Undesired Agglomeration Research Articles

Preparation and characterization of chitosan–silver nanocomposite films and their antibacterial activity against Staphylococcus aureus

In this work different variables have been analyzed in order to optimize the bactericidal properties of chitosan films loaded with silver nanoparticles. The goal was to achieve complete elimination of antibiotic resistant and biofilm forming strains of Staphylococcus aureus after short contact times. The films were produced by solution casting using chitosan as both a stabilizing and reducing agent for the in situ synthesis of embedded silver nanoparticles. We have applied an innovative approach: the influence of the chitosan molecular weight and its deacetylation degree (DD) were analyzed together with the influence of the bacterial concentration and contact time. The best results were obtained with high DD chitosan where a fast reduction was favored; leading to smaller nanoparticles (nucleation is promoted), and a sufficiently high polymer viscosity prevented the resulting nanoparticles from undesired agglomeration. In addition, for the first time, potential detachment of the silver nanoparticles from the films was evaluated and neglected, demonstrating that uncontrolled release of silver nanoparticles from the chitosan films is prevented. The influence of the ionic silver released from the films, silver loading, nanoparticle sizes, contact, and initial number of bacteria was also analyzed to elucidate the mechanism responsible for the strong bactericidal action observed.

Graphene formation by unzipping carbon nanotubes using a sequential plasma assisted processing

We report the realization of graphene nanosheets by means of unzipping carbon nanotubes grown on silicon substrates. The formation of carbon nanotubes is possible with a gas mixture of methane and hydrogen in a direct-current plasma enhanced chemical vapor deposition reactor at a temperature of 700°C. To avoid the undesired agglomeration of nickel islands as the catalyst layer, a hydrogen-assisted pre-treatment has been used. Vertically aligned CNTs are placed horizontally on a silicon substrate and unzipped using a sequential passivation and etching process in a reactive ion etching unit. A mixture of hydrogen, oxygen and SF6 gases are used to result in proper unzipping of horizontal CNTs. Scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy have been exploited to investigate the physical properties of the grown nano-structures. In addition, the composition of the passivation layer has been examined using energy dispersive spectroscopy. Multilayered graphene sheets with a height of 3nm have been obtained.

Open-Mouthed Metallic Microcapsules: Exploring Performance Improvements at Agglomeration-Free Interiors

Although artificial capsule structures have been thoroughly investigated, functionality at the surfaces of their interiors has been surprisingly overlooked. In order to exploit this aspect of capsular structure, we here report the breakthrough fabrication of metallic (platinum) microcapsules with sufficient accessibility and electroactivity at both interior and exterior surfaces (open-mouthed platinum microcapsules), and also we demonstrate improvements in electrochemical and catalytic functions to emphasize the practical importance of our concept. The open-mouthed platinum microcapsules were prepared by template synthesis using polystyrene spheres, where surface-fused crystalline nanoparticles formed a capsule shell. Subsequent removal of the polystyrene spheres induced formation of mouth-like openings. The open-mouthed platinum microcapsules exhibit a substantial increase of their electrode capability for methanol oxidation and catalytic activities for carbon monoxide (CO) oxidation. Notably, activity loss during CO oxidation due to undesirable particle agglomeration can be drastically suppressed using the open-mouthed microcapsules.

Predicting drying kinetic and undesired agglomeration during drying of granules containing amorphous water-soluble substances in a continuous horizontal fluid bed dryer

Various industries use fluid bed dryers for the drying of larger granules produced by extrusion, pan agglomeration or spray granulation. During such drying processes secondary agglomeration is undesired due to an increasing amount of oversize particles. In the current study the drying of granules containing amorphous substances is modelled. The model is based on the laws of heat and mass transfer as well as heat and mass balances around a differential volume element of the fluid bed. For each location in the bed and for different drying parameters the calculated moisture and temperature values are used to estimate the surface viscosity of the granules. The calculated viscosity allows estimating the risk of secondary agglomeration of granules. Viscosity values which are estimated for different drying conditions are compared with the experimentally determined amount of oversize particles. An increasing amount of oversize particles can be observed if the viscosity of the amorphous substance is below 10 4 Pa s.

Performing the Electrospraying Process for the Application of Textile Nano Finishing Particles

We have performed the electrospraying process via a conventional configuration for the application of nanoparticles, used for water and oil repellency of textile fabrics, onto the surface of the textile to avoid undesirable agglomeration of those particles. This approach shows by means of scanning electron microscopy (SEM) images that such an application (electrospraying) would avoid agglomeration by using the electrostatic forces produced and gave acceptable oil repellency, which also points to commercial market interest.

Hierarchical porous silica membranes with dispersed Pt nanoparticles

Multifunctional silica membranes with a hierarchical porosity and containing dispersed Pt nanoparticles were prepared by an original one pot microwave-assisted sol–gel route. These membranes exhibit three porosity levels: interconnected micropores (<2 nm) in silica walls, isolated ordered mesopores (∼4 nm), and isolated macropores (∼70 nm). They were directly coated on tubular macroporous alumina supports without any intermediate mesoporous layer contrary to conventional membrane architectures. The isolated macropores and mesopores enable to increase the membrane permeability whereas the interconnected microporosity defines the membrane cut-off. The catalytic Pt nanoparticles (∼4 nm) mainly hosted in the mesoporous volume, are stabilised against undesirable agglomeration under working conditions. A first series of multifunctional membranes were prepared, in which preferential adsorption of hydrocarbon gases and efficient propene oxidation were evidenced. In order to avoid any possible interconnection between macropores, several strategies were investigated, which prevented sol infiltration in the macroporous support during the deposition process. These original multifunctional membranes are potentially attractive for gas separation and catalytic reactor applications.

Comparison of fibre optical measurements and discrete element simulations for the study of granulation in a spout fluidized bed

Spout fluidized beds are frequently used for the production of granules or particles through granulation. The products find application in a large variety of applications, for example detergents, fertilizers, pharmaceuticals and food. Spout fluidized beds have a number of advantageous properties, such as a high mobility of the particles, which prevents undesired agglomeration and yields excellent heat transfer properties. A discrete element model is used describing the dynamics of the continuous gas phase and the discrete droplets and particles. For each element momentum balances are solved. The momentum transfer among each of the three phases is described in detail at the level of individual elements. The results from the discrete element model simulations are compared with local measurements of time time-averaged particle volume fractions as well as particle velocities by using a novel fibre optical probe in a fluidized bed of 400 mm I.D. Simulations and experiments were carried out for three different cases using Geldart B type aluminium oxide particles: a freely bubbling fluidized bed; a spout fluidized bed without the presence of droplets and a spout fluidized bed with the presence of droplets. It is found that the experimental and numerical results agree in a qualitative manner. It is demonstrated how the discrete element model can be used to obtain information about the interaction of the discrete phases, i.e. the growth zone in a spout fluidized bed. Additional analysis of the numerical results indicates that liquid breakthrough does not take place for the studied test case.

Selective photo-deposition of Cu onto the surface of monodisperse oleic acid capped TiO2nanorods probed by FT-IR CO-adsorption studies

A novel, non-aqueous, organometallic route to nanocomposite Cu@TiO2 materials is presented. TiO2 nanorods stabilized with oleic acid (OLA) were used as support for the photo-assisted deposition of Cu using the organometallic Cu(II) precursor [Cu(OCH(CH3)CH2N(CH3)2)2] (1). The copper precursor penetrates through the shell of OLA and is photo reduced to deposit Cu0 directly at the surface of the TiO2 rods. The obtained Cu decorated nanorods were still soluble in nonpolar organic solvents without change of the morphology of nanorods. The Cu@TiO2 colloid was characterized by means of UV-VIS, XRD, AAS, and HRTEM. FTIR CO adsorption studies provide evidence for Cu0 anchored at the titania surface by a characteristic absorption at 2084 cm-1. Comparative studies of Cu-deposition were performed using CuCl2 as simple Cu source which proved that the concept of organometallic disguise of the metal centre results in a higher reaction rate and the circumvention of non-selective reduction, parasitic side reactions and undesired agglomeration of the OLA stabilized titania nanorods.

Fluidization Behaviors for Coating Cohesive Particles

Cornstarch particles are difficult to fluidize owing to their small size and strong cohesive forces that can lead among other things to undesired agglomeration. To improve the fluidization quality the particles were coated with SiO2 particles (2.5 μm) in an axial magnetic fluidized bed. This surface modification results in a larger bed expansion and the coated particles have a longer minimum collapse time than the ones without a coating.

The effect of glass transition on the desired and undesired agglomeration of amorphous food powders

In the food manufacturing and pharmaceutical industry several agglomeration technologies are applied: fluidised bed agglomeration, steam jet agglomeration, agglomeration during drying and pressure agglomeration like extrusion, roller compaction or tabletting. In addition, caking or sticking of amorphous substances, which is a kind of undesired agglomeration, is frequently observed. Any desired or undesired agglomeration of amorphous substances is dependent on the mechanical properties of the entire particle or the particle surface. Changes in the mechanical properties of the material are linked to changes in moisture and temperature and can be predicted by applying the glass transition concept. Using this concept it is possible to estimate the viscosity and the Young's modulus for a given amorphous substance while knowing their glass transition temperature in dependence on the water content. Knowing the viscosity and the Young's modulus and applying equations derived from the sintering technology or the theory of viscoelasticity it is possible to define suitable conditions for most of the agglomeration processes mentioned above.

Experimental determination of capillary forces by crushing strength measurements

Mechanisms that lead to powder agglomeration are in many cases controlled by capillary forces. Indeed, in the earliest stage of agglomeration, minute amounts of liquid join solid particles by liquid bridges. Spontaneous formation of the bridge at contact points is caused by capillary condensation. Depending on solid/liquid interactions, particularly contact angle and spreading, liquid bridges may attract or repel individual particles. Undesired agglomeration may appear during storage and is called caking. On the other hand, powder agglomeration process is often required, for example, in enlargement of the particle size, i.e. granulation. A simple experimental device, designed from usual caking tests, was developed in order to estimate capillary forces transmitted by attracting liquid bridges joining particles. Crushing strength of wet cylindrical agglomerates was estimated. Influence of the low saturations of the void space (0< S<25%) and the surface tension of a liquid have been investigated. A normalised force which does not depend on the surface tension contribution has been calculated from experimental measurements and compared to Rumpf's model. It is possible to roughly estimate the solid/liquid contact angle by comparison with the model.

Agglomeration Tendency during Top-Spray Fluidized Bed Coating with Gelatin and Starch Hydrolysate

Top-spray fluidized bed coating of glass beads with gelatin and starch hydrolysate leads to an `all or nothing' side-effect agglomeration, that is, a drastic collapse of the fluid-bed when a critical spray rate is exceeded. This undesirable side-effect agglomeration is primarily influenced by the type of coating, and more specifically its hygroscopicity, water binding capacity and viscosity. Hydrolyzed gelatin permits a considerable increase in spray rate compared to the unhydrolyzed type, due to more pronounced coating losses and lack of gelling capacity. Starch hydrolysate enables working only at low spray rates, due to its high hygroscopicity. Increasing the atomization pressure decreases the agglomeration tendency of starch hydrolysate but simultaneously decreases the final coating thickness. Coating quality is primarily influenced by coating properties, such as molecular mass and viscosity during processing.

Aggregation Phenomena in AgX Precipitation in the Presence of Gelatin

Despite the continuous development of new synthetic polymers, gelatin remains as the principal component of the binder used in most silver halide photographic films and papers. The main reason for the longevity of gelatin in silver halide photographic systems is its remarkable property to play a unique role in almost every step of the manufacture as well as in the photographic processing of these products. The most important function of gelatin in the preparation of photographic emulsions is to provide colloid protection and stabilization for the AgX crystals. Colloid stability of fine AgX particles is provided through steric stabilization, facilitated by the adsorption of gelatin on the AgX surface. A critical level of gelatin is required for such stabilization. The experimentally estimated critical gelatin surface coverage required to prevent coalescence during precipitation is in good agreement with previous theoretical calculations and with equilibrium adsorption measurements. Inadequate peptization of AgX colloid particles during precipitation can cause aggregation that can lead to undesirable agglomeration and coalescence. But in some cases gelatin can attenuate flocculation and control coalescence resulting in desirable dislocations such as the formation of twinning dislocations, which is the key step in the nucleation and growth of tabular AgX crystals. This is demonstrated by a strong correlation between the degree of flocculation during nucleation and the resulting tabular grain population fraction.