Effect of support on rejection

Generally, a membrane is a composite and is made by forming a skin layer on a support. Then, the support will also affect the rejection, since the support affects the ion flux. In practical terms, however, the effect of support on membrane performances is almost always neglected. In this paper, the effect of support on the rejection is theoretically discussed to find a better structure of support for higher rejection. As the results, it is found that the thicker support is better for higher rejection in the system where the ion flux due to the ion migration is higher than the ion flux due to the solvent drag. On the other hand, if the ion flux due to the ion migration is lower than the ion flux due to the solvent drag, the thinner support is better for higher rejection.

The effect of support on the rejection was theoretically discussed keeping the parameters for the skin layer constant. As the results of discussion, it is found that it is very important to make the ion flux due to the ion migration lower than the ion flux due to the solvent drag to get a higher rejection. It is also found that the ion flux due to the ion migration decreases with the thickness of support, while the ion flux due to the solvent drag increases. Then, in the system where the ion flux due to the ion migration is higher than the ion flux due to the solvent drag, the thicker support is better for higher rejection. On the other hand, if the ion flux due to the ion migration is lower than the ion flux due to the solvent drag, the thinner support is better for higher rejection.