Enhanced corrosion protection coatings prepared from soluble electronically conductive polypyrrole‐clay nanocomposite materials

A series of electronically conductive nanocomposite materials that consisted of soluble polypyrrole (PPY) and layered montmorillonite (MMT) clay platelets were prepared by effectively dispersing the inorganic nanolayers of MMT clay in organic PPY matrix via an in situ oxidative polymerization with dodecylbenzene sulfonic acid (DBSA) as dopant. Organic pyrrole monomers were first intercalated into the interlayer regions of organophilic clay hosts and followed by a one‐step oxidative polymerization. The as‐synthesized electronically conductive polypyrrole–clay nanocomposite (PCN) materials were then characterized by Fourier transformation infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD), and transmission electron microscopy (TEM). PCNs in the form of coatings with low clay loading (e.g., 1.0 wt %) on cold‐rolled steel (CRS) were found to exhibit much better in corrosion protection over those of pristine PPY based on a series of electrochemical measurements including corrosion potential, polarization resistance, and corrosion current in 5 wt % aqueous NaCl electrolyte. Effects of the material composition on the thermal stability, optical properties, and electrical conductivity of pristine PPY along with PCN materials, in the form of fine powder, powder‐pressed pellet, and solution, were also studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), UV‐visible absorption spectra, and four‐point probe technique, respectively. The viscosity of PPY existed in PCN materials and pristine PPY were determined by viscometric analysis with m‐cresol as solvent. The heterogeneous nucleating effect of MMT clay platelets in PPY matrix was studied by wide‐angle powder XRD. The corresponding morphological images of the nucleating behavior of clay platelets in PPY matrix were investigated by scanning electron microscopy (SEM). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3264–3272, 2003     

Garlic reduces plasma lipids by inhibiting hepatic cholesterol and triacylglycerol synthesis

Prompted by the reported hypolipidemic activity of garlic, the present study was undertaken to elucidate the mechanism(s) underlying the cholesterol-lowering effects of garlic. Rat hepatocytes in primary culture were used to determine the short-term effects of garlic preparations on [1-¹⁴C]acetate and [2-³H]glycerol incorporation into cholesterol, fatty acids and glycerol lipids. When compared with the control group, cells treated with a high concentration of garlic extracts [i.e., petroleum ether- (PEF), methanol- (MEF) and water-extractable (WEF) fractions from fresh garlic] showed decreased rates of [1-¹⁴C]acetate incorporation into cholesterol (by 37–64%) and into fatty acids (by 28–64%). Kyolic containingS-allyl cysteine and organosulfur compounds inhibited cholesterogenesis in a concentration dependent manner with a maximum inhibition of 87% at 0.4 mM. At this concentration, Kyolic decreased [1-¹⁴C]acetate incorporation into fatty acids by 67%.S-allyl cysteine at 2.0 and 4.0 mM inhibited cholesterogenesis by 20–25%. PEF, MEF and WEF depressed the rates of [2-³H]glycerol incorporation into triacylglycerol, diacylglycerol and phospholipids in the presence of acetate, but not in the presence of oleate. The results suggest that the hypocholesterolemic effect of garlic stems, in part, from decreased hepatic cholesterogenesis, whereas the triacylglycerol-lowering effect appears to be due to inhibition of fatty acid synthesis. Primary hepatocyte cultures as used in the present study have been proven useful as tools for screening the anticholesterogenic properties of garlic principles.     

Electrical Properties of TiO2-K2Ti6O13 Porous Ceramic Humidity Sensor

Porous ceramic humidity sensors using pure TiO₂ doped with a few molar percent K₂CO₃ were studied. The conductance versus relative humidity (rh) sensitivity of the sensor sintered at 1200°C was as high as 4 orders of magnitude in the range of 15% to 95% rh at 200 Hz and 25°C. The sensors were reversible without repeated high-temperature thermal desorption processes. The electrical properties of the sensors under different rh were determined by both direct current (dc) and alternating current (ac) analysis techniques. The sensors could be polarized similar to electrolytes in a charging process as a result of the electrode and water molecular polarization effects, and the effects were enhanced with increasing rh. The conduction carriers of the sensors in a moist atmosphere were ions and electrons, and the dominant conduction carrier was ions. By complex impedance plots with a "non-Debye" capacitor concept, an equivalent circuit model was established which can simulate well all the electrical properties of the sensors in the range of 65% to 95% rh for all measured frequencies (5 Hz to 13 MHz). The relative dielectric dispersion k '(ω) increased with increasing rh and was almost proportional to ω^−1.85 at low frequencies. The relative dielectric absorption k "(ω) increased with increasing rh and was almost proportional to ω⁻¹ at low and median frequencies.     

Ultrafiltration on Sizing Agent Solution in Tubular-Membrane Module

Ultrafiltration of an aqueous solution of carboxymethyl cellulose (CMC) was carried out in a tubular-membrane model made of ZrO₂/carbon. Water was forced through the macroporous membrane as the permeate, while CMC was concentrated and recovered as the retentate. Correlation equations for calculating the permeate flux of membrane ultrafiltration were derived based on the resistance-in-series model. Correlation results were confirmed by the experimental data. Experimental results showed that the permeate flux increases as transmembrane pressure or fluid velocity increases, but decreases when feed concentration increases. Because membrane ultrafiltration is a pressure-driven process, high cross-flow velocity enhances the mass transfer coefficient of the solute and high solution concentration increases the thickness of the concentration polarization layer.     

Improving the sampling resolution of periodic signals by using controlled sampling interval method

A simple and reliable controlled sampling interval (CSI) method is proposed for improving the sampling resolution of periodic signals of analog-to-digital converters (ADC). The proposed CSI method uses K periods to obtain P sampling points. By combining these P sampling points into one period interval, the period is virtually sampled with a high number of samples. This new technique includes two main stages: (i) determining the values of P and K, and (ii) performing the sampling and signal recombination process. Experimental results show that the proposed CSI method, which requires no additional hardware, improves the sampling resolution of periodic signals.     

Electrical characteristics of amorphous In–Ga–Zn–O thin-film transistors prepared by radio frequency magnetron sputtering with varying oxygen flows

This study investigates impacts of oxygen flow during the deposition of amorphous indium–gallium–zinc oxide (a-IGZO) channel layer with a radio frequency (r.f.) magnetron sputter on the electrical characteristics of the fabricated thin-film transistors (TFTs). Results indicate that as the film was deposited with a higher oxygen flow, the transfer curves are positively shifted while the field-effect mobility (μ_FE) is significantly decreased. To get more insight about the effects, channel resistance (R_CH) and the parasitic source-to-drain resistance (R_SD) of the fabricated devices are extracted using the total resistance method. The extracted a-IGZO channel resistance per unit length (r_ch) and R_SD are found to increase while the extracted effective mobility (μ_E) is decreased with increasing oxygen flow during sputtering. These observations are postulated to be related the decrease in the In/(In + Ga + Zn) ratio and the increase in the Zn/(In + Ga + Zn) ratio of the a-IGZO films with increasing the oxygen flow rate which lead to higher resistivity and lower carrier concentration. The extracted R_SD can be comparable with R_CH for the devices prepared with high oxygen flow, resulting in the roll-off of μ_FE as the channel length is shorter than 20 μm.     

White spirit permeation resistance of polyethylene,polyethylene/modified polyamide,and polyethylene/blends of modified polyamide and ethylene vinyl alcohol bottles

The main objective of this study was to investigate the barrier properties of polyethylene (PE), PE/modified polyamide (MPA), and PE/blends of modified polyamide and ethylene vinyl alcohol (MPAEVOH) bottles against white spirit permeation. After MPAEVOH barrier resins were blended with PE, the resistance of the PE/MPAEVOH bottles against white spirit permeation was significantly improved compared to the PE bottle. Surprisingly, with proper compositions of MPAEVOH resins, the white spirit permeation resistance of PE/MPAEVOH bottles at 40°C improved by more than 3000 times compared to the PE bottle, wherein the best permeation resistance (4200 times barrier improvement) of the PE/MPAEVOH bottles was found as the weight ratio of MPA : EVOH reached 4:1. These interesting permeation properties of PE/MPAEVOH bottles were investigated in terms of the barrier and free‐volume properties of the base resins and their corresponding morphologies in blow‐molded bottles. POLYM. ENG. SCI. 45:25–32, 2005. © 2004 Society of Plastics Engineers.     

THE SEPARATION OF METHYL ACETATE FROM METHANOL BY EXTRACTIVE DISTILLATION

Methyl acetate cannot be completely removed from methyl acetate-methanol mixtures by distillation because of the presence of the minimum binary azeotrope. Methyl acetate can be readily removed as overhead product from mixtures containing it and methanol by using extractive distillation in which the extractive distillation agent is a higher boiling oxygenated, nitrogenous and/or sulfur containing organic compound or a mixture of these. Typical examples of effective agents are dimethylsulfoxide, glycerine plus propylene glycol, ethylene glycol plus dimethylsulfoxide plus 1,5-pentanediol. Methanol can be removed as the overhead product from methyl acetate when the extractive distillation agent is nitrobenzene, propylene carbonate or ethylene glycol phenyl ether.     

Effects of a tert‐butylphenylene substituent on the structure and optical,fluorescent and thermal properties of the poly(p‐phenylenevinylene) derivatives

Two soluble fluorescent polymers, poly(2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylenevinylene) (DtBP‐PPV) and poly(2‐decyloxy‐1,4‐phenylenevinylene) (DO‐PPV), were prepared by a method similar to the Gilch procedure. The DtBP‐PPV and DO‐PPV have a same chemical structure except for the conjugated tert‐bytulphenyl substituents in the former. The polymers are characterized by using ¹H NMR, FTIR, UV–vis, photoluminescence (PL), and electroluminescence (EL) spectroscopies and thermogravimetric analysis (TGA). The ¹H NMR spectra show no tolane‐bis‐benzyl (TBB) structure defects in DtBP‐PPV but some in DO‐PPV. Both UV–vis absorption and PL emission peaks of the DtBP‐PPV exhibit a red‐shift phenomenon as compared with those of the DO‐PPV. Moreover, with the DtBP‐PPV and DO‐PPV acting as light‐emitting polymers separately, EL devices were fabricated with a sequential lamination of ITO/PEDOT/DtBP‐PPV (or DO‐PPV)/Ca/Ag. The DtBP‐PPV‐based device shows a lower turn‐on voltage, a longer EL emission wavelength, and a higher brightness than the DO‐PPV‐based device. The maximum brightness of DtBP‐PPV‐based device is 57 cd/m² at an applied voltage of 12 V. POLYM. ENG. SCI., 47:1380–1387, 2007. © 2007 Society of Plastics Engineers     

Three-terminal CNTs gas sensor for N2 detection

A novel three-terminal gas sensor was fulfilled by utilizing the vertically aligned carbon nanotubes (CNTs) mat. Carbon nanotubes were synthesized by thermal chemical vapor deposition (thermal CVD) at 700 °C under C₂H₂ gas flow rate of 30 sccm. Upon exposure to a with and without N₂ environment at the room temperature of 25 °C, the electrical resistance of as-made devices was found to increase and to return back, respectively. Compared to a low bias one, the sensitivity increased when applying a high source drain bias voltage. Furthermore, the device became more sensitive for N₂ detection by applying a negative gate voltage. It was concluded that the alteration of free holes concentration in the CNTs mat played the major mechanism for the N₂ gas detection.