The effectiveness of a membrane in a separation process is based on the degree of its selectivity and its permeability or throughput. Unfortunately, selectivity and permeability are generally traded off - the same mechanisms which control selectivity, such as pore size, regulate the flux of material through the membrane. This SGER proposal suggests fabricating composite membranes in order to maximize both selectivity and permeability. A porous substrate is used as the backing material thus providing mechanical strength and insuring high permeability. Selectivity is then controlled by mounting a nonporous ultrathin microstructured film over the backing sheet. The PI suggests making these microstructured films out of cohesive, molecularly ordered, organic mono- or multi-layered films formed either by the Langmuir Blodgett technique or self assembly via adsorption from solution. The permeability of these films to gases of interest will be measured by using either a quartz crystal microbalance or a surface acoustic wave device. In this type of measurement this film is attached to a (typically) quartz piezoelectric crystal, and an oscillating electric field is applied to the crystal. This application causes an acoustic wave to propagate with a particular resonant frequency. Minute changes in mass of the film can be detected by shifts in the resonant frequency of the crystal. The film will be exposed to a gaseous environment, and frequency shifts will be measured in time in order to measure the permeability. The study will focus on how the microstructure architecture and physicochemical properties of the films relate to the permeability. Specifically films of different fluidity, surface characteristic, chemistries and defect structure will be examines.
