The effect of a MFI membrane nanostructure change on n-hexane/2,2-dimethylbutane (DMB) permeation is described. ne figure shows a) DMB transporting through the defects in an empty membrane, b) DMB permeation is blocked due to the initial defects closing by crystal expansion by n-hexane, c) both n-hexane and DMB permeation are blocked when the membrane is exposed to DMB first. The pores shrink and trap DMB so that almost all transport is blocked.