Defect free, mono-layer, continuous & free standing graphene film should be impremeable.. but graphene oxide bucky paper (the so-called ) is water permeable and Helium impermeable.. see this paper from Geim group: http://arxiv.org/ftp/arxiv/papers/1112/1112.3488.pdf
No thanks, please feel free to ask me on other books if you need them, may be they are available, I am not a specialist in your field of research, it is just the scientific curiosity. Regards