Synthesis and magnetorheological characteristics of ribbon‐like,polypyrrole‐coated carbonyl iron suspensions under oscillatory shear

One of the crucial problems of classical magnetorheological (MR) fluids is their high rate of sedimentation. This disadvantage may be substantially eliminated using core‐shell particles. The aim of this study is to prepare spherical carbonyl iron (CI) particles coated with conducing polymer polypyrrole (PPy) with ribbon‐like morphology. Scanning electron microscopy proved the formation of the ribbon‐like layer onto CI particles while Fourier transform infrared spectroscopy confirmed the chemical structure of PPy. The magnetic properties observed via vibrating sample magnetometer showed decreased magnetization saturation of core‐shell‐structured particles due to the existence of non‐magnetic surface layer. MR measurements performed under oscillatory shear flow as a function of the applied magnetic flux density, temperature, and particle concentration showed that core‐shell particle‐based MR suspension exhibits sufficient MR performance for practical applications. Moreover, the suspension stability is promoted significantly when core‐shell particles are used as a dispersed phase. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of phenolic resin infiltration content on the structural and electrochemical properties of hierarchical porous carbons

Hierarchical porous (micro-, meso- and macro-porous) carbons (HPCs) are synthesized by a facile replica template method with phenolic resin (PR) as a carbon source and hollow mesoporous silica as a hard template. The morphology of the HPCs can be easily controlled by altering the mass ratio of PR to SiO₂ spheres. Structural characterizations reveal that a well-defined HPC with a large surface area of 1141 m² g^?1 is formed when PR/SiO₂ is 1:1. With further increasing PR infiltration content, macropores of carbons disappear while solid structures appear. A possible formation mechanism for the morphological transformation of HPCs is proposed. The effect of phenolic resin infiltration content on the electrochemical properties of HPCs-based materials as supercapacitor electrodes is further evaluated. The HPCs-1(PR/SiO₂ = 1) electrode exhibits the highest specific capacitance of 256 F g^?1 due to its faster diffusion of electrolyte ions and lower charge transfer resistance. The relationship between the morphology and the electrochemical behavior of HPCs is also elucidated.     

Synthesis and electrorheological characteristics of titanate nanotube suspensions under oscillatory shear

In this study, titanate nanotubes (TNTs) were synthesized by hydrothermal treatment of TiO₂ powders (P25) in a NaOH solution. The as-synthesized TNTs exhibit high surface area and large aspect ratio. Rheological properties of TNTs suspensions were then investigated under oscillatory shear. The TNTs fluid shows the viscoelastic behavior and the dynamic moduli (G′, G″) increase significantly by about 4 orders of magnitude as the electric field strength is up to 2.0 kV/mm. Transient response under dynamic shear reveals different changes in the microstructure of TNTs fluid from steady shear. The complex modulus of TNTs fluids is sensitive to temperature while that of P25 fluid become insensitive at higher temperature. Dynamic viscoelastic behavior suggests that structure of P25 to TNTs transition merits the enhancement of ER activity of TNTs fluid.     

Web accessibility investigation of Slovenian municipalities’ websites before and after the adoption of European Standard EN 301 549

Universal Access in the Information Society - Digitalization and technological innovations provide many benefits for citizens worldwide, increasing the quality of life in several ways, including by...     

Effects of macropore size on structural and electrochemical properties of hierarchical porous carbons

Hierarchical porous carbons (HPCs) were synthesized by a colloid crystal template method with phenolic resin as carbon source and triblock copolymer Pluronic F127 as a soft template. The obtained HPCs with tunable macropore size of 242–420 nm exhibit large BET surface areas (~900 m² g⁻¹) and large pore volumes (~1.2 cm³ g⁻¹). With an increase in the diameters of silica template, the BET surface areas and pore volumes of HPCs decrease. The electrochemical properties of the HPCs with various macropore sizes used as supercapacitor electrodes materials were evaluated using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. The results show the HPC with the macropore size of 242 nm possesses the largest specific capacitance among the HPCs. The excellent capacitive behavior of HPC-242 can be attributed to its faster ion transport behavior and better ion-accessible surface area.     

The influence of ultraviolet radiation on the optical properties of glass fibre reinforcements for polyurethane matrix composites

Polyurethanes represent one of the most frequently used polymeric matrixes in composites. Although there have been many studies focused on the weather resistance of polyurethanes, this important property is unheeded during the reinforcing phase. In this article, the effects of ultraviolet (UV) radiation on the changes in optical properties of commercially available glass fibre reinforcements containing various polymeric binders used as compatibilising agents for the polymeric matrix in the final composite products were studied. The standardised experiments were performed using accelerated ageing equipment, q‐lab ultraviolet tester, in dry mode. Chemical modification of the binder in the form of polyesters or silanes by UV irradiation was studied using Fourier Transform–infrared spectroscopy. Changes in the optical properties caused by the degradation processes of polymeric components due to UV irradiation were evaluated based on colour changes in the examined samples using the yellowness index; statistical evaluation of the data obtained was conducted with an Anderson–Darling test of normality and an ANOVA test. It was demonstrated that both the amount of the binder and the glass fibre reinforcement's construction play a more important role than the chemical structure of the binder.