Scanning electrochemical microscopy measurements of photopolymerized poly(ethylene glycol) hydrogels

Scanning electrochemical microscopy has been used to examine the molecular transport properties of photopolymerized poly(ethylene glycol) (PEG) hydrogels having different mesh sizes. Both the molecular weight (508 Da or 3000 Da) of the PEG diacrylate macromer and its weight percent (20 wt%, 40 wt%, or 60 wt%) in solution prior to photopolymerization were varied. Mesh size was estimated from equilibrium swelling measurements and a thermodynamic model. Estimated mesh sizes ranged from ca. 10 Å for 60 wt% PEG 508 gels to ca. 100 Å for 20 wt% PEG 3000 gels. The electrochemically active diffusing species, ferrocenemethanol, was detected via oxidation at a platinum microelectrode. For a given hydrogel, multiple approach curves showed a consistent relationship between current and distance. Electrochemically estimated diffusivities followed the same trend as predictions based on mesh size and ranged from 25% to 80% of the diffusivity in aqueous solution. As a proof of concept, scanning electrochemical microscopy was successfully used to map the topography of hydrogels with complex architecture, which are being designed as cell scaffolds.     

Application of polymeric high‐internal‐phase‐emulsion‐coated stationary‐phase columns in open‐tubular capillary electrochromatography

The application of polymeric high‐internal‐phase emulsion (polyHIPE) capillary coatings for open‐tubular analytical separation columns was demonstrated in this study for the first time. Multiple polystyrene‐co‐divinylbenzene polyHIPE layers with an average total depth of 1.73 µm were coated onto internal capillary surfaces to create open‐tubular columns (20 cm coating and 32.5 cm effective length). With these columns for open‐tubular capillary electrochromatography, ethylbenzene and pentylbenzene were separated. Although the overall separation capacity of the produced columns was low, the polyHIPE coatings improved the analyte peak shape, decreased the total run time, and improved the peak symmetries relative to comparable unmodified open‐tubular columns. In addition, the use of these novel polyHIPE columns led to the use of 30% less organic modifier. These columns have the potential to improve the shelf life of open‐tubular columns typically used in capillary electrochromatography. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44237.     

Preparation and characterization of membranes obtained from blends of acrylonitrile copolymers with poly(vinyl alcohol)

New microfiltration and ultrafiltration membranes were obtained using acrylonitrile‐vinyl acetate copolymers in mixture with poly(vinyl alcohol) (PVA). Thus, a blend polymer solution was prepared in dimethylsulfoxide (DMSO) and used to obtain bicomponent polymer membranes by phase inversion. The rheological behavior of the DMSO polymer solutions was, mostly, dilatant at low shear gradients and pseudo plastic with quasi Newtonian tendency at higher gradients. Membranes were characterized by Fourier transform infrared spectrometry (FTIR), optical microscopy, atomic force microscopy, thermal gravimetric analysis‐differential thermal gravimetry, and pure water flux (PWF). FTIR spectra displayed the characteristic bands for acrylonitrile, vinyl acetate, and PVA. The morphology and the porosity can be tailored by the preparation conditions. PVA allows controlling the size of the pores and enables, in principle, to use the resulted membranes as supports for enzyme immobilization. PVA content influences the thermal stability. PWF values depend on the copolymer, on the content in PVA, but also on the coagulation bath composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41013.     

Influence of Thermodynamic,Material, and Bulk Properties on Electrical Resistivity of Particle Layers

Although the influence of gas humidity and particle size distribution on dust resistivity is well known, the impact of thermic and electric balancing periods on the measurement of dust resistivity is less familiar. The dust resistivity of quartz glass (SiO₂) and Al₂O₃ particle layers was measured and exhibits a non‐ohmic behavior as well as time dependence seen in a similar manner during electret formation. However, constant values of dust resistivity for the test dust were first measured after a rather long balancing period which cannot be explained in whole by adsorption and desorption kinetics of H₂O into the particle layers. Rather, it could be presumed that the thermic and electric balancing periods overlap, whereas the electric balancing periods take a much longer time.     

Asymmetric Homogeneous Hydrogenation in Flow using a Tube‐in‐Tube Reactor

In this update, the asymmetric homogeneous hydrogenation of a number of trisubstituted olefins utilizing the recently developed tube‐in‐tube gas‐liquid flow reactor is described. A number of chiral iridium‐ and rhodium‐based catalysts and other parameters such as pressure, solvent, temperature and catalyst loading were screened. The advantage of the flow set‐up for rapid screening and optimization of reaction parameters is illustrated. Furthermore, a comparative study using batch conditions aided in the optimization of the flow reaction set‐up. The set‐up was further modified to recycle the catalyst which prolonged catalytic activity.     

Eu(III)-coupled luminescent multi-walled carbon nanotubes in surfactant solutions

A carbon nanotube/inorganic hybrid material has been fabricated by coupling Eu(III) complexes onto multi-walled carbon nanotubes (MWCNTs). Successful coupling has been verified by X-ray photoelectron spectroscopy (XPS) measurement where a clear signal from Eu3d has been identified. When sonicated in hexaethylene glycol monododecyl ether (C₁₂E₆) or sodium dodecyl sulfate (SDS) aqueous solutions, the MWCNTs with Eu-complex attached (denoted as Eu-MWCNTs hereafter) can be dispersed. UV–vis measurements on a dilute dispersion of Eu-MWCNTs in SDS aqueous solution reveal the characteristic absorption from Eu(III) complexes, which gives further proof of the successful coupling. The strong luminescent properties of Eu-MWCNTs allow them to be observed directly under a fluorescence microscope. Interestingly, it is found that Eu-MWCNTs can undergo continuous movements in C₁₂E₆ or SDS dilute solutions. When Eu-MWCNTs are incorporated into the lyotropic liquid crystal phase formed by C₁₂E₆ (above 40% by weight), however, movements have been hindered. Small angle X-ray scattering measurements showed that Eu-MWCNTs are ordered in the lyotropic liquid crystal. Fluorescence microscopy observations reveal that the luminescent properties of the Eu-MWCNTs have not been affected by the liquid crystalline surfactant matrix.     

Enhanced light extraction in ITO-free OLEDs using double-sided printed electrodes

We show how nanoimprint lithographic techniques are particularly suited for the realization of OLED device structures. We tested them to realize nanopatterned metallic electrodes containing photonic crystals to couple the light out and plasmonic crystals showing extraordinary transmission. At similar current densities, a two-fold electroluminescence is achieved with devices having double-sided structured metallic electrodes as compared to a control OLED with an ITO anode. The use of combined nanoimprint lithography processes has the potential to expand the performance range of various organic optoelectronic devices.     

Prediction of the thermal conductivity anisotropy of Si nanofilms. Results of several numerical methods

The purpose of this work is to predict the in-plane and cross-plane thermal properties of crystalline silicon films. Several thicknesses from 20 nm to 6 μm and mean temperatures between 20 and 500 K have been investigated. Heat transport properties in silicon films have been studied through three different techniques: a semi-analytical method based upon the Kinetic Theory, a deterministic solution of the Boltzmann Transfer Equation (BTE) through the Discrete Ordinate Method and a statistical handling of the BTE by means of Monte Carlo Method. Each technique requires a model for the bulk material dispersion curves and the collision times of the different scattering processes. The three techniques have been validated through their correct prediction of silicon bulk thermal conductivity. Comparisons with in-plane thermal conductivity calculations and measurements have been also discussed. Thus, the cross-plane thermal conduction properties have been predicted. The expected temperature and thickness variations of the thermal conduction properties have been observed: the cross-plane thermal conduction appears to be less efficient than the in-plane thermal conduction, which proves that a significant anisotropy exists.     

Pathogens, personality, and culture: Disease prevalence predicts worldwide variability in sociosexuality, extraversion, and openness to experience.

Previous research has documented cross-cultural differences in personality traits, but the origins of those differences remain unknown. The authors investigate the possibility that these cultural differences can be traced, in part, to regional differences in the prevalence in infectious diseases. Three specific hypotheses are deduced, predicting negative relationships between disease prevalence and (a) unrestricted sociosexuality, (b) extraversion, and (c) openness to experience. These hypotheses were tested empirically with methods that employed epidemiological atlases in conjunction with personality data collected from individuals in dozens of countries worldwide. Results were consistent with all three hypotheses: In regions that have historically suffered from high levels of infectious diseases, people report lower mean levels of sociosexuality, extraversion, and openness. Alternative explanations are addressed, and possible underlying mechanisms are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)