EFFECT OF CHAIN FLEXIBILITY ON SELECTIVITY IN THE GAS SEPARATION PROCESS - MOLECULAR-DYNAMICS SIMULATION

We have investigated the effect of chain flexibility on the sieving ab ility of polymers by means of a molecular dynamics simulation method. As the size of penetrants and the rigidity of chains increase, the dif fusion coefficients decrease. The more rigid chains give a greater dif ference between the diffusion coefficients of smaller and larger penet rants, which results in an improvement of selectivity. In the case of the penetrant whose size is smaller than that of the polymer segment, it is observed that the condition with an optimum selectivity and perm eability exists resulting from a competition between the effect of the redistribution of dynamic free volume and that of the amount of stati c free volume on the diffusion of penetrants. One must take both the a vailable free volume and the chain flexibility into account when desig ning a membrane for gas separation process.