Gas Sorption in Polyaniline. 1. Emeraldine Base

Measurements of the sorption isotherms (at 298 K) for Ar, O 2, and N 2 in several polyaniline emeraldine base (PANi-EB) forms were made (as-cast film, powder, and fully undoped film) over the pressure range 100−1300 kPa. Model fits of the sorption isotherms were made using a modified Flory−Huggins equation (MFHE) and a dual mode sorption equation. In general, the variation of parameters for the MFHE was consistent with morphological interpretations from prior X-ray scattering studies. The ordering of gas sorption with respect to a particular PANi-EB form correlates with the relative sizes and condensabilities of the gas molecules. We see evidence that the morphological variations between different PANi-EB forms, as indicated by their He densities and X-ray scattering data, affects the ratio of O 2 /N 2 solubilities primarily through restricted access to available free volume. From our current measurements of solubilities and prior results for the O 2 and N 2 permeabilities, we conclude that the O 2 /N 2 ideal separation factor is due to diffusivity selectivity in an as-cast PANi-EB film and solubility selectivity in a fully undoped one.