MORPHOLOGICAL MODIFICATION OF POLYANILINE FILMS FOR THE SEPARATION OF GASES

We have recently reported a potentially useful application for conjugated polymer films in the field of gas separations (Science, 252, 1412, 1991). Here we report additional findings which show how selective control of gas permeability is facilitated by the doping, undoping and redoping (cycling) process of emeraldine films. Specifically, permeability data for H-2, He, CH4, CO2, O2, N2, and CH4 are given for films treated with perchloric acid. There is a large increase in permeability to all gases following the doping and undoping film treatment cycle. Moreover, controlled redoping (of the undoped films) results in large separation factors for industrially important gas pairs. These results are consistent with the model based on dopant occupation of free-volume of the ''pin-hole free'' film. This cycling phenomenon is also found in other conjugated polymers such as poly-dimethoxy-para-phenylene-vinylene (DMPPV). Another important variable for gas transport properties of polyaniline films is the film curing time. Permeability data for films cured at 125-degrees-C for 2, 3, and 6 hours, and then cycled, indicate that a three hour cure time produces the most fully dense films. We also present preliminary gas permeability data for a polyimide thin film by itself and, a polyimide blend containing polyaniline.