Membranes - Intrinsically a Nanotechnology: Potential Use of Different Kinds of Membranes

摘要

Synthetic membrane based separations enable separating components differing in size from hundreds of nanometers to subnanometer scales. Achieving these separations requires the engineering of morphologies and modules while achieving a cost effective manufacturing process. The membrane field, which traces its beginning back over 150 years, has been forced to focus on nanostructures and their creation long before these topics became the popular buzzwords that they are now. Discoveries of material processing techniques have been as crucial as those of new material compositions in creating such engineered structures. Especially over the past 30 years, not only new materials and processing techniques, but also emerging applications of membranes have encouraged advancement in the state-of-the-art and promoted the vitality of this discipline. For example, the established areas of micro- and ultrafiltration are vigorously exploring new intellectual challenges in response to the bio-revolution, which demands increasingly sophisticated separation capabilities. Indeed, ultrafiltration membrane molecular weight cutoff values or nominal pore sizes are insufficient to control separation of similarly sized solutes. Adding knowledge of the types and amounts of charge on solutes as well as the morphology and charge on the membrane, however, is helping to enable extraordinarily selective hydrodynamic-based separations. Superimposing these factors on top of the persistent issues of fouling and concentration polarization presents a significant theoretical and practical challenge. These challenges are being addressed by innovations in modeling, materials and analytical techniques as well as device design and operational strategies. Such innovations benefit every type of membrane process, since fluid dynamics potentially affects all membrane applications, due to boundary layers and flow distribution effects - even those focused on micro-molecular separations.