Organic and Inorganic Blocking Layers for Solution‐Processed Colloidal PbSe Nanocrystal Infrared Photodetectors

A PbSe solution‐processed nanocrystal‐based infrared photodetector incorporating carrier blocking layers is demonstrated, and significant reduction of dark current is achieved. Detectivity values close to 10¹² Jones are achieved by using poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐(4,4′‐(N‐(4‐sec‐butyl))diphenylamine)] (TFB) and ZnO nanocrystals (NC) as the electron blocker and hole blocker, respectively. An improvement in lifetime is also observed in the devices with the ZnO NCs hole blocking layer.     

Evaluation of the performance of metameric indices

Forty three metameric pairs were obtained by comparison, shade-adjustment, and redyeing of 660 self shades dyed with direct, azoic, vat, and reactive dyes. The pairs were regrouped shadewise and ranked visually in increasing order of metamerism. Spearman's rank correlation coefficients were calculated between 11 measures of metamerism and the visual metameric ranking under three illuminants A, D65, and TL84 in pairs. The illuminant-independent general indices included the indices based on reflectance differences (Bridgeman), weighted reflectance differences (Nimeroff and Yurow), Cohen-Kappauf's residual differences (proposed) obtained from the spectral decompositions of the reflectance spectra of the metameric pair. Illuminant-specific special indices included color-differences under test illuminant, addition, subtraction, division, and multiplication of color-differences under test and reference illuminants, indices based on ΔL*, Δa*, Δb* differences under two illuminants, based on chromatic adapted ΔL*, Δa*, Δb* differences with multiplicative corrections for tristimulus differences under reference illuminant (Berns-Billmeyer), differences of the color constancy indices. The present work showed that indices based on ΔL*, Δa*, Δb* differences under two illuminants, both unmodified and modified by Berns-Billmeyer performed best among the existing indices. The differences of color constancy indices showed good correlation with the degree of metamerism in some cases, and this may be utilized for developing newer indices of metamerism. © 1996 John Wiley & Sons, Inc.     

Influence of formic acid on electrochemical properties of high‐porosity Pt/TiN nanoparticle aggregates

Platinum‐deposited titanium nitride (Pt/TiN) nanoparticle aggregates with high porosities were successfully prepared via a self‐assembly‐assisted spray pyrolysis method. The addition of formic acid (HCOOH) had a significant influence on the process, promoting the simultaneous formation of metallic Pt and reduction on the surface of the TiN support material. Complete reduction of the Pt/TiN nanoparticle aggregates improved the catalytic activity. The electrochemical surface area (ECSA) of Pt/TiN with HCOOH (Pt/TiN_w/HCOOH) was 87.15 m²/g‐Pt, which was higher than that of Pt/TiN without HCOOH (Pt/TiN_w/o‐HCOOH). The catalytic durability of Pt/TiN_w/HCOOH was twice that of Pt/TiN_w/o‐HCOOH. An effective strategy for obtaining carbon‐free catalysts with high activities and durabilities was identified. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2753–2760, 2013     

Morphology‐dependent electrocatalytic activity of nanostructured Pt/C particles from hybrid aerosol–colloid process

An optimum nanostructure and pore size of catalyst supports is very important in achieving high catalytic performances. In this instance, we evaluated the effects of various carbon nanostructures on the catalytic performances of carbon‐supported platinum (Pt/C) electrocatalysts experimentally and numerically. The Pt/C catalysts were prepared using a hybrid method involving the preparation of dense, hollow, and porous nanostructured carbon particle via aerosol spray pyrolysis followed by microwave‐assisted Pt deposition. Electrochemical characterization of the catalysts showed that the porous Pt/C catalyst gave the best performance; its electrochemical surface area was much higher, more than twice than those of hollow or dense Pt/C. The effects of pore size on electrocatalysis were also studied. The results showed the importance of a balance between mesopores and macropores for effective catalysis with a high charge transfer rate. A fluid flow model showed that good oxygen transport contributed to the catalytic activity. © 2015 American Institute of Chemical Engineers AIChE J, 62: 440–450, 2016     

MoS2-Polyaniline Based Flexible Electrochemical Biosensor: Toward pH Monitoring in Human Sweat

Wearable pH sensors for sweat analysis have garnered significant scientific attention for the detection of early signs of many physiological diseases. In this study, a MoS₂-polyaniline (PANI) modified screen-printed carbon electrode (SPCE) is fabricated and used as a sweat biosensor. The exfoliated MoS₂ nanosheets are drop casted over an SPCE and are functionalized by a conducting polymer, polyaniline (PANI) via the electropolymerization technique. The as-fabricated biosensor exhibits high super-Nernstian sensitivity of −70.4 ± 1.7 mV pH⁻¹ in the linear range of pH 4 to 8 of 0.1 m standard phosphate buffer solution (PBS), with outstanding reproducibility. The sensor exhibits excellent selectivity against the common sweat ions including Na⁺, Cl⁻, K⁺, and NH₄⁺ with tremendous long-term stability over 180 min from pH 4 to 6. The enhanced active surface area and better electrical conductivity as a consequence of the synergistic effect between MoS₂ and PANI are correlated with the boosted performance of the as-produced biosensor. The feasibility of the sensor is further examined using an artificial sweat specimen and the successful detection confirms the potential of the biosensor for a real-time noninvasive, skin attachable, and flexible wearable pH sensor.     

Preparation,characterization and dielectric properties of polyetherimide nanocomposites containing surface‐functionalized BaTiO3 nanoparticles

Polyetherimide (PEI)/hydroxyl‐functionalized barium titanate (BaTiO₃) nanocomposite films were successfully prepared through solution‐casting followed by subsequent thermal imidization. The results of Fourier transform infrared spectroscopy confirmed that the chemical treatment with hydrogen peroxide (H₂O₂) could efficiently derive hydroxyl groups on the surface of BaTiO₃ nanoparticles. The strong interaction between the hydroxyl‐functionalized BaTiO₃ and the PEI matrix greatly enhanced the particle dispersion as well as the interfacial adhesion, as evidenced by scanning electron microscopy. The PEI nanocomposite with hydroxyl‐functionalized BaTiO₃ nanoparticles (50 vol% BaTiO₃ loading) showed an increased dielectric permittivity of 52.78 at 1 kHz compared with the dielectric permittivity (33.87) of PEI/raw BaTiO₃ composite. The loss tangent was still low (less than 0.03) when the content of hydroxyl‐functionalized BaTiO₃ was 50 vol%. For PEI/BaTiO₃ nanocomposites, the frequency and temperature dependences of the dielectric properties were significantly reduced through functionalizing the surface of BaTiO₃ nanoparticles with H₂O₂. Different theoretical approaches were employed to predict the effective permittivity of the nanocomposite systems and the results are compared with the experimental results. Copyright © 2012 Society of Chemical Industry     

Effects of neutralization on the structure and properties of an ionomer

The structure, morphology, and properties of an ionomer, poly(ethylene‐acrylic‐acid) neutralized by zinc salts (PI) depend on the free carboxylic acid content. In this work, metal acetates (Na, Zn, and Al acetates) were used to control the neutralization levels. A wide range of techniques were used, such as spectroscopic Fourier transform infrared spectroscopy (FTIR), thermal [thermogravimetric analysis, modulated differential scanning calorimetry (MDSC), and dynamic mechanical analysis (DMA)], mechanical (tensile measurement), and small angle neutron scattering (SANS). The melt rheological properties of the samples were also examined. The results show that metal acetate neutralizes free acrylic acid in the ionomer, which has the primary role in controlling ionic association. The number of ionic groups in ionic domains and multiplets in the matrix is dependent on the neutralization level. Metal valence determines the ionic domain or multiplet structure (FTIR), further properties of PI. Dynamic mechanical properties, the ionic transition behaviour, and the mechanical properties are improved compared with PI using monovalent cation (Na⁺), but decreased using trivalent cation (Al³⁺) or shows less significant changes due to steric effects. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Diffusivity of small molecules in polymers: Carboxylic acids in polystyrene

Gravimetry was used to study the diffusion of a homologous series of linear carboxylic acids (C_n, with n = 2, 6–16) in amorphous polystyrene at temperatures from 35 °C to 165 °C, that is, both below and above the polymer glass transition temperature of 100 °C. All the mass uptake results are well described by a simple Fickian model (for t < t_1/2) and were used to calculate the corresponding diffusion coefficients using the thin-film approximation. Acetic acid exhibits a peculiar diffusion rate: its diffusion coefficients in polystyrene do not follow the same trend of all the remaining acids, being smaller than those of hexanoic acid at the same temperatures. Polystyrene swells at a higher rate in hexanoic and octanoic acids than in acetic acid, at the same temperature. This peculiarity is confirmed using NMR spectroscopy for acetic and hexanoic acids. For all the carboxylic acids considered, the temperature dependence of the diffusion coefficients is non-Arrhenius in character. For each liquid penetrant, its log(D) increases linearly with the decrease in liquid viscosity associated with an increase in temperature. Plots of log(n²D) versus n suggest that higher-n carboxylic acids diffuse through a reptation-like mechanism at higher temperatures.     

Thermal and mechanical properties of a hydroxyl‐functional dendritic hyperbranched polymer and trifunctional epoxy resin blends

Curing characteristics of blends of a hydroxyl‐functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p‐amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0–20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (T_g) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single‐phase morphology.