Gas transport behaviors of oxygen (O(2)), nitrogen (N(2)) and propylene (C(3)H(6)) in polydimethylsiloxane (PDMS) mixed matrix membranes (MMM) containing modified silica (SiO(2)) nanoparticles are presented. Two surface modified SiO(2) nanoparticles, silica dimethyloctyl silane (Si-DMOS) and silica dimethylphenyl silane (Si-DMPS), were used as fillers. Surface modification was carried out through silanization, which was confirmed via Fourier transform infrared spectroscopy. From elemental analysis, degrees of modifications on Si-DMOS and Si-DMPS were estimated to be 29.64% and 79.89%, respectively. Field emission scanning electron microscopy showed uniform distribution of the modified SiO(2) fillers in MMMs. Both MMMs exhibited reduced O(2) and N(2) permeabilities as compared to pure PDMS, while enhanced C(3)H(6) permeabilities were observed. Consequently, C(3)H(6)/N(2) permselectivities were increased by 35 and 44% in MMMs filled with Si-DMOS and Si-DMPS, respectively. Results revealed that permeability was dependent on penetrant diffusivities, a parameter related to the structure of MMMs. Density measurements and differential scanning calorimetry were performed to elucidate the changes in MMM properties which affected the permeation behaviors of O(2), N(2) and C(3)H(6). Overall, both Si-DMOS and Si-DMPS show potential as fillers for the enhancement of PDMS permeation performance. (C) 2011 Elsevier B. V. All rights reserved.