Polymer rigidification in graphene based nanocomposites: Gas barrier effects and free volume reduction

- Nanocomposite membranes with dispersed Few Layer Graphene platelets in epoxy matrix.
- Gas permeability decreases by increasing the filler content.
- Rigidification effects at the filler-matrix interface explain gas transport data.
- Free volume structure was examined by Positron Annihilation technique.
- The thickness of the rigidified interface layer was evaluated by positron data.

The gas transport properties of polymer nanocomposite membranes made of Few Layer Graphene nanoplatelets dispersed in amine-modified epoxy resins were studied by gas phase permeation analysis with H2, N2 and CO2. The gas permeability of the nanocomposites decreases with increasing filler content. Filler addition does not change the gas selectivity of the pure epoxy membrane. Positron Annihilation Lifetime Spectroscopy analysis indicates that, by increasing the filler content, the free volume structure does not change but the fractional free volume decreases. Gas transport results were explained by the formation of a constrained polymer region of thickness lif at the filler-matrix interface. The lif parameter was evaluated from the reduction of the fractional free volume of the nanocomposite samples with respect to that of the epoxy matrix. The average value of lif, ∼ 20 nm, permits to reproduce quantitatively the experimental data at all examined temperatures, filler concentration and test gas.

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