In designing mixed-matrix membranes (MMMs), inorganic fillers such as titanium (IV) oxide (TiO2) nanoparticles are commonly added because of their excellent intrinsic properties and high affinity toward CO2. However, the addition of TiO2 nanoparticles causes formation of agglomerates because of their high surface energy and van der Waals forces. In this study, MMMs comprising caged hybrid framework, i.e., octaisobutyl polyhedral oligomeric silsesquioxane (OPOSS) incorporated with TiO2 nanoparticles were developed by phase inversion technique. The effectiveness of OPOSS as a dispersant was determined by using qualitative and quantitative methods. Based on the findings, OPOSS successfully enhanced the dispersion of TiO2 nanoparticles as it reduced the surface energy of TiO2 nanoparticles. The optimum amount of TiO2-OPOSS in the tetrahydrofuran/dimethylacetamide casting solution was at 4 wt TiO2 and 2 wt OPOSS based on qualitative and quantitative analyses. At 4/2-T/OPOSS MMM, the elemental mapping showed uniform dispersion of TiO2 nanoparticles without formation of large agglomerates. In addition, the free-space length and d-metric value were the lowest for 4/2-T/OPOSS, which implied that this membrane has the highest degree of particles' dispersion and distribution. Hence, the optimum CO2/CH4 gas selectivity performance was achieved by 4/2-T/OPOSS. © 2019 Académie des sciences