalytic materials and coatings

A new process is described for the suspension synthesis of polycrystalline Pt-γ-Al2O3-CeO2 catalytic materials and coatings, with maltose, C12H22O11, as a reductant and structure former. The process parameters have been optimized in terms of the dispersion medium composition and the way in which Pt is introduced. The coatings are highly uniform in chemical and phase composition, as evidenced by quantitative analysis, optical microscopy, and x-ray microanalysis results. Characteristically, the coatings have a highly porous structure and good adhesive properties. Catalysts prepared by the proposed process show high activity for the oxygen oxidation of CO. The process can be used to fabricate Pt-Pd-Rh catalysts on block supports for the purification of vehicle exhaust gases and industrial off-gases. It has the advantage that high-porosity multicomponent catalytic coatings can be produced on cordierite block supports in a single step.

Preparation of thermostable highly dispersed titanium dioxide from stable hydrosols

A large set of stable nanodispersed TiO2 hydrosols differing in particle structure and dispersion medium composition was synthesized. For highly dispersed TiO2 samples obtained by calcination of dried sols at 500°C phase compositions, sizes of primary crystallites, and specific surface areas were found. The factors affecting thermal stability of TiO2 nanoparticles were analyzed. The sol containing the most thermostable nanoparticles was used to produce a highly efficient catalyst for cyclohexanone ammoximation.

The Properties of Polymer-Containing BeO Dispersions in an Acetone–Chloroform Binary Medium

The properties of Newtonian and concentrated (non-Newtonian) BeO dispersions in solutions of acidic poly(vinyl acetate-co-vinyl chloride) in binary mixtures of chloroform (a Lewis acid) and acetone (a Lewis base) of different compositions were studied. In contrast to systems characterized by strong acid–base interactions at the particle–medium interface, the role of the steric stabilization factor was found to be extremely low in the studied dispersions. Polymer-containing BeO dispersions in acetone had the highest kinetic stability due to the specific interactions of this solvent with BeO particles and polymer macromolecules contributing to the redispersion of particles and the formation of protective solvation shells. The obtained data on the effect of the dispersion medium composition on the rheological properties of concentrated BeO dispersions can be used for the selection of optimal regimes for preparation of pastes for high-temperature ceramics.

Effect of the Surface Structure of Poly(styrene- co -acrolein) Microspheres and Its Modification by Protein on Electrosurface Properties

Disperse systems where polymeric microspheres of various natures are used for the immobilization of biologically active compounds are widely applied in practical medicine [1, 2]; however, the mechanism of interaction of biopolymers with the surface is yet scarcely studied. This is attributed to the complexity of systems studied, in particular, to the possibility of many-point interaction of adsorbate with the surface, and to its conformational rearrangements in the surface layer both in the course of adsorption and consequent storage, thus complicating the interpretation of experimental data. At the same time, the structure of complex organic macromolecule in the surface layer is responsible for its further biological activity and possible realization of its specific interaction [2‐4]. As a rule, such macromolecules contain diverse ionogenic groups and most often exhibit amphoteric properties. The presence of such macromolecules in the surface layer should essentially influence the structure of electrical double layer (EDL) and be responsible for the lability of its structure during the variation of dispersion medium composition. New procedures for the synthesis of polymeric microspheres with the preset surface structure and functionality that makes it possible to perform both physical adsorption and chemisorption are elaborated to conserve the specific activity of biological compounds after their binding with polymer substrate [5‐ 12]. In particular, microspheres obtained by the radical copolymerization of styrene and acrolein, securing the control of the fraction of acrolein units in the surface layer and hence the surface hydrophobicity allow us to immobilize protein macromolecules with no additional activation by a simple incubation of microspheres in alkaline protein solution where latexes are stable enough [7, 12‐14]. Chemical binding occurs as a result of the interaction of latex aldehyde groups with protein amine groups. Earlier [7], we have shown that, by their electrosurface properties, such microspheres occupy intermediate position between hydrophobic polystyrene [15] and homopolymers of aldehyde-containing monomers [8‐11]. They combine high adsorption capacity of polystyrene with respect to proteins and their strong chemical binding. Such microspheres are good models for studying the mechanism of specific adsorption of protein macromolecules; the study of their electrosurface properties after their modification by protein permits us to obtain information on the structure of protein coating.

Relationship between protective properties of lithium greases and composition of dispersion medium

Relationship between protective properties of lithium greases and composition of dispersion medium

Influence of group composition of dispersion medium on volatility of lithium greases

The rate of evaporation of the dispersion medium in lubricating greases depends on the hydrocarbon group composition of the lube oil base stock [I]~ The paraffinic--naphthenic hydrocarbons of petroleum oils evaporate at higher rates than the aromatic hydrocarbons [2, 3]. Lithium greases formulated with oils from naphthenic-base crudes are characterized by higher volatility than greases prepared with oils from paraffinic-base crudes [4].

Study of commodity properties of food emulsions Part 1. The effect of dispersion medium composition on kinetic stability of O/W emulsions containing proteins, acidic polysaccharides and calcium salts

AbstractThe effect of concentrations of acidic polysaccharide and calcium ions on the kinetic stability, viscosity and dispersity of protein‐containing O/W emulsions is studied. Variation of kinetic stability of the emulsions studied is independent of dispersion composition. In a wide range of calcium acetate concentrations a correlation is observed between kinetic stability and viscosity of emulsions at sodium alginate concentration in the dispersion medium ≤ 0.3%. The transition zone between liquid solution and gel is widened in the presence of sodium caseinate. Maximum kinetic stability is reached at calcium acetate: sodium alginate concentrations of 1.0‐1.2 and ∼ 6.0, corresponding to optimum conditions for formation of homogeneous crosslinked structures of calcium alginate and calcium caseinate.

Effect of composition of dispersion medium on reaction of complex aluminum (cAl) soap formation in manufacture of cAl greases

Effect of composition of dispersion medium on reaction of complex aluminum (cAl) soap formation in manufacture of cAl greases

Influence of composition of dispersion medium on gel formation process in systems thickened by complex aluminum soap

Influence of composition of dispersion medium on gel formation process in systems thickened by complex aluminum soap