Melamine Formaldehyde Particles Research Articles

Photoelectric method for determination of the relative radii of microparticles

Experimental results of relative radii of microparticles determination by the analysis of scattered on particles radiation are presented. Due to the monotonous dependence of the indicatrix of particle scattered radiation on particle radius at a specific angle, it becomes possible to determine the relative radii of particles in cloud of particles by one camera picture. Radii of three types of monodisperse powders of melamine formaldehyde particles with known sizes were analyzed by means of Mie theory. The results showed the possibility to determine relative radii of particles to each other in suspended clouds of particles.

Changes in the surface structure of melamine-formaldehyde particles in complex plasma

The surface modification of polymer microspheres by complex plasma was studied. Melamine-formaldehyde spherical microparticles, falling into neon dc glow discharge, acquired an electric charge on their surface and hung in a dust trap, where the electric field strength was strong enough. They were long trapped, forming three-dimensional ordered structures. Depending on the exposure time, the particle sizes and surface properties changed. Scanning electron microscopy provided insight in the particle morphology changing. The dependence of the particle size on the exposure in plasma was measured; the modification of the surface structure was investigated. The results of the statistical processing of the surface structure are presented.

Modification of the texture of a polymer material surface in dust plasma

We have analyzed the modification of the texture of polymer particle surface in a dust plasma. Monodisperse spherical melamine formaldehyde particles were injected into the glow discharge plasma in neon. At a certain discharge current and gas pressure in the discharge tube, the particles were suspended in dust-plasma traps and experienced the action of the plasma of 5–25 min. Then, the particles were extracted and the collected material was studied using the scanning electron microscope. Among the results, a change in the diameter and roughness of the surface depending on the residence time of particles in the dust plasma was established. It was found that the absolute deviation of all points of the surface profile averaged over the evaluation length were in the nanometer range. The time of complete degradation of particles in the experimental conditions has been established.

Study of the modification of spherical melamine-formaldehyde particles levitating in complex plasma

The surface modification of spherical melamine-formaldehyde particles during their levitation in a dusty plasma as a part of plasma–dust structures in a trap formed in strata in a neon glow discharge has been investigated using scanning electron microscopy. The dependence of the particle size on the time of plasma exposure has been found and measured, and the modification of the surface structure has been studied. The source of the observed modification has been interpreted.

Autowaves in a dc complex plasma confined behind a de Laval nozzle

Experiments to explore stability conditions and topology of a dense microparticle cloud supported against gravity by a gas flow were carried out. By using a nozzle-shaped glass insert within the glass tube of a dc discharge plasma chamber a weakly ionized gas flow through a de Laval nozzle was produced. The experiments were performed using neon gas at a pressure of 100 Pa and melamine-formaldehyde particles with a diameter of 3.43 μm. The capturing and stable global confining of the particles behind the nozzle in the plasma were demonstrated. The particles inside the cloud behaved as a single convection cell inhomogeneously structured along the nozzle axis in a tube-like manner. The pulsed acceleration localized in the very head of the cloud mediated by collective plasma-particle interactions and the resulting wave pattern were studied in detail.

Pearl-necklace-like structures of microparticle strings observed in a dc complex plasma

The observation of a well-developed treelike string structure supported by a gas flow in a three-dimensional dc complex plasma is presented. The dynamically stable strings, comprising 10-20 particles, were up to 5 mm long. The experiments were performed using neon gas at a pressure of 100 Pa and melamine-formaldehyde particles with a diameter of 3.43 μm. Inside the discharge glass tube a nozzle had been built in to supply the controllable gas (plasma) flux intensity distribution along the tube. The walls of the nozzle were transparent for the laser light illuminating the particles. That gave the opportunity to closely study the particle dynamics deep inside the nozzle.

Mass changes of microparticles in a plasma observed by a phase-resolved resonance method

The influence of a plasma environment on melamine formaldehyde particles is studied. High-precision measurements of the vertical confinement frequency with a phase-resolved resonance method indicate that the particle mass is affected in two ways: the deposition of sputtered material at the particle leads to a mass gain, whereas the outgassing of water causes a mass loss.

Laser-induced rocket force on a microparticle in a complex (dusty) plasma

The interaction of a focused powerful laser beam with micron-sized melamine formaldehyde (MF) particles was studied experimentally. The microspheres had a thin palladium coating on their surface and were suspended in a radio frequency argon plasma as a single layer (plasma crystal). A particle hit by the laser beam usually accelerated in the direction of the laser beam, consistent with the radiation pressure force mechanism. However, random-direction acceleration up to the speeds on the order 1 m/s was sometimes observed. Rocket-force mechanism is proposed to account for the random-direction acceleration. Similar, but much less pronounced, effect was also observed for MF particles without palladium coating.

Tracking the clustering dynamics in ternary particle mixtures by flow cytometry

Competitive heteroaggregation in a ternary mixture of polystyrene and melamine-formaldehyde particles was studied by multi-colour flow cytometric analyses. Flow cytometry is a very powerful technique for the determination of multi-dimensional cluster composition and its dynamic evolution. Three-dimensional cluster composition distributions were obtained that characterise the aggregation process separately for each species in a very detailed manner and pave the way for a higher dimensional analysis of cluster composition. The multi-species aggregation dynamics were analysed for systems with different mixing ratios of 1:1:1 and 1:20:1 as well as in dosage experiments. The results confirm the control of aggregation phenomena by the concentration ratios of constituent particle species, which might prove central for future tailoring of heteroaggregate compositions. Dosage experiments demonstrate the high sensitivity of flow cytometric measurements and their versatile technological applicability.

Polymerizable gemini surfactants at solid/solution interfaces: Adsorption and polymerization on melamine formaldehyde particles and capsule fabrication

Organic capsules have been fabricated via three steps, by using the polymerizable gemini surfactant (1,2-bis(dimethyl(11-methacryloyloxy)undecylammonio) hexane dibromide, PC11-6-11) as a single wall component. In the first fabrication step, the surfactant spontaneously adsorbs on acid-dissolvable melamine formaldehyde (MF) particles in aqueous media. The adsorption isotherm data reveal that the adsorbed amount of PC11-6-11 (per chain) is greater than that of the corresponding monomeric surfactant ((11-methacryloyloxy)undecyltrimethylammonium bromide, PC11), resulting from the greater intermolecular association of PC11-6-11 at the solid/solution interface. The closely packed adsorbed layer of PC11-6-11 provides an opportunity to give a polymer thin film, as a result of in situ photo-polymerization on MF particles (in the second fabrication step) and subsequent acid dissolution of the core MF particles (in the third fabrication step). The dynamic light scattering (DLS) measurements have shown that the apparent hydrodynamic diameter of PC11-6-11 capsules is reversibly changed in response to a change in ionic strength: the increased background electrolyte concentration results in deswelling of the capsules, and vice versa. It seems likely that this swelling/deswelling behavior is primarily driven by the electrostatic interaction between quaternary ammonium groups within the polymerized film. We have also studied the capture and release capabilities of glucose into/from the capsule core and found that (i) glucose is encapsulated into the capsule core at high electrolyte concentrations and (ii) the glucose molecules encapsulated into the core are gradually released when the outer electrolyte solution is replaced by pure water. We believe, therefore, that the PC11-6-11 capsules fabricated here are useful as stimulus-responsive smart vehicles.

Assembly of environmental sensitive microcapsules of PNIPAAm and alginate acid and their application in drug release

The objective of this research was to fabricate stable and environmentally sensitive (PNIPAAm/ALG) n microcapsules via layer-by-layer (LbL) technique. The structure, thermosensitive and pH-sensitive properties of the microcapsules were characterized by transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM), individually. MnCO 3 microparticles and melamine formaldehyde (MF) microparticles were used as templates separately. The microcapsules from MnCO 3 cores were stable over a large pH range with thermosensitive and pH-sensitive properties, while those from MF particles were unstable in basic solutions. To the end, ALG and PNIPAAm were adsorbed on recrystallized taxol alternatively, which obviously prolonged the release time of taxol above lower crystal solution temperature (LCST) of PNIPAAm.

Nonlinear waves externally excited in a complex plasma under microgravity conditions

An experimental study of intense induced oscillations and nonlinear waves in a complex plasma is presented. The neon plasma is created in the PK-3 Plus set-up on board the International Space Station (ISS) by using a capacitively coupled radio frequency (RF) discharge at a low gas pressure of 16 Pa. The excitation conditions are controlled by a function generator creating a periodic variable modulation at the RF electrodes. In the experiments, comparatively large melamine–formaldehyde particles of 9.2 μm diameter are used to reduce the damping rate coefficient. The elliptic-shaped particle cloud (with a small central void) of size 65 × 14 mm2 was stretched horizontally (parallel to the electrodes) and compressed vertically. Without excitation a weak 5 Hz global breathing mode and weak horizontal waves (approximately with the same frequency) are observed. Increasing the modulation frequency widens the spectrum. The modulation first excites a global vertical slashing mode (at the modulation frequency). At a frequency of 3 Hz intense shaking induces periodic nonlinear wave-ridges in the bottom and top parts of the cloud. The ridges travel at an approximately constant speed of 4–5 mm s−1. The modulation also intensifies horizontal waves localized at the horizontal cloud edges, though the regions of intensive waves are visibly disconnected. At higher frequencies the intense wave activity involves all the cloud, and ‘oblique’ (quasi-sound) wave-ridges start to propagate through the cloud. Distributions of wave velocity and force fields are analysed.

A new heterogeneous catalytic system for wastewater treatment: Fe-immobilized polyelectrolyte microshells for accumulation and visible light-assisted photooxidative degradation of dye pollutants

Fe-immobilized polyelectrolyte microshells have been successfully constructed by alternative adsorption of Fe(III) and alginate sodium (ALG) onto the precursor shells composed of chitosan (CHI) and ALG templated on melamine formaldehyde (MF) particles. Confocal laser scanning microscopy (CLSM) directly demonstrated that the as-synthesized (ALG/CHI) 4(ALG/Fe) n ( n = 1, 2) shells could accumulate efficiently rhodamine B (RhB), methylene blue (MB) and acridine orange (AO) in well-defined internal space under moderate conditions via a simple mix processing. Further, H 2O 2 could cross the Fe-immobilized shell walls and react with the dyes concentrated in the interior of shells under visible radiation. The photodegradation of dyes accumulated in the microshells in the presence of H 2O 2 was characterized by UV–vis adsorption spectra and CLSM. More importantly, the photooxidative reaction occurring in the Fe-immobilized microshells can be performed at a wide range of pH from acid to neutral media, which is superior to the conventional Fenton reaction that allows taking effect only under acid condition of pH <4. Electron paramagnetic resonance (EPR) and other studies into the mechanism of the light-activated reaction process give tentative evidence that distinct from the photoreaction occurring in neutral medium, the photoreaction taking place in confined microshells in acid medium proceeds mainly through HO radicals with high oxidative potential.

Microplasma Trapping of Particles

The localized potential gradients created by a microplasma are capable of trapping and concentrating micro- and nanoparticles. In this paper, argon microplasma is generated within a 350-mum discharge gap formed within a microstrip transmission line. Melamine formaldehyde particles (1 mum) are released approximately 2 cm away from the microplasma. The microparticles are then negatively charged by stray electrons, electrostatically drawn toward the potential well of the microplasma, and trapped within the microplasma. The particles are observed to form Coulomb crystals. Time-of-flight experiments show that the particles are trapped in the microplasma by balancing the electrostatic force of the potential well against the molecular drag force. Pulsed plasma data show that the particles retain a net negative charge after the plasma has been extinguished, allowing detection and sorting by electrostatic methods.

Effect of UV−Irradiation on Polyelectrolyte Multilayered Films and Hollow Capsules Prepared by Layer-by-Layer Assembly

Polymer multilayered films were assembled onto planar and particle substrates by the alternate adsorption of oppositely charged polyelectrolytes. Removal of the template from the coated melamine formaldehyde (MF) particles yields hollow polyelectrolyte capsules. The changes in morphology and chemical structure of the capsules after exposure to UV light over a range of intensities and time were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and quartz crystal microgravimetry (QCM). Pronounced shrinkage of the capsules was observed after UV irradiation for capsules formed with polyelectrolytes bearing aromatic groups, such as poly(sodium 4-styrenesulfonate) (PSS). Capsules composed of five bilayers of PSS and poly(diallyldimethylammonium chloride) (PDDA) shrunk to ca. 20% of their original diameter after UV irradiation (20 mW cm-2 at 365 nm) for 120 min. In contrast, negligible shrinkage was observed for capsules formed from polyelectrolytes without...

NRET from naphthalene labels in multilayer shell wall on melamine formaldehyde microparticles fabricated with layer-by-layer self-assembly to pyrene-labeled polyelectrolyte in solution

Core-shell colloidal particles were prepared with the core of monodisperse melamine formaldehyde particles (MF) with a diameter of 3.5 μm. The shell deposited on the core by the layer-by-layer (LbL) self-assembly was made with a copolymer ANp3 of 2-acrylamido-2-methylpropanesulfonate sodium (AMPS) and 3 mol% naphthalene label monomer and poly(diallyldimethylammonium chloride) (PD). Nonradiative energy transfer (NRET) from the naphthalene labels deposited on the MF particles to pyrene labels at a polyelectrolyte APy3, a copolymer of AMPS and 3 mol% pyrene label monomer, or to an ionic pyrene probe 1-pyrenemethylamine hydrochloride (PyMeA · HCl) in water was observed. The NRET efficiency was expressed as the emission intensity ratio I/ I 0 of naphthalene with and without existence of pyrene in the surrounding solution. With increasing pyrene concentration, I/ I 0 decreased down to about 0.2 and the mechanism for this NRET from the inner naphthalene label to the pyrene labels in solution is still ambiguous.

Incorporation of Carbon Nanotubes into Hollow Microcapsules Using a Removable Template Assembly

AbstractSummary: Carboxylated multiwalled carbon nanotubes (MWNTs) were assembled with poly(allylamine hydrochloride) (PAH) onto decomposable colloidal particles, to subsequently yield hollow microcapsules after core removal. A sandwich structure with MWNTs layer embedded in poly(styrenesulfonate sodium salt) (PSS)/PAH multilayers was designed and constructed on melamine formaldehyde particles. Transmission electron microscopy and confocal microscopy revealed the hollow structure and good dispersity of the resultant microcapsules. The MWNTs were uniformly distributed on the capsule walls.TEM images of (PSS/PAH)5/MWNT/(PAH/PSS)2 microcapsules templated on MF microparticles, after core decomposition (main). They still preserve their continuous and intact structure with no signs of rupture. Inset: magnified surface.imageTEM images of (PSS/PAH)5/MWNT/(PAH/PSS)2 microcapsules templated on MF microparticles, after core decomposition (main). They still preserve their continuous and intact structure with no signs of rupture. Inset: magnified surface.

Caracterización de compuestos de escayola reforzados, en relación con el tipo de refuerzo y la relación A/Y

This summary addresses the research conducted on scagliola reinforced with binary additions of fibres and polymer particles (patent P2001-02532 titled (in Spanish) “Scagliola or plaster tiles reinforced with binary additions of polypropylene fibres and melamine-formaldehyde particles”). The very strong plaster or scagliola obtained with this type of reinforcement is very well suited for the manufacture of largescale prefabricated cladding such as used in construction. The material consists in a matrix of any type of plaster or scagliola, preferably scagliola E-35 or similar, along with binary additions of polypropylene filaments cut to a length of 25 mm and melamine formaldehyde particles .The percentage composition of the material, by weight of scagliola or plaster is shown below: - 2% polypropylene fibre (25 mm long, diameter from 6 to 10 deniers) - 0.5% of melamine formaldehyde particles (Melment F-10 or Melment L-10). - Water/plaster ratio = 0.

Two-Component, Ultrathin Microcapsules Prepared by a Core-Mediated Layer-by-Layer Approach

We report the preparation of two-component microcapsules by a method termed core-mediated layer-by-layer (LbL) growth, which utilizes a core particle to mediate the formation of thin multilayer coatings on particles, followed by core removal. In the first (model) system to demonstrate the process, multilayers were prepared on spherical, decomposable melamine formaldehyde (MF) particles by the alternating deposition of poly(styrenesulfonate) (PSS) from solution and MF originating from partial decomposition of the MF core (in-situ acid-decomposed MF, dMF) in a pH 4.0 buffer. The core-mediated LbL method was also applied to a purely biocompatible system, consisting of a sodium alginate (Alg) coating on calcium phosphate (CaP) cores. Ultrathin, two-component PSS/dMF and Ca2+/Alg microcapsules were prepared by decomposing the multilayer-coated cores using 0.1 M hydrochloric acid. Confocal laser scanning microscopy and transmission electron microscopy verified the formation of ultrathin multilayer capsules. Binding of a positively charged fluorescent molecule (doxorubicin) to the multilayer capsules showed that the fluorescence intensity of the capsules regularly increased with increasing capsule wall thickness, confirming that the core mediates PSS/dMF and Ca2+/Alg multilayer formation. Unlike conventionally prepared polyelectrolyte capsules from sacrificial cores, which are three component systems due to the presence of decomposed core material in the oppositely charged polyelectrolyte multilayers, the microcapsules reported here are two-component, as the core material itself forms one of the multilayer components.

Comparative Analysis of Hollow and Filled Polyelectrolyte Microcapsules Templated on Melamine Formaldehyde and Carbonate Cores

AbstractSummary: A comparative study of polyelectrolyte microcapsules templated on melamine formaldehyde (MF) and manganese carbonate (MnCO3) particles was performed using confocal Raman microscopy, scanning electron microscopy and by force measurements with an atomic force microscope. There is no significant difference between the properties of the shells templated on the MF and completely decomposable carbonate particles. In the case of capsules filled with polystyrene sulfonate (PSS), the MF oligomers formed a network complex with the polymer which resulted in a gel‐like structure in the interior. The existence of such a structure was proved by characteristic MF and PSS bands in Raman spectra, the bulky morphology of the dried capsules and much stiffer resistance to applied force as compared with PSS‐filled capsules templated on carbonate particles.SEM images of PSS‐loaded PAH/PSS capsules assembled on the on the MF template core.magnified imageSEM images of PSS‐loaded PAH/PSS capsules assembled on the on the MF template core.