Search results for "SEP"
showing 10 items of 2642 documents
Equilibrium and transport properties of ion-exchange membranes
1984
Abstract Specific properties (ion-exchange capacity, water content, pore volume fraction) and transport properties (counterion transport number and electrical conductivity) have been measured in four commercial cation-exchange membranes loaded with a variety of cations of different nature and charge. Not surprisingly, equivalent conductances are lower than in free solution and transport numbers decrease with valency of the counterion. This behavior is explained by taking into account a “tortuosity factor”, due to a lengthening of the pores across the membrane, except for a membrane with a lower water content and for ions of higher charge, in which electrostatic interactions between mobile a…
Understanding the impact of poly(allylamine) plasma grafting on the filtration performances of a commercial polymeric membrane
2019
Abstract Commercial membranes often exhibit difficulties in rejecting specific ionic species, and especially multivalent cations, due to their usual negative charge. To face this drawback, it is proposed here to functionalize the membrane surface by allylamine plasma polymerization. The impact of this modification on both permeation flux and ion rejection is investigated for single salt solutions and ion mixtures. It is shown that the membrane behaves like a positive membrane from the point of view of cation rejection but the negative charge (and the corresponding electrical field) inside pores leads to high rejection of divalent anions like a negative membrane. This allows a high selectivi…
Effects of solvent-free microwave extraction on the chemical composition of essential oil of Calamintha nepeta (L.) Savi compared with the convention…
2008
The essential oil of Calamintha nepeta has been obtained by solvent-free microwave extraction (SFME) and by classical hydrodistillation (HD). A comparative qualitative-quantitative study on the composition of the oils was carried out. A total of 38 compounds, constituting 97.6% of the oil, were identified in the oil obtained by SFME, whereas 46 compounds, representing 95.4% of the oil, were characterized in the HD oil. SFME-distilled oil is richer in lightly oxygenated monoterpenes (LOM) than HD oil. It also has a higher amount of sesquiterpenes and a lower quantity of hydrocarbon monoterpenes. HD oil seems to be affected by chemical changes more than SFME oil.
Binding characteristics of molecularly imprinted polymers based on fungicides in hydroalcoholic media
2015
An iprodione-imprinted polymer was prepared by copolymerization of methacrylamide and ethylene glycol dimethacrylate using a noncovalent imprinting approach. Methacrylamide was chosen using molecular dynamics simulations. To concentrate iprodione from hydro-alcoholic solutions, batch sorption of iprodione on the imprinted polymer were conducted. The equilibrium time for iprodione sorption is 20 min, and the corresponding kinetic mechanism follows the pseudo-second order indicating a strong interaction between iprodione and the imprinted polymer. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to fit the isotherm of iprodione sorption. The imprinted polymer was found to be mo…
Determination of major carotenoids in vegetables by capillary electrochromatography.
2006
A simple and rapid method for the isocratic separation and determination of carotenoids (carotenes and xanthophylls) in vegetables by CEC is described. The capillary column (100 microm ID, 25 cm effective length) was packed with 3 microm Hypersil ODS particles. The optimized mobile phase contained 60% ACN, 35% THF and 5% of a 5 mM Tris aqueous buffer of pH 8. beta-Carotene, lycopene and lutein were separated with efficiencies of 66 000-128 000 plates/m within a short time (less than 12 min for the last peak eluted, 13/13'-cis-beta-carotene). An excellent resolution of the three carotenoids, as well as partial resolution of their geometrical isomers, was achieved. Application to the determin…
Iron oxide-based magnetic photocatalysts: Recent developments, challenges, and environmental applications
2021
Abstract Magnetic separation of the solid photocatalyst from the reacting suspension has received great interest in recent research because it offers a suitable way for removing and recycling the heterogeneous photocatalytic material particles preventing the agglomeration and sedimentation during and after their use. The use of iron oxides such as heterogeneous photocatalysts is an appropriate choice to obtain a suitable photocatalyst easily separable from the fluid. This chapter presents a detailed investigation of iron oxide-based magnetic photocatalysts (IOMPs). We will discuss the required conditions for the synthesis of these photocatalysts, followed by their applications for the remov…
PLLA/PLA scaffolds prepared via Thermally Induced Phase Separation (TIPS): tuning of properties and biodegradability
2008
Foams for tissue engineering applications were prepared via thermally induced phase separation (TIPS). Poly-L-Lactic Acid (PLLA) and blends of PLLA with PLA in different proportions were used (100/0, 90/10, 75/25, 50/50, 0/100 PLLA/PLA wt/wt) starting from ternary systems where dioxane was the solvent and water the non-solvent. Morphology was evaluated by Scanning Electron Microscopy (average pore size and interconnection) and the void fraction was measured by means of Hg porosimetry. Foams apparent density was also evaluated (porosity ranges from 87% to 92%). Biodegradability was estimated in a body mimicking fluid. Results show that structure and morphology (in terms of average pore size …
Effects of inhomogeneities of cross-links on a microphase separation of polymer mixtures
1994
We generalize de Gennes' theory of the microphase separation of cross-linked polymer mixtures to take into account the spatial fluctuations of the elasticity constant c, preventing the mixture from complete segregation. Within a mean-field analysis we found that the spatial fluctuations of c(r), which are assumed to obey the Poisson distribution, enlarge the size of the domains. The latter is obtained to be temperature dependent.
Biological evaluation of PLLA membranes, with different pore diameters, to stimulate cell adhesion and growth in vitro
2015
Polymeric membranes prepared via DIPS (Diffusion Induced Phase Separation) are widely studied and utilized as scaffolds for the regeneration of tissue. In this work, poly (L)-lactide membrane are prepared through a DIPS protocol starting from a ternary solution made of polymer, dioxane (solvent) and water (non-solvent). A three-dimensional, porous and mechanically stable membrane is desirable for ingrowth of human bronchial epithelial cells. Polymeric membranes prepared via DIPS (Diffusion Induced Phase Separation) are widely studied and utilized as scaffolds for the regeneration of tissue. In this work, poly (L)-lactide membrane are prepared through a DIPS protocol starting from a ternary …
Mesoscopic gel at low agarose concentration in water: a dynamic light scattering study
1995
Previous work in our laboratory has shown that at very low agarose concentration in water gelation still occurs within mutually disconnected, high concentration regions generated by spinodal demixing. The freely diffusing particles obtained in these conditions are studied in the present work by depolarized dynamic light scattering and probe diffusion experiments. These particles are found to behave as large (in fact, mesoscopic) polymer fibers entangled in a continuously rearranged mesh with scaling parameters typical of partially flexible, neutral chains. The present results allow specifying the notion of mesoscopic gelation. They also reveal that the same symmetry-breaking mechanism that …