Gas permeability, solubility and diffusivity in 1,2-polybutadiene containing brookite nanoparticles

Brookite (i.e., titanium dioxide) nanoparticles having a nominal diameter of 3 nm were dispersed in 1,2-polybutadiene (PB) via solution processing to form polymer nanocomposites. Atomic force microscopy and scanning transmission electron microscopy were used to characterize particle dispersion. A significant population of nanoparticle aggregates exhibited characteristic dimensions below 50 nm. However, some aggregates were over 1 μm in size. At high nanoparticle loadings (e.g., 27 nominal volume percent TiO₂), the permeability coefficients of CO₂, CH₄, N₂ and H₂ were more than 3 times higher than that in unfilled PB, which is opposite to the trend typically observed when impermeable particles are added to rubbery polymers. Gas solubility coefficients generally increased with increasing particle loading, whereas diffusion coefficients decreased with increasing particle loading. Therefore, the increase in permeability was due to an increase in gas solubility upon incorporating highly sorbing nanoparticles into the polymer. Interestingly, there was virtually no change in pure gas selectivity in the nanocomposites as compared to unfilled PB.