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Composite membranes were fabricated consisting of aligned domains of Nafion® 1100 surrounded by a supporting matrix of polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SEBS). The structure of the composite was controlled via the application of an electric field during solvent casting. Nafion® domains were aligned across the membrane thickness to provide paths for proton conduction. The surrounding SEBS domain limits methanol permeability. Compared to randomly structured Nafion®/SEBS composites, the membranes with field-aligned domains display significantly enhanced performance in direct methanol fuel cells (DMFCs). The membranes with field-aligned domains display DMFC performance better than commercial Nafion® 117 membranes under high methanol fuel concentration.

Hollow biodegradable poly(DL-lactide) (PLA) particles with porous shell walls were prepared by freeze drying small droplets of PLA solution formed by emulsification or spraying. The hollow freeze-dried particles were dispersed in water, and the resulting aqueous suspensions were exposed to plasticizing solvents, either dichloromethane or compressed carbon dioxide. The plasticizing solvent causes the pores in the shell wall to close, forming microcapsules surrounding an aqueous core. A water soluble drug, procaine hydrochloride, was successfully encapsulated in the microcapsule core. The encapsulation efficiency is affected by the hollow particle morphology, amount of solvent used, solvent exposure time, surfactant, and method of dispersing the freeze-dried particles in water. The encapsulation process is explained in terms of interfacial free energy of the hollow particles and mobility of the plasticized polymer. Controlled release of procaine hydrochloride from the microcapsules into phosphate buffer solution was observed. The microcapsules had a small burst release, with the remainder of encapsulated drug slowly released over 9 days. The novel hollow PLA particles produced by emulsification/freeze drying and spray/freeze drying can potentially be used as vehicles for controlled release.

Ionic dyes were successfully encapsulated in colloidal polymer particles by a CO2-based microencapsulation technique. The water-soluble dyes were made hydrophobic by forming ion pairs with several types of alkyl quaternary ammonium cations. The hydrophobic ion pairs were then encapsulated in preexisting size monodisperse polystyrene particles dispersed in water. High-pressure carbon dioxide swelled and plasticized polystyrene and thus facilitated mass transport of the dye into the particles. The results show that the particles maintain their size and morphology after exposure to CO2, and that ion-paired dyes have significantly higher loading in the polymer particles than the original dyes. The effects of cosolvent and surfactant are also discussed.

The etching of copper was studied using an aqueous chemical etchant dispersed in water-in-oil microemulsions droplets. The aqueous phase consisted of an equimolar copper chloride/potassium chloride solution, a typical copper etchant. The phase behavior, conductivity, copper etching rate, and surface roughness after etching were studied using microemulsions formed with ionic, nonionic, and mixed ionic/nonionic surfactants. The composition of each microemulsion was fixed, and the conductivities and copper etching rate were measured as a function of temperature. The conductivity offers a route to probe ion exchange between microemulsion droplets, while the etching rate is related to the interaction of the droplets with the solid surface. The data show a correlation between etching rate and electrical conductivity of the microemulsion. For a given microemulsion, the etching rate increases as the conductivity increases. Atomic force microscopy showed that the copper surface roughness after etching with the microemulsion was lower than the surface roughness when etched without the microemulsion. The results demonstrate that it is possible to adjust the etching rate and surface roughness by changing the microemulsion composition and temperature. Confinement in water-in-oil microemulsion droplets significantly alters the transport of the etchant to the surface and may find use in nanoscale metal patterning.

We have demonstrated that water in carbon dioxide (w/c) microemulsions extract copper and europium ions from a variety of solid substrates in high yields. The microemulsions are unique from bulk aqueous extractions in that the volume of water used is similar to that of the metal extracted, rather than that of the entire solid substrate, allowing grams of waste to be extracted with microliters of water. The microemulsion enhances wetting without saturation of the solid matrix, allowing almost complete recovery of the metal ions. Our results show that >98% of the metal can be recovered from a filter paper surface in a single extrtaction step. Extraction experiments using wood spiked with metal ions have shown that the microemulsions have enhanced diffusivity compared to bulk water. Pressure changes allow recovery and regeneration of the surfactant; in a test case, 81% of the initial capacity is achieved upon reexposure of the w/c microemulsion to a second batch of copper nitrate.

A new procedure is described for dyeing polymer beads using liquid carbon dioxide as a plasticizer to facilitate transport of dye into the particle phase. Aqueous latexes consisting of monodisperse polystyrene particles with surface-grafted poly(N-vinylpyrrolidone) were dyed with Sudan Red 7B using CO{sub 2} at 25 C and 310 bar. Adding CO{sub 2} to the headspace above the latex resulted in some dyeing of the polymer, but better results were obtained by forming an emulsion of CO{sub 2} in the aqueous latex phase. Emulsions were formed with both a fluorinated and a hydrocarbon-based surfactant. It was found that the carbon dioxide emulsion greatly enhances the transfer of dye into the polystyrene without altering the size or morphology of the particles.

An organic solvent-free method for encapsulating progesterone at high loadings within micron-sized inert latex polymer beads is reported. This approach makes use of a polymeric surfactant to emulsify carbon dioxide into an aqueous latex suspension. In this way, preformed approximately 4 microm polystyrene (PS) microparticles surface-grafted with poly(N-vinylpyrrolidone) (PVP) were plasticized and swollen followed by rapid partitioning of progesterone into the polymer matrix. The as-prepared polystyrene beads incorporated over 10% progesterone by weight while maintaining their initial size and morphological uniformity. Dissolution experiments were also carried out to obtain the release profile of progesterone entrapped within the PVP/PS particles.

Water in supercritical carbon dioxide microemulsions are examined as a new medium for the extraction of metal ions from contaminated surfaces, and are shown to extract >99% of the copper from a spiked filter paper with as little as a two-fold excess of surfactant.