Amphiphile polydimethylsiloxane‐based networks reinforced with in situ generated silica

Polydimethylsiloxanes, side functionalized in different degrees with chloromethyl groups, were reacted with 4,4′‐bipyridyl and crosslinking occurred by the formation of ionic (bipyridinium) groups. The reactions were carried out in a silica sol–gel system, and thus, two networks were generated simultaneously: amphiphile siloxane‐organic and silica networks. The samples, processed as films, were characterized by Fourier transform infrared spectroscopy to verify the occurrence of the crosslinking reactions. Different techniques were also used to evaluate the properties: differential scanning calorimetry for emphasizing the transitions, scanning electron microscopy, and atomic force microscopy for the evaluation of the morphology and surface topography. The modification of the film surface topography, which depends on the solvent polarity, was also emphasized. The sorption capacities of the water vapors and of liquid solvents (water and chloroform) were investigated, and the obtained values proved to be a function of the polar group's content. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Defect-Enhanced Polarization Switching in the Improper Ferroelectric LuFeO3

Results of switching behavior of the improper ferroelectric LuFeO₃ are presented. Using a model set of films prepared under controlled chemical and growth-rate conditions, it is shown that defects can reduce the quasi-static switching voltage by up to 40% in qualitative agreement with first-principles calculations. Switching studies show that the coercive field has a stronger frequency dispersion for the improper ferroelectrics compared to a proper ferroelectric such as PbTiO₃. It is concluded that the primary structural order parameter controls the switching dynamics of such improper ferroelectrics.     

Few-layer nano-graphene structures with large surface areas synthesized on a multifunctional Fe:Mo:MgO catalyst system

We present the synthesis of nano-graphene structures with large surface areas and high purity over a high-yield Fe:Mo:MgO catalytic system. Two different hydrocarbon sources, acetylene and methane, were used, and their role in determining the size and morphology of the few-layer graphene sheets was studied. In addition, varying the active metal loading of the catalyst system influenced the formation and type of the resulting carbon nano-structures, e.g., carbon nanotubes or few-layer graphene. Growth of nano-graphene sheets was detected after only 5-min reaction time over this multifunctional catalytic system. High purity and crystalline graphene structures were synthesized indicating another advantage of using this particular catalyst system. This catalytic chemical vapor deposition can be scaled up for large-scale few-layer graphene production.     

Improved Nyquist filter characteristics using spline interpolation

This paper presents and investigates a novel approach for constructing a family of intersymbol interference (ISI)-free pulses that shows comparable or better ISI performance in the presence of sampling errors, compared with some recently proposed pulses. We propose and discuss a new parametric method for the design of Nyquist filter characteristics using constraints in frequency characteristics construction. The method for constructing the filter characteristics uses a piecewise polynomial approximation of an ideal optimized staircase characteristic by spline functions. The spline polynomials are used to approximate a function that must pass through specified points. The performances of new ISI-free pulses are studied with respect to the ISI error probability. This family provides flexibility in designing an appropriate pulse even after the roll-off factor has been chosen. The results for error probability outperform the fourth-degree polynomial pulse [4].     

Pulsed LASER-(micro)TIG hybrid welding: Process characteristics

A variant from the laser-arc hybrid welding process family which combines a pulsed laser process (Nd:YAG) and a pulsed (micro)TIG welding process is described.For studying the present variant process’ characteristics experimental work was carried out using video data acquisition and thermal imaging. In this paper, the characteristics of the present hybrid welding process variant and the influence of TIG welding parameters onto the process stability and the welding process result are presented. The experimental work revealed that the transient hybrid coupling phenomena, which is specific to the present hybrid process variant, has an important influence onto the process stability and the processing result. At the same time a strong interaction between the controlled process parameters was observed and that rather small changes to the process parameters values have a strong effect onto the process stability. The recommended TIG frequency domain for using as well as the variant which provides the best option to attenuate the penetration variation, specific to pulsed laser welding, was determined. The TIG frequency values which seem to lead to a stable welding process are of the same order as the ones used for laser pulse repetition rates. The variant that leads to an attenuation of the penetration is pulsed TIG-laser (with TIG as the leading process).     

Wheat gluten composites reinforced with coconut fiber

Coconut fiber-reinforced wheat gluten (WG) biocomposites were fabricated. The coconut fibers (CCFs) were chemically modified by either sodium hydroxide or silane treatment, as well as following the alkali surface treatment with a silane treatment. (3-triethoxysilylpropyl)-t-butylcarbamate (carbamate silane), which is a masked isocyanate functional silane, was used for the first time to improve interfacial adhesion between WG and natural fibers. X-ray photoelectron spectroscopy (XPS) and gas chromatography/mass spectroscopy (GC/MS) analyses were employed to prove the presence of the silane on silane-treated coconut fiber (SCCF) and alkali-followed by silane-treated fiber (ASCCF). It was found that ASCCF has more silane content on the fiber surface than SCCF. The mechanical properties of composites with 15 mass% fiber loading were assessed by three-point bending tests. Moreover, scanning electron microscopy (SEM) was used to investigate fracture surface characteristics of composites. The WG/ASCCF composite provided an 80% increase in strength, and showed superior fiber–matrix interfacial adhesion.     

Photovoltaic device performance of single-walled carbon nanotube and polyaniline films on n-Si: device structure analysis

In this paper, we explore the use of two organic materials that have been touted for use as photovoltaic (PV) materials: inherently conducting polymers (ICPs) and carbon nanotubes (CNTs). Due to these materials' attractive features, such as environmental stability and tunable electrical properties, our focus here is to evaluate the use of polyaniline (PANI) and single wall carbon nanotube (SWNT) films in heterojunction diode devices. The devices are characterized by electron microscopy (film morphology), current-voltage characteristics (photovoltaic behavior), and UV/visible/NIR spectroscopy (light absorption). We have found that both PANI and SWNT can be utilized as photovoltaic materials in a simple bilayer configuration with n-type Silicon: n-Si/PANI and n-Si/SWNT. It was our aim to determine how photovoltaic performance was affected utilizing both PANI and SWNT layers in multilayer devices: n-Si/PANI/SWNT and n-Si/SWNT/PANI. The short-circuit current density increased from 4.91 mA/cm(2) (n-Si/PANI) to 12.41 mA/cm(2) (n-Si/PANI/SWNT), while an increase in power conversion efficiency by ~91% was also observed. In the case of n-Si/SWNT/PANI and its corresponding device control (n-Si/SWNT), the short-circuit current density was decreased by an order of magnitude. The characteristics of the device were affected by the architecture and the findings have been attributed to the more effective transport of holes from the PANI to SWNT and less effective transport of holes from PANI to SWNT in the respective multilayer devices.     

Positive and negative aspects of citation indices and journal impact factors

The Hirsch citation index h is nowadays the most frequently used numerical indicator for the performance of scientists as reflected in their output and in the reaction of the scientific community reflected in citations of individual contributions. A few of the possible improvements of h are briefly reviewed. Garfield??s journal impact factor (IF) characterizes the reaction of the scientific community to publications in journals, reflected in citations of all papers published in any given journal during the preceding 2?years, and normalized against all citable articles during the same period. Again, a few of the possible improvements or supplements of IF are briefly reviewed, including the journal-h index proposed by Braun, Gl?nzel, and Schubert. Ascribing higher weighting factors to citations of individual papers proportionally to IF is considered to be a misuse of useful numerical indices based on citations. At most, one could turn this argument on its head and one can find reasons to ascribe an inverse proportionality relative to IF for individual citations: if a paper is considered worthy to be cited even if it was published in a low-IF journal, that citation ought to be worth more than if the citation would have been from a higher-impact journal. A weight factor reflecting the prestige of the citing author(s) may also be considered.     

Fabrication of soft,stimulus-responsive structures with sub-micron resolution via two-photon polymerization of poly(ionic liquid)s

Soft, stimulus-responsive 3D structures created from crosslinked poly(ionic liquid)s (PILs) have been fabricated at unprecedented sub-micron resolution by direct laser writing (DLW). These structures absorb considerable quantities of solvent (e.g., water, alcohol, and acetone) to produce PIL hydrogels that exhibit stimulus-responsive behavior. Due to their flexibility and soft, responsive nature, these structures are much more akin to biological systems than the conventional, highly crosslinked, rigid structures typically produced using 2-photon polymerization (2-PP). These PIL gels expand/contract due to solvent uptake/release, and, by exploiting inherited properties of the ionic liquid monomer (ILM), thermo-responsive gels that exhibit reversible area change (30?±?3%, n?=?40) when the temperature is raised from 20?°C to 70?°C can be created. The effect is very rapid, with the response indistinguishable from the microcontroller heating rate of 7.4?°C?s^?1. The presence of an endoskeleton-like framework within these structures influences movement arising from expansion/contraction and assists the retention of structural integrity during actuation cycling.