Anomalous molecular infiltration in graphene laminates

Abstract

Graphene laminated (GL) coatings formed by stacked few layer graphene (FLG) nanocrystals were deposited on low-density polyethylene (PE) films by the mechanical rubbing technique. Molecular transport through the bilayer membrane was studied by the gas phase permeation technique by monitoring the CO₂, N₂ and ²H₂ transport fluxes in transient conditions. The results evidenced that the transport exhibited anomalous character. The experimental data could be reproduced assuming that the penetrant concentration in the GL coating, c_int(t), reached a saturation value c_s following compressed exponential kinetics c_int(t) = c_s[1 − e^{−(λ_relt)β}]. The relaxation time τ_rel = 1/λ_rel showed thermally activated behavior, and its value increased with the kinetic diameter of the penetrant molecules. The critical exponent β = 1.5 ± 0.1 for CO₂ and N₂ and β = 2.0 ± 0.1 for ²H₂ did not change with temperature. Positron annihilation lifetime spectroscopy (PALS) analysis indicated that the average cross-section (h_g) of the cavities in the GL coating exhibited comparable size to the kinetic diameter (σ_k) of the penetrant molecules. The results could be explained by assuming that the molecular infiltration in the GL structure occurred in nano-channels having distributed path lengths where the penetrant transport obeyed a configurational diffusion mechanism.