Correlation between macrovoid formation and the ternary phase diagram for polyethersulfone membranes prepared from two nearly similar solvents

The morphological structure of membranes prepared from two nearly similar systems consisting of water/N,N-dimethylacetamide (DMAc)/polyethersulfone (PES) and water/N-methyl-2-pyrrolidone (NMP)/polyethersulfone (PES) has been studied. The morphology of the prepared membranes showed that both systems exhibit an instantaneous liquid–liquid demixing that leads to the formation of macrovoids in the resulting structures. Nevertheless, the resulting macrovoid structures were contrary to the generally accepted concepts concerning macrovoid formation. The membranes morphologies showed that in spite of better miscibility between water and DMAc, which must promote the formation of channel- and finger-like structures, more sponge-like structures were observed in membranes prepared from the water/DMAc/PES system compared to those prepared from the water/NMP/PES system. To find the source of this unexpected phenomenon, the complete ternary phase diagrams consisting of theoretical binodal curves, vitrification boundaries, and gelation boundaries were constructed for both systems and it was shown that gelation process occurs earlier in the water/DMAc/PES system compared to the other system, which inhibits the growth of macrovoids in this system.     

Stability of Plasma Treated Non-vulcanized Polybutadiene Surfaces: Role of Plasma Parameters and Influence of Additives

Surface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of ~60 W and exposure time of ~30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase.     

Use of headspace solid-phase microextraction for the quantification of poly(3-hydroxybutyrate) in microbial cells

Biopolymers such as poly(hydroxyalkanoates) (PHAs) have received much attention due to their physico-chemical properties, biodegradability, and biocompatibility that make them good candidates for industrial and medical applications. Produced by some microorganisms PHAs accumulate within the cells of these organisms. The optimization of microbial processes to produce PHAs at a lower cost requires rapid and accurate techniques for quantification of the biopolymer in biomass. The present study describes a method based on solid-phase microextraction (SPME) coupled to gas chromatography (GC) for the determination of poly(3-hydroxybutyrate) (PHB) in Alcaligenes latus cells. First PHB was depolymerized by either methanolic or hydrolytic digestion into methyl 3-hydroxybutyrate (Me-3-HB) or crotonic acid (CA), respectively. The resulting analytes were then subjected to analysis by headspace SPME/GC with flame ionization detection (FID). The two depolymerization/SPME/GC-FID methods were optimized and applied to the analysis of PHB in bacterial biomass harvested from a fermentation process that uses A. latus. Results were compared with those obtained using GC-FID analysis of MeOH/CHCl(3) digested samples. Excellent agreement was found between the three methods but the two SPME-based methods were environmentally friendly and easier to perform.     

Homoclinic orbits for the perturbed sine‐Gordon equation

In this work, we study the persistence of a homoclinic orbit of the sine‐Gordon equation under diffusive and driven perturbations. An analytic perturbation method based on time‐dependent scattering theory, together with Fredholm theory, is used to establish persistence. The estimates are given in space‐time function spaces, with a certain time decay required for the existence of a homoclinic orbit. © 2000 John Wiley & Sons, Inc.     

High-efficiency ozone generation via electrochemical oxidation of water using Ti anode coated with Ni–Sb–SnO<Subscript>2</Subscript>

Ozone (O₃) has been generated on Ni–Sb–SnO₂/Ti electrode as anode immersed in acidic media at 25 °C by electrochemical process. The anode was electrochemically characterized by cyclic voltammetry and morphologically characterized by scanning electron microscopy (SEM) and X-ray diffraction. The concentration of dissolved ozone was determined by a UV/Vis spectrophotometer. The type of electrode with different times coating on the titanium mesh and different acid type and various concentrations (C _acid) were used, and the stability of the electrode was investigated under the experimental conditions by SEM images. Results shows that higher efficiency (53.7%) for O₃ generation by electrochemical oxidation of water were obtained in HClO₄ (1 M) and an applied potential of 2.4 V vs. Ag/AgCl in 150 ml volume undivided electrochemical cell.     

Optimization of ammonium removal from waste water by natural zeolite using central composite design approach

The aims of the present study are to investigate removal of ammonium ion from wastewater using natural Western Azarbaijan zeolite and to optimize effective parameters by experimental design. In order to remove ammonium ions from aqueous solutions, experiments were carried out using column method as functions of the initial ammonium concentration, flow rate and pH of the solution. The results clearly confirmed that all mentioned parameters have vital affects on removing ammonium ions from wastewater and effluents, so got optimized. Central composite design with response surface methodology was applied for the optimization of main experiment parameters. The significance of the independent variables and their interactions were tested by the analysis of variance ANOVA and f-test statistics. Optimization of the variables for maximum removal efficiency by natural zeolite was performed using the quadratic model. The model predicted maximum removal efficiency under the optimum conditions including initial ammonium concentration of 30?mg?l^?1; flow rate of 1?ml?min^?1 and pH 6, which was very close to the experimental value determined in column experiment. The cation exchange capacity of natural Western Azarbaijan zeolite was found to be 1.79?meq?g^?1. Based on the experimental results, it can be concluded that the natural Western Azarbaijan zeolite has an excellent potential for removing ammonium ions from aqueous solutions and it is suggested as a suitable material for wastewater treatment.     

Efficient One‐pot Synthesis of Alkyl 3‐(alkyl)‐4‐methyl‐2‐thioxo‐2,3‐dihydrothiazole‐5‐carboxylates in a Multi Component Reaction

A simple and efficient one‐pot synthesis of alkyl 2‐(alkyl)‐4‐methyl‐2‐thioxo‐2,3‐dihydrothiazole‐5‐carboxylates from the reaction of primary alkylamines and carbon disulfide in the presence of 2‐chloro‐1,3‐dicarbonyl compounds is described. This new protocol has several advantages such as lack of necessity of the catalyst, good yields, mild conditions and short times for reaction.     

Linear Stability Analysis of Double-Diffusive Convection in Porous Media,with Application to Geological Storage of CO<Subscript>2</Subscript>

Onset of double-diffusive buoyancy-driven flow resulted from vertical temperature and concentration gradients in a horizontal layer of a saturated and homogenous porous medium is investigated using amplification factor theory. After injection of CO₂ into a deep saline aquifer, the density of the brine saturated with CO₂ increases slightly. This increase in density induces natural convection. The effect of geothermal gradient is also considered in this work as a second incentive for convection and the double-diffusion convection was studied. Linear stability analysis is used to predict the inception of instabilities and initial wavelength of the convective instabilities. The analysis presented is applied to acid gas injection (as an analogue for CO₂ storage) into saline aquifers in the Alberta basin. It is found that the geothermal gradient does not have significant effect on the onset of convection for these aquifers. It is shown that the geothermal effects on the onset of natural convection are negligible as compared to the solutal effects induced by dissolution and diffusion of CO₂ in deep saline aquifers. Therefore, the linear stability analysis and the long-term numerical simulation of CO₂ sequestration into such saline aquifers may be assumed to be isothermal in terms of natural convection occurrence.