One-step preparation of poly(NIPAM-pyrrole) electroconductive composite hydrogel and its dielectric properties

Conductive polymers and hydrogels are two of the hot prospect polymer types that are used for new stimuli responsive materials. In this study, one-step preparation of electroconductive composite hydrogels containing polypyrrole (PPy) and N-isopropylacrylamide (NIPAM) using free radical polymerization technique was achieved with N,N-methylenebisacrylamide as a crosslinker and ammonium peroxy disulphate (APS) as initiator, in mixture of water/isopropyl alcohol. The equilibrium swelling degree of the poly(NIPAM)-pyrrole) electroconductive composite hydrogel was 9.88 g of H₂O/g dry polymer. According to TGA results, the thermal stability of the prepared composite poly(NIPAM-PPy) conductive hydrogel (700°C) hydrogel is higher than that of pure poly(NIPAM) hydrogel (600°C). Furthermore, prepared samples were characterized by FTIR, and SEM analyzes. Later, the samples were pressured into pellets so that electrical impedance spectroscopy (EIS) measurements were taken between 10 and 10 MHz at room temperature. The dielectric constant value of composite poly(NIPAM-PPy) hydrogel at 10 Hz is almost 10 times higher than that of poly(NIPAM) hydrogel. Both samples' real and imaginary parts of dielectric constant decreased with increased frequency. Samples exhibited non-Debye relaxation since experimental data fit into dielectric model of Havriliak-Negami. Moreover, low frequency data yielded d.c. conductivity of the pure and composite samples as 3.74 × 10⁻¹¹ and 1.02 × 10⁻⁸ S/cm, respectively. Real part of impedance at low frequencies also points out ~10³ times lower resistance values at 10 Hz for composite poly(NIPAM-PPy) hydrogel. Therefore, EIS results support that electroconductive composite hydrogel fabrication was achieved using free radical polymerization technique.     

Engineering Saccharomyces cerevisiae for next generation ethanol production

Conversion of cellulose, hemicellulose or starch to ethanol via a biological route requires enzymatic conversion of these substrates to monosaccharides that can be assimilated by a fermenting organism. Consolidation of these events in a single processing step via a cellulolytic or amylolytic microorganism(s) is a promising approach to low‐cost production of fuels and chemicals. One strategy for developing a microorganism capable of such consolidated bioprocessing (CBP) involves engineering Saccharomyces cerevisiae to expresses a heterologous enzyme system enabling (hemi)cellulose or starch utilization. The fundamental principle behind consolidated bioprocessing as a microbial phenomenon has been established through the successful expression of the major (hemi)cellulolytic and amylolytic activities in S. cerevisiae. Various strains of S. cerevisiae were subsequently enabled to grow on cellobiose, amorphous and crystalline cellulose, xylan and various forms of starch through the combined expression of these activities. Furthermore, host cell engineering and adaptive evolution have yielded strains with higher levels of secreted enzymes and greater resistance to fermentation inhibitors. These breakthroughs bring the application of CBP at commercial scale ever closer. This mini‐review discusses the current status of different aspects related to the engineering of S. cerevisiae for next generation ethanol production. © 2013 Society of Chemical Industry     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

Synthesis and spectroelectrochemistry of new phthalocyanines with ester functionalities

Metal-free (H₂Pc) and metallophthalocyanines (MPc; M: Co, Zn) with four n-pentyl ester of thioglycolic acid groups have been synthesized by the esterification of the corresponding carboxylic acid derivatives with n-pentanol. The novel phthalocyanine compounds were characterized by elemental analyses, mass, FT-IR and UV-Vis spectral data. The aggregation investigations carried out in different concentrations and solvents indicate that ester substituted metal-free and metallo-phthalocyanine compounds have not shown any aggregation behavior in the concentration range of about 10⁻⁵ M. Electrochemical and in-situ spectroelectrochemical measurements give common MPc based redox behaviors which supported the proposed structure of the complexes. While CoPc gives both metal-based and ring-based redox processes, H₂Pc and ZnPc give only ring-based electron transfer processes. In-situ electrocolorimetric method was applied to investigate the color of the electro-generated anionic and cationic forms of the complexes.     

Embedding complete binary trees in product graphs

This paper shows how to embed complete binary trees in products of complete binary trees, products of shuffle‐exchange graphs, and products of de Bruijn graphs with small dilation and congestion. In the embedding results presented here the size of the host graph can be fixed to an arbitrary size, while we define no bound on the size of the guest graph. This is motivated by the fact that the host architecture has a fixed number of processors due to its physical design, while the guest graph can grow arbitrarily large depending on the application. The results of this paper widen the class of computations that can be performed on these product graphs which are often cited as being low‐cost alternatives for hypercubes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Selecting the suitable material handling equipment in the presence of vagueness

Selection of the suitable material handling equipment (MHE) is a very difficult task for the manufacturing companies because of the considerable capital investment required. There are many tangible and intangible factors for choosing the suitable MHE. Multiple criteria decision making (MCDM) has been found to be a useful approach to analyze these conflicting factors. The evaluation of MHE alternatives within the frame of various subjective criteria and the weights of the criteria are usually expressed in linguistic terms. This makes fuzzy logic a more natural approach to this kind of problems. This paper proposes a combined MCDM methodology for evaluation and selection of MHE types for a company in the steel construction industry in Istanbul, Turkey. Fuzzy analytic network process (FANP) is utilized for assigning weights of the criteria for MHE selection and fuzzy technique for order preference by similarity to ideal solution (TOPSIS) is used to determine the most proper system alternative using the criteria weights attained by FANP. The selection is based on the compatibility between MHE and production characteristics. Objective is to select the most efficient MHE considering also the cost efficiency. The study was followed by the sensitivity analyses of the results.     

Direct shear strength of rebar-coupler anchor systems for steel-plate composite (SC) walls

International Journal of Steel Structures - This paper focuses on the direct shear behavior of rebar-coupler anchor systems, and their use for anchorage of steel-plate composite (SC) walls to the...     

The effects of text structure and prior knowledge of the learner on computer-based learning

This study is an attempt to investigate the effects of document structure and knowledge level of the reader on reading comprehension, browsing, and perceived control. Four types of texts are distinguished, differing in structure (linear text, hierarchical hypertext, mixed hypertext, and generative text). All the materials were on a PC. In all conditions, participants were allowed 1 h to read through the document. After completing the reading part of the experiment, they were asked to fill out the perceived control questionnaire followed by the reading comprehension test. As far as reading comprehension was concerned, knowledgeable participants had higher reading comprehension scores than non-knowledgeable participants only in the linear text. In addition, there were no significant differences in terms of the reading comprehension scores of the knowledgeable participants among the four topologies. However, the performance of non-knowledgeable participants differed with respect to the type of the topology. In particular, non-knowledgeable participants in the hierarchical and generative conditions performed better than those in the other two conditions. With respect to perceived control, the performance of knowledgeable and non-knowledgeable participants was equivalent in all four conditions. The results are discussed in terms of their implications for the computer-based learning.