Granulation of core particles suitable for film coating by agitation fluidized bed II. A proposal of a rapid dissolution test for evaluation of bitter taste of ibuprofen

To prepare powdered drugs that do not have a bitter taste, a film coating covering the surfaces of the core particles is required. The dissolution rate of ibuprofen from the coated particles changes according to the physical properties of the core particles. In this study, the effects of the physical properties of granules prepared by using several scales of agitation fluidized beds on the drug dissolution rate were investigated. The dissolution rate of ibuprofen decreased when the apparent density and shape factor of the granules increased. In contrast, the dissolution rate of the drug increased with the friablility of the granules increased. Thus, the structures of the granules appear to affect the dissolution rate of the drug to a large degree. A rapid dissolution test that can be used to investigate the early dissolution rate of ibuprofen in vitro was proposed to evaluate the taste-masking level of the coated particles. The bitter taste-masking level of the coated particles was successfully confirmed by using this novel test method.     

Silica–silver core–shell particles for antibacterial textile application

The silica–silver core–shell particles were synthesized by simple one pot chemical method and were employed on the cotton fabric as an antibacterial agent. Extremely small (1–2 nm) silver nanoparticles were attached on silica core particles of average 270 nm size. The optimum density of the nano silver particles was found which was sufficient to show good antibacterial activity as well as the suppression in their surface plasmon resonance responsible for the colour of the core–shell particle for antibacterial textile application. The change in the density and size of the particles in the shell were monitored and confirmed by direct evidence of their transmission electron micrographs and by studying surface plasmon resonance characteristics. The colony counting method of antibacterial activity testing showed excellent results and even the least silver containing core–shell particles showed 100% activity against bacterial concentration of 10⁴ colony counting units (cfu). The bonding between core–shell particles and cotton fabric was examined by X-ray photoelectron spectroscopy. The antibacterial activity test confirmed the firm attachment of core–shell particles to the cotton fabric as a result 10 times washed sample was as good antibacterial as that of unwashed sample. The bacterial growth was inhibited on and beneath the coated fabric, at the same time no zone of inhibition which occurs due to the migration of silver ions into the medium was observed indicating immobilization of silver nanoparticles on silica and core–shell particles on fabric by strong bonding.     

Preparation of uniform Au@SiO2 particles by direct silica coating on citrate-capped Au nanoparticles

Preparation of Au@SiO₂ particles by direct silica coating on three different sized citrate-capped Au nanoparticles (17, 25 and 33 nm) with Stöber method was investigated in this work. It was found that the uniformity of the resulting Au@SiO₂ particles was related to both the sizes of the Au nanoparticles and the concentration of citrate during the particle synthesis. When the citrate concentration during the particle synthesis was low, the 25 and 33 nm Au nanoparticles could be well dispersed in the Stöber system, thus resulting the formation of uniform Au@SiO₂ particles containing single core. However, small Au nanoparticles (17 nm) were identified to show poor stability in the Stöber system even under low citrate concentration, the silica coating must be performed in a pre-hydrolyzed Stöber system to get the uniform Au@SiO₂ particles. This approach was also applicable to citrate capped Ag nanoparticles. After removal of the excess citrate in the Ag prepared by citrate reduction, uniform Ag/SiO₂ particles containing single core colloids could also be prepared by the direct silica coating.     

Synthesis of highly monodisperse particles composed of a magnetic core and fluorescent shell

Highly monodisperse particles composed of a magnetic silica core and fluorescent polymer shell were synthesized with a combined technique of heterocoagulation and soap-free emulsion polymerization. Prior to heterocoagulation, monodisperse, submicrometer-sized silica particles were prepared with the Stober method, and magnetic nanoparticles were prepared with a modified Massart method in which a cationic silane coupling agent of N-trimethoxysilylpropyl- N, N, N-trimethylammonium chloride was added just after coprecipitation of Fe (2+) and Fe (3+). The silica particles with negative surface potential were heterocoagulated with the magnetic nanoparticles with positive surface potential. The magnetic silica particles obtained with the heterocoagulation were treated with sodium silicate to modify their surfaces with silica. In the formation of a fluorescent polymer shell onto the silica-coated magnetic silica cores, an amphoteric initiator of 2,2'-azobis[ N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) was used to control the colloidal stability of the magnetic cores during the polymer coating. The polymerization of St in the presence of a hydrophobic fluorophore of pyrene could coat the cores with fluorescent polymer shells, resulting in monodisperse particles with a magnetic silica core and fluorescent polymer shell. Measurements of zeta potential for the composite particles in different pH values indicated that the composite particles had an amphoteric property originating from VA-057 initiator.     

Stimuli-sensitive core/shell template particles for immobilizing inorganic nanoparticles in the core

We synthesize and characterize stimuli-sensitive core/shell particles with functional group (or material) localized in the core. We previously reported two types of hybrid particles prepared by using the template particles which were synthesized by soap-free emulsion copolymerization with N-isopropylacrylamide and glycidyl methacrylate (GMA) as monomers but by different preparation methods. GMA has advantages in immobilizing materials having several functional groups such as thiol ones. In this study, to obtain the suitable template particles for immobilizing any inorganic nanoparticles in the core, we investigated the effect of feed ratio of the two monomers. Obtained template particles were modified by thiol compounds to introduce ionic groups. They were characterized by dynamic light scattering and scanning electron microscopy. After in situ synthesis of magnetic nanoparticles in the templates, the hybrid particles were characterized directly by transmission electron microscopy. Consequently, we could obtain the hybrid core/shell particles which contained a large amount of magnetic nanoparticles (∼33 wt%) in the core.     

Preparation of core-shell polymer colloid particles by encapsulation

 By means of heterocoagulation anionic poly-[styrene] particles were coated with smaller electrosterically stabilised cationic particles of poly-[butyl methacrylate]. On heating the heterocoagulated units 45 °C above the glass transition temperature of poly-[butyl methacrylate], as predicted theoretically, the latter polymer spread over the surface of the poly-[styrene] particle to give a composite particle with a core-shell structure. It was found that the extent of packing of the small particles on the larger core particle was a critical feature of the coating process. Received: 12 September 1996 Accepted: 18 September 1996     

Drying and pyrolysis of wood particles: experiments and simulation

The objective of this study is to develop a flexible and stable numerical method to predict the thermal decomposition of large wood particles due to drying and pyrolysis. At a later stage, this model is applied to each particle of a packed bed and thus, forms the entire packed bed process as a sum of individual particle processes. Therefore, this approach can deal with particles of different sizes, shapes and properties. A general formulation of the conservation equations allows the geometry of a fuel particle to be treated as a plate, cylinder or sphere. The various processes such as heat-up, drying and pyrolysis are described by a set of one-dimensional and transient conservation equations for mass and energy. This allows for simultaneous processes e.g. reactions in time and covers the entire range between transport-limited (shrinking core) and kinetically limited (reacting core) reaction regimes. The particles interact with a gas phase by heat and mass transfer taking into account the Stefan correction due to the gas outflow during conversion. Experiments carried out span a temperature range between T=300 and 900 °C for particle sizes varying between 8 and 17 mm. A comparison between measurements and predictions of drying models yielded satisfactory agreement only for the constant evaporation temperature model and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles. Likewise, predicted results of pyrolysis for the above-mentioned range of temperatures and sizes agreed satisfactorily with measurements.     

Influence of velocity and surface temperature of alumina particles on the properties of plasma sprayed coatings

In this paper are described the main characteristics of the plasma spraying process of alumina deposits, i.e., the temperature and flow field of the plasma jets obtained with the classical spraying torches, the injection of the particles into the plasma jet, the particle surface temperature and velocities in the plasma (measured for calibrated alumina particles), and the coating generation. The measurements on the alumina particles are compared with the predictions of a mathematical model. The experimental and computed particle velocities are in rather good agreement. However, this is not the case for the particle surface temperature. Possible reasons for the discrepancy are proposed (influence of the carrier gas, thermophoretic forces, and poor penetration of the particles into the plasma core even for an injection velocity twice that of the optimal calculated one, as shown by recent measurements). Finally the correlations between the particle velocities and surface temperature, and the properties of the alumina coating (porosity, crystal structure, mechanical properties) are studied.     

Formulation design of taste-masked particles, including famotidine, for an oral fast-disintegrating dosage form

In this study, the taste-masking of famotidine, which could apply to any fast-disintegrating tablet, was investigated using the spray-dry method. The target characteristics of taste-masked particles were set as follows: the dissolution rate is not to be more than 30% at 1 min and not less than 85% at 15 min, and the particle size is not to be more than 150 microm in diameter to avoid a gritty feeling in the mouth. The target dissolution profiles of spray-dried particles consisting of Aquacoat ECD30 and Eudragit NE30D or triacetin was accomplished by the screening of formulas and the appropriate lab-scale manufacturing conditions. Lab-scale testing produced taste-masked particles that met the formulation targets. On the pilot scale, spray-dried particles with attributes, such as dissolution rate and particle size, of the same quality were produced, and reproducibility was also confirmed. This confirmed that the spray-dry method produced the most appropriate taste-masked particles for fast-disintegrating dosage forms.     

Synthesis of monodisperse,magnetic latex particles with polystyrene core

A novel method for producing monodisperse, submicron-sized magnetic latex particles is described. The method provides coating of polymer particles with surface-modified magnetic particles during soap-free polymerization. Experiments were performed with styrene monomer, potassium persulfate initiator, Fe ₃O ₄ magnetic particles, and silane-coupling reagents of methacryloxypropyltrimethoxysilane (MPTMS) and methacryloxypropyldimethoxysilane (MPDMS). The morphology of the magnetic particles depended on the silane-coupling reagents. Use of the tri-functional coupling reagent MPTMS produced particles having a disk-like or concave-like shape, whereas use of the di-functional coupling reagent MPDMS produced spherical particles that had a coefficient of variation of 4.4%, which was much smaller than the standard criteria of monodispersity, 10%.     

Coating of open tubular capillaries with discoidal and spherical high-density lipoprotein particles in electrochromatography

A new method was developed for the coating of fused-silica capillaries with human high-density lipoproteins (HDLs) for use in electrochromatography. The HDL particles used for the coating differed in particle shape and composition. Both discoidal and spherical particles formed a monolayer on the inner silica wall as confirmed by atomic force microscopy. The effect of coating conditions, such as HDL concentration and coating time, was investigated with spherical HDL particles. Examination of the influence of pH on the coating stability also allowed the determination of pI values for the HDL particles attached to the capillary wall. The pI values for spherical and discoidal HDL particles were close to 5.0. The repeatabilities of the EOF mobility and the retention factors of the uncharged steroid hormones used as model compounds were exploited in the evaluation of the coating stability. The optimal coating was achieved with 0.1 mg/mL HDL protein and 50 min flushing with coating solution followed by 15 min standing time. Electrochromatography with HDL-coated open tubular capillaries offers a new tool for the study of HDL particle structure and transformations.     

Preparation of silica-coated poly(styrene-co-4-vinylpyridine) particles and hollow particles

This paper presents a novel method for preparation of polymer-silica colloidal nanocomposites based on emulsion polymerization and subsequent sol-gel nanocoating process. The polystyrene latex particles bearing basic groups on their surfaces were successfully synthesized through emulsion polymerization using 4-vinylpyridine (4VP) as a functional comonomer and polyvinylpyrrolidone (PVP) as a surfactant. A series of poly(styrene-co-4-vinylpyridine)/SiO2 nanocomposite particles with smooth or rough core-shell morphology were obtained through the coating process. The poly(styrene-co-4-vinylpyridine) particles could be dissolved subsequently or simultaneously during the sol-gel coating process to form hollow particles. The effects of the amount of 4VP, PVP, NH(4)OH, and tetraethoxysilane (TEOS) on both the nanocomposite particles and hollow particles were investigated. Transmission electron microscopy showed that the morphology of the nanocomposite particles and hollow particles was strongly influenced by the initial feed of the comonomer 4VP and the coupling agent PVP. The conditions to obtain all hollow particles were also studied. Thermogravimetric analysis and energy dispersive X-ray spectroscopy analyses indicated that the interiors of hollow particles were not really "hollow".     

Determination of silica coating efficiency on metal particles using multiple digestion methods

Nano-sized metal particles, including both elemental and oxidized metals, have received significant interest due to their biotoxicity and presence in a wide range of industrial systems. A novel silica technology has been recently explored to minimize the biotoxicity of metal particles by encapsulating them with an amorphous silica shell. In this study, a method to determine silica coating efficiency on metal particles was developed. Metal particles with silica coating were generated using gas metal arc welding (GMAW) process with a silica precursor tetramethylsilane (TMS) added to the shielding gas. Microwave digestion and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) were employed to solubilize the metal content in the particles and analyze the concentration, respectively. Three acid mixtures were tested to acquire the appropriate digestion method targeting at metals and silica coating. Metal recovery efficiencies of different digestion methods were compared through analysis of spiked samples. HNO₃/HF mixture was found to be a more aggressive digestion method for metal particles with silica coating. Aqua regia was able to effectively dissolve metal particles not trapped in the silica shell. Silica coating efficiencies were thus calculated based on the measured concentrations following digestion by HNO₃/HF mixture and aqua regia. The results showed 14-39% of welding fume particles were encapsulated in silica coating under various conditions. This newly developed method could also be used to examine the silica coverage on particles of silica shell/metal core structure in other nanotechnology areas.     

Highly monodisperse chemically reactive sub-micrometer particles: polymer colloidal photonic crystals

Chemically reactive particles with controllable sizes from 383 to 756 nm in very narrow size distributions (well below 5%) have been synthesized by the modified surfactant-free emulsion homopolymerization of inhibitor-free glycidyl methacrylate with the dropwise addition of ionic initiators during the initial reaction of 10 min. The effects of monomer concentration and the amount of initiator were systematically studied on the particle diameter. In addition, changes of the particle diameter and its size distribution during the whole synthesis process were also investigated. The mechanism for the formation of coalesced and highly monodisperse chemically reactive colloidal particles was discussed based on the colloidal stability governed by chemical reaction and physical interactions between the precursor or primary particles. Colloidal photonic crystals with different brilliant visible colors in a large scale were prepared by shearing assembly of such chemically reactive monodisperse particles with spin coating technique. The reflection wavelengths in the visible spectrum range are from the high-order including the second-order light diffraction of the as-prepared PGMA photonic crystals. Such monodisperse chemically reactive particles will be very useful in optical and sensing technologies, and in biochemical analysis.     

Melting of non-spherical ultrafine particles

The behaviour of lead particles, with size up to 100 nm, embedded in a SiO matrix have been investigated versus temperature by dark field electron microscopy. When the particle is not spherical, it is shown that the melting process initiates on the surface regions of the particle where curvature is maximum. The process is continuous and reversible as far as a solid core exists. When the temperature increases, the volume of the solid core decreases and its shape evolves towards a sphere. Final melting of the core occurs as a first order transition (with size effect). These direct observations are in good agreement with previous results deduced from a high-sensitive reflectance experiment which gives an information averaged on the size and the state of the particles. Emphasis is laid on the dimension of the particle perpendicular to the substrate which is not generally obtained through electron microscopy measurements and appears here as an important parameter.     

Gold nanoparticle localization at the core surface by using thermosensitive core-shell particles as a template

We report novel thermosensitive hybrid core-shell particles via in situ gold nanoparticle formation using thermosensitive core-shell particles as a template. This method for the in situ synthesis of gold nanoparticles with microgel interiors offers the advantage of eliminating or significantly reducing particle aggregation. In addition, by using thermosensitive microgel structures in which the shell has thermosensitive and gel properties in water--whereas the core itself is a water-insoluble polymer--we were able to synthesize the gold nanoparticles only at the surface of the core, which had reactive sites to bind metal ions. After the gold nanoparticles were synthesized, electroless gold plating was carried out to control the thickness of the gold nanoshells. The dispersions of the obtained hybrid particles were characterized by dynamic light scattering and UV-vis absorption spectroscopy, and the dried particles were also observed by electron microscopy. Adaptation of the technique shown here will create a number of applications as optical, electronic, and biomedical functional materials.     

Magnetic Fe2O3-polystyrene/PPy core/shell particles: bioreactivity and self-assembly

This paper describes the synthesis of new magnetic, reactive polystyrene/polypyrrole core/shell latex particles. The core consists of a polystyrene microsphere containing gamma-Fe2O3 superparamagnetic nanoparticles (PSmag), and the shell is made of reactive N-carboxylic acid-functionalized polypyrrole (PPyCOOH). These PSmag-PPyCOOH latex particles, average diameter 220 nm, were prepared by copolymerization of pyrrole (Py) and the active carboxyl-functionalized pyrrole (PyCOOH) in the presence of PSmag particles. PNVP was used as a steric stabilizer. The functionalized polypyrrole-coated PSmag particles were characterized in terms of their particle size, surface morphology, chemical composition, and electrochemical and magnetic properties using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry, and SQUID magnetometry. Activation of the particle surface carboxyl groups was achieved using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS), which helps transform the carboxyl groups into activated ester groups (NSE). The activated particles, PSmag-PPyNSE, were further evaluated as bioadsorbents of biotin used as a model biomolecule. It was shown that biotin was immobilized at the surface of the PSmag-PPyNSE particles by forming interfacial amide groups. The assemblies of PSmag-PPyCOOH particles on glass plates were further investigated. When no magnetic field is applied, the particles assemble into 3D colloidal crystals. In contrast, under a magnetic field, one-particle-thick chains gathered in hedgehog-like architectures are obtained. Furthermore, PSmag-PPyCOOH coated ITO electrodes were shown to be electroactive and electrochemically stable, thus offering potentialities for creating novel high-specific-area materials for biosensing devices where the conducting polymer component would act as the transducer through its conductive properties.     

Fabrication and morphology control of hollow polymer particles by altering core particle size

Particles with various morphologies were fabricated by changing the size of carboxyl-containing core particles and performing seeded emulsion polymerization as well as alkali posttreatment. The distribution of carboxyl groups, size, and morphology of the resultant particles were characterized with conductometric titration, dynamic light scattering (DLS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Results indicated that the size of carboxyl-containing core latex particles could be varied from 95 to 240 nm by adjusting the concentration of sodium dodecyl sulfate (SDS). The percentage of carboxyl groups buried inside particles increased clearly along with the encapsulation of core by interlayer and shell polymers, and seeded emulsion copolymerization performed smoothly except the system using core particles with size less than 99 nm. After alkali posttreatment, the morphologies of corresponding particles showed porous, hollow, and bowl-like structure, respectively. Moreover, the relationship between core particle size and alkali-treated particle morphology was elucidated briefly.     

Analysis of stepwise heterocoagulation for the preparation of soft core/hard shell composite polymer particles

The stepwise heterocoagulation of small cationic hard particles (SPs) onto a large anionic soft particle (LP) for the preparation of soft core/hard shell composite polymer particles was examined using dynamic light scattering and spectrophotometry. The effects of the pH value, the emulsifier content which was pre-added to the LP emulsion, and the heat treatment time on the covering of a LP by SPs, and the stability of the heterocoagulated emulsion were clarified. Received: 12 May 1998 Accepted: 31 July 1998     

Plasmon modes of curvilinear metallic core/shell particles

The plasmon hybridization method is generalized to calculate the plasmon modes and optical properties of solid and dielectric-core/metallic-shell particles of geometrical structures that can be described using separable curvilinear coordinates. The authors present a detailed discussion of the plasmonic properties of hollow metallic nanowires with dielectric cores and core/shell structures of oblate and prolate spheroidal shapes. They show that the plasmon frequencies of these particles can be expressed in a common form and that the plasmon modes of the core/shell structures can be viewed as resulting from the hybridization of the solid particle plasmons associated with the outer surface of the shell and of the cavity plasmons associated with the inner surface.