Hybrid Spheres Research Articles

Plate–sphere hybrid dispersions: Heterocoagulation kinetics and DLVO evaluation

We have studied the formation of colloidal composite particles through the controlled heterocoagulation of anionically charged polystyrene (PS) and poly(isobutyl methacrylate) (PiBMA) latex spheres with positively charged gibbsite platelets. The latex particles, synthesized by emulsion polymerization, varied in size and surface charge density. The heterocoagulation was studied as a function of the number ratio between small latex particles and large gibbsite platelets ( N S/ N P), ionic strength and pH of the aqueous medium. The coagulation kinetics of latex spheres with inorganic platelets in aqueous dispersions were determined by time resolved dynamic light scattering (TR-DLS) experiments. The N S/ N P values should be sufficiently high to prevent the formation of multilayer aggregates. It was shown that the heterocoagulated colloidal particles were stable up to an ionic strength of 2.5 mM for latex particles with a diameter of about 80 nm and ∼30 mM for those of 35 nm, respectively. The effect of pH on the colloidal dispersions was verified by the classical DLVO theory.

Synthesis and Magnetic Properties of Biocompatible Hybrid Hollow Spheres

Magnetic hybrid hollow spheres of about 200 nm were prepared by a core-template-free route, that is, adding Fe3O4 nanoparticles stabilized by poly(vinyl alcohol) (PVA) to an aqueous solution of polymer-monomer pairs composed of a cationic polymer, chitosan (CS), and an anionic monomer, acrylic acid (AA), followed by polymerization of acrylic acid and selective cross-linking of chitosan at the end of polymerization. The obtained hybrid spheres were characterized by dynamic light scattering (DLS) in aqueous solution and observed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) in the solid state. Fourier transform infrared spectroscopy (FTIR) and X-ray and electron diffractions revealed that the Fe3O4 nanoparticles were incorporated into the shells of chitosan-poly(acrylic acid) (CS-AA) hollow spheres. Magnetization studies and Mössbauer spectroscopy suggested that the chains (or islands) of iron oxide nanoparticles were most likely formed in the walls of the hollow spheres. The phantom test of magnetic resonance imaging showed that the synthesized hybrid hollow spheres had a significant magnetic resonance signal enhancement in T2-weighted image.

Preparation and characterization of hollow magnetic silica (CoFe 2O 4–SiO 2) microspheres

Hollow magnetic-silica-bilayered microsphere was prepared by the ionic polymer sphere template. After calcination at 600 °C for 5 h, the hollow cobalt ferrite–SiO 2 hybrid spheres were formed. The hollow magnetic (CoFe 2O 4, 73 wt%)/silica (SiO 2, 27 wt%) hybrid sphere was uniform and its thickness was about 50 nm. The hollow CoFe 2O 4/SiO 2 spheres exhibit a superparamagnetic behavior at room temperature.

Multiple Energy Transfers in Rare Earth Complex-Doped SiO 2 Spheres

Silica spheres doped with Eu(TTFA) 3 and/or Sm(TTFA) 3 were synthesized by using the modified Stober method. The transmission electron microscope image reveals that the hybrid spheres have smooth surfaces and an average diameter of about 210 nm. Fluorescence spectrometer was used to analyze the fluorescence properties of hybrid spheres. The results show that multiple energy transfer processes are simultaneously achieved in the same samples co-doped with Eu (TTFA) 3 and Sm(TTFA) 3, namely between the ligand and Eu 3+ ion, the ligand and Sm 3+ ion, and Sm 3+ ion and Eu 3+ ion. Energy transfer of Sm 3+ → Eu 3+ in the hybrid spheres leads to fluorescence enhancement of Eu 3+ emission by approximately an order of magnitude. The lifetimes of the hybrid spheres were also measured.

Improved Thermal Stability of Europium Complex Nanoclusters Embedded in Silica Colloidal Spheres

Abstract Europium complex nanoclusters are introduced into monodisperse colloidal silica spheres by a modified Stöber method. Transmission electron microscopy measurements confirm that the hybrid spheres possess smooth surface and core-shell structure. The hybrid spheres display strong characteristic luminescence of the Eu3+ ions. Furthermore they exhibit an improved thermal stability compared with the pure rare earth (RE) complex.

Modified spontaneous emission of europium complex nanoclusters embedded in colloidal silica spheres

Europium complex nanoclusters were encapsulated inside silica colloidal spheres by a wet-chemical method. The hybrid spheres were characterized to possess a core-shell structure by transmission electron microscopy. The spheres present strong characteristic emissions of Eu 3+ ions, and the fluorescence decay time decreases when the spheres are dispersed in two dielectric polymers. Temperature-dependent decay dynamics indicates that europium complex in sphere-polymer systems display higher spontaneous emission rate compared with free hybrid spheres in air. Our results are suggestive for optimizing the luminescence quantum yield of lanthanide complexes, and also provide a promising probe to investigate modified spontaneous emission in photonic crystals.

Laser selective spectroscopy of europium complex embedded in colloidal silica spheres

Monodisperse colloidal silica spheres embedded with Eu(DBM) 3phen complex were synthesized by a modified Stöber method. The europium complex dispersed in the hybrid spheres display the characteristic luminescence of the Eu 3+ ions. Low-temperature laser selective spectroscopy and decay dynamics were performed to study the luminescence properties of the pure europium complex and the hybrid spheres. Our results indicate that the method of incorporating the Eu complex into the SiO 2 spheres may have a great potential to reduce the contribution of non-radiative processes and optimize the luminescence quantum yield of lanthanide complexes.

The moduli space of the modular group in complex hyperbolic geometry

We construct the space of discrete, faithful, type-preserving representations of the modular group into the isometry group of complex hyperbolic 2-space up to conjugacy. This is the first Fuchsian group for which the entire complex hyperbolic deformation space has been constructed. We also show how the ℂ-spheres of Falbel-Zocca are related to the ℝ-spheres (hybrid spheres) of Schwartz.

Preparation of homogeneous microspheres for optical cavity

Using phenyltriethoxysilane (PTES) as a starting material, preparation of pore-free organic–inorganic hybrid spheres of micrometer sizes have been investigated for their application to optical cavities. Undesirable imperfections such as inside pores which scatter light decrease the quality factor ( Q value) of a sphere. Centrifugation technique using potassium tartrate aqueous solution as a density-changing solvent from 1.0 to 1.4 was developed to separate pore-free particles from as-prepared particles. The percentage of pore-free particles was estimated about 5% of the weight of as-prepared samples. The size distribution of precipitated particles in various density solvents was estimated by scanning electron micrograph. Larger density, pore-free particles had a smaller size compared with those of low density, pore-containing spheres.

Synthesis of monodispersed organic-inorganic hybrid spheres

This paper describes the attempt to prepare a new group of monodispersed silica-polymer hybrid particles, which consists of silica and amide polymer: poly(vinylpyrrolidone) (PVP) and poly(2-ethyloxazoline) (POXZ). Preparation method is based on the growth of hybrid seeds by the addition of TEOS-polymer solution.

A Design Study of Thick Multilayered Composite Spherical Pressure Vessels

A design study of a multilayered spherical composite pressure vessel is presented. Layers of the vessel are composed of quasi-isotropic lay-ups of composite laminae. For the stress analysis layers are assumed to be homogeneous, having the three- dimensional properties equivalent to that of the quasi-isotropic laminates. The linear theory of elasticity is employed so that the analysis is not limited to any thickness of the vessel. The Tsai Wu failure criterion is found suitable for the strength analysis. Based on coupon tests, the value of interaction term F*yz of the failure criterion is found approx imately to be - 0.84. The failure criterion is applied to each lamina using the lamina con stitutive law and lamination angle. It is found that the first-ply-failure (FPF) controls the final failure. Further, a design study of a spherical vessel for operating at 200 MPa of in ternal pressure is presented. In view of current manufacturing difficulties a design restric tion of b/a ≤ 1.25 (b: outer radius, a: inner radius) was imposed for this design. How ever, a two-layered hybrid sphere of b/a = 1.25 with T300/5208 and IM6/epoxy outside is considered to be an acceptable design. The test data of two vessels are also reported in this study.

Cell labeling and magnetic separation by means of immunoreagents based on polyacrolein microspheres

Polyacrolein (PA) microspheres were synthesized by means of ionizing radiation and shown to contain aldehyde groups which form covalent bounds with amino compounds and proteins. PA microspheres made fluorescent after reaction with fluorescein-labeled antibodies were found to specifically label sensitized sheep red blood cells (SRBC). PA microspheres could also be grafted onto a variety of polymeric spheres of different sizes and composition by ionizing radiation. These hybrid spheres, i.e., preformed polymeric spheres with PA microspheres grafted on their surfaces could bind antibodies which retained specificity of reaction with cell surface receptors. Purification of sensitized SRBC from a mixture containing chicken red blood cells (CRBC) by means of hybrid magnetic spheres in a magnetic field was demonstrated.