The micro structure of various novel polyelectrolyte complex membranes (PECMs) was investigated by means of molecular dynamics (MD) simulation and positron annihilation lifetime spectroscopy (PALS). These PECMs that differed in their chemical structure design were applied to dehydrate a 90 wL% ethanol aqueous solution by pervaporation, and their separation performance was correlated with their microstructure. Free volume size and free volume size distribution were determined both by the PALS and MD simulation techniques. To describe the free volume shape and the polymer chain flexibility and stiffness. MD simulation analysis in terms of radial distribution function and mean square displacement was also conducted. Results obtained from PALS and those from MD simulation were in agreement with each other. These results were highly consistent with the chemical structure of the PECMs designed in this study and were demonstrated to correlate well with the membrane pervaporation separation performance. (C) 2013 Elsevier B.V. All rights reserved