One-step synthesis of large-aspect-ratio single-crystalline gold nanorods by using CTPAB and CTBAB surfactants

Gold nanorods were prepared in high yields by using a one-step seed-mediated process in aqueous cetyltripropylammonium bromide (CTPAB) and cetyltributylammonium bromide (CTBAB) solutions in the presence of silver nitrate. The diameters of the nanorods range from 3 to 11 nm, their lengths are in the range of 15 to 350 nm, and their aspect ratios are in the range of 2 to 70. The diameters of the Au nanorods obtained from one growth batch in CTPAB solutions decrease as their lengths increase, and their volumes decrease as the aspect ratios increase. The diameters of the Au nanorods obtained from one growth batch in CTBAB solutions first decrease and then slightly increase as their lengths increase, and their volumes increase as the aspect ratios increase. These Au nanorods are single-crystalline and are seen to be oriented in either the [100] or [110] direction under transmission electron microscopy imaging, irrespective of their sizes. To the best of our knowledge, this is the first report of the preparation by using wet-chemistry methods of single-crystalline Au nanorods with aspect ratios larger than 15.     

Blends of nylon‐6 with phenol‐containing polymers

The miscibility of nylon‐6 with poly(4‐vinylphenol) (PVPh) or poly(1‐hydroxy‐2,6‐methylphenylene) (p‐Cl‐novolac) was studied with differential scanning calorimetry and small‐angle X‐ray scattering techniques. Both PVPh and p‐Cl‐novolac are miscible with nylon‐6 at the molecular level. The presence of the phenolic polymers affects the crystallization of nylon‐6 and suppresses its melting point. PVPh increases the long space order in crystalline nylon‐6 because it increases the thickness of the amorphous layers. In contrast, a small quantity of p‐Cl‐novolac tends to decrease the long space order. It seems that p‐Cl‐novolac distributed in the amorphous regions introduces more order in these regions and makes the amorphous layers thinner. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 841–850, 2001     

Gold and Silver Nanomaterial‐Based Optical Sensing Systems

Gold and silver nanomaterials (NMs) such as nanoparticles (NPs) and nanoclusters (NCs) possessing interesting optical properties have become popular sensing materials. With strong surface plasmon resonance (SPR) absorption, extraordinary stability, ease in preparation, conjugation, and biocompatibility, Au NPs are employed to develop sensitive and selective sensing systems for a variety of analytes. However, small sizes of Au and Ag NCs with interesting photoluminescence (PL) properties are used in many PL‐based sensing systems for the detection of important analytes. In addition, many bimetallic AuM NMs possessing strong catalytic activity are used to develop highly sensitive fluorescent sensors. This review article is categorized in four sections based on the NMs used in the sensing systems, including Au NPs, bimetallic AuM NMs, Au NCs, and DNA–Ag NCs. In each section, synthetic strategies and optical properties of the NMs are provided briefly, followed by emphasis on their analytical applications in the detection of small molecules, metal ions, DNA, proteins, and cells. Current challenges and future prospects of these NMs‐based sensing systems will be addressed.     

Spiro‐Configured Bipolar Host Materials for Highly Efficient Electrophosphorescent Devices

In this study, we synthesized and characterized a series of spirobifluorene‐based bipolar compounds (D2 ACN, DNPACN, DNTACN, and DCzACN) in which a dicyano‐substituted biphenyl branch, linked orthogonally to a donor biphenyl branch bearing various diarylamines, acted as an acceptor unit allowing fine‐tuning of the morphological stability, triplet energy, bipolar transport behavior, and the HOMO and LUMO energy levels. The promising physical properties of these new compounds, together with their ability to transport electrons and holes with balanced mobilities, made them suitable for use as host materials in highly efficient phosphorescent organic light‐emitting diodes (PhOLEDs) with green iridium‐based‐ or red osmium‐based phosphors as the emitting layer (EML). We adopted a multilayer structure to efficiently confine holes and electrons within the EML, thus preventing exciton diffusion and improving device efficiency. The device incorporating D2 ACN doped with the red emitter [Os(bpftz)₂(PPhMe₂)₂] (bpftz=3‐(trifluoromethyl)‐5‐(4‐tert‐butylpyridyl)‐1,2,4‐triazolate) gave a saturated red electrophosphorescence with CIE coordinates of (0.65, 0.35) and remarkably high efficiencies of 20.3 % (21 cd A^?1) and 13.5 Lm W^?1 at a practical brightness of 1000 cd m^?2.     

Effect of Polydispersity on the Phase Behavior of Polymer Blends

Summary: The effect of polydispersity on polymer blend phase behavior is studied by in situ small‐angle X‐ray scattering. In a polydisperse polyethylene (PE)/isotactic poly(propylene) (iPP) blend, the enthalpic portion of the interaction parameter is greater than that of a corresponding blend with lower polydispersity. This is attributed to the presence of long chains, which provide a higher interaction energy and packing constraint, reducing the system miscibility. As expected, the radius of gyration is higher in the system with higher polydispersity.

Comparison of phase diagrams of the iPP/PE system used in this study (thin lines) with that obtained from the literature (thick lines). The solid lines represent binodals and the dashed lines are spinodals.     

Strain-Enhanced Metallic Intermixing in Shape-Controlled Multilayered Core–Shell Nanostructures: Toward Shaped Intermetallics

Controlling the surface composition of shaped bimetallic nanoparticles could offer precise tunability of geometric and electronic surface structure for new nanocatalysts. To achieve this goal, a platform for studying the intermixing process in a shaped nanoparticle was designed, using multilayered Pd-Ni-Pt core–shell nanocubes as precursors. Under mild conditions, the intermixing between Ni and Pt could be tuned by changing layer thickness and number, triggering intermixing while preserving nanoparticle shape. Intermixing of the two metals is monitored using transmission electron microscopy. The surface structure evolution is characterized using electrochemical methanol oxidation. DFT calculations suggest that the low-temperature mixing is enhanced by shorter diffusion lengths and strain introduced by the layered structure. The platform and insights presented are an advance toward the realization of shape-controlled multimetallic nanoparticles tailored to each potential application.     

Maxima in hypercubes

We derive a Berry‐Esseen bound, essentially of the order of the square of the standard deviation, for the number of maxima in random samples from (0,1)^d. The bound is, although not optimal, the first of its kind for the number of maxima in dimensions higher than two. The proof uses Poisson processes and Stein's method. We also propose a new method for computing the variance and derive an asymptotic expansion. The methods of proof we propose are of some generality and applicable to other regions such as d‐dimensional simplex. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005     

Butane Dehydrogenation Reaction on Sulfur Poisoned Group 10 Metal/SiO2 Catalysts

Butane cracking and dehydrogenation reactions on silica supported Ni, Pt, Pd, and S, Pb modified Ni, Pt, Pd catalysts were studied via a fixed bed reaction system. Cracking reaction path prevailed when butane reaction was catalyzed by clean Ni, Pt, Pd and sulfur poisoned Ni catalysts. The addition of sulfur into Pt and Pd catalytic systems can shift the reaction path to dehydrogenation reaction. However, the deactivation problem due to carbonaceous deposit is not improved by the addition of sulfur into the catalytic system. The origin of the sulfur effect on the change of butane reaction pathway is discussed on the basis of the concentrations of Ph and S additives, oxygen perturbation effect, metal loading, carbonaceous deposit and reaction temperatures.     

New 3 D Tubular Porous Structure of an Organic–Zincophosphite Framework with Interesting Gas Adsorption and Luminescence Properties

A new 3D tubular zinc phosphite, Zn₂(C₂₂H₂₂N₈)_0.5(HPO₃)₂?H₂O ( 1 ), incorporating a tetradentate organic ligand was synthesized under hydro(solvo)thermal conditions and structurally characterized by single‐crystal X‐ray diffraction. Compound 1 is the first example of inorganic zincophosphite chains being interlinked through 1,2,4,5‐tetrakis(imidazol‐1‐ylmethyl)benzene to form a tubular porous framework with unusual organic–inorganic hybrid channels. The thermal and chemical stabilities, high capacity for CO₂ adsorption compared to that for N₂ adsorption, and interesting optical properties of LED devices fabricated using this compound were also studied.     

Stereospecific Bromine Replacement in the Synthesis of 4(e) and 4(a)-Deuterioadamantan-2-ones

Stereospecific introduction of deuterium on the adamantane skeleton has been accomplished with LiAID(OCH₃)₃-CuI.