Search

We demonstrate the fabrication of inorganic inverse opals of silica and titania by a colloidal templating method. Hetero-colloids of polymeric particles and inorganic nanoparticles are formed and, on subsequent heat treatment, were found to yield inverse opals. The presence of nanoparticles does not interfere with the packing of the polymeric particles. The inverse opals exhibit photonic bandgaps in the wavelength of visible light that can be tuned by changing the size of the polymeric particles and the calcination temperatures.

Commercial amidine polystyrene microspheres were self-organized to obtain colloidal microclusters from water-in-oil emulsion droplets as confining geometries. For demulsification process, microwave was irradiated to remove water droplets selectively resulting in the shrinkage of water droplets which induces inward capillary pressure for the particle self-assembly. The amidine polystyrene clusters were coated with silica nanospheres or titania nanoparticles by co-organizing the mixed particle suspensions inside water droplets by microwave heating. Titania-coated polystyrene clusters were calcined to produce hollow macroporous titania powders. Finally, sulfate-coated polystyrene microspheres were self-assembled with silica nanoparticles to generate polystyrene/silica composite clusters by microwave irradiation method.

Monodisperse cross-linked polystyrene nanospheres were self-organized to obtain colloidal aggregates from toluene-in-water emulsion droplets employed as confining geometries. During evaporation of toluene droplets by heating, the polystyrene nanospheres were packed into higher-order clusters, supraparticles with intermediate ordering or supraballs with hexagonally ordered structures, depending on the size of the emulsion droplets, and the number of constituent polystyrene particles inside the droplets. The shrinkage of toluene droplets induced inward capillary pressure, leading to particle self-assembly into ordered spherical supraballs when a large number of polystyrene particles were contained inside the droplets. Ink-jet technology was adopted to generate monodisperse toluene droplets containing polystyrene particles, which were transformed into monodisperse supraballs after evaporation-driven self-assembly of the polystyrene nanospheres. As an alternative approach, water-in-toluene droplets were also adopted as confining geometries for the generation of supraballs.

A self-assembled monolayer (SAM) of octanethiol was vapor-deposited onto the surface of copper ( Cu ) nanoparticles as a means of preventing oxidation. The presence of octanethiol on the surface of Cu nanoparticles was verified using Fourier transform infrared spectroscopy and transmission electron microscopy. The electrical resistance of copper nanoparticles with deposition of a 12-nm thickness of octanethiol on the surface was found to be 100 times greater than that of uncoated powders, indicating uniform SAM coating of the particles.

A colloidal dispersion of indium tin oxide (ITO) nanoparticles in an organic solvent was achieved using a milling process in which β-diketones or titanate coupling agents were used as a dispersing agent. Isopropyl tri(N-ethylenediamino)ethyl titanate and 2,4-pentanedione were found to be the most suitable dispersants for stabilizing ITO nanoparticles in a mixed organic solvent. The secondary particle size of the colloidal ITO dispersion was markedly affected by operational parameters in the milling process. Stable dispersions of antimony-doped tin oxide (ATO) nanoparticles in organic solvent, using β-diketones as dispersants, were also prepared. The stable dispersions of ITO and ATO nanoparticles were used as conductive transparent film coatings on cathode-ray tube panels. We found that the electrical conductivity of the film coating was affected by the boiling point of the dispersion stabilizers.

This paper reports a continuous roll-to-roll printing of mesh patterns of silver oxide pastes on flexible polymer films and subsequent thermal treatment at 150 °C of the patterned pastes to convert...

Monodisperse microspheres of high-refractive-index substances have a variety of potential applications, including optical resonators, microlenses, light diffusers, and chemical and biological probes. Equal-size microspheres can be obtained by the sol–gel reaction of precursors for silica particles and seeded emulsion or dispersion polymerizations for polymeric particles. However, since these conventional microspheres are made from silica and polymeric materials with relatively low refractive indices (1.4< n< 1.6), the optical properties of the particles should be improved by either modifying their shape towards an optimal optical geometry or by increasing their refractive index to fully realize their potential for the aforementioned applications. Recently, several research groups have reported clever ways of fabricating microparticles with complex optical geometries using microfluidic devices. Doyle and his colleagues developed a photolithography technique using a continuous flowing stream inside a microfluidic chip for creating microparticles with 2D complex morphologies. Also, Nisisako and his co-workers produced bicolored Janus particles using thermally polymerizable monodisperse emulsion droplets that were generated from microfluidic devices. However, these approaches are still limited to polymeric particles, the refractive indices of which are not high enough for optics/ photonics applications.

The spontaneous crystallization of colloidal particlesprovides a simple and cheap alternative to nanolithographyfor creating three-dimensional periodic structures. Colloidalcrystals with long-range order diffract light and displayphotonic bandgaps, which is of practical significance forphotonic and phononic crystal devices

In this study, we demonstrate the surfactant-assisted synthesis of uniform-sized titania microspheres and their clusters for highly responsive optical materials. Monodisperse titanium glycolate microspheres were produced by controlled hydrolysis of glycolated titanium butoxide in acetone using surfactant as a stabilizer. The diameter of as-prepared particles ranged from 230 to 650 nm and was finely controlled by changing the concentrations of titanium butoxide and surfactant. In particular, the tunable range of the particle size was at a few tens of nanometers scale by the surfactant concentration, which was much finer than that by the concentration of titanium butoxide. Then, as-prepared titanium glycolate microspheres were transformed into monodisperse titania microspheres of anatase phase by heat treatment. Pure clusters of titania microspheres with an identical configuration were obtained by encapsulating a certain number of microspheres in emulsion droplets and subsequently evaporating the emulsion p...

We prepared polymeric microparticles with coordinated patches using oil-in-water emulsion droplets which were stabilized by adsorbed colloidal polystyrene (PS) latex particles. The oil phase was photocurable ethoxylated trimethylolpropane triacrylate (ETPTA), and the particle-armored oil droplets were solidified by UV irradiation within a few seconds to produce ETPTA-PS composite microparticles without disturbing the structures. Large armored emulsion drops became raspberry-like particles, while small emulsion drops with a few anchored particles were transformed into colloidal clusters with well-coordinated patches. For high-molecular-weight PS particles with low chemical affinity to the ETPTA monomer, the morphology of the patchy particle was determined by the volume of the emulsion drop and the contact angle of the emulsion interface on the PS particle surface. Meanwhile, for low-molecular-weight PS particles with high affinity, the ETPTA monomers were likely to swell the adsorbed PS particles, and distinctive morphologies were induced during the shrinkage of emulsion drops and the phase separation of ETPTA from the swollen PS particles. In addition, colloidal particles with large open windows were produced by dissolving the PS particles from the patchy particles. We observed photoluminescent emission from the patchy particles in which dye molecules were dispersed in the ETPTA phase. Finally, we used Surface Evolver simulation to predict equilibrium structures of patchy particles and estimate surface energies which are essential to understand the underlying physics.

Multi-faceted microstructures of titanium glycolate have been produced by room-temperature polyol process in which titanium alkoxide and polymethylene glycol were mixed rigorously and then the mixture was aged to settle down as white precipitate. Depending on types of titanium alkoxides and polymethylene glycols, stirring time, and composition, a variety of polygonal microrods were generated. Unlike unidentified structures produced from polyol process at elevated temperature, the titanium glycolate products obtained at room temperature revealed well-defined rod-like or plate-like structures with polygonal cross sections. Then, as-prepared titanium glycolate microstructures were transformed into higher refractive index titania of anatase or rutile phase by annealing. The characterization of as-prepared and annealed structures was conducted using scanning and transmission electron microscopes, X-ray diffractomer, and thermal analyzer for thermogravimetry and differential scanning calorimetry.

Colloidal spheres with unique internal morphologies were prepared by blending symmetrical poly(styrene)-block-poly(butadiene) (PS-b-PB) and polystyrene homopolymer (hPS) in emulsion droplets and ca...

We prepared polymeric structures with unusual complexity in surface morphology derived from photocurable emulsion droplets dispersed in an aqueous medium. The emulsion droplets a few tens of micrometers in size were stabilized with relatively small hydrophobic particles that were bound to the emulsion interfaces. The particle binding tended to immobilize the oil-in-water emulsion interface and dramatically increased the structural relaxation time of the interface deformation over a few days relative to a few milliseconds for an otherwise clean interface. In particular, perfectly immobilized emulsion drops maintained nonspherical elongated structures that were formed by shear-induced emulsification and could not be relaxed to a spherical shape. This property is useful for broad research areas ranging from crystallography and buckling phenomena to materials fabrication. The configuration of small particles on the interface and the “raspberry” shape of particle-stabilized emulsions were captured successfully...

In present paper, various industrial applications of the sol-gel technology will be briefly introduced. In particular, the current development status and technological issues of sol gel derived functional nanoparticles in electronic and industrial materials will be reviewed. Productions and surface modifications of nanoparticles by sol-gel processing, their incorporations into nanocomposites and final applications are described.

In this paper, we demonstrated a unique and simple method for fabricating colloidal particles of complex structures using oil-in-water emulsion droplets as confined geometries. A variety of structural motifs were produced using binary colloids of microspheres of polystyrene (PS) or silica and nanosized particles as the second component. When PS or silica microspheres and PS macromolecules were dispersed in oil-in-water emulsion droplets, particles with well-coordinated patches were obtained because the PS macromolecules partially covered the microsphere clusters. When silica or gold nanoparticles were dispersed together with the PS microspheres in oil-in-water emulsion droplets instead of PS macromolecules, composite particles with patches were obtained. In this case, silica or gold shell structures with well-coordinated windows were produced by selectively removing the large PS microspheres from the organic−inorganic composite clusters.

Polystyrene-coated gold nanoparticles (molecular weight (Mn) of PS ∼1300 g/mol, average particle diameter d (core + shell) ∼ 9.2 ± 2.2 nm, corresponding to a high areal chain density of PS) are incorporated into symmetric poly(styrene-b-2 vinylpyridine) diblock copolymers with total Mn ∼ 60 000−380 000 g/mol at volume fractions of 0.07−0.32. For all Mn of diblock copolymers and particle filling fractions examined, particles are centralized in the PS domains with Gaussian distribution profiles. The distribution width generally decreases as the PS domain size decreases or as the particle weight fraction increases. These observations are discussed in terms of the relative entropic contributions of the polymer chains and particles.

Colloidal crystals can be formed by self-assembly in which structural reflective color can be highly sensitive to interparticle distance or reflective index mismatch between particle and matrix. Therefore, if either matrix or particles are made out of stimuli-responsive materials, various environmental parameters can be sensed such as pH, temperature, pressure, mechanical deformation and so on. Also, by introducing chemical probes, various biomolecules (DNA) or toxic chemicals including gas and volatiles can be detected, which would be further extended to biomedical sensor platform. Compared with other sensor device, colloidal crystals are mechanically and chemical stable and their color change is reversible and could be operated without external (electrical or photon) energy. In this chapter, basic design principle of colloidal photonic crystals and sensors are described and representative examples of sensors are provided for various stimulus.

The theoretical extinction coefficients of gold nanoparticles (AuNPs) have been mainly verified by the analytical solving of the Maxwell equation for an ideal sphere, which was firstly founded by Mie (generally referred to as Mie theory). However, in principle, it has not been directly feasible with experimental verification especially for relatively large AuNPs (i.e., >40 nm), as conventionally proposed synthetic methods have inevitably resulted in a polygonal shaped, non-ideal Au nanosphere. Here, mono-crystalline, ultra-smooth, and highly spherical AuNPs of 40–100 nm were prepared by the procedure reported in our recent work (ACS Nano, 2013, 7, 11064). The extinction coefficients of the ideally spherical AuNPs of 40–100 nm were empirically extracted using the Beer–Lambert law, and were then compared with the theoretical limits obtained by the analytical and numerical methods. The obtained extinction coefficients of the ideally spherical AuNPs herein agree much more closely with the theoretical limits, compared with those of the faceted or polygonal shaped AuNPs. In addition, in order to further elucidate the importance of being spherical, we systematically compared our ideally spherical AuNPs with the polygonal counterparts; effectively addressing the role of the surface morphology on the spectral responses in both theoretical and experimental manners.

We report on synthetic strategies to fabricate DNA-coated micrometer-sized colloids that, upon thermal annealing, self-assemble into various crystal structures. Colloids of a wide range of chemical compositions, including poly(styrene), poly(methyl methacrylate), titania, silica, and a silica-methacrylate hybrid material, are fabricated with smooth particle surfaces and a dense layer of surface functional anchors. Single-stranded oligonucleotides with a short sticky end are covalently grafted onto particle surfaces employing a strain-promoted alkyne–azide cycloaddition reaction resulting in DNA coatings with areal densities an order of magnitude higher than previously reported. Our approach allows the DNA-coated colloids not only to aggregate upon cooling but also to anneal and rearrange while still bound together, leading to the formation of colloidal crystal compounds when particles of different sizes or different materials are combined.

Block copolymers (BCPs) can create various morphology by self-assembly in bulk or film. Recently, using BCPs in confined geometries such as thin film (one-dimension), cylindrical template (two-dimension), or emulsion droplet (three-dimension), nanostructured BCP particles have been prepared, in which unique nanostructures of the BCP are formed via solvent annealing process and can be controlled depending on molecular weight ratio and interaction parameter of the BCPs, and droplet size. Moreover, by tuning interfacial property of the BCP particles, anisotropic particles with unique nanostructures have been prepared. Furthermore, for practical application such as drug delivery system, sensor, self-healing, metamaterial, and optoelectronic device, functional nanoparticles can be incorporated inside BCP particles. In this article, we summarize recent progress on the production of structured BCP particles and composite particles with metallic nanoparticles.

Rational synthesis of coordinated spherical colloids is reported by site-selective growth of secondary hemispherical patches on primary spherical particles with quasi-defined coordination numbers and positions. We clarify the importance of mass transport phenomena on the site-specific secondary nucleation/growth in nanoparticulate colloidal systems. By comparing ultrasonic and conventional agitation during patch growth, we found that enhanced mass transfer is the key to controlled, homogeneous transport of the molecular precursors in a solvent onto the nanoparticles. With chemically defined nucleation sites, the surfaces of spherical silica particles were modified for use as a new kind of colloid with patches at desired coordination positions. Our observations represent a significant breakthrough in colloidal chemistry and self-assembly.

Sensing and manipulating targets hidden under scattering media are universal problems that take place in applications ranging from deep-tissue optical imaging to laser surgery. A major issue in these applications is the shallow light penetration caused by multiple scattering that reflects most of incident light. Although advances have been made to eliminate image distortion by a scattering medium, dealing with the light reflection has remained unchallenged. Here we present a method to minimize reflected intensity by finding and coupling light into the anti-reflection modes of a scattering medium. In doing so, we achieved more than a factor of 3 increase in light penetration. Our method of controlling reflected waves makes it readily applicable to in vivo applications in which detector sensors can only be positioned at the same side of illumination and will therefore lay the foundation of advancing the working depth of many existing optical imaging and treatment technologies. (C) 2015 Optical Society of America

Atomic force microscope (AFM)-enabled manipulation of individual metallic nanoparticles (NPs) has proven useful for assembling diverse structural motifs of metamolecules. However, for the reliable verifications of their electric/magnetic behaviors and translations into practical applications (e.g., metasurfaces), currently available assembly of polygonal shaped metallic NPs with size and shape distributions should be further advanced. Here, we discover conditions for AFM-enabled, deterministic assembly of highly uniform, super-spherical gold NPs (AuNPs) into the metamolecules, which can show the designed electric/magnetic resonance behaviors in a highly reliable fashion. The use of super-spherical AuNPs together with the controlled adhesive properties of an AFM tip allows us to linearly and continuously push AuNPs toward the pre-programed directions and positions with minimized slipping away effect. Thus, a versatile and fast (as little as few minutes per each metamolecule) assembly of metamolecules with unprecedented structural fidelity becomes possible via AFM-enabled manipulation; enabling a high precision engineering of electromagnetic properties with metamolecules. (C) 2015 Optical Society of America

Nanosized colloidal indium tin oxide (ITO) dispersion was prepared for electrically conductive and transparent coating materials. A titanate coupling agent, isopropyl tri(N-ethylenediamino)ethyl titanate, was chosen as a dispersant for the stabilization of ITO nanoparticles in organic solvent. ITO sol was deposited on a cathode ray tube panel for antistatic or electromagnetic shielding purposes, and alkyl silicate was used for the formation of an antireflective over-coat layer. The resulting double-layered coating showed low sheet resistance, which satisfied semi-TCO regulation and low reflectance of visible light. To control the electrical and optical properties of the coating layer, the effects of secondary particle size of ITO aggregates and the dispersant concentration of ITO sol were studied. The stability of ITO sol was estimated by measuring the particle size as a function of the storage days and the aggregation of colloidal ITO dispersion with storage day was explained by depletion flocculation.

the Creative Research Initiative Program of the Ministry of Science and Technology. the Brain Korea 21 Program.

Monodisperse aqueous emulsion droplets encapsulating colloidal particles were produced in the oil phase, and controlled microwave irradiation of the aqueous drop phase created spherical colloidal crystals by so-called evaporation-induced self-organization of the colloidal particles. Unlike usual colloidal crystals, colloidal crystals in spherical symmetry (or photonic balls) possessed photonic band gaps for the normal incident light independent of the position all over the spherical surface. While the consolidation of colloidal particles in emulsion droplets in an oven took several hours, the present microwave-assisted evaporation could reduce the time for complete evaporation to a few tens of minutes. Under the microwave irradiation, the aqueous phase in emulsions was superheated selectively and the evaporation rate of water could be controlled easily by adjusting the microwave intensity. The result showed that the packing quality of colloidal crystals obtained by the microwave-assisted self-organization was good enough to show photonic band gap characteristics. The reflectance of our photonic balls responded precisely to any change in physical properties including the size of colloidal particles, refractive index mismatch, and angle of the incident beam. In particular, for polymeric particles, the photonic band gap could be tuned by the intensity of microwave irradiation, and the reflection color was red-shifted with stronger microwave irradiation. Finally, for better photonic band gap properties, inverted photonic balls were prepared by using the spherical colloidal crystals as sacrificial templates.

Electrospun nanofibers were used as confining geometries for fabricating 1-D colloidal assemblies. Silica particles dispersed in several different polymer solutions were cast into nanofibers by an electrospinning process. The silica particle configurations were examined in terms of the size ratio of silica particles to nanofibers and the properties of the dispersing medium. As the electrospun fiber was extended highly, the silica particles dispersed in the polymer solution began to assemble spontaneously into a pearl-necklace structure. We also demonstrated the alignment of 1-D silica assemblies using a designed configuration of collector electrodes.

Most of the colloidal clusters have been produced from oil-in-water emulsions with identical microspheres dispersed in oil droplets. Here, we present new types of binary colloidal clusters from phase-inverted water-in-oil emulsions using various combinations of two different colloids with several size ratios: monodisperse silica or polystyrene microspheres for larger particles and silica or titania nanoparticles for smaller particles. Obviously, a better understanding of how finite groups of different colloids self-organize in a confined geometry may help us control the structure of matter at multiple length scales. In addition, since aqueous dispersions have much better phase stability, we could produce much more diverse colloidal materials from water-in-oil emulsions rather than from oil-in-water emulsions. Interestingly, the configurations of the large microspheres were not changed by the presence of the small particles. However, the arrangement of the smaller particles was strongly dependent on the nature of the interparticle interactions. The experimentally observed structural evolutions were consistent with the numerical simulations calculated using Surface Evolver. These clusters with nonisotropic structures can be used as building blocks for novel colloidal structures with unusual properties or by themselves as light scatterers, diffusers, and complex adaptive matter exhibiting emergent behavior.

We report a general method for small aggregates (or clusters) of water-borne colloids inside water-in-oil (W/O) emulsions. First, an aqueous suspension of monodisperse polystyrene or silica (SiO2) microspheres was emulsified into polydisperse water droplets on micrometer scales in oil phase and colloidal aggregates were produced spontaneously during slow evaporation of water. Then, the colloidal clusters consolidated by complete removal of water were separated from the oil phase and re-dispersed in water for the subsequent fractionation according to the number (n) of the constituent spheres by a density gradient ultracentrifugation. Each cluster of n particles possessed a unique configuration except for a few particular cases of n = 7, 8, and 11, in which we observed some isomeric structures, depending on their surface properties of colloidal microspheres. These isomers have not been reported in the preceding studies for colloidal clusters fabricated from the phase-inverted oil-in-water emulsions.

We fabricated colloidal crystals on a fiber by a dip-coating method. The self-assembly of monodisperse colloidal particles was affected by the curvature of the fiber (the reciprocal of the fiber radius). As the fiber became smaller in diameter, fewer layers of the colloidal spheres were coated for a given lift-up speed. The hollow colloidal crystal cylinders were used as a template for creating macroporous structure having three-dimensionally interconnected air cavities. Specifically, the polymer precursor was infiltrated into the colloidal crystal template and the macroporous polymer structures were obtained after the selective etching of colloidal particles.

We fabricated patterned polymer photonic crystals by holographic lithography in conjunction with soft lithography. A patterned SU-8 photoresist film was created by preformed pattern of a hard-baked SU-8 photoresist, transferred by a PDMS mold. Then, four-beam holographic exposure carved 3D photonic crystal structures onto the patterned photoresist. Because of refractive index matching of the photoresist and the hard-baked photoresist, scattering, which might have caused a distortion of interference pattern, did not occur. Eventually, an f.c.c. polymer structure with a line pattern was successfully created after development.

Uniform assemblies of all-identical colloidal particles, so-called photonic balls, are produced by injecting an aqueous suspension of polymer latex spheres into a surfactant-laden oil phase at an oil/water junction of capillary tubes or soft-microfluidic devices. The size of these assemblies can be controlled by varying the injection pressure or particle concentration. © 2003 Elsevier Science B.V. All rights reserved.

We report our direct Brownian motion observation of Fe2O3 magnetic cube chains under external magnetic fields, where the possibility of tuning the Brownian motion characteristics, such as diffusivity, by magnetic fields is realized. It has been experimentally demonstrated that the diffusivity is modified with an angular dependency on the magnetic field direction, well explained based on the Stokes-Einstein relation considering an effective cross-sectional change of magnetic cube chains.

Flexible thin-film sensors have been developed for practical uses in invasive or noninvasive cost-effective healthcare devices, which requires high sensitivity, stretchability, biocompatibility, skin/organ-conformity, and often transparency. Graphene nanoplatelets can be spontaneously assembled into transparent and conductive ultrathin coatings on micropatterned surfaces or planar substrates via a convective Marangoni force in a highly controlled manner. Based on this versatile graphene assembled film preparation, a thin, stretchable and skin-conformal sensor array (144 pixels) is fabricated having microtopography-guided, graphene-based, conductive patterns embedded without any complicated processes. The electrically controlled sensor array for mapping spatial distributions (144 pixels) shows high sensitivity (maximum gauge factor ≈1697), skin-like stretchability (

Light-activated self-propelled colloids are synthesized and their active motion is studied using optical microscopy. We propose a versatile route using different photoactive materials, and demonstrate a multiwavelength activation and propulsion. Thanks to the photoelectrochemical properties of two semiconductor materials (\alpha Fe2 O3 and TiO2 ), a light with an energy higher than the bandgap triggers the reaction of decomposition of hydrogen peroxide and produces a chemical cloud around the particle. It induces a phoretic attraction with neighbouring colloids as well as an osmotic self- propulsion of the particle on the substrate. We use these mechanisms to form colloidal cargos as well as self-propelled particles where the light-activated component is embedded into a dielectric sphere. The particles are self-propelled along a direction otherwise randomized by thermal fluctuations, and exhibit a persistent random walk. For sufficient surface density, the particles spontaneously form "living crystals" which are mobile, break apart and reform. Steering the particle with an external magnetic field, we show that the formation of the dense phase results from the collisions heads-on of the particles. This effect is intrinsically non-equilibrium and a novel principle of organization for systems without detailed balance. Engineering families of particles self-propelled by different wavelength demonstrate a good understanding of both the physics and the chemistry behind the system and points to a general route for designing new families of self-propelled particles., Comment: Invited Contribution to a theme issue of Phil. Trans. Soc. A: "New trends in active liquid crystals: mechanics, dynamics and applications"

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2–3 layer pristine graphene platelets temporally solvated with N-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility.

Ordered macroporous particles of silica and titania were fabricated by colloidal templating. The colloidal templates were assembled through colloidal crystallization of suspended polystyrene latex sphere particles in aqueous droplets straddling an air−oil interface. The procedures involve first preparing spherical colloidal crystalline particles of polystyrene latex spheres and then infusing them with metal precursor solutions that form silica or titania in the interstices. Finally, calcination decomposes the polystyrene latex spheres, leaving macropores at their sites. The shape of the template was controlled by the presence of additive surfactant or by the action of an applied electric field. Specifically, spherical, concaved disklike, and ellipsoidal colloidal crystals were prepared successfully and used as templates for the fabrication of ordered macroporous particles. The SEM images of the prepared macroporous particles showed that the pores were interconnected and ordered into a hexagonal arrangement.

Harmonic combination of microprism-based holographic lithography (μHL) and surfactant templating was used to create arrayed and free-standing hierarchical structures in a facile manner. The multiscale ordered structure obtained had a triple hierarchy: micrometer scale 2D array of submicrometer scale 3D macropores produced from μHL, and mesopores from surfactant self-assembly.

Onionlike block copolymer particles containing a well-ordered gold nanoparticle array were prepared with the help of amphiphilic block copolymer used as a surfactant. The location of gold nanoparticles ordered in the specific position of block copolymer domain was systematically investigated by tuning the invariant polymerization index of the block copolymer and the areal chain density (Σ) of gold nanoparticles.

Ordered porous materials were produced from macrocrystalline emulsion templates. The templates were prepared by a repeated fractionation technique from polydisperse aqueous and nonaqueous emulsions with a drying control chemical additive. The aqueous emulsion drops tended to migrate and floc in relatively mobile local regions during the capturing process, which eventually led to the nonuniform pore distribution in the final inorganic matrix. On the other hand, the monodisperse nonaqueous emulsions led to uniformly distributed pore structure.

Bioreducible carboxymethyl dextran (CMD) derivatives are synthesized by the chemical modification of CMD with lithocholic acid (LCA) through a disulfide linkage. The hydrophobic nature of LCA allows the conjugates (CMD-SS-LCAs) to form self-assembled nanoparticles in aqueous conditions. Depending on the degree of LCA substitution, the particle diameters range from 163 to 242 nm. Doxorubicin (DOX), chosen as a model anticancer drug, is effectively encapsulated into the nanoparticles with high loading efficiency (>70%). In vitro optical imaging tests reveal that the fluorescence signal of DOX quenched in the bioreducible nanoparticles is highly recovered in the presence of glutathione (GSH), a tripeptide capable of reducing disulfide bonds in the intracellular compartments. Bioreducible nanoparticles rapidly release DOX when they are incubated with 10 mm GSH, whereas the drug release is greatly retarded in physiological buffer (pH 7.4). DOX-loaded bioreducible nanoparticles exhibit higher toxicity to SCC7 cancer cells than DOX-loaded nanoparticles without the disulfide bond. Confocal laser scanning microscopy observation demonstrate that bioreducible nanoparticles can effectively deliver DOX into the nuclei of SCC7 cells. In vivo biodistribution study indicates that Cy5.5-labeled CMD-SS-LCAs selectively accumulate at tumor sites after systemic administration into tumor-bearing mice. Notably, DOX-loaded bioreducible nanoparticles exhibit higher antitumor efficacy than reduction-insensitive control nanoparticles. Overall, it is evident that bioreducible CMD-SS-LCA nanoparticles are useful as a drug carrier for cancer therapy.

Coalescence of two kinds of pre-processed droplets is necessary to perform chemical and biological assays in droplet-based microfluidics. However, a robust technique to accomplish this does not exist. Here we present a microfluidic device to synchronize the reinjection of two different kinds of droplets and coalesce them, using hydrostatic pressure in conjunction with a conventional syringe pump. We use a device consisting of two opposing T-junctions for reinjecting two kinds of droplets and control the flows of the droplets by applying gravity-driven hydrostatic pressure. The hydrostatic-pressure operation facilitates balancing the droplet reinjection rates and allows us to synchronize the reinjection. Furthermore, we present a simple but robust module to coalesce two droplets that sequentially come into the module, regardless of their arrival times. These re-injection and coalescence techniques might be used in lab-on-chip applications requiring droplets with controlled numbers of solid materials, which can be made by coalescing two pre-processed droplets that are formed and sorted in devices.

We report on the synthesis of two types of Ag nanoparticles (NPs) and the influence of adsorbed surfactant size on the NP surface for surface-enhanced Raman scattering (SERS) signals. Both particles were of similar size and morphology but were covered by surfactants of different sizes; one surfactant was sodium citrate (molecular weight: 258) and the other was sodium polyacrylate (molecular weight: 2100). For SERS measurement, 4-mecapobenzoic acid and 4-naphthalene thiol as Raman-active dyes were immobilized on the surface of each AgNP. The signals from Raman-active dyes on AgNPs covered with citrate displayed 10 times higher intensity than those from polyacrylate-stabilized AgNPs. Elemental analysis (EA) revealed that the average weight percentage of sulfur is 0.94 wt% and 0.12 wt% for citrate-stabilized and polyacrylate-stabilized AgNPs, respectively. The sulfur content difference was attributed to the size of the existing surfactant influencing the ligand exchange by steric hindrance and subsequently the amount of sulfur content of the particles. These experimental results suggest that the size of initial surfactant should be taken into account when synthesizing a metal particle for enhancing SERS signal.

A rapid two-step metallization for fabrication of a "black" transparent conductive film on a flexible substrate for display applications is presented, using a mixture of silver oxide (Ag2O) and silver neodecanoate (C10H19AgO2), and its electrical conductivity and colour transition behaviours are investigated. Silver nanoparticles, which are physicochemically converted from silver oxide microparticles in the presence of silver neodecanoate in the course of the first metallization step at 150 °C for 10 min, are chemically annealed by immersing them in an acidic ferric chloride (FeCl3) solution at room temperature for 10 s. During this second metallization step, silver nanoparticles are found to be tightly packed through Ostwald ripening, which eventually leads to the dramatic enhancement of electrical conductivity by six orders of magnitude from 1.33 S m(-1) to 1.0 × 10(7) S m(-1), which corresponds to 15.9% of the electrical conductivity of bulk silver. In addition to the enhancement of electrical conductivity, the silver chloride (AgCl) layer formed on the surface of the silver layer due to ferric ions (Fe(3+)) enhances the blackness of the transparent conductive film by a factor of 1.69, from 36.29 B to 61.51 B. The sheet resistance and optical transparency of a roll-to-roll printed black transparent conductive film for a touch screen panel are found to be as low as 0.9 Ω□(-1) and 81%, respectively, after conducting the proposed two-step metallization.