Layer-by-layer assembled graphene coatings on polyurethane films as He permeation barrier

Flexible barrier films that resist to gas permeation have a wide range of applications in various industrial sectors, from food packaging to electronics and aerospace. Especially for the latter, it is important to use lightweight materials that demonstrate sufficient diffusion resistance. Thermoplastic Polyurethane (TPU) films are widely used in this sector, as they combine flexibility, elasticity and chemical resistance. Nevertheless, their inherent permeability to gases is a major drawback that needs improvement. In the present work, we prepare stacks of chemical vapor deposited (CVD) graphene films, via a facile transfer method and layer-by-layer assembly, which are then deposited on TPU films as coatings. Raman and transmittance spectroscopy measurements are carried out to monitor the deposition of graphene on the TPU membrane. The graphene /TPU membranes exhibit reduced gas diffusion properties towards He permeation by 9.9 % with respect to bare TPU. By increasing the number of graphene layers to five, the permeation of the graphene coatings is reduced by 25.2 %. The above performance is attributed to the intrinsic nature of the mixed order-stacked graphene layers, which prevents local defects from coincidence, thus decreasing the leakage of the He gas through the film. This work indicates a novel promising approach towards the preparation of graphene-based gas-barrier coatings, that can be of interest for numerous applications.