Preparation of polyacrylamide hydrogels at various charge densities by postmodification

In this study, first polyacrylamide hydrogels were synthesized by free‐radical crosslinking polymerization of acrylamide monomer with N,N′‐methylenebis(acrylamide) as a crosslinker in an aqueous solution at 22°C. Then, a series of hydrogels at various charge densities were prepared by partial hydrolysis of polyacrylamide precursors in a 0.1M sodium hydroxide solution at 60°C. The hydrolysis time was varied between 20 and 180 min. The chemical structures and internal morphologies of the hydrogels before and after alkaline hydrolysis were characterized with attenuated total reflectance/Fourier transform infrared and scanning electron microscopy measurements. The swelling ratio of the hydrolyzed hydrogels was measured in buffer solutions at various pHs. From differential curves of dQ_v/dpH versus pH (where Q_v is the equilibrium swelling ratio of the hydrogels), the volume phase transition pH of the hydrogels was found to be 4.33 ± 0.05, regardless of the charge density of the hydrogels. In water at 22°C, the hydrogels with greater charge density showed a more rapid swelling rate because of their higher porosity and hydrophilicity. Moreover, in buffer solutions with the pH changing from 9.0 to 2.0 at 22°C, the hydrogels with greater charge density also exhibited a more rapid deswelling rate than the hydrogels with less charge density. In conclusion, the postmodification method is a good way of preparing pH‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improvement of anthocyanin content in the cv. Öküzgözü wines by using pectolytic enzymes

The effect of the addition of two commercial pectolytic enzymes on the anthocyanin and chemical composition of Öküzgözü wines was studied. A rapid HPLC-diode array detection (DAD) method was developed for the analysis of anthocyanins in wines. Direct injection of filtered wine samples followed by selective detection at 520 nm allowed quantitation of these compounds in red wines. Thirteen anthocyanin compounds were detected in wines and, addition of the two enzyme preparations improved the extraction of anthocyanins. Moreover, the wines treated with enzymes had higher values in total phenolics, tannins, and colour intensity than the control wines.     

Effect of AC interference on the corrosion behavior of cathodically protected mild steel in an artificial soil solution. Part I: Investigation on formed corrosion product layer

AC-induced corrosion is a big threat even for cathodically protected pipelines nowadays. While this phenomenon was intensively investigated in the last decades, the corrosion mechanisms due to AC interference remain unclear. In the present work, investigations on the surface processes on cathodically protected mild steel during AC polarization have been performed. They utilized high-speed potential measurements that have demonstrated the influence of the polarization parameters on the resulting alternating voltage. The corrosion product layer was characterized with scanning electron microscopy, electron probe microanalysis, and Raman spectroscopy, which clearly show the effect of the parameters of the applied alternating current on the surface under different cathodic protection (CP) conditions. It was demonstrated that the properties of the formed corrosion product layer, meaning the layer thickness, amount of oxygen, and so on, is not only dependent on the AC polarization parameters but also on the CP potential itself.     

Efficient production of l-lactic acid from chicken feather protein hydrolysate and sugar beet molasses by the newly isolated Rhizopus oryzae TS-61

The aim of this study was to investigate production of l-lactic acid from molasses and chicken feather protein hydrolysate (CFP) by the newly isolated Rhizopus oryzae TS-61. R. oryzae TS-61 was capable of utilizing molasses sucrose and CFP as carbon and nitrogen sources, respectively. In contrast to yeast extract and ammonium sulfate, CFP had potential not only to prevent excessive pH changes and foaming but also to provide smaller uniform pellet formation in during fermentation. Thanks to these properties, it was concluded that CFP might have resulted in higher l-lactic acid production than the other two nitrogen sources (yeast extract and ammonium sulfate). At the end of 42-h optimal cultivation period, the highest (38.5 g/L) and lowest (28.8 g/L) concentrations of l-lactic acid were obtained with CFP and ammonium sulfate, respectively. This is the first report on use of waste chicken feather as a lactic acid production substrate. In addition, a new R. oryzae strain, being capable of using molasses sucrose as carbon source in order to produce l-lactic acid, was isolated.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Evaluation of SeaWiFS chlorophyll‐a in the Black and Mediterranean Seas

The performance of NASA's OC2 and OC4 algorithms to estimate chlorophyll‐a concentrations from SeaWiFS radiometric measurements on the global scale was tested in two contrasted bio‐optical environments, the Black Sea and the Mediterranean Sea. The in situ bio‐optical measurements were made during October 1999 at 25 stations. Comparisons of the in situ measurements with the concurrent SeaWiFS retrievals indicate that the OC2 and OC4 algorithms are not working satisfactorily in both seas. Case 2 waters dominate the Black Sea and the failure of the algorithms is expected. On the other hand, failure of the algorithms in the case 1 waters of the Mediterranean Sea may be due to their specific optical properties. Modifying the OC4 algorithm to include SeaWiFS information at 412?nm yields a better performance in the Mediterranean Sea without degrading performance in the Black Sea. Combining a local algorithm adapted to oligotrophic waters of the Mediterranean Sea and OC4 provides the best results overall.     

Polyindene/organo‐montmorillonite conducting nanocomposites. I. Synthesis,characterization, and electrokinetic properties

In this study, Na‐montmorillonite was organically modified with cetyltrimethylammoniumbromide (CTAB) and intercalated with in‐situ polymerized indene. Polyindene(PIn)/Organo‐MMT nanocomposites were obtained with three different compositions and coded as: K1: [PIn(94.5%)/O‐MMT(5.5%)], K2: [PIn(92.8%)/O‐MMT(7.2%)], and K3: [PIn(87.9%)/O‐MMT(12.1%)]. These nanocomposites were subjected to full characterization with various techniques. Electrokinetic studies were conducted to reveal the zeta (ζ)‐potential characteristics of the nanocomposites. ζ‐potentials of the materials were observed to decrease with increasing O‐MMT content. The cationic (CTAB) and anionic (sodium dodecylsulfate) surfactants were shifted the ζ‐potentials of the colloidal dispersions to more positive and more negative regions, respectively whereas nonionic surfactant (Triton X‐100) caused almost no change. The pH and temperature were observed to shift the ζ‐potential values of the nanocomposites to more negative and slightly more positive regions, respectively. With the addition of mono (NaCl), di (BaCl₂) and three (AlCl₃) valent salts, the ζ‐potential of the nanocomposites were shifted to more negative, more positive, and much more positive regions, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of sample size on strength distribution of advanced ceramics

Strength distribution of advanced ceramics is mostly characterized by Weibull distribution function. The question whether the Weibull distribution always gives the best fit to strength data has been being considered in the last years. The sample size affects the reliable decision of discrimination of different distribution functions (e.g. normal, log-normal, gamma or Weibull). In this paper, 5100 experimental alumina strength data and virtual strength data generated by Monte Carlo simulations are used in order to investigate the effect of sample size on strength distribution of advanced ceramics. It is suggested that, at least 150–200 samples should be used for determination of best fitting distribution function with a statistical fallibility of 10%. Extreme Value Analysis performed with the experimental strength data showed that the Weibull distribution fits the data best and difference between the Weibull and Gumbel distributions appear at the tails.     

Synthesis of MnFe2O4 nanocrystals by wet-milling under atmospheric conditions

This work reports an original method for synthesis of well-crystallized manganese ferrite (MnFe₂O₄) nanoparticles via a high energy wet milling technique under atmospheric conditions, starting from metallic Mn and Fe powders in the presence of distilled water. The effects of milling conditions on the formation and magnetic properties of MnFe₂O₄ nanoparticles were investigated in detail. Fully stoichiometric MnFe₂O₄ nanocrystals with an average crystallite size of 14.5 nm were produced after 24 h of milling. As-synthesized MnFe₂O₄ nanocrystals were found to show soft magnetic behavior at room temperature with saturation magnetization of 53 emu/g. Due to reduced thermal effects, the saturation magnetization increased to 68 emu/g at 5 K. Results show that this method is simple and efficient for the mass production of MnFe₂O₄ nanoparticles.