| Nanofiltration (NF) is a powerful separation technique, capable of operation in both large- and small-scale applications. Despite extensive developments in the NF field, increased permeate fluxes as well as greater control over membrane properties are constant objectives. A common target for NF performance enhancement is the membrane, which is the selective barrier between the feed and permeate solutions. In this dissertation I detail how the deposition of ultrathin polymer films on porous supports yields selective, high flux membranes.; To form composite NF membranes with ultrathin polymer skins, I employ alternating adsorption of polycations and polyanions on a porous support. Separations can be optimized by varying the constituent polyelectrolytes, and in general, the use of polycations and polyanions with lower charge densities allows greater passage of larger analytes, presumably because ionic crosslinking decreases with decreasing charge density. In situ ellipsometry confirms that lower charge densities result in highly water-swollen films. Careful selection of polyelectrolytes results in membranes capable of separating salts, sugars, or, remarkably, even proteins such as myoglobin and bovine serum albumin. Additionally, membrane transport characteristics such as rejection and solution flux can be optimized by simple changes in the film deposition process. Moreover, water fluxes through these films are 1.5--5 times greater than through commercial NF membranes. |
