Conjugated Polymer Films for Gas Separations

Science  07 Jun 1991:
Vol. 252, Issue 5011, pp. 1412-1415
DOI: 10.1126/science.252.5011.1412


Permeabilities for a series of gases through free-standing films of the conjugated polymer polyaniline are reported. A remarkable selectivity has been achieved for important gas pairs incuding hydrogen-nitrogen, oxygen-nitrogen, and carbon dioxide-methane. The selectivity values of 3590 for H2/N2, 30 for O2/N2, and 336 for CO2/CH4 surpass the highest previously reported values of 313, 16, and 60 for the nonconjugated polymers poly(trifluorochloroethylene), cellulose nitrate, and a fluorinated polyimide, respectively. The process for tailoring gas selectivity of a polyaniline membrane involves first enhancing the permeabilities of gases with small diameters [<3.5 angstroms (Å)] by doping and undoping the polymer film with counterions of an appropriate size. High selectivities are then achieved by decreasing the permeabilities of larger gases (>3.5 Å diameter) through controlled redoping of the polymer. The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.