The role of particle size on the deposition efficiency of ink on plastic spheres

Experimental investigation of the effect of carbon particle size on its deposition efficiency on the surface of plastic particles has been performed in stirred vessel. A model based on Langmuir kinetics was used, and it provided a good fit for the experimental results. The effect of de-inking conditions such as, carbon particle size, calcium chloride concentration, and carbon concentration has been investigated.

Different sizes of carbon particles were tested. It was found that the deposition rate and the deposition efficiency were generally higher for the larger carbon particles.

The effect of CaCl₂ concentration on the deposition efficiency was investigated. Results showed that the deposition rate increased when the concentration of CaCl₂ increased from 0.05 to 0.10 g/l (the stochiometric ratio needed to react with sodium stearate). Moreover, the deposition efficiency was higher at this concentration. Concentrations above the stochiometric ratio did not show a systematic behavior for the deposition rate and the deposition efficiency.

Finally, the effect of carbon concentration was examined. Carbon concentration of 0.25, 0.30, and 0.40 g/l were used. Results showed that the concentration of carbon did not affect the deposition efficiency nor the rate of deposition.

This study confirmed the applicability of the method of ink removal from recycled waste paper using plastic particles, proposed by previous investigators.     

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.     

Inertial Deposition of Aerosol Particles on Fiberous Filters

The inertial deposition of aerosol particles on model filters at low and intermediate Stokes numbers and low Reynolds numbers was studied. It was shown that the efficiency of the inertial deposition of submicron particles is markedly affected by retarded van der Waals forces and the gas slip in the vicinity of thin fibers.     

The effect of electrolyte conductivity on electrophoretic deposition

In this work, the influence of electrolyte conductivity on the electrophoretic deposition of alumina particles from ethanol suspensions was studied. Deposition experiments in a Hull cell showed that high-conductivity ethanol-based suspensions yield uniform deposits, while low-conductivity suspensions result in nonuniform deposits. The difference in the deposition, behavior is due to the resistance increase over the deposit during polarization. Impedance measurements during electrophoretic deposition showed that during EPD the relative deposit resistance increases much faster for the high- than for the low-conductivity suspension. The impedance measurements also showed that the resistance increase dropped almost to the suspension resistance after the electric field was turned off. This means that the resistance over the deposit is caused by the interaction of ions with the deposit and by the depletion of ions at the deposition electrode. Negatively charged ions are depleted in the deposit by migration toward the positively charged counterelectrode, while positively charged ions undergo electrochemical reactions at the deposition electrode. This change in ion concentrations near the deposition electrode changes the acid/base properties of the particles in the deposit, as proven by adsorbed pH indicators on the particles. The change in acid/base behavior is quasi-irreversible and results in a memory effect of the deposit resistance when the voltage is reapplied.     

Site-specific Deposition of Colloidal Pd Nanoparticles on Self-assembled Microtubules from Biolipid

Lipid microtubules with wound ribbon features were fabricated by self-assembling method, and the deposition patterns of colloidal Pd particles on tubular template were investigated. The result indicates that colloidal Pd nanoparticles are preferentially decorated on the helical markings in the interior and on the exterior of preformed tubule and to the edge of loosely helical ribbons to obtain helical deposition features. The multi-bilayer microstructure of tubules can be marked by fine Pd nanoparticles deposited at the edge of helical ribbon. There are the site-specific interactions between lipid tubular template and colloidal Pd particles at the helical edge. A new route was illustrated that colloidal Pd particles firstly attach at the edge of thin flat membranes, and then thin membranes roll up and reassemble into tubule together with particles to form helical deposition patterns. The site-specific deposition of Pd is unbeneficial to obtain the homogeneous metal film on tubules, but it can be utilized to reveal the different chemical nature of lipid molecular assembly.     

Spatially selective photochemical reduction of silver on nanoembossed ferroelectric PZT nanowires

It is well known that photochemical reaction in an aqueous solution can be chosen by selectively patterning the domain structures of ferroelectrics. In this work, we investigate the photochemically induced deposition of Ag particles on ferroelectric lead zirconate titanate [Pb(Zr(x),Ti(1?-?x))O(3)] nanowires fabricated by nanoembossing technology. The photochemical reduction of Ag particles is found to occur preferentially along the embossed nanowires. By imaging domain configurations of the embossed films using the piezoresponse force microscope, the spatially selective deposition of Ag particles can be associated with the underlying ferroelectric domain structures created by the nanoembossing process. The controllable and selective deposition of metal species onto nanoembossed ferroelectric nanostructures without the need for an external electrical field is promising for providing a new route to nanoferroelectric lithography.     

Deposition of magnetic colloidal particles on graphite and mica surfaces driven by solvent evaporation

The deposition of colloidal magnetite particles onto graphite and mica surfaces induced by solvent evaporation is studied using atomic force microscopy. After evaporation under ambient conditions we observe polydisperse beadlike aggregates; the mean aggregate diameter is larger on graphite than on mica. After evaporation at elevated temperatures we observe a variety of effects, including enhanced particle aggregation and spinodal-like deposition patterns. To explain these trends, we propose mechanisms involving the wetting properties of the solvent. We have also made a brief study of the effects of applied magnetic fields on the formation of aggregates. A field applied parallel to the surface enhances aggregation and favors deposition patterns characteristic of hole-nucleation processes. A perpendicular field leads to a reduction in aggregate size and favors a homogeneous distribution of particles on the surface. These effects are explained in terms of the likely orientation of the dipolar particles on the surface.     

Adsorption and desorption of colloidal particles on glass in a parallel plate flow chamber—Influence of ionic strength and shear rate

The adsorption and desorption rates of 736 nm diameter polystyrene particles on glass were studiedin situ using a parallel plate flow chamber and automated image analysis. Adsorption and desorption rates were measured simultaneously during deposition, enabling the determination of initial deposition rates, blocked areas per particle, desorption rate coefficients, and the number of adhering particles in the stationary state. Deposition experiments were done from suspensions with different potassium nitrate concentrations (1, 10 and 50 mM) and at varying shear rates (15 to 200 s^–1). The initial deposition rate, the desorption rate, the blocked area per particle and the number of adhering particles in the stationary state showed major variations with the shear rate and the ionic strength of the suspension. At low ionic strength, the number of adhering particles showed an oscillatory behavior in time, presumably due to a varying interaction between particle and collector surface. Blocked areas, determined from deposition kinetics, ranged 705 to 2374 cross-sections at low ionic strength, and from 10 to 564 at high ionic strength and corresponded well with those estimated from local pair distribution functions which were obtained from an analysis of the spatial arrangement of the adhering particles.     

Structure of submonolayer oleic acid coverages on inorganic aerosol particles: evidence of island formation

A series of submonolayer deposition studies of oleic acid on both hydrophobic and hydrophilic surfaces has shown that oleic acid self-associates into islands rather than uniformly covering the surfaces. The studies were performed by vapor deposition on 1.6 mum diameter polystyrene aerosol particles as well as on polystyrene and silica surfaces. The surfaces were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), ellipsometry and contact-angle goniometry. After timescales of minutes to hours of vapor deposition at 70 degrees C, the oleic acid arranged itself in the form of islands with diameters of about 100 nm. Many of the islands are 25-30 A high, suggesting that the oleic acid sits vertically on the surface. The surface structure of oleic acid on particles is expected to impact on several atmospherically relevant properties such as the reactivity of the oleic acid and the hygroscopicity of the particles.     

Deposition of colloid particles on protein layers: fibrinogen on mica

Colloid particle deposition was applied to characterize fibrinogen (Fb) monolayers on mica, which were produced by controlled adsorption under diffusion transport. By adjusting the time of adsorption and the bulk Fb concentration, monolayers of desired surface concentration were obtained. The surface concentration of Fb was determined directly by AFM enumeration of single molecules adsorbed over the substrate surface. It was proven that Fb adsorbed irreversibly on mica both at pH 3.5 and at pH 7.4 with the rate governed by bulk transport. The electrokinetic properties of Fb monolayers produced in this way were studied using the streaming potential method. The dependence of the apparent zeta potential of Fb monolayers was determined as a function of the coverage. It was shown that for pH 3.5 the initial negative zeta potential of the mica substrate was converted to positive for Fb coverage exceeding 0.16. On the other hand, for pH 7.4, the zeta potential of a Fb-covered mica remained negative for the entire coverage range. The charge distribution in Fb monolayers was additionally studied using the colloid deposition method, in which negatively and positively charged polystyrene latex particles (ca. 800 nm in diameter) were used. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH 3.5 and 7.4, respectively. These results suggested that for pH 7.4, the distribution of charge on Fb molecules was heterogeneous, characterized by the presence of positive patches, whereas the average zeta potential was negative, equal to -19 mV. The utility of the colloid deposition method for studying Fb monolayers was further demonstrated in deposition experiments involving positive latex particles. It was shown that for a rather broad range of fibrinogen coverage, both the positive and the negative latex particles can adsorb on surfaces covered by Fb, which behaved, therefore, as superadsorbing surfaces. It was also concluded that the colloid deposition method can be used to determine the Fb bulk concentration for the range inaccessible for other methods.     

Reversibility in particle deposition: the effect of mobile fraction of particles on monolayer structures

In this work, the degree of reversibility in particle deposition was introduced by surface diffusion. The effect of mobile fraction of triangular-well particles on the surface among the immobile ones was explored by varying number of particles added at a time in modified sequential quenching model. It was found that at low temperatures, as the number of added mobile particles increased, the structures was composed of more compact clusters connecting to one another, thereby, decreasing the percolating density while at high temperatures, the structures are more disordered and the final structures were independent on the deposition flux, leading to the unchanged percolating density.     

Electroreduction of molecular oxygen on carbon electrode modified by dispersed silver

Silver particles are formed by electrochemical deposition on the carbon electrode surface. It is found that the deposition process occurs according to the progressive nucleation mechanism, which results in formation of silver particles with the size of 95 to 190 nm as dependent on the electrodeposition time. The values of silver particle size and support surface coverage by metal obtained on the basis of microphotographs indicate that cathodic polarization in the presence of dissolved oxygen results in particle size redistribution due to the reaction of silver particle dissolution with further deposition simultaneously with oxygen electroreduction. The reaction of molecular oxygen electroreduction on a carbon electrode with deposited dispersed silver occurs via a mixed two- and four-electron mechanism. The observed limiting reaction current is of diffusion nature.     

Underpotential deposition of copper on electrodes modified with colloidal gold

This communication is concerned with the electrochemical addressability of gold colloidal particles deposited on a conducting substrate. Cyclic voltammetry of electrodes modified with gold colloid layers indicates that an underpotential deposition of copper onto the gold surface takes place. Analysis of the charge associated with the underpotential deposition permits the electroactive gold area to be calculated. The total gold area may be determined from transmission electron microscopy (TEM) images. Comparison of the geometric and electroactive areas obtained indicates that electrochemically all the gold particles are addressable and the entire colloid surface is accessible.     

Synthesis of CuCorePtShell Nanoparticles as Model Structures for Core–Shell Electrocatalysts by Direct Platinum Electrodeposition on Copper

The synthesis of Cu(core)Pt(shell) model catalysts by the direct electrochemical deposition of Pt on Cu particles is presented. Cu particles with an average diameter of 200 nm have been deposited on glassy‐carbon electrodes by double pulse electrodeposition from a copper sulfate solution. Subsequent deposition from a platinum nitrate solution under potential control allows for a high selectivity of the Pt deposition towards Cu. Using a combination of cyclic voltammetry, XPS and sputtering, the structure of the generated particles has been analyzed and their core–shell configuration proven. It is shown that the electrocatalytic activity for the oxygen reduction is similar to that of other PtCu catalyst systems. The synthesized structures could allow for the analysis of structure–activity relations of core–shell catalysts on the way to the simple and controlled synthesis of supported Cu(core)Pt(shell) nanoparticles as oxygen reduction catalysts.     

Deposition of silica thin films formed by sol–gel method

Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6 decreased the deposition rate due to aggregation of the primary silica particles.     

Surface selective deposition of Mo(IV) on Ni/TiO2 particles in aqueous solutions

The selective depositions of MoS2 and MoO2 over Ni surfaces are demonstrated on Ni/TiO2 particles in a mild electroless deposition process. High-resolution transmission electron microscopy (HRTEM) images show the uniform distribution of 10-30 nm spherical and hemispherical Ni particles on TiO2 surface, and three to six layers of MoS2 on the surface of Ni particles. The as-prepared MoS2-Ni/TiO2 is used as a catalyst for the hydrodesulfurization (HDS) reaction of dibenzothiophene (DBT), and shows a significant increase over commercial catalysts in turnover frequencies as the result of unique distribution of active components in the binary catalyst. The selective material deposition is explained in the context of Ni catalyzed KBH4 decomposition, which produces strong reducing species responsible for the site selective deposition of Mo. The synthetic method can be potentially used to prepare bimetallic materials with similar nanostructures such as those of Mo-Co, Mo-Pd, and Mo-Rh.     

Surface clusters of colloid particles produced by deposition on sites

The possibility of producing surface clusters of well-defined structure formed by colloid particles was analyzed theoretically and experimentally. Theoretical results were derived by performing Monte Carlo-type simulations according to the generalized random sequential adsorption (RSA) mechanism. In these simulations, the jamming coverage of particles adsorbing irreversibly on spherical sites was determined as a function of the particle-to-site size ratio lambda. It was revealed that, by properly choosing lambda, a targeted site coordination can be achieved; for example, there can be one, two, three, and so forth particles attached to one site. The structure of the heterogeneous clusters produced in this way was described in terms of the pair correlation function. It was predicted that the extent of ordering within surface clusters was diminished as the concentration of sites increased. These theoretical predictions were checked by performing deposition experiments of negatively charged polystyrene latex particles (average diameter 0.9 mum) under the diffusion-controlled transport regime. Mica sheets precovered by positively charged polystyrene latex (average diameters 0.45 and 0.95 microm) were used as the substrate surface in these experiments. Positive latex (site) deposition was also carried out under diffusion-controlled transport conditions. The concentration of the sites and the adsorbed particles was determined by direct particle counting using optical microscopy. It was found, in quantitative agreement with theoretical simulations, that the structure of surface clusters produced in this way exhibits a significant degree of short-range ordering. It also was proven experimentally that clusters containing a targeted number of colloid particles (e.g., 2 and 4) could be produced by the deposition procedure.     

Parameters influencing the electrodeposition of a Ni-Cu coating on Fe powders. I. Effect of the electrolyte composition and current density

Electrochemical deposition of a two-component Ni-Cu coating onto Fe powder particles was studied by constant current electrolysis. The influence of the Ni(II) to Cu(II) salts ratio in the electrolyte, of the addition of sodium citrate as complexing agent to the electrolyte, and of the current density with respect to the total surface of compact and dispersed electrodes was studied. It was shown that the less noble Ni deposition is facilitated mainly by its large excess in the electrolyte and by an increase in current density. The addition of a complexing agent exhibits only a very slight influence on the coating composition but does suppress the spontaneous deposition of Cu. The current efficiencies of Ni, Cu and Ni-Cu deposition on the powder particles decrease with increasing sodium citrate concentration and current density.     

Underpotential deposition and involved alloy formation of cadmium on silver particles modified HOPG substrates

Cadmium underpotential deposition (UPD) on Ag particles modified highly ordered pyrolytic graphite (HOPG) surfaces, and the involved alloy formation were studied by conventional electrochemical techniques. Voltammetric results indicated that the Cd UPD followed an adsorption behavior different from that observed for massive Ag electrodes and Ag particles supported on vitreous carbon. Nanometer-sized bimetallic Cd–Ag particles were characterized by ex situ atomic force microscopy (AFM). Initially, AFM images show Ag deposits of similar size distributed preferably on HOPG step edges. No remarkable morphological changes are observed on the surface after the subsequent Cd deposition, suggesting that the Cd particles are deposited selectively over the Ag crystals. From the analysis of desorption spectra, employing different polarization times, and density functional theory (DFT) calculations, the formation of a Cd–Ag surface alloy could be inferred.     

Cathodic electrodeposition of ceramic and organoceramic materials. Fundamental aspects

Electrodeposition of ceramic materials can be performed by electrophoretic (EPD) or electrolytic (ELD) deposition. Electrophoretic deposition is achieved via motion of charged particles towards an electrode under an applied electric field. Electrolytic deposition produces colloidal particles in cathodic reactions for subsequent deposition. Various electrochemical strategies and deposition mechanisms have been developed for electrodeposition of ceramic and organoceramic films, and are discussed in the present article. Electrode-position of ceramic and organoceramic materials includes mass transport, accumulation of particles near the electrode and their coagulation to form a cathodic deposit. Various types of interparticle forces that govern colloidal stability in the absence and presence of processing additives are discussed. Novel theoretical contributions towards an interpretation of particle coagulation near the electrode surface are reviewed. Background information is given on the methods of particle charging, stabilization of colloids in aqueous and non-aqueous media, electrophoretic mobility of ceramic particles and polyelectrolytes, and electrode reactions. This review also covers recent developments in the electrodeposition of ceramic and organoceramic materials.