ABC triblock terpolymers containing polylactide, poly(dimethylacrylamide) and polystyrene, which can self-assemble as aligned cylinders, are etched to give nanoscopic pores. The diffusion of gases through these pores is quantitatively consistent with Knudsen diffusion. The flow of water liquid in the pores is consistent with the Hagen-Poiseuille law. If these polymers can be produced as commercial ultrafiltration membranes, they should give a larger hydraulic permeability and a sharper molecular weight cut-off. (c) 2006 Elsevier B.V. All rights reserved.