Gas sorption and permeation of glassy polymers with microvoids

摘要

Gas sorption and permeation of physically treated glassy polymeric membranes is studied from the viewpoint of the transport mechanism and the control of microvoids in the membrane.Physical treatments,such as sub-T_g annealing,thermal quenching,and CO_2 pressure conditioning were found to be effective for the control of microvoids in the glassy state,as well as gas sorption and permeation.Teh Langmuir saturation constant C'_H of the dual-mode sorption model decreased with a sub-T_g annealing period for the copolymer (vinylidene cyanide-alt-vinyl acetate),copoly(VDCN-VAc).On the other hand,Henry's solubility coefficient k_D and Langmuir affinity constant b did not change markedly with sub-T_g annealing.The permeability coefficient of copoly(VDCN-VAc)decreased with the sub-T_g annealing period.Furthermore,the dual-mode parameter C'_H and the CO_2 permeability coefficient of polyamic acid,polyimide,poly(2,6-dimethyl-,4-phenylene oxide),and polycarbonate increased markedly upon thermal quenching and CO_2 presure conditoning from the liquid state.The gas sorptin isotherm and pressure dependence of te permeability coefficients for the polymers studied here are explained in terms of the dual-mode sorption model and partial immobilization model characteristic to a glassy polymer,respectively.It was found tht sub-T_g annealing,thermal quenching,and CO_2 pressure conditionin control gas sorption and permeation,as well as the occurrence of microvoids in glassy polymeric membranes.