Preparation of large, ultra-flexible and free-standing nanomembranes of metal oxide–polymer composite and their gas permeation properties

In this work, fabrication of free-standing nanomembranes of metal oxide (MO_x) and polymers by simple spin-coating method is discussed. First, double-layer nanomembranes containing MO_x and epoxy resin of polyethyleneimine and poly[(o-cresyl glycidyl ether)-co-formaldehyde] were prepared. Free-standing nanomembranes were successfully prepared, but defects formed in the metal oxide nanolayer during sharp bending of the nanomembrane. To overcome fragility of MO_x nanolayer, poly(vinyl alcohol) nanolayers were introduced between MO_x nanolayers by layer-by-layer (LbL) assembly process. The LbL nanomembrane was also free-standing and was highly flexible during macroscopic membrane manipulations. Even after transfer of the LbL nanomembrane onto a porous support, it did not have apparent cracks, confirmed by scanning electron microscopy (SEM). The LbL nanomembrane sustained low gas permeance, confirming the absence of significant defects, although it shows excellent flexibility. We believe that the presented LbL nanomembrane could be a platform useful for the design of molecular nanochannels, which is the next challenge for efficient gas separation.