AWWA MTC61226

The objective of this research was to fabricate near perfect polymeric microfiltration membranes with highly ordered pore sizes, shapes, and spacing, thereby overcoming several problems associated with currently available membranes. To date, only ceramic, silicon nitride membranes have been produced with potentially similar characteristics as the ones attempted by this study. Because polymeric membranes are substantially less expensive than ceramic ones, this constitutes an important gap in membrane technology. Aperture Array Lithography was used in this research. In this process, a thin stencil mask, containing a regular array of circular openings (the aperture array pattern), was placed in close proximity to a substrate and is illuminated by a broad beam of highly collimated, energetic helium ions. Ions that strike the opaque regions of the mask are stopped while the ions that pass through the openings form an array of ion beamlets that expose portions of an ion-sensitive resist coating that is applied to the substrate. For positive tone resists, the exposed portions dissolve during a subsequent development step, leaving a replica of the mask pattern in the resist. This pattern is then further transferred through a thin polyimide membrane to form a free-standing membrane filter. Pore size distributions were measured by digital image analysis of electron micrographs of the membrane surface obtained using a Field Emission Scanning Electron Microscope. Includes 11 references, figures.