Effects of CF4 plasma treatment on the moisture uptake,diffusion, and WVTR of poly(ethylene terephthalate) flexible films

We studied the effects of CF₄ plasma surface treatment on moisture uptake, diffusion, and the water-vapor-transmission-rate (WVTR) of poly(ethylene terephthalate) (PET) films using a CF₄ plasma generated by a radio-frequency (13.56 MHz) reactive ion etcher at 60 W. After CF₄ plasma treatment, moisture uptake in PET film was reduced with increasing treatment time due to (1) lower adsorption of water molecules onto the hydrophobic surface, as confirmed by contact angle measurement and XPS analysis, and (2) reduced diffusion coefficient through the denser fluorinated top-layer as detected by XRR. In addition, the WVTR of untreated PET is found to be 2.7 g/m²/day, while a significant reduction (84%) of WVTR to 0.43 g/m²/day, is achieved for CF₄ plasma-treated PET film (60 W, 15 min), which alters the surface hydrophobicity (~ 107°) and simultaneously builds a denser, fluorinated top-layer (47 nm). The surface fluorinated layer has a diffusivity of to 8.7 × 10^?12 m²/s and a WVTR of ~ 1.0 × 10^?4 g/m²/day based on a series resistance model.     

Isothermal crystallization of polyethylene oxide/silver nanoplate composites

This research was accomplished to investigate the kinetics of isothermal crystallization of polyethylene oxide (PEO)/silver nanoplate composites. It was obtained that the spherulites increased in size and numbers with time for the composites with various particle loadings. Additionally, the spherulite growth rate of composites decreased with an increase in the crystallization temperature and increased with the addition of nanoplates. The spherulite growth rate was further analyzed by the theory developed by Lauritzen and Hoffman. The product of the lateral surface free energy (σ) and the end surface free energy (σ_e) decreased with an increase in the content of nanoplates. We proposed the possible crystallization mechanisms of these PEO/nanoplate composites according to the change of σ and σ_e with the presence of nanoplates. A controlled experiment showed a minor change in PEO crystallization with the presence of a surfactant C₁₆TAB. This implied that the unique size and shape of nanoplates plays a key role on hindering the primary nucleation of PEO and increasing the spherulite growth rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of conformity and learning anxiety on intrinsic and extrinsic motivation: the case of Facebook course groups

Universal Access in the Information Society - The objective of this study is to enhance our understanding of whether learners’ conformity behaviors and learning anxiety can affect their...     

A thermal study on the use of immobilized penicillin G acylase in the formation of 7‐amino‐3‐deacetoxy cephalosporanic acid from cephalosporin G

Penicillin G acylase (PGA) is an important enzyme for the industrial production of 7‐amino‐3‐deacetoxy cephalosporanic acid (7‐ADCA) from cephalosporin G (Ceph‐G), and 6‐aminopenicillanic acid (6‐APA) from penicillin G (Pen‐G). These products are used for the manufacture of semi‐synthetic cephalosporins and penicillins. In this study, immobilized PGA was utilized to catalyze the conversion of Ceph‐G to 7‐ADCA. The optimal conditions were found to be an operating temperature of 45 °C, 0.2 M phosphate buffer, a substrate concentration of 30 mg cm^?3 and a catalyst particle concentration of 0.01 g cm^?3 (specific activity of 623.2 U g^?1). Up to 45 °C the reaction was characterized by an activation energy of 38.66 kJ mol^?1. Beyond 57.5 °C there was a sharp decline of activity, characterized by a deactivation energy of 235.88 kJ mol^?1. Copyright © 2004 Society of Chemical Industry     

Polyol Process Synthesis of Copper Particles onto Bamboo Charcoal and the Composite’s Thermal Conductivity Characteristics

Copper particles (Cu) are deposited on bamboo charcoal (BC) by a polyol process using Cu(CH₃COO)₂ ·H₂O as a precursor and ethylene glycol as both solvent and reducing agent. The composition of the resulting Cu/BC composites was confirmed by X-ray diffraction patterns and scanning electron microscopy (SEM) images, individually. It was found that Cu particles coated on the surface of BC can be irregular shape, depending on the various reaction conditions. The SEM morphology of the smallest copper particle coated on modified BC was determined, and sizes of the particles ranged from 100 to 300 nm. When there was 12 wt% of Cu in the Cu/BC composite, the thermal conductivity of the composite was 0.36 W/mK.     

Graphite Oxide as a Photocatalyst for Hydrogen Production from Water

A graphite oxide (GO) semiconductor photocatalyst with an apparent bandgap of 2.4–4.3 eV is synthesized by a modified Hummers' procedure. The as‐synthesized GO photocatalyst has an interlayer spacing of 0.42 nm because of its moderate oxidation level. Under irradiation with UV or visible light, this GO photocatalyst steadily catalyzes H₂ generation from a 20 vol % aqueous methanol solution and pure water. As the GO sheets extensively disperse in water, a cocatalyst is not required for H₂ generation over the GO photocatalyst. During photocatalytic reaction, the GO loses some oxygen functional groups, leading to bandgap reduction and increased conductivity. This structural variation does not affect the stable H₂ generation over the GO. The encouraging results presented in this study demonstrate the potential of graphitic materials as a medium for water splitting under solar illumination.     

5.7 GHz Gilbert I/Q Downconverter Integrated With a Passive LO Quadrature Generator and an RF Marchand Balun

A 5.7 GHz downconversion mixer is demonstrated in this letter using 0.35 mum SiGe BiCMOS technology. A quarter-wavelength coupled line and two center-tapped transformers are utilized to generate differential quadrature LO signals. A miniaturized Marchand balun is placed before the common-base-configured RF input stage of each Gilbert mixer to generate balanced RF signals. All the reactive passive elements are placed directly on the standard silicon substrate. The 5.7 GHz downconverter achieves 7 dB conversion gain, 26dBm _1dB, and 18dBm IIP₃ at the power consumption of 3.875 mW and 2.5 V supply voltage.     

Tunable Moiré Superlattice of Artificially Twisted Monolayers

Twisting between two stacked monolayers modulates periodic potentials and forms the Moiré electronic superlattices, which offers an additional degree of freedom to alter material property. Considerable unique observations, including unconventional superconductivity, coupled spin‐valley states, and quantized interlayer excitons are correlated to the electronic superlattices but further study requires reliable routes to study the Moiré in real space. Scanning tunneling microscopy (STM) is ideal to precisely probe the Moiré superlattice and correlate coupled parameters among local electronic structures, strains, defects, and band alignment at atomic scale. Here, a clean route is developed to construct twisted lattices using synthesized monolayers for fundamental studies. Diverse Moiré superlattices are predicted and successfully observed with STM at room temperature. Electrical tuning of the Moiré superlattice is achieved with stacked TMD on graphite.     

A current-controlled oscillator with temperature,voltage, and process compensation

Microsystem Technologies - This paper presents a current-controlled oscillator (CCO) circuit design with temperature, voltage, and process compensation. A current reference biasing circuit...     

Efficient heating with a controlled microwave field

To uncover the intriguing non-thermal microwave effect, an experiment was conducted using an amplifier rather than an oscillator as the radiation source, which was injected into an applicator with strong electromagnetic field enhancement. The characteristics of the applicator are discussed and the enhancement of the microwave field is illustrated and explained. Thermal distribution is simulated based on the calculated microwave field profile. It was demonstrated that the proposed system heated a SiC susceptor to a temperature of 637 °C with the input power of 60 W. The reasons for such an efficient heating are discussed.