3D Ridge-Valley Structure of a Pt-Ceria Catalyst: HRTEM and EELS Spectrum Imaging

Nano-ridge and valley structures formed as a result of self-aligned individual ceria nano-crystals, and HRSTEM/EELS revealed the 3-dimensional morphology profiles of the ridge and valley structures of the ceria support. After preparation of a Pt/ceria catalyst, HRSTEM indicated the preferential alignment of Pt nanoparticles inside the nano-valleys of the ceria support. EELS analyses confirmed changes in the oxidation state of ceria in the vicinity of Pt nanoparticles that are present at different depth in the valleys.     

Preparation and characterization of high permittivity and low loss PTFE/CaTiO3 microwave laminates

This article discusses the preparation and characterization of CaTiO₃ filled PTFE flexible laminates for microwave substrate applications. Single phase CaTiO₃ filler composition was prepared through solid‐state ceramic route. Phase formation was confirmed by powder X‐ray diffraction studies. Morphology and filler distribution of the composites were studied using scanning electron microscopic technique. Permittivity and loss tangent of the composite substrates were measured at X‐band frequency region (8.2–12.4 GHz) using waveguide cavity perturbation technique. Effective permittivity of the composites was compared with theoretically predicted values. Temperature coefficient of permittivity (τ_εr) of the composites was also measured in the 0–100°C temperature range. PTFE/CaTiO₃ composite has an effective permittivity of 11.8 and a loss tangent of 0.0036 at optimum filler loading. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Preparation and microwave characterization of PTFE/PEEK blends

Present paper describes the preparation and characterization of the PTFE / PEEK blends. The surface morphology of different volume percentage of PTFE/PEEK blends is investigated using Scanning Electron Microscopy. The permittivity and loss tangent of the blends up to 40 MHz are studied using a Precision Impedance Analyzer. The variation of permittivity with respect to temperature (τ_εr) of the composite blends are also measured in the 0–100°C temperature region using a microprocessor controlled hot and cold chamber. The microwave dielectric properties of the polymer blends are studied in the X‐band (8.2–12.4 GHz) region by waveguide cavity perturbation technique using a Vector Network Analyzer. Rectangular cavity resonator is used to measure the complex permittivity of the PTFE/PEEK blends. Different modeling approaches are used to predict the theoretical permittivity of the blends and the results are compared with the experimental values. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Flax‐fabric‐reinforced arylated soy protein composites: Brittle‐matrix behavior

Biocomposites were successfully prepared by the reinforcement of soy protein isolate (SPI) with different weight fractions of woven flax fabric. The flax‐fabric‐reinforced SPI‐based composites were then arylated with 2,2‐diphenyl‐2‐hydroxyethanoic acid (DPHEAc) for 4 h to obtain arylated biocomposites. A new method was proposed to determine the amount of carbon dioxide evolved during the arylation of the soy protein in the presence of DPHEAc. Characterizations of the arylated and nonarylated biocomposites were done by Fourier transform infrared spectroscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis. The results indicate that the arylated soy‐protein‐based composites exhibited mechanical behavior like brittle‐matrix composites, which differentiated them from nonarylated soy‐protein‐based composites, which showed mechanical behavior similar to polymer–matrix composites. In the arylated composites, there was clear evidence of a stick–slip mechanism, which perhaps dominated and, therefore, prevented easy deformation of the reinforced film. Scanning electron microscopy studies revealed cracks in the arylated soy protein composites when they were subjected to tensile tests. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

RAFT polymerization of N‐vinyl pyrrolidone using prop‐2‐ynyl morpholine‐4‐carbodithioate as a new chain transfer agent

RAFT polymerization of N‐vinyl pyrrolidone (NVP) has been investigated in the presence of chain transfer agent (CTA), i.e., prop‐2‐ynyl morpholine‐4‐carbodithioate (PMDC). The influence of reaction parameters such as monomer concentration [NVP], molar ratio of [CTA]/[AIBN, i.e., 2,2′‐azobis (2‐methylpropionitrile)] and [NVP]/[CTA], and temperature have been studied with regard to time and conversion limit. This study evidences the parameters leading to an excellent control of molecular weight and molar mass dispersity. NVP has been polymerized by maintaining molar ratio [NVP]: [PMDC]: [AIBN] = 100 : 1 : 0.2. Kinetics of the reaction was strongly influenced by both temperature and [CTA]/[AIBN] ratio and to a lesser extent by monomer concentration. The activation energy (E_a = 31.02 kJ mol^?1) and enthalpy of activation (ΔH^?= 28.29 kJ mol^?1) was in a good agreement to each other. The negative entropy of activation (ΔS^? = ?210.16 J mol^‐1K^‐1) shows that the movement of reactants are highly restricted at transition state during polymerization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Biomimetic peptide nanosensors

The development of a miniaturized sensing platform tailored for sensitive and selective detection of a variety of biochemical analytes could offer transformative fundamental and technological opportunities. Due to their high surface-to-volume ratios, nanoscale materials are extremely sensitive sensors. Likewise, peptides represent robust substrates for selective recognition due to the potential for broad chemical diversity within their relatively compact size. Here we explore the possibilities of linking peptides to nanosensors for the selective detection of biochemical targets. Such systems raise a number of interesting fundamental challenges: What are the peptide sequences, and how can rational design be used to derive selective binders? What nanomaterials should be used, and what are some strategies for assembling hybrid nanosensors? What role does molecular modeling play in elucidating response mechanisms? What is the resulting performance of these sensors, in terms of sensitivity, selectivity, and response time? What are some potential applications? This Account will highlight our early attempts to address these research challenges. Specifically, we use natural peptide sequences or sequences identified from phage display as capture elements. The sensors are based on a variety of nanomaterials including nanowires, graphene, and carbon nanotubes. We couple peptides to the nanomaterial surfaces via traditional surface functionalization methods or self-assembly. Molecular modeling provides detailed insights into the hybrid nanostructure, as well as the sensor detection mechanisms. The peptide nanosensors can distinguish chemically camouflaged mixtures of vapors and detect chemical warfare agents with sensitivities as low as parts-per-billion levels. Finally, we anticipate future uses of this technology in biomedicine: for example, devices based on these sensors could detect disease from the molecular components in human breath. Overall, these results provide a novel platform for the development of highly sensitive and selective "nanoelectronic noses".     

Dielectric behavior of polyetheretherketone (PEEK) using TSDC technique

The dielectric relaxation behavior of Polyetheretherketone (PEEK) has been investigated by using thermally stimulated discharge current (TSDC) technique. The dependence of TSDC characteristics of PEEK on poling temperature (T_P) [50–200 °C], poling field (E_P) [200–500 kV/cm], storage time (t_S) [2–120 hrs] and various thicknesses 25 μm, 50 μm and 75 μm have been investigated in the temperature range [60–230 °C]. The TSDC spectra shows a prominent maxima around glass transition temperature (T_g) i.e. at 143 °C named as α-peak and the other peak is observed around 200 °C named as β-peak. The α-dipolar relaxation is taking place because of the movement of ketone (>C = 0) dipoles linked to the main chain. The β-peak is attributed to the space charges. It is observed that the magnitude of α-peak increases with the increase in poling field. The peak current and area under the α-peaks are found to be diminished with the increase of storage time (t_s) for electrets. The amplitude of α-peak decreases with the increase in thickness. The activation energies for PEEK sample at different conditions in the present work are found to be 0.38 eV–1.70 eV. The values of activation energy (U) and pre-exponential factor (τ _o) for α- relaxation are determined using Bucci plot method and support the nature of the relaxations.     

Creep and Dynamic Mechanical Analysis Studies of Peroxide‐Crosslinked Ethylene‐Octene Copolymer

An ethylene‐octene copolymer (EOC) (45 wt% octene) is crosslinked using dicumyl peroxide (DCP). Differential scanning calorimetry (DSC) reveals a very low melting temperature (50 °C). The network density is evaluated by gel content. While 0.2–0.3 wt% of peroxide leads only to a molecular weight increase (samples completely dissolved in xylene), 0.4–0.6 wt% of peroxide caused network formation. High‐temperature creep was measured at 70, 120, and 200 °C at three stress levels. At 200 °C and above 0.6 wt% of peroxide, degradation due to chain scission is observed by rubber process analyzer (RPA) and is again supported by creep measurements. Residual strain at 70 °C is found to improve with increasing peroxide level. Dynamic mechanical analysis (DMA) reveals a strong influence of peroxide content on storage modulus and tan δ, in particular in the range 30–200 °C.

     

Experimental investigations on phase change material based finned heat sinks for electronic equipment cooling

This paper reports the results of an experimental investigation of the performance of finned heat sinks filled with phase change materials for thermal management of portable electronic devices. The phase change material (PCM) used in this study is n-eicosane and is placed inside a heat sink made of aluminium. Aluminium acts as thermal conductivity enhancer (TCE), as the thermal conductivity of the PCM is very low. The heat sink acts as an energy storage and a heat-spreading module. Studies are conducted for heat sinks on which a uniform heat load is applied for the unfinned and finned cases. The test section considered in all cases in the present work is a 80 × 62 mm² base with TCE height of 25 mm. A 60 × 42 mm² plate heater with 2 mm thickness is used to mimic the heat generation in electronic chips. Heat sinks with pin fin and plate fin geometries having the same volume fraction of the TCE are used. The effect of different types of fins for different power level (ranging from 2 to 7 W) in enhancing the operating time for different set point temperatures and on the duration of latent heating phase were explored in this study. The results indicate that the operational performance of portable electronic device can be significantly improved by the use of fins in heat sinks filled with PCM.     

Polyvalent choline phosphate as a universal biomembrane adhesive

Phospholipids in the cell membranes of all eukaryotic cells contain phosphatidyl choline (PC) as the headgroup. Here we show that hyperbranched polyglycerols (HPGs) decorated with the 'PC-inverse' choline phosphate (CP) in a polyvalent fashion can electrostatically bind to a variety of cell membranes and to PC-containing liposomes, the binding strength depending on the number density of CP groups per macromolecule. We also show that HPG-CPs can cause cells to adhere with varying affinity to other cells, and that binding can be reversed by subsequent exposure to low molecular weight HPGs carrying small numbers of PCs. Moreover, PC-rich membranes adsorb and rapidly internalize fluorescent HPG-CP but not HPG-PC molecules, which suggests that HPG-CPs could be used as drug-delivery agents. CP-decorated polymers should find broad use, for instance as tissue sealants and in the self-assembly of lipid nanostructures.