Synthesis of monodisperse, highly cross-linked, fluorescent PMMA particles by dispersion polymerization

We describe a facile method to synthesize sterically stabilized monodisperse fluorescent poly(methyl methacrylate) (PMMA) colloids in the polar solvent mixture water/methanol with either a core-shell or a homogeneously cross-linked structure by dispersion polymerization. The particles were sterically stabilized by the polymer poly(vinylpyrrolidone) (PVP). The morphology of the particles was controlled by varying the moment at which the gradual addition of cross-linker and dye was started. The absence of these extra agents at a time when the particle nuclei formed reduced the negative effects on this important process to a minimum and produced a core-shell structure, whereas an essentially homogeneously cross-linked fluorescent polymer colloid structure could be obtained by reducing the starting time of the addition of dye and cross-linker to zero. Three different dyes were chemically incorporated into the polymer network. Such dyes are important for the use of the particles in confocal scanning laser microscopy studies aimed at characterizing concentrated dispersions quantitatively in real space. A series of PMMA particles with different sizes were obtained through the variation of the weight ratio of solvents and the content of cross-linker. Furthermore, the swelling properties of the cross-linked PMMA particles in a good solvent (tetrahydrofuran) were investigated. The particles were stable in polar solvents (water and formamide) but could also successfully be transferred to apolar solvents such as decahydronaphthalene (decalin). The PVP stabilizer also allowed the particles to be permanently bonded in flexible strings by the application of an external electric field.     

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.     

Preparation of highly monodisperse fluorescent polymer particles by miniemulsion polymerization of styrene with a polymerizable surfactant

Miniemulsion polymerization of styrene (St) in the presence of a hydrophobe (hexadecane:HD) using a cationic polymerizable surfactant (N,N-dimethyl-N-n-dodecyl-N-2-methacryloyloxyethylammonium bromide:C(12)Br) and a cationic initiator (2,2'-azobis(2-amidinopropane) dihydrochloride:V50), called St/C(12)Br/V50 hereafter, proceeded efficiently compared with that using sodium dodecyl sulfate (SDS) and potassium persulfate (KPS), i.e., St/SDS/KPS, providing monodisperse polystyrene latex particles with a narrower particle size distribution. In St/C(12)Br/AIBN, where an oil-soluble initiator, i.e., 2,2'-azobisisobutyronitrile (AIBN), was used in place of V50, little changes in polymerization kinetics or in particle size distribution were observed, while a significant drop in polymerization rate and a broad particle size distribution were observed with St/SDS/AIBN. A polymerizable pyrene derivative (1-pyrenylmethyl methacrylate: PyMMA) was quantitatively incorporated into monodisperse latex particles in St/PyMMA/C(12)Br/V50 compared to pyrene (Py) in St/Py/C(12)Br/V50. Contrary to our expectation, however, increased excimer emission was observed with St/PyMMA/C(12)Br/V50 particles, indicating less evenly distributed pyrene chromophores in the particles. The fluorescence lifetime of pyrene chromophores in St/Py/C(12)Br/V50 particles was determined to be 286 ns, which was 17 times longer than that of pyrene in THF solution.     

TEM, XRD, and thermal stability of adsorbed paranitrophenol on DDOAB organoclay

Water purification is of extreme importance to modern society. Organoclays through adsorption of recalcitrant organics provides one mechanism for the removal of these molecules. The organoclay was synthesised through ion exchange with dimethyldioctadecylammonium bromide labeled as DDOAB of formula (CH3(CH2)17)2NBr(CH3)2. Paranitrophenol (pnp) was adsorbed on the organoclay at a range of concentrations according to the cation exchange capacity (CEC) of the host montmorillonite. The paranitrophenol in solution was analysed by a UV-260 spectrophotometer at 317 nm, with detection limits being 0.05 mg/L. The expansion of the montmorillonite was studied by a combination of X-ray diffraction and transmission electron microscopy. Upon adsorption of the paranitrophenol the basal spacing decreased. The thermal stability of the organoclay was determined by a combination of thermogravimetry and infrared emission spectroscopy. The surfactant molecule DDOAB combusts at 166, 244, and 304 degrees C and upon intercalation into Na-montmorillonite is retained up to 389 degrees C thus showing the organoclay is stable to significantly high temperatures well above the combustion/decomposition temperature of the organoclay.     

XRD,SAXS, and PALS investigations of three different polymers reinforced with tetraoctylammonium exchanged montmorillonite

Three different polymer nanocomposites were prepared using clay modified with tetraoctylammonium (4C8) surfactant. The dispersion of clay silicate layers was studied using X-ray diffraction and small-angle scattering. Free-volume cavity sizes were studied with positron annihilation lifetime spectroscopy. Scattering methods confirmed disruption of all polymer lamellae organization upon organoclay addition and the creation of partially intercalated systems for polyamide and polycaprolactone. The presence of organoclay in the polymers enlarges the lower value of average positronium lifetime τ₃ of polyamide and reduces the higher value of τ₃ for polycaprolactone and polyethylene.     

Synthesis of highly crosslinked monodisperse polymer particles: Effect of reaction parameters on the size and size distribution

Monodisperse polystyrene particles crosslinked with different concentrations of divinylbenzene were synthesized in the 3.2–9.1 μm size range by dispersion polymerization in an isopropyl alcohol/toluene mixed‐dispersion medium with poly(N‐vinylpyrrolidone) as a steric stabilizer and 2,2′‐azobisisobutyronitrile as a radical initiator. The effects of the reaction parameters such as the crosslinking agent concentration, media solvency (controlled by varying the amount of toluene addition), the initiator concentration, and the stabilizer concentration on the particle size and size distribution were investigated with reference particles with a monodisperse size distribution and crosslinked by 1.5 wt % divinylbenzene. The appropriate increase in media solvency was a prerequisite for preparing crosslinked particles without coagulated and/or odd‐shaped particles. The investigation of the effects of the polymerization parameters also shows that only specific sets of conditions produce particles with a monodisperse size distribution. The glass‐transition temperatures of the particles increased with increasing divinylbenzene concentration. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4368–4377, 2002     

XRD,TEM and thermal analysis of Fe doped boehmite nanofibres and nanosheets

Iron doped boehmite nanofibres with varying iron content have been prepared at low temperatures using a hydrothermal treatment in the presence of poly(ethylene oxide) surfactant. The resultant nanofibres were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). TEM images showed the resulting nanostructures are predominantly nanofibres when Fe doping is no more than 5%; in contrast nanosheets were formed if Fe doping was above 5%. For the 10% Fe doped boehmite, a mixed morphology of nanofibres and nanosheets were obtained. Nanotubes instead of nanofibres were observed in samples with 20% added iron. The Fe doped boehmite and the subsequent nanofibres/nanotubes were analysed by thermogravimetric and differential thermogravimetric methods. Boehmite nanofibres decompose at higher temperatures than non-hydrothermally treated boehmite and nano-sheets decompose at lower temperatures than the nanofibres.     

XRD,TEM and thermal analysis of yttrium doped boehmite nanofibres and nanosheets

Yttrium doped boehmite nanofibres with varying yttrium content have been prepared at low temperatures using a hydrothermal treatment in the presence of poly(ethylene oxide) surfactant (PEO). The resultant nanofibres were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM images showed the resulting nanostructures are predominantly nanofibres when Y-doping is less than 5%; in contrast Y-rich phases were formed when doping was around 10%. The doped boehmite and the subsequent nanofibres/nanotubes were analyzed by thermogravimetric and controlled rate thermal analysis methods. The boehmite nanofibres produced in this research thermally transform at higher temperatures than boehmite crystals and boehmite platelets. Boehmite nanofibres decompose at higher temperatures than non-hydrothermally treated boehmite.     

Structural investigation on bulk poly(3-hexylthiophene): Combined SAXS, WAXD, and AFM studies

A detailed structural and morphological study on bulk poly(3-hexylthiophene), having high regioregularity (about 98%) and molecular weight of 16 kDa, has been performed. The combination of wide- and small-angle X-ray diffraction techniques, for the first time on bulk semicrystalline conjugated polymer, allowed to get insight on the structural features of poly(3-hexylthiophene), subjected to different thermal treatments. The evolution or the periodicity, the crystallite dimension and defects, as a function of the annealing were determined. Fibrillar organization, evidenced atomic force microscopy, results in the coexistence of disordered areas where fibrils are randomly oriented and ordered regions where fibrils are organized into stacks, with periodic pattern matching the periodicity determined by X-ray scattering.     

First in-situ SAXS studies of the mesostructuration of spherical silica and titania particles during spray-drying process

Meso-organisation of SiO2 and TiO2 particles prepared by spray drying have been for the first time analysed through in-situ SAXS. Both processing and chemical parameters are critical to obtain meso-organised spheres.     

Dispersion copolymerization of styrene and divinylbenzene: Synthesis of monodisperse,uniformly crosslinked particles

Monodisperse, crosslinked polystyrene latexes were prepared by the dispersion technique. Some general observations regarding the effect of initial reagent concentrations on final particle size and size distribution are offered, in addition to a detailed discussion concerning the problems encountered with the use of the crosslinker divinylbenzene (DVB) in latex preparation. Particles synthesized in very polar media were found to reach their growth plateau sooner than those made in less polar surroundings. This trend was proposed to be the result of more effective nucleation in polar environments, which increases available surface area, thereby allowing the rapid replacement of monomer consumed within the particle phase during the polymerization. Attempts to favorably influence the growth rate and size distribution of particles during the reaction were unsuccessful, underlining the importance of the nucleation period in defining particle size characteristics. Up to 1% DVB was successfully incorporated in the synthesis of coagulum-free, monodisperse, 5 μm beads, by controlling the entry of the crosslinker into the particle phase during the major particle growth period. Latex stability is proposed to be largely dependent on the mobility of the adsorbed steric stabilizer. © 1995 John Wiley & Sons, Inc.     

Synthesis of NiGa layered double hydroxides. A combined EXAFS, SAXS, and TEM study. 3. Synthesis at constant pH

The present paper focuses on the direct synthesis of NiGa layered double hydroxides (LDHs) by concomitant addition of Ni and Ga chloride in solution with NaOH solution, at a constant pH value of 6.5. Various Ni/Ga ratios (Ni/Ga = 2, Ni/Ga = 4, or Ni/Ga = 6) were investigated, and samples were collected after successive additions. Each sample was then analyzed by small-angle X-ray scattering (SAXS) to derive information about the shape of the objects formed upon synthesis. In parallel Ni K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS) analysis were carried out on relevant samples to obtain information on the local structure of the species in suspension. SAXS curves reveal significant changes. At the beginning of the synthesis, for low added volumes (V(s)), the suspension appears to contain both monodimensional and bidimensional objects. For higher V(s), the monodimensional objects disappear and only platelike particles are detected in the suspension. EXAFS results show that all the added gallium atoms are involved in a solid Ni-Ga LDH phase throughout the whole synthesis. In contrast, some nickel cations do not precipitate in the Ni-Ga LDH. At the beginning of the synthesis, for low added volumes they are also involved in the formation of fibrous polycations. For higher added volumes, the fibers are not observed anymore and monomeric nickel species are then present in the suspension.     

Acetate- and thiol-capped monodisperse ruthenium nanoparticles: XPS, XAS, and HRTEM studies

Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.     

Synthesis and characterization of monodisperse, mesoporous, and magnetic sub-micron particles doped with a near-infrared fluorescent dye

Recently, multifunctional silica nanoparticles have been investigated extensively for their potential use in biomedical applications. We have prepared sub-micron monodisperse and stable multifunctional mesoporous silica particles with a high level of magnetization and fluorescence in the near infrared region using an one-pot synthesis technique. Commercial magnetite nanocrystals and a conjugated-NIR-dye were incorporated inside the particles during the silica condensation reaction. The particles were then coated with polyethyleneglycol to stop aggregation. X-ray diffraction, N₂ adsorption analysis, TEM, fluorescence and absorbance measurements were used to structurally characterize the particles. These mesoporous silica spheres have a large surface area (1978 m²/g) with 3.40 nm pore diameter and a high fluorescence in the near infrared region at λ=700 nm. To explore the potential of these particles for drug delivery applications, the pore accessibility to hydrophobic drugs was simulated by successfully trapping a hydrophobic ruthenium dye complex inside the particle with an estimated concentration of 3 wt%. Fluorescence imaging confirmed the presence of both NIR dye and the post-grafted ruthenium dye complex inside the particles. These particles moved at approximately 150 μm/s under the influence of a magnetic field, hence demonstrating the multifunctionality and potential for biomedical applications in targeting and imaging.     

Thermal, UV, FTIR, and XRD studies of urinary stones

Various crystals are seen in human urine. Oxalate, Phosphate, Uric acid, and Urate crystals are generally seen in urinary calculi. Calcium stones are most common, comprising 75 % of all urinary calculi. They may be pure calcium oxalate or calcium phosphate or a mixture of both. Many stones are not homogeneous. Low calcium intake increases the intestinal absorption of calcium, thus decreasing the amount of calcium available in the intestinal tract to form insoluble complexes with Oxalate. Consequently, a higher amount of oxalate is available for intestinal absorption and as a result, urinary oxalate excretion increases. Mineral water consumption did not reduce urinary oxalate excretion. High urinary excretion and concentration of magnesium decrease both the nucleation and growth rates of calcium oxalate crystals in urine, because of the higher solubility of magnesium oxalate compared with calcium oxalate. Analytical results show calcium oxalate to be one of the major inorganic components of renal stones and found to be present in almost all kidney and bladder stones. About 39.5 % of the total composition of the calculi is found to contain purely calcium oxalate and also hydroxyl apatite. The ten samples are a mixture of calcium oxalate and phosphate stones. Four samples are calcium oxalate as major composition and the remaining are calcium phosphate as major composition. These kidney stones are taken photographically and size of the stone are measured using optical microscopy. These qualitative analyses are also confirmed by UV, FTIR, DSC, and XRD analysis.     

SrP3N5O: a highly condensed layer phosphate structure solved from a nanocrystal by automated electron diffraction tomography

The oxonitridophosphate SrP₃N₅O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH₂)₃, thiophosphoryl triamide SP(NH₂)₃, SrS, and NH₄Cl enclosed in evacuated and sealed silica‐glass ampoules up to 750 °C. The compound was obtained as nanocrystalline powder with needle‐shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X‐ray powder diffraction data. SrP₃N₅O crystallizes in the orthorhombic space group Pnma (no. 62) with unit‐cell data of a=18.331(2), b=8.086(1), c=13.851(1) Å and Z=16. The compound is a highly condensed layer phosphate with a degree of condensation κ=1/2. The corrugated layers ${{{\hfill 2\atop \hfill \infty }}}The oxonitridophosphate SrP(3)N(5)O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), SrS, and NH(4)Cl enclosed in evacuated and sealed silica-glass ampoules up to 750 °C. The compound was obtained as nanocrystalline powder with needle-shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X-ray powder diffraction data. SrP(3)N(5)O crystallizes in the orthorhombic space group Pnma (no. 62) with unit-cell data of a=18.331(2), b=8.086(1), c=13.851(1) ? and Z=16. The compound is a highly condensed layer phosphate with a degree of condensation κ=?. The corrugated layers (∞)(2){(P(3)N(5)O)(2-)} consist of linked, triangular columns built up from P(O,N)(4) tetrahedra with 3-rings and triply binding nitrogen atoms. The Sr(2+) ions are located between the layers and exhibit six-, eight-, and ninefold coordination. FTIR and solid-state NMR spectra of SrP(3)N(5)O are discussed as well.     

Synthesis and properties of monodisperse oligofluorene-functionalized truxenes: highly fluorescent star-shaped architectures

This paper describes the strategy toward novel monodisperse, well-defined, star-shaped oligofluorenes with a central truxene core and from monofluorene to quaterfluorene arms. Introduction of solubilizing n-hexyl groups at both fluorene and truxene moieties results in highly soluble, intrinsically two-dimensional nanosized macromolecules T1-T4. The radius for the largest oligomer of ca. 3.9 nm represents one of the largest known star-shaped conjugated systems. Cyclic voltammetry experiments reveal reversible or quasi-reversible oxidation and reduction processes (Eox = +0.74 to 0.80 V, Ered = -2.66 to 2.80 eV vs Fc/Fc+), demonstrating excellent electrochemical stability toward both p- and n-doping, while the band gaps of the oligomers are quite high (EgCV = 3.20-3.40 eV). Close band gaps of 3.05-3.29 eV have been estimated from the electron absorption spectra. These star-shaped macromolecules demonstrate good thermal stability (up to 400-420 degrees C) and improved glass transition temperatures with an increase in length of the oligofluorene arms (from Tg = 63 degrees C for T1 to 116 degrees C for T4) and show very efficient blue photoluminescence (lambdaPL = 398-422 nm) in both solution (PhiPL = 70-86%) and solid state (PhiPL = 43-60%). Spectroelectrochemical experiments reveal that compounds T1-T4 are stable electrochromic systems which change their color reversibly from colorless in the neutral state (approximately 340-400 nm) to colored (from red to purple color; approximately 500-600 nm) in the oxidized state.     

Synthesis of NiGa layered double hydroxides. A combined EXAFS, SAXS, and TEM study. 2. Hydrolysis of a Ni2+/Ga3+ solution

Takovites are nickel-based layered double hydroxides (LDH) with a general formula that can be written as Ni(1-x)Al(x)(OH)2, A(z-)(x/z), yH(2)O, where A is a compensating interlayer anion. As in some other LDH samples, the positive charge of the layer can be adjusted upon synthesis and various anions can be exchanged in the interlayer region. It is then important to understand the synthesis pathway of these materials. We then undertook a study on the hydrolytic behavior of pure Ni salts and mixtures of Ni and Ga salts. This paper focuses on the hydrolysis of Ni(2+) and Ga(3+) ions, together in solution, carried out by base addition. The samples will be defined by their hydrolysis ratio R = [OH(-)]/([Ni(2+)] + [Ga(3+)]). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to obtain information on the colloidal species size and shape on a large scale. Each hydrolyzed sample was also studied by Ni K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS) to obtain information on the local structure of the species in suspension. SAXS curves reveal the presence of bidimensional objects whatever the R values. The platelets formed for R values >/=1.1 are slightly thicker and smaller in size, which may be linked to their different natures. Complementary information is provided by TEM analysis: the first colloids formed have a structure very close to that of alpha-GaOOH, as shown by electronic diffraction. Those structures are progressively replaced by Ni-Ga LDH platelets with increasing hydrolysis ratio, which are the only species in suspension for R = 2.0, as shown by XRD. EXAFS results confirm the complete hydrolysis of gallium before the formation of Ni-Ga LDH phases.