We studied the effect of polar/nonpolar sequences on the structure and water transport of Nafion 117 with 20 wt.% water by molecular dynamics (MD) simulations. Although the systems show clear hydrophilic/hydrophobic segregation in all conditions studied, we observe that increased blockiness leads to better phase segregation, with the anionic moieties unevenly distributed in the interface leaving big hydrophobic patches of polymer/water contact. The vehicular diffusion of water and hydronium was not affected by the blockiness. (C) 2004 Elsevier B.V. All rights reserved.