Ureasil–polyether hybrid blend with tuneable hydrophilic/hydrophobic features based on U-PEO1900 and U-PPO400 mixtures

Urea-cross-linked polyether-siloxane hybrid blends with tuneable hydrophilic/hydrophobic features were prepared from a mixture of poly(ethylene oxide) (PEO1900) and poly(propylene oxide) (PPO400), hybridized by end-chain functionalization with (3-isocyanatopropyl)triethoxysilane. The aim of this study was to demonstrate that the combination of the different polyether phases produces materials with hydrophilic and hydrophobic properties. An anti-fog coating and a transparent monolithic swellable hydrogel were produced from the PEO1900 hybrid. Swellability and drug release profiles could be easily tuned by varying the ureasil–PEO/ureasil–PPO ratio in the hybrid matrix. Differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) analyses indicated that the nanostructure of the hybrid blends could be described by the existence of a biphasic mixture of PEO1900-rich and PPO400-rich phases, with a fraction of the lamellar domains being derived from the PEO1900 crystallinity. A correlation between the nanoscopic features and the kinetics of the swelling mechanism is proposed, based on the results of in situ SAXS analyses. In vitro monitoring using UV–Vis spectroscopy indicated that the kinetics of drug release from the PEO1900:PPO400 hybrid blends could be controlled by varying the proportions of the hydrophilic (PEO1900) and hydrophobic (PPO400) hybrids. The response to pH change and to application of a magnetic field to the PEO1900-magnetite nanocomposite indicated that the production of stimuli-responsive delivery devices based on ureasil–PE should be feasible in the near future.     

Molecular dynamics study of phonon-mediated thermal transport in a Ni50Al50 melt: case analysis of the influence of the process on the kinetics of solidification

The phonon-mediated contribution to the thermal transport properties of liquid NiAl alloy is investigated in detail over a wide temperature range. The calculations are performed in the framework of equilibrium molecular dynamics making use of the Green–Kubo formalism and one of the most reliable embedded-atom method potentials for the intermetallic alloy. The phonon-mediated contribution to the thermal conductivity of the liquid alloy is calculated at equilibrium as well as for the steady state. The relative magnitude of the thermal conductivity decrease induced by the transition to the steady state is estimated to be less than 2% below 2000 K and less than 1% at 3000 and 4000 K. It is also found that the phonon-mediated contribution to the thermal conductivity of the liquid alloy can be accurately estimated (well within 1%) on the basis of an approximation which invokes the straightforwardly accessible microscopic expression for the total heat flux without demanding calculations of the partial enthalpies needed for the precise evolution of the reduced heat flux (pure heat conduction). On the basis of these calculations, the correspondence between the experimentally observed and modelled kinetics of solidification due to a difference in thermal conductivity is discussed.     

Hydrophobic behavior,ROS production,and heme degradation of hemoglobin upon interaction with <Emphasis Type="Italic">n</Emphasis>-alkyl sulfates

The oxygen-containing free radical species form upon interaction of amphiphilic substances such as sodium dodecyl sulfate and hemoglobin. Under these conditions, hemoglobin is converted to methemoglobin and simultaneously results in heme degradation. Since heme is located in a hydrophobic moiety of hemoglobin, we hypothesized that other hydrophobic substances or amphiphilic xenobiotics can dispose hemoglobin to oxidative stress. Here this hypothesis was tested by investigating heme degradation of hemoglobin during interaction with n-alkyl sulfates. This was accomplished using UV–Vis and fluorescence spectroscopy, chemometric analysis, and chemiluminescence methods. We determined whether a relationship exists between the alkyl tail length (surfactant hydrophobicity) of n-alkyl sulfate homologues, reactive oxygen species (ROS) production, and heme degradation pattern of hemoglobin. We also proposed a mechanism for these types of interactions and induction of heme degradation. Our results indicated that hemoglobin structural–functional changes including globin denaturation are the key factors in starting the heme degradation process, and heme degradation product patterns were dependent on each alkyl sulfate. However, the number of fluorescent components (heme degradation products) was independent of the alkyl sulfate type. The reason for this phenomenon was the mechanism of reaction in which the amount of hydrogen peroxide was changed with each homologue, but the mechanism of degradation remained the same. Thus, an increase in hydrophobic chain length of the surfactants correlated with the enhanced ROS production and heme degradation of hemoglobin.     

Effect of polyethylene glycol on sulfonated polyether imide (SPEI) for fuel cell applications

The sulfonated polyetherimide (sPEI) was synthesized by direct sulfonation method using chlorosulfonic acid as a sulfonating agent. Different sulfonation degrees of sPEI was obtained by varying the ratio of PEI to chlorosulfonic acid and reaction time. Then, sulfonated polyetherimide was blended with polyethylene glycol (PEG) and thermally cross-linked in order to achieve high performance proton exchange membrane. It was found that the addition of PEG resulted in a significant increase in porosity and water uptake of the membranes, which favored proton transport at low temperature. The maximum proton conductivity was 11 mS/cm at 75°C for the blend membrane containing 20% PEG. The sulfonation and blend modification of PEI were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.     

Highly selective and sensitive copper(II) membrane coated graphite electrode based on a recently synthesized Schiff’s base

A PVC membrane electrode based on bis-2-thiophenal propanediamine (TPDA) coated directly on graphite is described. The electrode exhibits a Nernstian response for Cu²⁺ over a very wide concentration range (1.0×10⁻¹ to 6.0×10⁻⁸ M) with a detection limit of 3.0×10⁻⁸ M (2.56 ng ml⁻¹). It has a fast response time and can be used for at least 2 months without any major deviation. The proposed sensor revealed very good selectivities for Cu²⁺ over a wide variety of other metal ions and could be used in the pH range of 3.0–7.0. It was successfully used for direct determination of copper in black tea and as an indicator electrode in potentiometric titration of copper ion.