Observation of Nucleation and Growth of CdS Nanocrystals in a Two-phase System

The nucleation and growth kinetics of CdS nanocrystals in a two-phase synthesis system have been investigated. It was found that the nucleation process is quite lengthy and overlapped with the growth process; nevertheless, as formed nanocrystals show extremely narrow size distribution owing to the unique heterogeneous reacting environment and Ostwald ripening growth. The nucleation and growth kinetics of the nanocrystals were also influenced strongly by the monomer concentration, capping agent concentration, and solvent polarity. It was also found that a high monomer concentration, a low capping agent concentration, and low solvent polarity lead to a higher maximum nucleus concentration and nanocrystal concentration, while high polarity solvents are favorable for the formation of nanocrystals with narrower size distribution and higher photoluminescence quantum yield.

Controlled synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes

The synthesis of monodisperse nanocrystals is an important topic in the field of nanomaterials not only for practical applications, but also for scientific interest in fundamental research. In this feature article, we mainly focus on synthesis of monodisperse nanocrystals by a two-phase approach without the separation of nucleation and growth processes, and report some progress made recently in the observation and understanding of nucleation and growth of semiconductor nanocrystals. Firstly, a novel two-phase approach to monodisperse nanocrystals, which is different from the well-established synthesis models, is discussed. We demonstrate that the two-phase approach has a quite lengthy nucleation process, and can be applied to the synthesis of many kinds of binary monodisperse nanocrystals.

Convenient preparation of tunably loaded chemically converted graphene oxide/epoxy resin nanocomposites from graphene oxide sheets through two-phase extraction

We report a facile method to create the chemically converted graphene oxide/epoxy resin nanocomposites from graphene oxide sheets through two-phase extraction. Great improvements in mechanical properties such as compressive failure strength and toughness have been achieved for the chemically converted graphene oxide/epoxy resin for a 0.0375 wt% loading of chemically converted graphene oxide sheets in epoxy resin by 48.3% and 1185.2%, respectively. In addition, the loading of graphene is also conveniently tunable even to 0.15 wt% just by increasing the volume of the graphene oxide dispersion.

Synthesis of Ruthenium Dioxide Nanoparticles by a Two-Phase Route and Their Electrochemical Properties

Dissolvable, size- and shape-controlled ruthenium dioxide nanoparticles are successfully achieved through a two-phase route. The influence of reaction time, temperature, and monomer concentration and the nature of capping agents on the morphologies of nanoparticles are studied through transmission electron microscopy (TEM). A possible mechanism for the formation and growth of nanoparticles is also involved. X-ray powder diffraction (XRD) confirms the amorphous structure for as-prepared ruthenium dioxide nanoparticles. Samples are immobilized by simple dip-coating on a current collector, and the cyclic voltammetry measurement is utilized to investigate their electrochemical properties. The specific capacitance of one sample can teach as high as 840 F g(-1), which reveals the promising application potential to electrochemical capacitors.

Ordered macroporous films from self-assembly of two-armed polymer with a crown ether core

Highly ordered honeycomb-like macroporous films were obtained via self-assembly of a two-armed polymer with a crown ether core under controlled conditions. A possible mechanism is speculated, primarily based on the strong affinity between the crown ether cores. The pore size and arrangement are sensitive to the solvent evaporation rate and the solution concentration. Upon spontaneous drying, the pore diameter (D) depends on the concentration (c) by a relation of D=518c(-0.610).

Formation and photoluminescence of silver nanoparticles stabilized by a two-armed polymer with a crown ether core

Silver nanoparticles were synthesized by the use of a two-armed polymer with a crown ether core [poly(styrene)]-dibenzo-18-crown-6-[poly(styrene)] based on the flexibility of the polymer chains and the complex effect of crown ether with Ag+ and Ag. The size of silver nanoparticles could be tailored by controlling the initial concentrations of the polymer and Ag+, and the molecular weight of the polymer. The emission of silver nanoparticles was blue-shifted, and the intensity of the photoluminescence of silver nanoparticles stabilized by the polymer was significantly increased due to the complex effect between the crown ether embedded in the polymer and the silver nanoparticles.

Two-phase synthesis of shape-controlled colloidal zirconia nanocrystals and their characterization

We have developed a two-phase approach for the synthesis of shape-controlled colloidal zirconia nanocrystals, including spherical-, teardrop-, rod-, and rice grain-shaped particles. We found that the key factors for controlling the shape were the reaction time, the nature of the capping agent, and the monomer concentration. We have analyzed the morphologies, crystallinity, optical properties, and structural features of the as-prepared ZrO2 nanoparticles by using transmission electron microscopy (TEM), high-resolution TEM, X-ray powder diffraction, and UV-vis absorption and fluorescence spectroscopy. The possible nucleation and growth process is also discussed.

Novel prefractionation method can be used in proteomic analysis

For the first time, a novel prefractionation method used in proteomic analysis was developed, which is performed by a novel aqueous two-phase system (NATPS) composed of n-butanol, (NH4)(2)SO4, and water. It can separate proteomic proteins into multigroups by one-step extraction. The phase-separation conditions of n-butanol solutions were studied in the presence of commonly used inorganic salts. The NATPS was subsequently developed. Using human serum albumin, zein, and gamma-globulin as model proteins, the separation effectiveness of the NATPS for protein was studied under affection factors, i.e., pH, n-butanol volume, protein, or salt concentration. The model and actual protein samples were separated by the NATPS and then directly used for gel electrophoresis without separating the target proteins from phase-forming reagents. It revealed that the NATPS could separate proteomic proteins into multigroups by one-step extraction. The NATPS has the advantages of rapidity, simplicity, low cost, biocompability, and high efficiency. It need not separate target proteins from the phase-forming reagents. The NATPS has great significance in separation and extraction of proteomic proteins, as well as in methodology.

Luminescent CdSe and CdSe/CdS core-shell nanocrystals synthesized via a combination of solvothermal and two-phase thermal routes

A new solvothermal route has been developed for synthesizing the size-controlled CdSe nanocrystals with relatively narrow size distribution, and the photoluminescence (PL) quantum yields (QYs) of the nanocrystals can reach 5-10%. Then the obtained CdSe nanocrystals served as cores to prepare the core/shell CdSe/CdS nanocrystals via a two-phase thermal approach, which exhibited much higher PL QYs (up to 18-40%) than the CdSe core nanocrystals. The nanocrystal samples were characterized by ultraviolet-visible (UV-vis) absorption spectra, PL spectra, wide-angle Xray diffraction (WAXD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Fabrication of a metal particle array based on a self-assembled template from a two-armed polymer

A two-armed polymer with a crown ether core self-assembles to produce macroporous films with pores perpendicularly reaching through the film down to the substrate. A possible assembling mechanism is discussed. The pore size can be conveniently adjusted by changing the solution concentration. These through-hole macroporous films provide a template for fabricating an array of Cu nanoparticle aggregates.

Extraction mechanism of rare earths with sec-octylphenoxy acetic acid by two-phase titration technique

The compositions of the extracted complexes of La, Gd, Er and Y with sec-octyl-phenoxy acetic acid in heptane and the related apparent extraction equilibrium constants K-M were determined using two-phase titration technique. The stoichiometric compounds for La, Gd, Er and Y should be LaA(3) . 2.5HA, GdA(3) . 3HA, ErA(3) . 3.1HA and YA(3) . 4.3HA respectively. And their pK(M) are 3.43, 3.46, 3.08 and 2.58 respectively.

A FLOW-THROUGH ACOUSTIC WAVEGUIDE FOR TWO-PHASE BUBBLY FLOW VOID FRACTION MEASUREMENT

In the Spallation Neutron Source (SNS) facility at Oak Ridge National Laboratory (ORNL), the deposition of a high-energy proton beam into the liquid mercury target forms bubbles whose asymmetric collapse cause Cavitation Damage Erosion (CDE) to the container walls, thereby reducing its usable lifetime. One proposed solution for mitigation of this damage is to inject a population of microbubbles into the mercury, yielding a compliant and attenuative medium that will reduce the resulting cavitation damage. This potential solution presents the task of creating a diagnostic tool to monitor bubble population in the mercury flow in order to correlate void fraction and damage. Details of an acoustic waveguide for the eventual measurement of two-phase mercury-helium flow void fraction are discussed. The assembly’s waveguide is a vertically oriented stainless steel cylinder with 5.08cm ID, 1.27cm wall thickness and 40cm length. For water experiments, a 2.54cm thick stainless steel plate at the bottom supports the fluid, provides an acoustically rigid boundary condition, and is the mounting point for a hydrophone. A port near the bottom is the inlet for the fluid of interest. A spillover reservoir welded to the upper portion of the main tube allows for a flow-through design, yielding a pressure release top boundary condition for the waveguide. A cover on the reservoir supports an electrodynamic shaker that is driven by linear frequency sweeps to excite the tube. The hydrophone captures the frequency response of the waveguide. The sound speed of the flowing medium is calculated, assuming a linear dependence of axial mode number on modal frequency (plane wave). Assuming that the medium has an effective-mixture sound speed, and that it contains bubbles which are much smaller than the resonance radii at the highest frequency of interest (Wood’s limit), the void fraction of the flow is calculated. Results for water and bubbly water of varying void fraction are presented, and serve to demonstrate the accuracy and precision of the apparatus.

Heat and mass transfer in two-phase porous materials under intensive microwave heating

Computational results for the intensive microwave heating of porous materials are presented in this work. A multi-phase porous media model has been developed to predict the heating mechanism. Combined finite difference time-domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent both on temperature and moisture content. The model was able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change.