Large Particle Aggregates Research Articles

Briefing: The effects of power washing on concrete durability

The cleaning of concrete is often undertaken on health and safety grounds, especially in a marine environment when controlling algal biofouling on stepped sea defences. Despite the fact that more local authorities are doing this, there is no published research or guidance on possible durability issues when exposing a marine concrete to regular power washing regimes. Surface analysis of concrete revetment armour at a UK study site was undertaken in order to investigate the effects of power washing over 3 years on durability. Revetment armour units were monitored from casting to placing on site and surface roughness was found to have doubled. Surface hardness and uniformity have also been measured indicating degradation. When casting revetment units upside down, vibration may encourage the larger aggregate to migrate downwards towards the exposed surface once inverted at the site. Large aggregate particles at the surface leave no surface zone, giving no erosion protection. It is at the top surface where the strongest, most impermeable and most wear-resistant concrete is needed. Continual water jet cleaning practices lead to a higher surface roughness, thereby increasing the surface area offering a bioreceptive surface for further, quicker and denser colonisation; these phenomena provoke and encourage each other.

Effects of serum on cytotoxicity of nano- and micro-sized ZnO particles

Although an increasing number of in vitro studies are being published regarding the cytotoxicity of nanomaterials, the components of the media for toxicity assays have often varied according to the needs of the scientists. Our aim for this study was to evaluate the influence of serum—in this case, fetal bovine serum—in a cell culture medium on the toxicity of nano-sized (50–70 nm) and micro-sized (<1 μm) ZnO on human lung epithelial cells (A549). The nano- and micro-sized ZnO both exhibited their highest toxicity when exposed to serum-free media, in contrast to exposure in media containing 5 or 10 % serum. This mainly comes not only from the fact that ZnO particles in the serum-free media have a higher dosage-per-cell ratio, which results from large aggregates of particles, rapid sedimentation, absence of protein protection, and lower cell growth rate, but also that extracellular Zn2+ release contributes to cytotoxicity. Although more extracellular Zn2+ release was observed in serum-containing media, it did not contribute to nano-ZnO cytotoxicity. Furthermore, non-dissolved particles underwent size-dependent particle agglomeration, resulting in size-dependent toxicity in both serum-containing and serum-free media. A low correlation between cytotoxicity and inflammation endpoints in the serum-free medium suggested that some signaling pathways were changed or induced. Since cell growth, transcription behavior for protein production, and physicochemical properties of ZnO particles all were altered in serum-free media, we recommend the use of a serum-containing medium when evaluating the cytotoxicity of NPs.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-013-1829-5) contains supplementary material, which is available to authorized users.

Facile, Green Synthesis of Large Single Crystal Copper Micro and Nanoparticles with Ascorbic Acid and Gum Arabic

Large single crystal colloidal copper particles with diameters between 0.5 - 2 μm were created using a green synthesis process. The process used ascorbic acid to reduce Schweizer’s reagent created in situ using copper salts in the presence of various concentrations of gum arabic. The Schweizer’s reagents were created by varying the concentrations of ammonium hydroxide and copper nitrate solutions, copper hydroxide, or copper sulfate. The pH of the solution was controlled by the addition of ascorbic acid. Particle formation was favored at high temperature using copper sulfate at pH values ranging from 7.5 to 9, while the optimal formation occurred at a pH value of 8.5. At high concentrations, copper particle formation was found to occur from the aggregation of smaller particles which continued to nucleate once aggregated, and this resulted in the creation of globular particles and large aggregates of micron-sized particles. The addition of gum arabic resulted in the creation of large single crystal particles that did not aggregate. SEM was used to observe the effect of increasing gum arabic concentrations and EDX was used to confirm the elemental purity of the particles.

Sites for High Efficient Photocatalytic Hydrogen Evolution on a Limited-Layered MoS2 Cocatalyst Confined on Graphene Sheets―The Role of Graphene

The development of an advanced cocatalyst is critical for improving the efficiency of the photocatalytic hydrogen evolution reaction. Noble metals such as platinum (Pt) have been identified to be the most active cocatalyst for this reaction; however, due to their low-abundance, high cost, their usage in the scale-up setup is impeditive. Here, we report a high active cocatalyst, limited-layered MoS2 confined on RGO sheets as an alternative of Pt, for hydrogen evolution in dye-sensitized photocatalytic systems. Growing a MoS2 cocatalyst on RGO sheets provides more available catalytically edge sites and thus exhibits much higher activity than large aggregated pristine MoS2 particles under visible light irradiation (≥420 nm). The apparent quantum efficiency (AQE) of 24% at 460 nm over an Eosin Y-sensitized MoS2/RGO photocatalyst has been achieved. In addition, the electrical coupling and synergistic effect between MoS2 and RGO sheets greatly facilitate the efficient electron transfer from photoexcited dye to the active edge sites of MoS2; as a result, the prolonged lifetime of photogenerated electrons and the improved charge separation efficiency have been accomplished, and the photocatalytic hydrogen evolution activity has been enhanced significantly. This work demonstrates that the structural integration of MoS2 with RGO will be a new promising strategy to develop a high efficient and low-cost non-noble metal cocatalyst for solar hydrogen generation.

Colloidal lithography using silica particles: Improved particle distribution and tunable wetting properties

Colloidal lithography rests on the adhesion of colloids in a relatively ordered pattern on a charged surface owing to electrostatic interactions. However, due to capillary forces, the colloids tend to form aggregates during the drying process. These capillary forces are especially strong for large hydrophilic particles. In this paper, different experimental approaches are explored to limit the aggregation of large (500nm) silica particles deposited on glass substrates that were previously treated with polyallylamine (PAH), a polycation. These approaches consist in the addition of smaller colloids between the large ones, or of a layer of macromolecules (PAH or albumin) on top of the deposit. Scanning electron microscopy observations show that the addition of PAH and even better of albumin on top of the adherent colloids efficiently limits the formation of aggregates. Interestingly, the water contact angle of the surface obtained after silica colloid deposition and albumin adsorption is very high (∼95°), while very hydrophilic surfaces are obtained after calcination. This is discussed in light of the Wenzel and Cassie–Baxter models. In conclusion, the proposed method allows a nanoscale topographic pattern with tunable wettability to be created on large surface areas using a soft and inexpensive technique.

Fabrication of catalytically active nanocrystalline samarium (Sm)-doped cerium oxide (CeO2) thin films using electron beam evaporation

Samarium (Sm)-doped cerium oxide (CeO2) thin films were fabricated using electron beam evaporation technique. The synthesized films were deposited either on glass or ITO substrates and studied their nature by annealing at different temperatures. The optical properties and other morphological studies were done by UV–Vis, XRD, XPS, SEM, EDS, and FT-IR analysis. XRD and XPS analysis clearly confirm the presence of Sm in the ceria site. From the SEM study, it was found that after annealing at high temperature (~300 or 500 °C), the particles size was reduced due to breakdown of large aggregates of particles which is also confirmed from UV–Vis, XPS, and XRD analyses. The FT-IR study proves the presence of –COO–, –OH, or ammonium group on the particles surface. The deposition of Sm-doped CeO2 nanomaterials was found more feasible on ITO substrate compared to that of glass substrate in terms of stability and depth of film thickness. The Sm-doped CeO2 nanomaterial acts as a re-usable catalyst for the reduction of organic dye molecules in the presence of NaBH4. The catalysis rate was compared by considering the electron transfer process during the reduction. The synthesized Sm-doped CeO2 thin films might find wide variety of applications in various emerging fields like solid oxide fuel cells (SOFCs), oxygen sensor or as catalyst in different types of organic and inorganic catalytic reactions. The fabrication process is very simple, straightforward, less time consuming, and cost effective.

Physics of a rapid CD4 lymphocyte count with colloidal gold

The inherent surface charges and small diameters that confer colloidal stability to gold particle conjugates (immunogold) are detrimental to rapid cell surface labeling and distinct cluster definition in flow cytometric light scatter assays. Although the inherent immunogold surface charge prevents self aggregation when stored in liquid suspension, it also slows binding to cells to timeframes of hours and inhibits cell surface coverage. Although the small diameter of immunogold particles prevents settling when in liquid suspension, small particles have small light scattering cross sections and weak light scatter signals. We report a new, small particle lyophilized immunogold reagent that maintains activity after 42°C storage for a year and can be rapidly dissolved into stable liquid suspension for use in labelling cells with larger particle aggregates that have enhanced scattering cross section. Labeling requires less than 1 min at 20°C, which is ∼30 times faster than customary fluorescent antibody labeling. The labeling step involves neutralizing the surface charge of immunogold and creating specifically bound aggregates of gold on the cell surface. This process provides distinct side-scatter cluster separation with blue laser light at 488 nm, which is further improved by using red laser light at 640 nm. Similar comparisons using LED light sources showed less improvement with red light, thereby indicating that coherent light scatter is of significance in enhancing side-scatter cluster separation. The physical principles elucidated here for this technique are compatible with most flow cytometers; however, future studies of its clinical efficacy should be of primary interest in point-of-care applications where robust reagents and rapid results are important.

Deactivation mechanism of Pd supported on ordered and non-ordered mesoporous silica in the direct H 2O 2 synthesis using CO 2-expanded methanol

The deactivation mechanism of Pd supported on silica and mesoporous silica (SBA-15) using CO 2-expanded methanol as solvent was studied in the direct synthesis of H 2O 2 in batch and semi-continuous batch reactor tests as well as its hydrogenolysis. Fresh and used catalysts were characterized by TPR and CO chemisorption. The results evidence the presence of deactivation, which can be correlated to the loss of accessible active metal surface area due to sintering of Pd, but there is also an effect of the presence of the ordered mesoporous structure and of the reaction conditions. The higher concentration of H 2 in solution in semi-continuous batch reactor tests with respect to batch reactor tests leads to a more relevant deactivation in Pd-SiO 2 with respect to Pd-SBA-15, but a higher initial activity, due to the fact that H 2 accelerates the reduction of the Pd species which are less reducible in Pd-SiO 2 than in Pd-SBA-15. Pd-SBA-15 shows a higher H 2O 2 selectivity and productivity with respect to Pd-SiO 2 in batch reactor tests, related to the presence of easier reducible Pd species. Another difference is related to the different mechanism of sintering. On the SBA-15 support, due to the presence of the ordered mesoporosity, the Pd particles migrate into the SBA-15 channels forming elongated 1D-type particles. In Pd-SiO 2 catalyst, instead, the sintering of the Pd particles leads to large aggregates of Pd particles in the range of 20–25 nm.

Influence of the Hydrophobicity of Polyelectrolytes on Polyelectrolyte Complex Formation and Complex Particle Structure and Shape

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n−/n+ ratio of the molar charges of the polyelectrolytes and the procedure of formation were varied. The colloidal stability of the systems and the size, shape, and structure of the PEC particles were investigated by turbidimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). Dynamic light scattering indicates that beside large PEC particle aggregates distinct smaller particles were formed by the copolymers which have the highest hydrophobicity (styrene). These findings could be proved by AFM. Fractal dimension (D), root mean square (RMS) roughness and the surface profiles of the PEC particles adsorbed on mica allow the following conclusions: the higher the hydrophobicity of the polyelectrolytes, the broader is the particle size distribution and the minor is the swelling of the PEC particles. Hence, the most compact particles are formed with the very hydrophobic copolymer.

A Novel Bio-Nanocomposites Composed of Hydroxyapatite Reinforced with TiO2 Electrospun Nanofiber Consolidated Using High-Frequency Induction Heating

Titanium dioxide (TiO2) nanofibers prepared by the electrospinning technique have been used as reinforcement to improve the fracture toughness of hydroxyapatite (HAp). The required TiO2 nanofibers with diameters of 50–400 nm were first prepared by the calcining and presintering of as-prepared electrospun nanofibers of polyvinyl acetate (PVac)/titania composite at different temperatures. The composite consisting of HAp and 5 wt% of electrospun TiO2 nanofibers was then sintered at 1050° C by the high-frequency induction heat-sintering technique and its mechanical properties are evaluated by three-point bending tests, indentation tests, and a compression test. The results indicated that the morphology and crystalline phase of TiO2 nanofibers were strongly influenced by the calcination temperature. Additionally, the scanning electron microscopic results showed that the nanofibers calcined at 600°C are a porous structure due to the low densification. There was a significant change of microstructure by increasing the calcination temperature to 800°C. The nanofibers appeared with a dense microstructure due to the high-temperature calcination. A number of large size particles or particle aggregates connected by a small neck were found after the nanofibers were calcined at 1000°C. The sintering behaviors, toughness, and hardness of the resulting composites were significantly affected by the calcination temperature of the included TiO2 nanofibers. The bending and compressive strength values of HAp/5 wt% TiO2 sintered compacts were 119 and 120 Mpa, respectively, in the case of the TiO2 nanofiber calcined at 800°C, while the strength decreased with the decreasing or by increasing calcination temperature higher than 800°C.

In situ formation of silver nanoparticles in photocrosslinking polymers

Nanocomposites of cross-linked methacrylate polymers with silver nanoparticles have been synthesized by coupling photoinitiated free radical polymerization of dimethacrylates with in situ silver ion reduction. A polymerizable methacrylate bearing a secondary amino functional group was used to increase the solubility of the silver salt in the hydrophobic resin system. Fourier transform infrared spectroscopy (FTIR) revealed that the silver ion reduction had no significant effect on the degree of vinyl conversion of the methacrylate. X-ray photoelectron spectroscopy (XPS) measurements showed an increased silver concentration at the composite surface compared to the expected concentration based on the total amount of silver salt added. Furthermore, the surface silver concentration leveled off when the silver salt mass fractions were 0.08% or greater. Composites with low concentrations of silver salt (< 0.08% by mass) exhibited comparable mechanical properties to those containing no silver. Transmission electron microscopy (TEM) confirmed that the silver nanoparticles formed within the polymer matrix were nanocrystalline in nature and primarily ≈ 3 nm in diameter, with some large particle aggregates. Composites containing silver nanoparticles were shown to reduce bacterial colonization with as little as 0.03% (by mass) silver salt, while additional amounts of silver salt did not further decrease their surface colonization. With a substantial effect on bacterial growth and minimal effects on mechanical properties, the in situ formation of silver nanoparticles within methacrylate materials is a promising technique for synthesizing antibacterial nanocomposites for biomedical applications.

Combustion activities of the Ru catalysts supported on hexagonal YbFeO3

Hexagonal YbFeO3 (h-YbFeO3) were prepared by solvothermal and Pechini methods. Although the morphology of h-YbFeO3 synthesized by solvothermal method was hexagonal plate, h-YbFeO3 synthesized by the Pechini method was composed of large aggregates of irregularly-shaped fine particles. Activities of Ru catalysts supported on h-YbFeO3 for combustion reaction of propane or propene were investigated. For the support of the Ru catalyst, h-YbFeO3 synthesized by the solvothermal method was superior to that prepared by the Pechini method. Effects of the reaction temperatures of the solvothermal synthesis upon the activities of the Ru catalysts supported on the products were examined and it was found that the catalyst supported on crystallized h-YbFeO3 showed higher activity than the catalyst supported on an amorphous product having a large surface area.

Mechanism of chain formation in nanofluid based MR fluids

Mechanism of structure formation in bidispersed colloids is important for its physical and optical properties. It is microscopically observed that the mechanism of chain formation in magnetic nanofluid based magnetorheological (MR) fluid is quite different from that in the conventional MR fluid. Under the application of magnetic field the magnetic nanoparticles are filled inside the structural microcavities formed due to the association of large magnetic particles, and some of the magnetic nanoparticles are attached at the end of the chains formed by the large particles. The dipolar energy of the large particles in a magnetic nanofluid matrix becomes effective magnetic permeability ( μ eff) times smaller than that of the neutral medium. Inclusion of magnetic nanoparticles (∼10 nm) with large magnetic particles (∼3–5 μm) restricts the aggregation of large particles, which causes the field induced phase separation in MR fluids. Hence, nanofluid based MR fluids are more stable than conventional MR fluids, which subsequently increase their application potentiality.

Magnetic studies and scanning electron microscopy — X-ray energy dispersive spectroscopy analyses of road sediments, soils and vehicle-derived emissions

Human health and environmental problems related to particulate matter emission from vehicles has become a topic of research interest in recent years. These airborne particles can not only be directly inhaled, but are also present as suspended and deposited particles on paved areas and roadside soils. Here we report on magnetic studies, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and chemical analyses of vehicle-derived particles collected from both primary sources and as deposited particles on roads and soils. Preliminary results, recently published by the authors, have revealed that the magnetic signal of such particles is controlled by a magnetite-like phase with magnetic grain size ranging between 0.1 µm and 5 µm. An enrichment of some trace elements: Ba, Cr, Cu, Zn and Pb was also found. In this study we focus on SEM and EDS complementary studies of magnetic extracts. SEM observations showed small individual particles or spherulites, small aggregates in the form of chains or clusters, large aggregates of spherules, flake-like bodies, fibre-like particles, sheet-like particles, irregular debris and large particle agglomerates, i.e. a wide variety of shapes. Grain size distribution is also in agreement with magnetic grain size estimations. Additionally the following elements: C, O, Na, Mg, Al, Si, S, K, Ca, V, Ba, Ti, Cr, Mn, Fe, Cu, Zn and Pb were detected by EDS analysis.

Effect of the clay size on the dispersion morphology and emulsion stability of ABS/layered silicate nanocomposites

AbstractABS/layered silicate nanocomposites were synthesized through an emulsion polymerization with different sizes of silicates. The particle sizes of Laponite, Cloisite‐Na and Kunipia‐F are about 20–30, 70–150, and 300–500 nm, respectively. When ABS was synthesized by the emulsion polymerization in the presence of Laponite and Cloisite‐Na, ABS/layered silicate nanocomposite emulsion showed a stable suspension without the precipitation of solid particle. On the other hand, ABS/layered silicate nanocomposite synthesized with Kunipia‐F showed the precipitation of large aggregated particles and the phase separation. Smaller sizes of silicates like Laponite and Cloisite‐Na than polymerized particle worked as resided barrier preventing the emulsion particle from coagulation. Larger size of silicate like Kunipia‐F than emulsion particle was not able to enclose the emulsion particle delicately because of its stiffness and large aspect ratio. The monomers inserted into the intercalated Kunipia‐F connected the ABS particles and clay particles. The Kunipia‐F particles anchored ABS particles around them inducing the aggregation and precipitation of ABS particles. ABS copolymer emulsion and aqueous silicate dispersion were mixed to compare with synthesized ABS/layered silicate nanocomposites and showed a stable suspension. With small amount of Laponite or Cloisite‐Na, nanocomposite emulsion of Kunipia‐F was also stabilized. Laponite and Cloisite‐Na worked as a steric stabilizer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Experimental Study on Convective Thermal–Fluid Flow Transport Phenomena in Circular Tube Using Nanofluids

The aim of the present study is to disclose the thermal–fluid flow transport phenomenon of nanofluids in the heated horizontal circular tube. Consideration is given to the effects of volume fraction of the nanoparticle and Reynolds number on the turbulent heat transfer and pressure loss. It is found that (i) each viscosity, for three different nanofluids, increases with an increase in the volume fraction of nanofluid, (ii) the corresponding pressure loss increases slightly in comparison with that of pure water, and (iii) substantial heat transfer enhancement is caused by suspending nanoparticles, but its effect is attenuated by large particle aggregation.

Hydrogen feed gas purification over bimetallic Cu–Pd catalysts – Effects of copper precursors on CO oxidation

The bimetallic Pd–Cu catalysts were synthesized from different copper precursors, and their catalytic properties for CO oxidation were investigated. The characterization results indicate that chloride and sulfate precursors lead to formation of the high dispersed Cu metallic particle, while acetate and nitrate precursors lead to formation of the large aggregated Cu particles. The highly dispersed catalysts exhibit better catalytic activities for CO oxidation. In the Pd–Cu catalyst prepared from chloride and sulfate precursors, the Pd and Cu exist in alloy state and can be reduced easily, which might be the reason for the excellent properties for CO oxidation. The increase of Cu content can promote the catalytic activities of catalyst prepared from nitrate precursor. Pd species dispersed as the Cu-rich alloy on catalysts prepared with nitrate precursor, while the Pd species segregated on catalyst surface prepared with chloride precursor.

Oriented aggregation of BaTiO3 nanocrystals and large particles in the ultrasonic-assistant synthesis

BaTiO3 particles were prepared under ultrasonic irradiation. Sphere-like and confetti-like BaTiO3 particles composed of ca. 10 nm nanocrystals and hollow sphere particles composed of ca. 40 nm nanoparticles were obtained at different concentrations. The BaTiO3 particles were identified as mesocrystals and the oriented aggregation, caused by ultrasonication, of 5–10 nm nanocrystals and ca. 40 nm nanoparticles, respectively, was identified.

Assemblies of poly(styrene/⇌-tert-butoxy-ω-vinyl-benzyl-poryglycidol) Microspheres with different diameters deposited on mica plates

Formation of poly(styrene/α-tert-butoxy-ω-vinyl-benzyl-polyglycidol) microsphere assemblies on mica plates modified with 3-aminopropyltriethoxysilane was investigated. Microsphere assemblies contained two types of particles similar with respect of their chemical structure but with different diameters (D n = 1000 and 350 nm). Methods of particle deposition included: deposition from water suspension of a mixture of small and large particles on mica plates placed at the bottom of suspension container, deposition of particles from a drop of ethanol suspension (containing large and small microspheres) placed on the mica substrate, deposition of microspheres on modified mica plates crossing the liquid-air interface-sequential deposition of large and small particles, and one-batch deposition from a mixed water suspension of large and small microspheres. Deposition from water suspension containing large and small microspheres on plates placed on the bottom of suspension container yielded assemblies with large particles randomly distributed among the small ones. Fraction of large particles in adsorbed particle assembly was smaller than fraction of large particles in suspension. Particle assemblies prepared by placement of ethanol suspension of large and small microspheres on mica were composed of quite regularly distributed large particles among the small ones. A two step process consisting of withdrawal of mica plate from water suspension of large particles and then on using this plate as substrate in a second step during which the plate was withdrawn from suspension of small particles yielded particle assemblies containing aggregates of large particles randomly distributed among the small ones. Withdrawal of mica plates from water suspension of large and small microspheres resulted in particle assemblies composed of regularly distributed stripes of large and small microspheres. Formation of the described above microsphere assemblies is possible only in case of reversible adsorption of particles.

Influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles

The experimental results on the influence of surfactant surface coverage and aging time on physical properties of silica nanoparticles were reported. The spherical silica nanoparticles have been synthesized using polyethylene glycol (PEG) as the surfactant and oil shale ash (OSA) as a new silica source. In order to identify the optimal condition for producing the best quality silica nanoparticles with the good dispersion and uniformity, the effects of surfactant surface coverage and aging time were investigated. It was found that the particle size and distribution of silica nanoparticles depend on the concentration of PEG in dispersion. At relatively low concentration, 0–2 wt.%, the existing PEG is not sufficient to prevent further growth of the initially formed silica nanoparticles, leading to large aggregates of silica particles. When the PEG concentration increases to 3 wt.%, self-assembled PEG layer on the surface stabilizes the initially formed silica nanoparticles and the silica particles with average diameter of 10 nm are uniformly distributed. With further increasing the concentration of PEG, the number of PEG aggregates increases and silica nanoparticles are mainly formed inside the entangled PEG chains, resulting in an observation of clusters of silica nanoparticles. Moreover, it was found that as the aging time increased, the shape of silica nanoparticles becomes regular and the particle size distribution becomes narrow.