27Al NMR diffusometry of Al13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al₁₃, [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, ²⁷Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO₄ core of the ϵ-Al₁₃ cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO₄ center of the ϵ-Al₁₃ cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T₁ and T₂ ²⁷Al NMR relaxation coefficients for ²⁷Al PFGSTE NMR studies. Stokes–Einstein relationship was used to relate the ²⁷Al diffusion coefficient of the ϵ-Al₁₃ cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published ¹H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that ²⁷Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.     

Effect of surface modifier on flow properties of epoxy suspensions containing model plate-like nanoparticles

The influence of inter-particle interaction on the rheology of an uncured epoxy containing model α-zirconium phosphate (ZrP) nanoplatelets with aspect ratio of 160 is reported. Epoxy suspensions containing nanoplatelets exfoliated with tetra-n-butyl ammonium hydroxide (TBA), a low molecular weight quaternary ammonium cation, show short-range repulsive potential with weak elastic response at low concentration. At semi-dilute concentrations, the suspensions are solid-like at intermediate frequency and transition to viscous flow for time scales longer than the rotary diffusion process. The weak elasticity at intermediate frequency is attributed to the effect of Brownian motion on the rotational motion of the isolated plates. Suspensions containing nanoplatelets exfoliated with hydrophilic polyetheramine oligomers show similar behaviour to the ZrP-TBA system, but shifted to lower concentration. The rheological behaviour is attributed to steric stabilization of the nanoplatelets by extended oligomer brushes with short-range repulsive interactions. For suspensions containing nanoplatelets exfoliated with hydrophobic polyetheramines with shorter length, there is evidence for elastic response on local length scales and the flow behaviour shows strong history and temperature dependence. Rheological signatures associated with equilibrium nanoplatelet dispersions with repulsive interactions are discussed.     

Polyolefin soluble polyisobutylene oligomer‐bound metallophthalocyanine and azo dye additives

Metallophthalocyanines prepared with polyisobutyl (PIB) substituents have very high solubility in organic solvents including saturated hydrocarbons, toluene, and other low polarity organic solvents. In heptane, PIB‐bound metallophthalocyanines have solubility of about 0.1 g/mL at 25 °C, solubility values that are significantly higher than other substituted metallophthalocyanines. PIB terminally functionalized with metallophthalocyanines as well as PIB containing terminal azo dye groups also dissolve in molten hydrocarbon polymers like polyethylene or polypropylene. Thus, these highly chromogenic PIB‐bound dyes can be incorporated uniformly into the polyolefins to form colored polymer solids on cooling. Because only a low concentration of a highly hydrocarbon compatible dye is used, the crystallinity and thermal properties of the colored polyolefin products are not significantly affected. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 545–551     

Structure modification and annealing effect of polymer bulk heterojunction solar cells based on polyfluorene derivatives

Three low bandgap polyfluorene copolymers containing a donor–acceptor–donor moiety have been synthesized via Suzuki and Stille polymerization reactions. Their bandgaps and molecular energy levels (highest occupied molecular orbital and lowest unoccupied molecular orbital) varied with different polymerization methods. The molecular weight of the copolymer increased significantly through copolymerizing with a monomer having a long alkyl side chain. In order to investigate their photovoltaic properties, polymer solar cell devices based on the copolymers were fabricated with a structure of indium tin oxide/poly(styrene sulfonic acid)‐doped poly(ethylene dioxythiophene)/copolymers:[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/LiF/Al under the illumination of AM 1.5G, 100 mW/cm². We found that the annealing temperature had a profound effect on the power conversion efficiency (PCE) of the devices with a blend of poly[9,9‐didodecylfluorene‐alt‐(bis‐thienylene) benzothiadiazole] (PF12‐TBT) and PCBM. The PCE of the solar cell based on PF12‐TBT/PCBM (1:4) annealing at 70 °C for 20 min was 4.13% with an open‐circuit voltage (V_oc) of 1.02 V, fill factor of 55.9%, and a short‐circuit current (J_sc) of 7.24 mA/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Resonant Hopf–Hopf Interactions in Delay Differential Equations

A second-order delay differential equation (DDE) which models certain mechanical and neuromechanical regulatory systems is analyzed. We show that there are points in parameter space for which 1:2 resonant Hopf–Hopf interaction occurs at a steady state of the system. Using a singularity theoretic classification scheme [as presented by LeBlanc (1995) and LeBlanc and Langford (1996)], we then give the bifurcation diagrams for periodic solutions in two cases: variation of the delay and variation of the feedback gain near the resonance point. In both cases, period-doubling bifurcations of periodic solutions occur, and it is argued that two tori can bifurcate from these periodic solutions near the period doubling point. These results are then compared to numerical simulations of the DDE.     

Is the Static Magnetic Vector Potential Screened by a Thick Superconducting Shield

In 1986 Tonomura and his co-workers reported the results of a test for the existence of the magnetic Aharonov-Bohm (AB) effect using permalloy toroids with a superconducting niobium coating. Classical Maxwell theory suggests that the group may have been able to observe the AB effect only because their superconducting shield was quite thin (2.5 penetration depths), and that, had a very thick shield been used, no AB effect would have been observable. However, orthodox quantum mechanics predicts that a static vector potential penetrates a superconducting shield of any thickness in cases where the magnetic flux inside the sample is an odd integer times h/2e. Regardless of which view is correct, it is argued in this paper that a superconductor only screens leakage or fringing field to the extent that it screens vector potential, so that there are doubts that the experiment answered the critics of earlier experiments, as was claimed.     

Amperometric Determination of Sugars at Activated Barrel Plating Nickel Electrodes

We report amperometric determination of sugars by using a disposable barrel plating nickel electrode (Ni‐BPE) in this study. The activated Ni‐BPE possesses good reproducibility in flow injection analysis of sugars with a relative standard deviation of 3.16% for 10 consecutive injections of glucose. The electrocatalytic mechanism for the detection of sugars as well as the use as a detector in high‐performance liquid chromatography (HPLC) is investigated. We achieve a good separation of four sugars (glucose, fructose, sucrose, and maltose) in HPLC with favorable sensitivity at a detection potential of +0.55 V vs. Ag/AgCl. The results of wide linear calibration ranges and detection limits in the μM range meet the need of real sample analysis. This detection method is successfully used for quantitative determination of sugars in honey to identify its authentication.