GAS-TRANSPORT PROPERTIES OF ANNEALED POLYIMIDE FILMS

Sorption and permeation of CO2 in various annealed polyimide (PI) films were investigated. Dual-mode sorption and partial immobilization models were used to analyze the data. Sorption of CO2 in PI film quenched from above the glass transition temperature (T(g)) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO2 can be attributed to a change in the Langmuir sorption capacity C'H by annealing, since the other dual-mode sorption parameters, k(D) and b, are almost independent of annealing. the value of C'H is increased by quenching, and decreased by slow cooling from above T(g). The two diffusion coefficients D(D) and D(H) according to the Henry and Langmuir modes, respectively, for CO2 also depend markedly on annealing. Diffusion coefficients of quenched PI film are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change in D(H) is larger than that in D(D). The permeability coefficient of quenched PI film at 100 cmHg is about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permselectivity.