Ultrathin (< 100 nm) and transparent composite films created by the alternate layering of water-soluble polymers and clay platelets (1 nm thick and 200 nm diameter) are useful for a variety of packaging applications, such as the protection of food and flexible electronics (e.g., displays). Inorganic oxides or bulk polymer composites, suffer from cracking when flexed and poor transparency, respectively. Layer-by-layer (LbL) assembly of polyethylenimine (PEI), poly(acrylic acid) (PAA), PEI, montromillonite (MMT) clay quadlayers (QL) produces a nanobrick wall structure (with clay as impermeable bricks and the polymer as mortar). Flexible and transparent films as thin as 51 nm require only 4 clay layers (12 total layers) to achieve an oxygen permeability below that of SiOx or metalized plastic film. These extremely low oxygen permeability films could improve the shelf life of food products and operational lifetime of flexible organic light-emitting diodes (FOLEDs).  Additionally, these films exhibit size selective behavior that suggests they could be used to purify hydrogen or helium.  Thicker versions of these films actually exhibit some barrier to these very light gases, reducing the helium transmission rate by 100X relative to uncoated PET film.

Gas barrier and separation ability of nanobrick wall multilayer thin films

248th National Meeting (2014)

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