Effect of supermolecular structure on transport phenomenon in polymeric membranes

experimental data pertinent to the free volume approach are presented.

The positron lifetime measurements performed on vinyl polymers showed that the free volume of the amorphous phase varied with the pendant group change. The transport phenomena depend on both the free volume and the mobility of the segments creating the supermolecular structure of the membrane. The former factor seems to play a dominant role at temperatures much lower then Tg. The relaxation process is very slow, then the polymer structure behaves as if it were very rigid locally. A penetrant molecule is not able to swell the cavities which are necessary for the creation of the paths/channels for the transport. The fluidity of the chains is very important when the transport through the membrane takes place at temperatures much above Tg. Moreover, we should distinguish between both the fraction of the amorphous phase that gives better description of relaxation and transport phenomenon. Sometimes the transport occurs in either the ‘real’ or the ‘ordered’ amorphous regions. It means that the diffusion in the membrane depends on the local supermolecular structure. It is tempting to believe that the new formula and the new approach to the transport process of molecules through the membrane will advance the theoretical understanding of such a process. Also, it will allow better modelling of the membranes for utility purpose.