Cationic and anionic poly(N-isopropylacrylamide) based submicron gel particles: electrokinetic properties and colloidal stability

A cationic and an anionic poly(N-isopropylacrylamide) (poly(NIPAM)) microgel latex were synthesized via batch radical polymerization under emulsifier-free conditions. The hydrodynamic properties, colloidal stability, and electrokinetic characteristics of these two samples were studied. The hydrodynamic particle size variation was discussed by considering the effect of salinity and temperature on the shrinkage of the thermally sensitive polymer domains. The colloidal stability also depended on temperature and electrolyte concentration. A stability diagram with two well-defined domains (stable and unstable) was obtained. The flow from one domain to the other was fully reversible due to the peculiar (de)hydration properties of the polymer. The electrokinetic behavior, which depends on electrical and frictional properties of the particles, was analyzed via electrophoretic mobility measurements. Results were discussed by considering both the particle structure dependence on temperature and salinity, and the electric double layer compression. In addition, the electrophoretic mobility data were analyzed using Ohshima's equations for particles covered by an ion-penetrable surface charged layer, as well as using another simpler equation for charges located on a hydrodynamic equivalent hard sphere. Differences between the properties of both latexes were justified by the presence of a hydrophilic comonomer, aminoethyl methacrylate hydrochloride (AEMH), in the cationic microgel.     

Growth and photoelectrochemical properties of ordered CuInS2 nanorod arrays

CuInS(2) nanorod array structures are synthesized via a template-free and non-vacuum route for the first time. The obtained CuInS(2) thin films show promising conversion efficiency in a two-electrode photoelectrochemical cell.     

Local properties of cake in cross-flow microfiltration of submicron particles

The local properties of filter cakes, such as porosity and specific filtration resistance, in cross-flow microfiltration of submicron particles are studied based on an analysis of force. The packing of particles in a filter cake can be divided into two modes. When the solid compressive pressure is smaller than the critical value, there exists an equilibrium distance between neighbouring particles due to the electrostatic repulsive force, and the local cake porosity can be estimated by using the cell model proposed in this study. When the solid compressive pressure is greater than the critical value, the compressive force can overcome the repulsive barrier, the particles then come into contact with neighbours, and the power-type empirical relationship between cake porosity and solid compressive pressure can be employed to estimate the local cake porosity. It can be found that the half of the cake near the filter membrane has a compact structure, and a high filtration resistance within the operating conditions of this study. On the other hand, the portion of cake near the cake surface has a high porosity due to the separation of particles. By using this model, the effect of electrolyte concentration on cake properties can be analyzed, and the estimated values of average porosity and average specific filtration resistance under various electrolyte concentrations, cross-flow velocities, and filtration pressures agree fairly well with the experimental data.     

Two-dimensional ordered arrays of monodisperse silica particles grafted with concentrated polymer brushes

Hybrid particles which have a core of monodisperse silica particle and a shell of well-defined poly(methyl methacrylate) chains end-grafted on the core surface with a surface density as high as 0.8 chains/nm² were prepared by surface-initiated atom transfer radical polymerization of methyl methacrylate with an initiator-fixed silica particle. Monolayers of the hybrid particles were formed at the air-water interface by depositing a defined amount of the particle suspension onto water surface. Transmission electron microscopic and atomic force microscopic observations of these monolayers showed that the hybrid particles formed a two-dimensional hexagonally ordered lattice with a wide controllability of interparticle distance. This lattice structure was utilized as a template for the fabrication of a negatively patterned surface of poly(dimethylsiloxane) elastomer.     

Automatic decoding of sensor types within randomly ordered,high-density optical sensor arrays

In this paper automatic sensor identification of sensor classes within a high-density randomized array, without a priori knowledge of sensor locations, is demonstrated. Two different fluorescence-based sensor types, with hundreds of replicates each, were randomly distributed into an optical imaging fiber array platform. The sensor element types were vapor-sensitive microspheres with the environmentally-sensitive fluorescent dye Nile Red adsorbed on their surface. Nile Red undergoes spectral changes when exposed to different microenvironmental polarity conditions, e.g. microsphere surface polarity or odor exposure. These reproducible sensor spectral changes, or sensor-response profiles, enable sensors within a randomized array to be grouped into categories by optical decoding methods. Two computational decoding methods (supervised and unsupervised) are introduced; equal classification rates were achieved for both. By comparing sensor responses from a randomized array with those obtained from known (control) arrays, 587 sensors were correctly classified with 99.32% accuracy. Although both methods were equally effective, the unsupervised method, which uses sensor response changes to odor exposure, is a better decoding model for the vapor-sensitive arrays studied, because it relies only on the odor-response profiles. Another decoding technique employed the emission spectra of the sensors and is more applicable to other types of multiplexed fluorescence-based arrays and assays. The sensor-decoding techniques are compared to demonstrate that sensors within high-density optical chemosensor arrays can be positionally-registered, or decoded, with no additional overhead in time or expense other than collecting the sensor-response profiles.     

Synthesis, characterization and optical properties of ordered macroporous organosilicas

Ordered macroporous organosilica materials with uniform pore size in the range of 0.2-1.35 [micro sign]m have been fabricated by using self-assembled colloidal crystals as templates, and characterized with SEM, TGA, FTIR, MAS NMR, and optical reflectance spectrometry.     

Manipulating the optical properties of pyramidal nanoparticle arrays

This paper reports the orientation-dependent optical properties of two-dimensional arrays of anisotropic metallic nanoparticles. These studies were made possible by our simple procedure to encapsulate and manipulate aligned particles having complex three-dimensional (3D) shapes inside a uniform dielectric environment. Using dark field or scattering spectroscopy, we investigated the plasmon resonances of 250-nm Au pyramidal shells embedded in a poly(dimethylsiloxane) (PDMS) matrix. Interestingly, we discovered that the scattering spectra of these particle arrays depended sensitively on the direction and polarization of the incident white light relative to the orientation of the pyramidal shells. Theoretical calculations using the discrete dipole approximation support the experimentally observed dependence on particle orientation with respect to incident field. This work presents an approach to manipulate--by hand--ordered arrays of particles over cm(2) areas and provides new insight into the relationship between the shape of well-defined, 3D particles and their supported plasmon resonance modes.     

Synthesis and optical properties of silver nanoparticles and arrays.

This Minireview systematically examines optical properties of silver nanoparticles as a function of size. Extinction, scattering, and absorption cross-sections and distance dependence of the local electromagnetic field, as well as the quadrupolar coupling of 2D assemblies of such particles are experimentally measured for a wide range of particle sizes. Such measurements were possible because of the development of a novel synthetic method for the size-controlled synthesis of chemically clean, highly crystalline silver nanoparticles of narrow size distribution. The method and its unique advantages are compared to other methods for synthesis of metal nanoparticles. Synthesis and properties of nanocomposite materials using these and other nanoparticles are also described. Important highlights in the history of the field of metal nanoparticles as well as an examination of the basic principles of plasmon resonances are included.     

Dielectrophoretic separation of micron and submicron particles: A review

This paper provides an overview on separation of micron and submicron sized biological (cells, yeast, virus, bacteria, etc.) and nonbiological particles (latex, polystyrene, CNTs, metals, etc.) by dielectrophoresis (DEP), which finds wide applications in the field of medical and environmental science. Mathematical models to predict the electric field, flow profile, and concentration profiles of the particles under the influence of DEP force have also been covered in this review. In addition, advancements made primarily in the last decade, in the area of electrode design (shape and arrangement), new materials for electrode (carbon, silicon, polymers), and geometry of the microdevice, for efficient DEP separation of particles have been highlighted.     

Synthesis and properties of sol-gel submicron silica powders doped with partly oxidized iron particles

Magnetic powders based on metallic iron crystallites encapsulated in submicron-sized spherical silica particles have been obtained and investigated. The metallic iron clusters have been produced by the exploding wire method. The silica shells have been prepared via the modified sol-gel Stöber method and the metallic particles have been entrapped by occlusion during the silica powder formation. The entrapped iron particles are partially oxidized due to the nature of the synthetic methods employed. The obtained hybrid materials have been investigated by electron microscopy, X-ray diffraction, magnetic and ζ-potential techniques. Such materials can be employed in such applications as e.g. magnetically-controlled drug vectors or electromagnetic field-shielding.     

Large-scale Ni-doped ZnO nanowire arrays and electrical and optical properties

Large-scale Ni-doped ZnO nanowire (NW) arrays are grown. The electrical conductivity of a single Ni-doped ZnO NW has been increased for 30 times. The photoluminescence (PL) spectrum of the doped ZnO NWs has a red shift, suggesting possible doping induced band edge bending. The doped NW arrays could be the basis for building integrated nanoscale transistors, sensors, and photodetectors.     

Ordered nickel oxide nanowire arrays and their optical absorption properties

Ordered NiO nanowire arrays embedded in anodic alumina membranes have been prepared by using an electrochemical deposition method. After annealing at 300 °C, the NiO nanowire arrays were characterized using SEM, TEM, SAED, and XRD. SEM and TEM observations reveal that these nanowires are dense, continuous and arranged roughly parallel to one another. XRD and SAED analysis together indicate that these NiO nanowires crystallize with a polycrystalline structure. The optical absorption band gap of NiO nanowire arrays is 3.74 eV, and no obvious blue shift or red shift with respect of that of the bulk NiO can be observed.     

3-D ordered macroporous cuprous oxide: Fabrication, optical, and photoelectrochemical properties

Cuprous oxide 3-D ordered macroporous material was constructed by electrochemical deposition using a polystyrene colloidal crystal as template. The highly ordered macroporous structure with a hexagonal array can be extended over hundreds of square micrometers. The photonic stop bands of both the PS colloidal crystal and Cu2O 3DOM were found. Due to the highly ordered porous structure, the optical absorption and the charge carrier transportation are better in Cu2O 3DOM than in bulk Cu2O, which makes the reduction of oxygen faster on Cu2O 3DOM than on bulk Cu2O under visible light illumination. The higher photocurrent efficiency under visible light illumination makes the 3DOM Cu2O more suitable for solar applications.     

Ellipsometric identification of collective optical properties of silver nanocrystal arrays

The optical properties of silver nanocrystal arrays are investigated using spectroscopic ellipsometry in combination with polarized reflection measurements. Analysis of the ellipsometry and reflectometry spectra in terms of the "thin island film" theory enables a transparent identification of the contribution of collective effects to the optical response. Negligible image charge effects imply that only dipole contributions have to be considered. The interactions between the hexagonally ordered silver nanocrystals give rise to an effective modification of the spherical response to oblate entities with different polarizabilities parallel and perpendicular to the substrate, expressed in terms of corresponding depolarization factors. The effect of nanocrystal ordering, nearest-neighbor distance, size distribution, surrounding ambient, and the optical properties of the single nanocrystals on the optical response are analyzed. The extent of plasmon resonance peak splitting as a function of surface coverage is discussed.     

Preparation and characterization of submicron hybrid magnetic latex particles

Micrometer magnetic hybrid particles are of great interest in biomedical field, and various morphologies have been prepared via encapsulation processes. Regarding submicron, only few processes have been investigated and the most recent one leading to highly magnetic submicron magnetic hybrid particles is based on oil in water magnetic emulsion (MES) transformation. The encapsulation of magnetic iron oxide nanoparticles forming oil in water MES was investigated using different styrene/cross‐linker divinylbenzene volume ratio in the presence of potassium persulfate initiator. The encapsulation performed in this work is basically conducted by using well‐defined oil in water MES as a seed in radical emulsion polymerization. The chemical composition, morphology, iron oxide content, magnetic properties, electrokinetic properties, particle size, and size distribution of the prepared magnetic hybrid particles were examined using various techniques. The desired perfect magnetic core and polymer shell morphology were successfully obtained, and the final magnetic hybrid particles are superparamagnetic in nature and exhibit high iron oxide content (64 wt %). Copyright © 2015 John Wiley & Sons, Ltd.     

Anisotropic particles with different morphologies of silver nanoshell: Synthesis and optical properties

Hydrosols of spindle-shaped composite particles with the core of iron(III) oxyhydroxide and silver shell are synthesized by enlarging metal seeding nanoparticles adsorbed on the surface of the cores in the solution containing silver nitrate and mild reducing agent. It is revealed that the character of the growth of shells on gold seeding particles greatly depends on the type of reducing agent. When using ascorbic acid, seeding particles grow primarily in the direction normal to the core surface due to the blocking of some of the particle faces by ions present in the solution. As a result, the forming shell is characterized by a fairly nonuniform structure. At the same time, when using formaldehyde, the growth of seeding nanoparticles proceeds predominantly in the lateral direction to form first an island-like film, then a continuous thin metal shell on the core surface. It is demonstrated that the position of localized surface plasmon resonance of such structure can be fine tuned to the preset wavelength by controlled variations in the thickness of Ag shell with very small step (up to 1 nm).     

Microstructure and optical properties of PMMA/gel silica glass composites

FT-Raman and near infrared (NIR) spectroscopies have been used to investigate PMMA/gel silica composites prepared by the post-doping method. The changes of the vibrational features of silanols on the silica surface and ester carbonyls from PMMA indicate that the two phases in the organic-inorganic hybrids interact with each other through hydrogen-bonding. Unlike unmodified gel silica, the as-prepared composites are hydrophobic due to the elimination of the accessible adsorbing sites provided by the surface silanols. Residual water inherited from the preparation process is not evenly distributed in the composites but locally enriched on the silica surface by hydrogen-bonding to limited surface silanols. The conversion efficiency of MMA-to-PMMA depends not only on the polymerisation conditions applied, but also on the initial structure of the sol-gel substrate used. The composites show high optical transmittance in the near UV and visible region due to a reduction of scattering from an originally porous structure. However, their application in the near IR is restricted due to the combined vibrational energy absorptions by different silanol and water species, and in particular by C-H functional groups from organic modifiers.     

Ag-SiO2 core-shell nanorod arrays: morphological, optical, SERS, and wetting properties

Using the hydrolysis of tetraethylorthosilicate, a uniform and conformal layer of porous SiO(2) with controlled thickness has been coated onto the oblique angle deposited Ag nanorod (AgNR) array to form an aligned AgNR-SiO(2) core-shell array nanostructure. The morphology, optical property, SERS response, and surface wettability of the AgNRs with different SiO(2) shell thicknesses have been obtained by multiple characterization techniques. The morphological characterization shows that each AgNR on the array is coated with a uniform and porous silica shell independently and the growth of shell thickness follows a linear function versus the coating time. Thickening of the shell induces a monotonic decrease of the apparent contact angle, red-shift of the transverse mode of the localized surface plasmon resonance peak, and makes the SiO(2) shell more compact. The SERS response of 4-Mercaptophenol on these substrates exhibits an exponential decay behavior with the increasing coating time, which is ascribed to the decreasing Ag surface coverage of core-shell nanorods. Under the assumption that the Ag surface coverage is proportional to the SERS intensity, one can estimate the evolution of SiO(2) coverage on AgNRs. Such coverage evolution can be used to qualitatively explain the LSPR wavelength change and quantitatively interpret the contact angle change based on a double Cassie's law.     

One-dimensional trapped atoms: critical coupling parameter and critical number of particles

In this paper we consider the case of a Bose gas in low dimension in order to illustrate the applicability of a method that allows us to construct analytical relations, valid for a broad range of coupling parameters, for a function which asymptotic expansions are known. The method is well suitable to investigate the problem of stability of a collection of Bose particles trapped in one- dimensional configuration for the case where the scattering length presents a negative value. The eigenvalues for this interacting quantum one-dimensional many particle system become negative when the interactions overcome the trapping energy and, in this case, the system becomes unstable. Here we calculate the critical coupling parameter and apply for the case of Lithium atoms obtaining the critical number of particles for the limit of stability.