Researchers from ETH Zurich and LG Electronics developed a stable porous membrane made from only 2 layers of graphene. They say that this is the thinnest possible porous membrane that is technologically possible to make.
The new membrane can be used as a filter for several different purposes - such as waterproof clothing. In fact the researchers say that their membrane will be a thousand fold more breathable than Goretex! Other applications may include water filteration and gas and liquid flow rate measurements.
To produce the membrane, the researchers developed a technique called focused ion beam milling to etch pores into the graphene film. The helium (or gallium) beam is controlled with a high level of precision in order to etch away material. The researchers were able to etch pores of a specified number and size into the graphene with unprecedented precision. The researchers tweaked the process so it took them only hours to make the membrane - down from several days.
Two layers of graphene are required because the graphene is not perfect and some atoms are missing. With a two-layer graphene, the probability of two defects settling directly above one another is extremely low. But at two layers the membrane is still very thin of course - which means its permeation resistance is very low - and so it is more efficient at filteration (i.e. very little energy is required).
Currently the researchers developed a membrane that is less than one-hundredth of a square millimeter in size. They are now attempting to create larger membranes - and they are also working on further improvement to the manufacturing process.