Clay-Polymer Nanolayers Improve Gas-Barrier Films

A composite sheet composed of alternating nanolayers of clay and polymer could provide improved transparent and flexible gas-barrier films to protect electronics, food, and pharmaceutical products, report Morgan A. Priolo, Daniel Gamboa, and Jaime C. Grunlan of Texas A&M University (ACS Appl. Mater. Interfaces, DOI: 10.1021/am900820k). Currently, such films are made from inorganic oxides, which are prone to cracking, and bulk clay-polymer composites, which offer poor transparency and serve as only a weak barrier to gases such as oxygen in the air. Grunlan and colleagues tried a new approach by layering sodium montmorillonite clay platelets with branched polyethylenimine, tuning the thickness of the polymer layers by adjusting the pH of the solution. The researchers liken the structure of the films to that of a brick wall, with the clay platelets as the bricks and the polymer as the mortar. A film of 70 clay-polymer bilayers, 231 nm thick when prepared at pH 10, remains flexible and transparent and has oxygen permeability lower than that reported for other clay-polymer composites, the researchers say. Grunlan’s group is working toward developing gas barriers with fewer layers to make the composite sheets even more attractive for commercial applications.