With the aim to make newly developed materials to be more industrially relevant, multi-layer composite hollow fiber membranes were molecularly designed by surface coating ultrathin layers of a poly(ethylene glycol) (PEG) containing hybrid material onto the polyethersulfone (PES) porous substrate for CO2/N-2 separation. The asymmetric PES hollow fiber substrate was prepared by a dry-jet wet spinning process. Multiple ultrathin layers of the PEG containing hybrid polymer were then coated onto the substrate by continuous coating equipment that can be readily scaled up for industrial applications. The effects of substrate characteristics, coating concentration, pre-wetting agent, number of coating and testing conditions on gas separation performance of composite membranes have been investigated and elucidated. Positron annihilation spectroscopy (PAS) was used to investigate the evolution of coating thickness. The ultimate thickness of the dense selective layer is approximately 150 nm. The membrane fabricated from a 0.5 wt% coating solution shows an impressive CO2/N-2 selectivity of 50 with the CO2 permeance of 30 GPU at 25 degrees C and 0.2 MPa (2 atm). (C) 2011 Elsevier B.V. All rights reserved.