Size Control Method Research Articles

Methodological Improvement in Pulsed Laser-Induced Size Reduction of Aqueous Colloidal Gold Nanoparticles by Applying High Pressure

By applying high pressures well above the critical pressure of water (22.1 MPa), we prepared gold nanoparticles (Au NPs) using a nanosecond pulsed laser-induced size-reduction technique. The Au NPs thus obtained exhibited a narrow size distribution and size-selectivity dependent on the applied laser energy density (fluence). This is significant because previous attempts under ambient pressure failed to achieve such size-selective generation. Spherical Au NPs of diameters 46 and 33 nm, with a standard deviation of only 2–3 nm, were obtained at the expense of original faceted 58 nm Au NPs. We ascribed our results to the formation of a supercritical water layer surrounding the liquid droplet NP transformed by laser heating. The supercritical layer originates from heat transfer from the particle, leading to water temperatures above the critical point of 647 K. The supercritical water layer acts as an effective heat sink for photothermal layer-by-layer size reduction to release small fragments, leaving behind a core particle. The supercritical water can retard evaporation of atoms and clusters from the droplet, thus controlling the evaporation rate. In contrast, at an ambient pressure of 0.1 MPa, the size reduction takes place inside the bubble that can form through the explosive evaporation of superheated water. In this case, particles of various sizes were produced, accompanied by connected structures. This is because thermal insulation is achieved inside the bubble, where the size reduction takes place with insufficient cooling. This study clearly showed nanosecond laser-induced size reduction of Au NPs, better than that achieved previously, by introducing an additional parameter, pressure. This study provides a refined method for size control in laser ablation NP generation. We expect that a rich chemistry can proceed in this transient supercritical water layer surrounding the NP droplets as a reaction medium.

A Coordinating Procedure for Tracing Static Bifurcation Points of Voltage Instability

Based on static bifurcation theory, a systematic procedure for tracing the bifurcation points of power system voltage instability was presented. Two main kinds of bifurcations, a common saddle node bifurcation (SNB) and a kind of bifurcation—limit induced bifurcation (LIB), which can cause the voltage collapse, were studied simultaneity and all types of device limits were considered. Firstly, make sure the mathematical model of the system. Secondly, starting from the basic running point of power systems, a predictor scheme was presented to find all the limit points (LP) and identify the LIB points; an adaptive step size control method considering the curvature of the manifold was introduced for tracing the equilibrium manifold and the detection of the SNB points without the existing of LPs. The two schemes were combined to lead a more effective method for SNB, LP, and LIB detection.

Size control of nanopores formed on SiO2 glass by swift-heavy-ion irradiation and its application to highly sensitive biomolecular detection

Swift-heavy-ion irradiation creates latent tracks in SiO2 glass and nanopores with a high aspect ratio can be formed along these ion paths by selective etching of the latent tracks using hydrogen fluoride (HF) vapor. Here we report that the size of nanopores can easily be controlled by simply changing the temperature of the HF solution generating the vapor and/or that of the SiO2 glass exposed to the vapor. Furthermore, this method of size control was used to produce SiO2 glass sheets with nanopores of different sizes and number densities for use as the waveguide layer in the sensing plates for a waveguide-mode sensor. In comparison with nonperforated plates, the increased surface area due to the formation of nanopores was found to create up to a tenfold increase in sensitivity.

Transparent Infrared-Emitting CeF3:Yb−Er Polymer Nanocomposites for Optical Applications

Bright infrared-emitting nanocomposites of unmodified CeF(3):Yb-Er with polymethyl-methacrylate (PMMA) and polystyrene (PS), which offer a vast range of potential applications, which include optical amplifiers, waveguides, laser materials, and implantable medical devices, were developed. For the optical application of these nanocomposites, it is critical to obtain highly transparent composites to minimize absorption and scattering losses. Preparation of transparent composites typically requires powder processing approaches that include sophisticated particle size control, deagglomeration, and dispersion stabilization methods leading to an increase in process complexity and processing steps. This work seeks to prepare transparent composites with high solids loading (>5 vol%) by matching the refractive index of the inorganic particle with low cost polymers like PMMA and PS, so as to circumvent the use of any complex processing techniques or particle surface modification. PS nanocomposites were found to exhibit better transparency than the PMMA nanocomposites, especially at high solids loading (>/=10 vol%). It was found that the optical transparency of PMMA nanocomposites was more significantly affected by the increase in solids loading and inorganic particle size because of the larger refractive index mismatch of the PMMA nanocomposites compared to that of PS nanocomposites. Rayleigh scattering theory was used to provide a theoretical estimate of the scattering losses in these ceramic-polymer nanocomposites.

Sonochemical synthesis of silver nanoparticles in Y-zeolite substrate

Silver ions can be reduced by 24 kHz ultrasonic waves in ion-exchanged Ag+–Y zeolite. In this research, silver ions were introduced into the nano-porous (1.2 nm) zeolite lattice by ion-exchange route. After the reduction process, silver nanoparticles were placed in the cavities, with a size of about 1 nm and also on the external surfaces of the zeolite, with sizes about less than 10 nm. Fast and simple lab-scale reduction of silver ions in the zeolite is important for researchers who work on catalytic properties of metallic silver–zeolite. Several reduction methods have been reported but reduction by ultrasonic waves is a new, simple, and size-controllable method with a high practical value which does not need any complicated facilities. In a sonochemical process, a huge density of energy is provided by the collapse of bubbles which formed by ultrasonic waves. The released energy causes the formation of reducing radicals that consequently reduce the silver ions. It is concluded that the higher silver content may result in the formation of larger silver crystals on the external surface of zeolite crystals. Also, the addition of 1-propanol and 2-propanol to the aqueous reaction medium does not cause better reduction. In addition, increasing the irradiation time and ultrasonic power does not affect the silver crystal growth significantly but the extent of silver ion reduction increases when the power of ultrasonic waves increases. All samples were irradiated under the same ultrasonic conditions. The samples were analyzed by XRD, EDS, SEM, and TEM.

Nanoscaled redox active protein adsorption on Au-dot arrays: An electrochemical scanning probe microscopic investigation for application in nano-biodevices

Highly dense and uniform protein dot arrays on Au-nanodots using size controllable method were fabricated on indium tin oxide (ITO) substrate in order to develop an electrochemical nanobiochip. Cysteine modified azurin was directly immobilized on the fabricated Au-nanodots without any linker materials. Atomic force microscopy was used for characterizing Au-dots formed on ITO substrate. Electrochemical scanning tunneling microscopy (ECSTM) revealed the monolayer formation with an in situ cyclic voltammetry to observe redox behaviour of both bare Au-dots and protein immobilized Au-dots. I– V characteristics were obtained on both bare Au-dots and protein immobilized Au-dots structured on ITO conductive electrodes.

Synthesis of Macroporous Thermosensitive Hydrogels: A Novel Method of Controlling Pore Size

Macroporous thermosensitive poly(N-isopropylacrylamide) hydrogels were synthesized in the presence of dodecyl dimethyl benzyl ammonium bromide (DDBAB). Poly(vinyl alcohol) (PVA) was involved to control the pore size of the hydrogels. The morphology of the resulting hydrogels was studied by both an optical microscope and a scanning electron microscope. Moreover, the pore size and its distribution were examined by mercury intrusion porosimetry. The results indicated that size of the pores decreased with the increase of the amount of PVA added. The mechanism was explained after dynamic light scattering measurement of the size of hydrophobic initiator DDBAPS aggregates that were formed in situ in PVA aqueous solutions of various concentrations as the product of the reaction between DDBAB and the water soluble initiator ammonium persulfate. Swelling ratio and deswelling/reswelling kinetics of the hydrogels were also measured to investigate the response properties of the hydrogels. It would be a promising method of pore size control for synthesizing hydrogels of other vinyl monomers that could be initiated by persulfates.

Room-Temperature Size Evolution of Thiol-Protected Gold Nanoparticles Assisted by Proton Acids and Halogen Anions

In the present work, a mild size-control method for thiol-protected Au NPs was developed. When thiol-protected Au NPs were reacted with tetra-n-octylammonium bromide and trifluoroacetic acid, the size of Au NPs was tuned in the range from 2 to 6 nm at room temperature. Larger Au NPs could be obtained by mild heating at 55 degrees C. This size evolution method assisted by proton acid and bromide anion is a first example of the size tuning of thiol-protected Au NPs at room temperature. Because of the mild reactivity of acid and bromide ions to organic molecules, various thiol derivatives sensitive to heat, base, and reducing agent can be utilized for this method.

ZnO Nanoparticles Prepared by Thermal Decomposition of Batch Supercritical Antisolvent Processed Zinc Acetate

ZnO wurtzite nanoparticles (crystallite sizes ca. 15 nm) were prepared via thermal decomposition of batch supercritical antisolvent (SAS) processed zinc acetate precursor. Batch SAS could produce nanoscale zinc acetate particles (average sizes ca. 35 nm) at 4°C and 15 MPa when choosing the optimum flow of the supercritical fluid. ZnO nanoparticles were formed by decomposing nanoparticles of zinc acetate at 150, 300 and 450°C, respectively. The Zinc acetate and ZnO nanoparticles were characterized based on TEM, FTIR spectroscopy and X-ray powder diffraction. TGA and FTIR spectra were used to the thermal decomposition course of the zinc acetate particles. ZnO nanoparticles were ultrapure and have no residual organic group. Calcination temperatures of zinc acetate particles have no significantly negative influence on the size of final ZnO particle. The ZnO crystalline agglomeration, particle size and size distribution are determined by the quality of the SAS processed precursors. The present work is helpful to develop a clean, size controllable nanoparticle preparation method.

Application of Ant Colony Optimization for Image Segmentation

Ant colony optimization application for two-dimensional electrophoresis gel image segmentation is investigated. Standard ACO model with one ants’ colony is presented also provided ants’ colony size control method. Presented modified ACO model for twodimensional electrophoresis gel image segmentation. Created synthetic image and experimentally estimated model parameters for segmentation are provided. Image pre-processing operations and processing results for decrease of processing time and increase segmentation accuracy are presented. Obtained results show that model is suitable for overlapped protein spots segmentation. Was reached average segmentation result that depends on number of overlapped spots and how close they centers are to each other. Model parameters and their influence on ant’s behaviour and segmentation results are provided. Segmentation dynamics analyzed and intermediate segmentation results are provided. Population changes analyzed and population size change is proposed as a stopping parameter for segmentation process. Segmentation accuracy was about 67% improve over simple threshold function segmentation. Processing times are commented. Segmentation result can be improved by the use of real electrophoresis images for parameters estimation, also by the use of more effective optimal model parameters estimation algorithm. Ill. 7, tabl. 2, bibl. 12. (in English; summaries in English, Russian and Lithuanian).

Design and Analysis of Optimization Methods for Subdivision Surface Fitting

We present a complete framework for computing a subdivision surface to approximate unorganized point sample data, which is a separable nonlinear least squares problem. We study the convergence and stability of three geometrically-motivated optimization schemes and reveal their intrinsic relations with standard methods for constrained nonlinear optimization. A commonly-used method in graphics, called point distance minimization, is shown to use a variant of the gradient descent step and thus has only linear convergence. The second method, called tangent distance minimization, which is well-known in computer vision, is shown to use the Gauss-Newton step, and thus demonstrates near quadratic convergence for zero residual problems but may not converge otherwise. Finally, we show that an optimization scheme called squared distance minimization, recently proposed by Pottmann et al., can be derived from the Newton method. Hence, with proper regularization, tangent distance minimization and squared distance minimization are more efficient than point distance minimization. We also investigate the effects of two step size control methods -- Levenberg-Marquardt regularization and the Armijo rule -- on the convergence stability and efficiency of the above optimization schemes.

A step size control algorithm for the weak approximation of stochastic differential equations

A vriable step size control algorithm for the weak approximation of stochastic differential equations is introduced. The algorithm is based on embedded Runge–Kutta methods which yield two approximations of different orders with a negligible additional computational effort. The difference of these two approximations is used as an estimator for the local error of the less precise approximation. Some numerical results are presented to illustrate the effectiveness of the introduced step size control method.

Controlled synthesis of rod-likeLiVMoO6 nanocrystals for application in lithium-ion batteries

This paper reports a newly developed method for the shapeand size control of transition metal composite oxides, such asLiVMoO6, to obtain significantly enhanced electrode properties for lithium-ion batteries. Rod-likeLiVMoO6 nanocrystals were synthesized through a designed route of partial reduction, self-assembly and re-oxidation.V5+ andMo6+ ionswere used with low-grade starting materials to get a mixed valence of V and Mo. It is believed that ionpairs of V5+/V4+ or Mo6+/Mo5+ in the resultant mixture play an important role in the formation of a templateprecursor by self-assembly during a rheological phase reaction, althoughfurther explanation is required. The electrochemical performance of theLiVMoO6 obtained has been much improved due to the increased crystallinity and reduced particle size of thismaterial. 176 mA h g−1 and 166 mA h g−1 capacity was delivered in the initial discharge with a reversible capacity retention of 94.8%and 95.3% after 100 cycles in the range of 3.6–1.80 V versus metallic Li at 1 and 3 C currentrate, respectively.

A Facile Size-control Method of CdS Nanoparticles In-situ Synthesized in Polymer Matrix by Adjusting Ratio of Acidic Acid with Metallic Complex in Acrylate Photoresist Resin

Abstract A facile method with efficient control of nanoparticles size in polymer matrix by combination of in situ synthesis and photopolymerization is proposed and investigated. The photoluminescence of the CdS–polymer nanocomposites was easily tuned by adjusting the molar ratio of acrylic acid to cadmium acrylate in designed photoresist resins.

A novel method for the pore size control of the battery separator using the phase instability of the ternary mixtures

AbstractThe battery separator plays a key role in determining the capacity of the battery. Since separator performance mainly depends on the pore size of membrane, development of a technique for the fabrication of the membrane having controlled pore size is essential in producing a highly functional battery separator. In this study, microporous membranes having the desired pore size were produced via thermally‐induced phase separation (TIPS) process. Control of the phase boundaries of polymer‐diluent blends is the main concern in manipulating pore size in TIPS process, because pore size mainly depends on the temperature gap between phase separation temperature of the blend and the crystallization temperature of polymer. Microporous membranes having controlled pore size were produced from polyethylene (PE)/dioctyl phthalate (DOP) blends, PE/isoparaffin blends, and polymer/diluent‐mixture ternary blends, that is, PE/(DOP/isoparaffin) blends. PE/DOP binary blends and PE/(DOP/isoparaffin) ternary blends exhibited typical upper critical solution temperature (UCST) type phase behavior, while PE formed a homogeneous mixture with isoparaffin above the crystallization temperature of PE. When the mixing ratio of polymer and diluent‐mixture was fixed, the phase separation temperature of PE/diluent‐mixture blend first increased with increasing DOP content in the diluent‐mixture, went through a maximum centered at about 80 wt % DOP and then decreased. Furthermore, the phase separation temperatures of the PE/diluent‐mixture blends were always higher than that of the PE/DOP blend when diluent‐mixture contained more than or equal to 20 wt % of DOP. Average pore size of microporous membrane prepared from PE/DOP blend and that prepared from PE/isoparaffin blend were 0.17 and 0.07 μm, respectively. However, average pore size of microporous membrane prepared from ternary blends was varied from 0.07 to 0.5 μm by controlling diluent mixing ratio. To understand the phase behavior of ternary blend, phase instability of the ternary mixture was also explored. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2025–2034, 2006

Size control of self-assembled nanoparticles by an emulsion/solvent evaporation method

A novel and simple method for size control of self-assembled nanoparticles is suggested in this paper. Polymeric nanoparticles were prepared from amphiphilic chitosan derivatives fluorescein isothiocyanate (FITC)-conjugated glycol chitosans (FGCs). The attachment of hydrophobic FITC onto hydrophilic glycol chitosan induced the amphiphilic conjugate to form self-assembled nanoparticles in aqueous media, depending on degree of substitution. The size of self-assembled nanoparticles was controlled by a novel emulsion/solvent evaporation method. Adding a small amount of an immiscible solvent with water (chloroform) to FGC nanoparticle suspensions in aqueous media followed by ultrasonification and solvent evaporation led to partial dissociation and subsequent reformation of nanoparticles. The evaporation of chloroform facilitated the hydrophobic association, which resulted in more dense and hardened hydrophobic cores. The size of nanoparticles was closely related with the FGC concentration in the emulsion. The mean diameters of self-assembled nanoparticles were 150–500 nm at the FGC concentrations of 0.3–2.5 mg/ml. Higher FGC concentration resulted in larger particles. The polydispersity factors (μ 2/Γ 2) of the reformed nanoparticles were fairly low (0.001–0.094), indicating narrow size distribution. The FGC nanoparticles were stable in phosphate-buffered saline at 37°C up to 20 days. Lactose was a good excipient for maintaining the structural integrity of nanoparticles during freeze-drying. Without lactose, the freeze-dried nanoparticles were not homogeneously redispersed in aqueous media. However, the freeze-dried nanoparticles with lactose were spontaneously redispersed in aqueous milieu with their own sizes.

A New Variable Step Size Control Method for the Transform Domain LMS Adaptive Algorithm

This paper develops a new adaptive step size control method for the transform domain least mean-square (TDLMS) adaptive algorithm. The time-varying step size is an efficient approximation of an optimal step size based on a proposed cost function, therefore leading to significant improvements in the performance characteristics of the TDLMS algorithm. Mean-square analysis is provided, and an expression for the steady-state excess mean-squared error (MSE) is derived. Simulation experiments confirm the algorithm's enhanced convergence properties and verify the theoretical steady-state MSE results.

A New Method for Size Control of Ultrafine Particles and Effect of Electric Field

A simple method to change the feature of smoke was found. Smokes of In2O3 and Al were used in the model experiment. The size of smoke particles is smaller, i.e., 0.6 (Al)–0.5 (In2O3), than those of ordinarily produced smoke particles. The oxide smoke curved in an electric field. In this case, various sizes of particles were obtained depending on the location of the collection point. Truncated In2O3 tetrahedron particles less than 100 nm in size were predominantly obtained. The oxygen defects in small In2O3 particles have been discussed as being due to a definite array of oxygen. The curve of oxide smoke in the electric field has been discussed in terms of being due to the structure of the oxide.

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S2- to St- (stearateion). Chnracterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i.e. CdS particle inserts in the CdSt2, molecular layers to form a sandwirh-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.

Grain size refinement and mechanical properties of foil metallurgically processed 7475 aluminium alloy

Foil metallurgical processing has been performed to investigate the possibility of a grain size control method. In the present work, a stack of 7475 aluminium alloy foils, each 15 or 40 μm in thickness, was press bonded at a temperature of 573 K under heavy thickness reduction, followed by annealing at 773 K for 1.2 ks. The laminate grain size in the thickness direction was clearly decreased with increasing thickness reduction ratio of up to 15–10: 1 and was controlled to the attained foil thickness. In the laminate with an attained foil thickness of 10 or 18 μm, rectangular grains were aligned along the bonding interfaces to form a brickwork pattern. Grain size control and grain refinement could be achieved during foil metallurgical processing by the grain growth inhibition function of the oxide particles at the interfaces, which were ∼ 50–100 nm in thickness and 100–200 nm in length. The fine grained laminates showed an increase in proof stress with decrease in grain size at room temperature and an increase in the optimum strain rate for superplastic flow.