Monodisperse Colloidal Spheres Research Articles

Fabrication of high-quality colloidal crystal films by vertical deposition method integrated with a piezoelectric actuator

In recent years the self-assembling of monodispersed colloidal spheres has gained much attention due to their potentials in many fields. Though many self-assembling methods have been put forward, the existence of many defects in colloidal crystals is still an open question restricting the dimensions of ordered domains and the performance thereof in many applications. In this paper we introduced a modified vertical deposition method to improve film quality of colloidal crystal films. A piezoelectric actuator was integrated with the conventional vertical deposition method, which excited the substrate vibrating along the vertical direction. The vibratory amplitude and frequency of the actuator could be controlled by the driving voltage. Our experimental observations indicated that, grown at proper driving parameters, frequency of 300 Hz and vibratory amplitude of 310 nm in our current observations, film quality could be greatly improved with less defects. The mechanism was also briefly illuminated.

A Two-Step Hydrothermal Synthesis Approach to Monodispersed Colloidal Carbon Spheres

This work reports a newly developed two-step hydrothermal method for the synthesis of monodispersed colloidal carbon spheres (CCS) under mild conditions. Using this approach, monodispersed CCS with diameters ranging from 160 to 400 nm were synthesized with a standard deviation around 8%. The monomer concentration ranging from 0.1 to 0.4 M is in favor of generation of narrower size distribution of CCS. The particle characteristics (e.g., shape, size, and distribution) and chemical stability were then characterized by using various techniques, including scanning electron microscopy (SEM), FT-IR spectrum analysis, and thermalgravity analysis (TGA). The possible nucleation and growth mechanism of colloidal carbon spheres were also discussed. The findings would be useful for the synthesis of more monodispersed nanoparticles and for the functional assembly.

Synthesis and Plasmon‐Induced Charge‐Transfer Properties of Monodisperse Gold‐Doped Titania Microspheres

Monodisperse gold-doped titania microspheres have been synthesized under high concentration of a titanium precursor (9.34 mM) by introducing a trace amount of chloroauric acid (CA) into the reaction system; the size of the microspheres can be easily tuned (from approximately 587 to approximately 392 nm) by varying the amount of the CA added. The plausible formation mechanism has been discussed in detail. Chloroauric acid was found to act as the stabilizing agent to induce the formation of monodisperse colloidal spheres. Gold-doped anatase titania spheres with approximately 7 nm gold nanodots on the surface were synthesized by calcination. Interestingly, results from surface photocurrent, surface photovoltage, and transient photovoltage measurements indicate that the gold nanodots exhibit different electronic properties when the gold-doped anatase titania spheres were illuminated by different wavelengths of light: one is an electron acceptor in the UV region, while the other is an electron donor in the visible region. Furthermore, the decay time of the injected plasmon-induced electrons was found to be on the millisecond timescale and increased with increasing amounts of gold doped.

Confocal microscopy of geometrically frustrated hard sphere crystals

Confocal microscopy has been used to study the crystallization of two colloidal model systems that are geometrically frustrated in a completely different way: (I) hard colloidal polyhedrals, where crystallization is frustrated due to the incommensurate particle shape and (II) large spherical impurities in a sea of monodisperse colloidal hard spheres, where crystallization is frustrated by the introduction of impurities. As a reference system, we analyzed the crystallization of pure monodisperse colloidal hard spheres. We show that although the crystal structures of both systems are highly dissimilar on the individual particle level, both sources of geometrical frustration have a similar effect on the structure on the grain level. We quantitatively characterize the polycrystalline structures and study the crystallization process in time. Whereas grain boundaries persist in the frustrated systems due to structural arrest, the majority of grain boundaries anneals out quite rapidly in the reference system. Therefore, we argue that both sources of geometrical frustration cause a polycrystalline structure.

Controlled Synthesis, Growth Mechanism, and Properties of Monodisperse CdS Colloidal Spheres

Highly monodisperse submicrometer CdS colloidal spheres (CSCS) with a controllable and tunable size (between 80 and 500 nm) have been synthesized through a facile solvothermal technique. Owing to the controllability of the reaction process, the growth mechanism of the colloidal spheres has been elucidated in detail. The whole growth process can be summarized as homogenous and slow nucleation of nanocrystals, formation of "cores" through 3D-oriented attachment of nanocrystals, and further surface-induced growth to monodisperse colloidal spheres through in situ formation and random attachment of additional nanocrystals. It has been demonstrated that the obtained CSCS colloidal particles are able to be assembled into films which show characteristic stop band gaps of photonic crystals. By using the CSCS as a template, Ag2S, Bi2S3, Cu2S, HgS, and Sb2S3 colloidal spheres, which are difficult to obtain directly, have also been prepared successfully through ion exchange.

Multiphase coexistence in polydisperse colloidal mixtures

The authors study the phase behavior of mixtures of monodisperse colloidal spheres with a depletion agent which can have arbitrary shape and can possess a polydisperse size or shape distribution. In the low concentration limit considered here, the authors can employ the free-volume theory and take the geometry of particles of the depletion agent into account within the framework of fundamental measure theory. The authors apply their approach to study the phase diagram of a mixture of (monodisperse) colloidal spheres and two polydisperse polymer components. By fine tuning the distribution of the polymer, it is possible to construct a complex phase diagram which exhibits two stable critical points.

Synthesis and characterization of monodisperse colloidal spheres of Pb containing superparamagnetic Fe 3O 4 nanoparticles

Monodisperse colloidal spheres of Pb embedded with superparamagnetic Fe 3O 4 nanoparticles have been synthesized by refluxing lead acetate in the presence of a magnetite-based ferrofluid in tetra(ethylene glycol), followed by quenching with cold ethanol. Depending on the amounts of ferrofluid and lead acetate fed to the reaction mixture, the molar ratio of encapsulated Fe 3O 4 to Pb could be varied in the range of 0.001–0.06. Both superparamagnetic and superconducting properties were characterized by SQUID measurements. These results demonstrate a simple, solution-phase approach to the controlled synthesis of composite colloidal spheres displaying a combination of superconducting and superparamagnetic properties.

Colloidal transport through optical tweezer arrays

Viscously damped particles driven past an evenly spaced array of potential energy wells or barriers may become kinetically locked in to the array, or else may escape from the array. The transition between locked-in and free-running states has been predicted to depend sensitively on the ratio between the particles' size and the separation between wells. This prediction is confirmed by measurements on monodisperse colloidal spheres driven through arrays of holographic optical traps.

Colloidal building blocks with potential for magnetically configurable photonic crystals.

This contribution highlights some recent advances in the synthesis of monodispersed colloidal spheres loaded with superparamagnetic components for external manipulation. We firstly discuss how FeO nanoparticles can be directly coated with silica to form core-shell particles using a sol-gel approach. We then focus on the demonstration of new materials for such an application, with Pb and amorphous Se as the typical examples of metals and semiconductors, respectively. We also illustrate how colloidal spheres of amorphous Se can be converted into AgSe and then MSe (M = Zn, Cd, and Pb) without changing the spherical shape. Combined together, these synthetic methods could enable the synthesis of monodispersed colloidal spheres with controlled size, smooth surface, and superparamagnetic features for fabricating photonic crystals whose band structures can be configured using an external magnetic field.

Fabrication of large area ordered metal nanoring arrays for nanoscale optical sensors

In contrast to metal nanodots, nanoring structures are accessible to various sensing and spectroscopy applications at nanometer scale due to their tunable plasmon resonances and large empty volume confined that provides more spaces for molecular attachment. In almost all the applications, fabrication of large area ordered metal nanoring arrays represents the first and one of the most significant challenges. This paper describes a simple and low-cost method of producing large area ordered metal nanoring arrays based on self-assembled monolayers of monodisperse colloidal spheres by combining reactive ion etching, sputtering and ion polishing techniques. Inner diameter, wall thickness and wall height of nanorings are controllable by varying the process conditions of reactive ion etching, sputtering, ion polishing or any combination thereof while their period can be changed by using colloidal spheres of various sizes. This new approach will surely facilitate further exploration of metal nanorings for applications in nanoscale optical sensors.

Modification of spontaneous emission of solid-state organic molecules embedded in photonic crystals

Highly monodisperse colloidal silica spheres in submicron size were synthesized by a chemical method and close-packed face-centered-cubic photonic crystals (PCs) were prepared. Tris (8-hydroxyquinoline) aluminum (Alq 3) has been in-filled in this structure to investigate the photonic band gap effect on the spontaneous emission. Because of the overlap of the photonic band gap and the photoluminescence (PL) band of Alq 3, both suppression and enhancement in the photoluminescence of the organic molecules were observed. The PL of Alq 3 molecules in PCs exhibited a small blue shift compared with the ones deposited on glass slide, which was believed to arise from the reduced interaction between organic molecules.

Some New Developments in the Synthesis, Functionalization, and Utilization of Monodisperse Colloidal Spheres

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Some New Developments in the Synthesis, Functionalization, and Utilization of Monodisperse Colloidal Spheres

AbstractThis article provides an overview of some recent developments related to the synthesis and functionalization of monodisperse colloidal spheres, a class of colloidal materials that has found widespread use in applications such as the fabrication of photonic crystals, optical sensing, and drug delivery. Traditionally, the choice of materials has been limited to polystyrene and silica. We and other groups have recently expanded the scope of materials by developing a number of methods for producing monodisperse colloidal spheres from various semiconductors and metals. This article is confined to our own work; it covers three different synthetic strategies: the bottom–up approach, the top–down approach, and template‐directed synthesis. The colloidal spheres may have a solid, hollow, or core–shell structure, and the chemical compositions can include Se, Bi, Pb, In, Sn, Cd, Pt, Ag2Se, CdSe, PbS, or TiO2. As an example to illustrate the attractive features of these colloidal spheres, we demonstrate the fabrication of Ag2Se‐based photonic crystals whose stop bands can be thermally switched between two spectral positions.

Fabrication of Spherical Colloidal Crystals Using Electrospray

We demonstrated the use of electrohydrodynamic atomization to prepare uniform-sized emulsion droplets in which equal spheres of silica or polystyrene were dispersed. The size of the emulsion droplets was easily controlled by the electric field strength and the flow rate, independently of the diameter of the nozzles. During the evaporation of solvent in the droplets, spherical colloidal crystals were formed by self-assembly of the monodisperse colloidal spheres. The diameter of the spherical colloidal crystals was in the range of 10-40 microm. Depending on the stability of colloidal particles, the morphology of the self-assembled structure was varied. In particular, silica spheres in ethanol droplets were self-assembled into compactly packed silica colloidal crystals in spherical shapes, whereas polystyrene latex spheres in toluene droplets self-assembled into spherical colloidal crystal shells with hollow cores. The silica colloidal assemblies reflected diffraction colors according to the three-dimensionally ordered arrangement of silica spheres.

Monodisperse Magnetizable Composite Silica Spheres with Tunable Dipolar Interactions

We demonstrate that magnetic particles of maghemite (gamma-Fe(2)O(3)) and cobalt ferrite (CoFe(2)O(4)) can be irreversibly attached to colloidal silica that is grafted with 3-mercaptopropyl(trimethoxy)silane (followed by the controlled growth of a silica layer) to obtain stable dispersions of monodisperse colloidal silica spheres that contain a dense shell of ferrite particles at an adjustable distance from the sphere surface. Magnetization of the ferrite shell induces a large dipole moment, and adjusting the thickness of the outer silica layer enables one to tune the contact attraction. This novel type of magnetizable silica colloid exhibits structure formation in a homogeneous field that varies from isotropic distributions to elongated dipolar chains.

Hollow Colloidal Particles Obtained by Nano-Extrusion in the Presence of Phospholipids

Using nano- and microsize extrusion, a simple synthetic procedure of preparing hollow monodispersed colloidal particles dispersed in an aqueous phase was developed. Hydrophobic styrene monomer containing 2-hydroxy-2-methyl propiophenone photoinitiator was forced into desired diameter membrane channels and stabilized by the hydrophobic regions of a liposome obtained from 1,2-dilauroyl-phosphocholine phospholipid in an aqueous phase. Such moieties exposed to 254-nm UV radiation polymerize monomers in the hydrophobic zone of the liposome, thus resulting in reinforced hollow vesicles. The size of such particles is controlled by the size of the membrane channels in the extruder and may vary from a few nanometers to micrometers, thus allowing the synthesis of monodisperse hollow colloidal spheres.

Self-assembled colloidal crystalline arrays using hollow colloidal spheres

Well-defined mesoporous colloidal crystals are generally prepared using templates, but these procedures are often very complicated. In this paper, we report a simple one-step method for forming three-dimensionally (3-D) ordered mesoporous polymer colloidal crystalline arrays (CCA). The CCA were formed by self-assembly of monodispersed hollow colloidal spheres obtained by classification of polydispersed hollow colloidal spheres in gravitational field, combined with separation using membrane technology. Four different methods have been employed to self-assemble polymer colloidal crystals, which were then experimentally evaluated. The polymer CCA formed by this method should be useful for preparing photonic band-gap materials and other applications.

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.

Synthesis of Monodisperse Colloidal Spheres, Capsules, and Microballoons by Emulsion Templating

New types of monodisperse, micrometer-sized, hollow particles (see Figure) are obtained by encapsulation of emulsion droplets in solid shells and dissolution of the cores. A facile fabrication method is used in which, by simply tuning the thickness of the shells, different types of particles with tunable properties are obtained.

Rapid Self-Assembly of Monodisperse Colloidal Spheres in an Ink-Jet Printed Droplet

An array of hemispherical particle assemblies with ordered nanoporous structures is fabricated by ink-jet printing of colloidal ink on a hydrophobic solid surface. The ordered structure is generated by evaporating the solvent of the colloidal ink, which induces monodisperse silica particles self-assembled within a droplet template.