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Nanoporous membranes containing monodisperse pores of 24 nm diameter are fabricated using poly(styrene-b-lactide) block copolymers to template the pore structure. A 4 mum thin film of the block copolymer is cast onto a microporous membrane that provides mechanical reinforcement; by casting the copolymer film from the appropriate solvents and controlling the solvent evaporation rate, greater than 100 cm(2) of a thin film with polylactide cylinders oriented perpendicular to the thin dimension is produced. Exposing the composite membrane to a dilute aqueous base selectively etches the polylactide block, producing the porous structure. The ability of these pores to reject dissolved poly(ethylene oxide) molecules of varying molecular weight matches existing theories for transport through small pores.

Ultrafiltration membranes based on cylinder-forming block copolymers are made by orienting the cylinders perpendicular to the membrane surface followed by selective etching of the minority component. Such membranes promise fast fluxes and superior molecular weight cut-offs. The perpendicular orientation of the cylindrical domains results from the solvent concentration profile that develops when drying the polymer casting solution. As solvent evaporates, it first causes nucleation of the ordered morphology at the vapor-solution interface. This is followed by cylinder growth. The rate of cylinder growth is the product of two terms;a polymer relaxation rate and a thermodynamic driving force. In regions of high solvent concentration the polymer relaxation rate is high and the driving force is small; in regions of low solvent concentration, the opposite is true. This concentration dependence results in the solvent concentration profile established by evaporation dictating how the growth rate varies as a function of position. For a concentration profile that causes the relaxation rate to increase less rapidly with position than the driving force decreases, the growth rate decreases moving into the film, so cylinders grow parallel to membrane surface. Conversely, when the concentration profile results in the relaxation rate increasing more rapidly with position than the driving force decreases, the growth rate increases further into the film, causing perpendicularly oriented cylinders to form. Analysis based on this picture agrees with a variety of experimental results.

Hollow-fiber contactors can provide fast mass transfer without flooding or loading. They are a promising alternative to packed towers for gas treating, and to centrifugal extractors for liquid-liquid extraction. Hollow-fiber contractors can be designed effectively using the mass transfer correlations reported in this paper. The correlations, based on aqueous deaeration and carbon dioxide absorption, are similar to earlier heat and mass transfer correlations, but can be complicated by diffusion across the fiber wall and by alterations in fiber geometry.

We report a new morphology in a poly(isoprene-block-styrene-block-dimethylsiloxane) ABC triblock copolymer. The most probable symmetry of the morphology (Ia3̄d) was determined from two-dimensional SAXS measurements performed on a sample with long-range order induced by an oscillatory shear field. By comparing the predictions of self-consistent field theory with TEM and SAXS and SANS powder diffraction patterns, we deduced that the morphology is a core−shell gyroid comprised of two independent and triply periodic poly(dimethylsiloxane) networks encased in poly(styrene) shells and separated by a continuous poly(isoprene) domain. Thus, this unique nanostructure divides space into five independent, three-dimensionally continuous domains.

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