Nano-voids in epoxy resins: Role in the transport of light gases

Epoxy membranes with same chemical structure but different free volumes were prepared using aliphatic epoxide and polyether diamines as cross-linking agents. Their fractional free volume fhðTÞ was previously evaluated as a function of temperature and cross-linking density [P. N. Patil et al., Phys- ChemChemPhys 18 (2016) 3817e3824]. Original H2 permeation measurements were performed changing sample temperature and network structure and compared with CO2 and N2 transport data. Modelling gas permeability F in the framework of the free volume theory we observe that the Arrhenius-type behavior of F for test gases is consequence of the fhðTÞ linear increase with temperature and that at equal fh value membranes exhibit increasing F values by decreasing the cross-linking density. Analysis of permeability data on this set of test molecules with different size and condensation properties suggests that increasing the cross-linking between polymer chains limits their thermal fluctuations and the redistribution of the free volume elements where diffusional jumps of penetrant molecules occur