Direct Preparation of Ultrathin Polymer Membranes on Porous Substrates for the Separation of Helium From Methane

Ultrathin polymer membranes on porous substrates exhibit excellent gas and ion permeability and have important applications in many fields, such as membrane separation and batteries. However, there is still a lack of facile and general methods for the direct preparation of ultrathin polymer membranes on porous substrates, especially from polymer solutions. Within this work, a new strategy to fabricate centimeter-size ultrathin polymer membranes (thickness down to 16 nm) is presented directly on porous supports by using the liquid-liquid interfacial spin-coating technique. The method allows the preparation of ultrathin polymer membranes with a wide range of polymers, and the membranes are smooth and intact without cracks. The helium/methane separation performance is evaluated. As the membrane thickness increased from 40 to 180 nm, the He/CH₄ selectivity increased and then decreased. The ultrathin membrane provides a good He/CH₄ selectivity of 8.8 and He permeance of 1 × 10⁵ GPU, which is the highest value reported so far and more than 150 times higher than that of membranes with He/CH₄ selectivity above eight in the literature. This new approach provides the possibility to explore the great potential of ultrathin membranes for separation.