Melamine Formaldehyde Particles Research Articles

Enhanced Biomacromolecule Encapsulation by Swelling and Shrinking Procedures

Reversible growth: Microcapsules were fabricated by layer-by-layer assembly of poly(diallyldimethyl ammonium chloride)/poly(styrene sulfonate) onto removable melamine formaldehyde particles. The capsules with swelling and shrinking features (see graphic) provide a novel route for microencapsulation. Loading of biomacromolecules such as dextran with ultrahigh molecular weight is achieved by spontaneously opening the capsule during core removal procedure, followed by closing the capsule in salt solution.

Formation of Uniform Polyaniline Thin Shells and Hollow Capsules Using Polyelectrolyte-Coated Microspheres as Templates

Multilayers of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) precoated onto melamine formaldehyde (MF) particles via the layer-by-layer (LbL) self-assembly procedure were used as templates for the subsequent deposition of polyaniline (PANI). Transmission electron microscopic (TEM) and scanning electron microscopic (SEM) images reveal that the as-prepared PANI-containing polyelectrolyte (PE)−MF core−shell particles are narrowly dispersed and possess uniform surface morphology. Intact hollow PANI/PE capsules can also be produced by extracting the MF cores in an acidic solution. FTIR spectra of the hollow capsules indicate that PANI and PE are both present and suggest that the PANI exists in the emeraldine form. The incorporation of PANI in the shells was found to enhance the rigidity of these composite materials, and the PANI/PE-coated MF core−shell particles have comparable conductivities with other PANI-coated colloidal particles. The amount of PANI incorporation was also foun...

Enhanced Raman imaging and optical spectra of gold nanoparticle doped microcapsules

Gold nanoparticle doped hollow polyelectrolyte microcapsules (gold-doped capsules) were prepared by the layer-by-layer self-assembly method. After sequential adsorption of oppositely charged polyelectrolytes of poly(styrenesulfonate) sodium salt (PSS), poly(allylamine hydrochloride) (PAH) or gold nanoparticles onto melamine formaldehyde particles (MF), intact gold-doped capsules were obtained by dissolving the MF templates via low pH. The maximum absorbance peaks of gold-doped capsules shifted to long wavelengths with increasing filling factor of the gold nanoparticles in accordance with Maxwell–Garnet theory. Due to protection of the nanoparticle surfaces by the polyelectrolyte multilayer surroundings, stable optical properties of gold-doped capsules were observed in low pH solution or organic solvent. Gold nanoparticles in the multilayer enhance the Raman spectra of the polyelectrolyte multilayers, in contrast with the weak Raman signal, which was observed for normal capsules. High-resolution surface Raman imaging was performed by controlling the filling factor.

Layer-by-Layer Engineered Microreactors for Bio-Polymerization of 4-(2-aminoethyl) phenol hydrochloride

ABSTRACTThis study presents the results of polymerization of phenol to yield fluorescent polymer encapsulated within shells fabricated via layer-by-layer (L-b-L) assembly. Hollow polyelectrolyte microcapsules (shells) were prepared using weakly cross-linked melamine formaldehyde (MF) particles. Dissolution of the MF cores was achieved by changing the pH of the solution. Horseradish peroxidase (HRP), the catalyzing enzyme, was loaded in these capsules by taking advantage of the “open/close” mechanism of the capsules by altering the pH. The empty shells were then suspended in a concentrated solution of monomer. Since the monomer is a low molecular weight species, it freely permeates through the polyion wall into the shells. Addition of aliquots of hydrogen peroxide initiated the polymerization reaction and the polymer formed from the ensuing reaction was confined in the shells due to its high molecular weight. The model used for demonstrating this synthesis is polymerization of 4-(2-aminoethyl) phenol hydrochloride commonly known as tyramine hydrochloride to its corresponding polymeric form by reacting it with hydrogen peroxide. Fluorescence spectrometry (FS), confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM) were the characterization methods employed to confirm polymerization in situ shells.

Novel capsules with high stability and controlled permeability by hierarchic templating.

Nanoporous shell or sphere-in-sphere structures have been constructed by consecutive alternating adsorption of polyelectrolytes and SiO2 on melamine formaldehyde particles, followed by removal of the cores with HCl and SiO2 with HF. The shells have been distinguished by confocal laser scanning microscopy imaging (see picture) by partially labeling the inner shell with fluorescein (yellow emission) and the outer sphere with rhodamine B (red emission).

Melamine Formaldehyde Core Decomposition as the Key Step Controlling Capsule Integrity: Optimizing the Polyelectrolyte Capsule Fabrication

Capsule integrity as a function of the acid concentration, the acid-adding sequence, the outermost layer of the deposited multilayers, and the capsule wall thickness was investigated using confocal laser scanning microscopy. Optimal conditions for fabricating good quality polyelectrolyte capsules templated on melamine formaldehyde (MF) particles are elaborated. Intact capsules in a yield of higher than 90% can be normally obtained by injecting a small amount of MF particles coated with 10 polyelectrolyte layers (with positively charged species as the outermost layer) into a large amount of acid solution at pH 1.1. The capsule integrity depends on the interplay between the rate of the core decomposition and the permeation of the degraded products through the capsule walls. A larger permeability and an appropriate core-decomposition speed would be favorable for releasing the tension, thus facilitating the permeation of intact capsules.

Polyelectrolyte multilayer capsule permeability control

Abstract The permeability properties of hollow polyelectrolyte multilayer capsules for different substances were investigated as a function of pH and salt concentration. Capsules were prepared by layer-by-layer (LBL) adsorption of oppositely charged polyelectrolytes onto the surface of melamine formaldehyde and CdCO3 particles followed by core removal. It was shown that the capsules are closed at a pH value of 8 and higher, but at a pH lower than 6 the macromolecules permeate into the capsule interior. For low molecular weight molecules capsules, templated on CdCO3 cores were found to be less permeable than MF-derived capsules. The open and closed states of the capsule wall are reversible. It provides thus an opportunity to encapsulate different materials into polyelectrolyte capsules.

Layer-by-Layer Self-Assembly of Polyelectrolyte and Low Molecular Weight Species into Capsules

Composite capsules containing low molecular weight species together with charged macromolecules have been prepared both in aqueous and organic solutions. Dyes were used as building blocks to quantify the adsorption. The Figure shows a tapping mode scanning force microscopy image of capsules consisting of poly(styrene sulfonate) and benzoquinone layers templated on melamine formaldehyde particles (see also inside front cover).

Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles. Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte Capsules

Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb3+/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature. Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb3+/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed.

Formation of macroparticle structures in an rf induction discharge plasma

It was demonstrated experimentally that macroparticles may undergo levitation and form ordered structures in an rf induction discharge plasma. The experiments were carried out using 1.87 μm melamine formaldehyde particles in neon at a pressure of 25–500 Pa. The generator frequency was 100 MHz.

Influence of Polyelectrolyte Multilayer Coatings on Förster Resonance Energy Transfer between 6-Carboxyfluorescein and Rhodamine B-Labeled Particles in Aqueous Solution

The Förster resonance energy transfer (FRET) between 6-carboxyfluorescein (6-CF) (donor) and rhodamine B-labeled melamine formaldehyde (RhB-MF) particles (acceptor) in aqueous solution was exploited to investigate the layer properties of polyelectrolyte (PE) multilayers preadsorbed on the particle surface. The formation of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) multilayers on the RhB-MF particles was confirmed by electrophoretic mobility measurements. The FRET process was found to proceed via adsorption of 6-CF onto the RhB-MF particles and was thus dependent on the degree of surface coverage of the PE on the surface. The PE surface coverage could be altered by depositing the layers with or without added electrolyte. The extent of FRET was also influenced by the number of PE layers (and hence layer thickness) surrounding the RhB-MF particles. Increasing the number of PE layers resulted in less energy transfer, reflecting less accessible sites on the RhB-MF particles for 6-CF adsorption. The PE layers were found to be permeable to 6-CF, with no diffusion effects evident on the time scale of the steady-state fluorescence measurements. Further, 6-CF was found to interact with PAH when the outer PE layer on the particles was PAH. This interaction presents a novel way of detecting amino sites of PAH not interacting with PSS in the PE multilayer films.