Solution-cast Membranes Research Articles

Structure of poly ( p-phenylenebenzobisoxazole) (PBZO) and poly ( p-phenylenebenzobisthiazole) (PBZT) for proton exchange membranes (PEMs) in fuel cells

The structures of membranes of PBZO and PBZT extruded with counter rotating dies (CRD) were studied by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), atomic force, scanning electron and transmission electron microscopy (AFM, SEM, and TEM). The structure of CRD-extruded PBZO was compared with that of a solution-cast membrane. The extruded membranes have sheet structures typical of rigid-rod polymers. The heterocyclic rings of the extruded membranes are oriented approximately parallel to the membrane surface, while those of the cast membrane are oriented perpendicular to the surface. The parallel orientation of the rings of the extruded membranes may be due to the normal force exerted during extrusion. The polymer molecules near the surfaces of the extruded membranes are oriented along the shear directions of the extruder, while those in the middle are oriented randomly. There is little cholesteric nature. These materials have potential as microporous PEMs holding ion conducting polymers (ICPs).

Poly(3-dodecylthiophene) membranes for gas separations

Solution cast membranes of poly(3-dodecylthiophene) (PDDT) were studied for the room temperature separation of N 2, O 2, and CO 2. A procedure for fabricating reproducible, smooth, uniformly thick (∼35 μm), defect-free membranes is described. Permeability values were measured for as-cast PDDT membranes ( P N 2 =9.4, P O 2 =20.2, P CO 2 =88.2 Barrers) and selectivity values were calculated ( α O 2/N 2 =2.2, α CO 2/N 2 =9.4). Chemically induced oxidation (∼23%) with SbCl 5 resulted in a decrease in permeability ( P N 2 =3.5, P O 2 =10.5, P CO 2 =48.5 Barrers) and a corresponding increase in permselectivity ( α O 2/N 2 =3.0, α CO 2/N 2 =14.0). Reduction of the oxidized membrane with hydrazine partially reversed these trends ( P N 2 =5.4, P O 2 =15.1, P CO 2 =62.9 Barrers, α O 2/N 2 =2.8, α CO 2/N 2 =11.6). The chemical compositions of as-cast, oxidized, and hydrazine-treated PDDT membranes were determined using elemental analysis and energy dispersive X-ray spectrometry. Membrane microstructure was investigated by optical microscopy, TappingMode™ atomic force microscopy and scanning electron microscopy. The composition and microscopy results were correlated with changes in gas-transport properties.

Study of Permeation of Bis(2-Chloroethyl)Sulfide Through Elastomer Membranes

An investigation was made of the effect of the nature of elastomer, thickness of the membrane and its formulation, and the temperature and relative humidity of the surroundings, on the permeation of bis(2-chloroethyl)sulfide (SM), a well-known chemical warfare agent, through solution-cast elastomer membranes. The permeation was evaluated in terms of the breakthrough time of the agent through the membrane, using the spot disk test and the weight gain method. Butyl rubber exhibited the highest permeation resistance, which increased linearly with thickness and was increased by incorporation of an optimum of 20 phr carbon black in the membranes. Increase in temperature and relative humidity lowered the permeation resistance. The observed data were correlated with permeation parameters and it is postulated that permeation of SM through elastomers is non-Fickian in nature.

Impedance spectroscopy of a perfluorosulfonated ionomer polymer electrolyte

Impedance spectroscopy was performed on solution cast perfluorosulfonated ionomer (PFSI) membranes in an attempt to characterize their electrical properties, and an overall account of the structure-property relationships of as-received and solution cast PFSI will be presented in this report. No large scale massive ion motion occurred in the solution cast PFSI. Instead, only polymer chain polarization was observed and has been determined to be the γ-relaxation occurring at ca 215–235 K depending on the membrane type. The room temperature d.c. conductivity of the solution cast membranes is lower by at least 4 orders of magnitude (≈ 10 −7 to 10 −6S cm −1) than that of the as-received and converted forms of membranes. Wide angle X-ray diffraction revealed that structural changes have occurred in the solution cast PFSI.

Blends of Nafion and Dow Perfluorosulfonated Ionomer Membranes

Solution-cast membranes from perfluorosulfonated ionomers (PFSI) and their blends were prepared from E. I. du Pont de Nemours's Nafion 117 and Dow Chemical's experimental membrane XUS. Water sorption and ac impedance measurements were performed on the solution-cast membranes in an attempt to characterize their electrical properties. Water uptake versus relative humidity for the solution-cast membranes was measured and it was observed that the solution-cast membranes imbibe less water than as-received membranes. The dc conductivity was extracted from the impedance measurements, and the room temperature dc conductivity of the solution-cast membranes was found to be approximately 10 -7 -10 -6 S/cm, ≃10 4 times lower than the room temperature conductivity of the original PFSI membranes

Transport properties of polyvinylpyrrolidone-polyisocyanate interpolymer membranes

The polyvinylpyrrolidone (PVP)-polyisocyanate system forms a series of hydrophilic materials, the water permeability and selectivity of which can be varied over a wide range. Insolubilization of the linear water-soluble PVP, by forming a highly intertwined interpolymer with methylenebis-(4-phenylisocyanate), or polymethylene polyphenylisocyanate, has been used to control the water sorption of the resultant polymeric material. Solution-cast membranes of these materials have excellent physical properties and, based on observations in direct and reverse osmosis experiments, the membranes appear to be imperfection-free. The permeability to both water and solutes is strongly dependent on the equivalent ratio of isocyanate to vinylpyrrolidone; these properties can be reproducibly varied and controlled. Water sorption data indicate a largely random distribution of water at low sorptions, with some clustering at high water contents. Hydraulic permeabilities of the materials prepared range from 1× 10 -10 to 5 × lO -8 cm 2/sec-atm, while apparent permeabilities to sodium chloride in direct osmosis experiments range from 5 × 10 -11 to 4 × 10 -6 cm 2/sec. Permeability studies of high water content membranes in solutions of magnesium sulfate, sodium sulfate, sucrose, sodium chloride, ethylene glycol, and urea indicate that coupling occurs between water and solute flows, the importance of the coupling for the various solutes increasing in the order listed.

Performance of solution‐cast membranes of poly(hydroxythyl methacrylate) in osmosis and reverse osmosis

AbstractNoncrosslinked copolymers of hydroxyethyl methacrylate (HEMA) with ethyl methacrylate (EMA) were prepared and investigated as candidate materials for reverse osmosis membranes. Water and salt flux were calculated from the results of osmosis experiments, compared with cellulose acetate and found to be somewhat smaller. The mobility of water varies by several orders of magnitude between a high flux cellulose acetate membrane and a low flux HEMA‐EMA membrane.