Dual Aspect Ratio Vermiculite−Laponite Layer-by-Layer Assembled Nanocomposites for Improved Barrier and Water Resistance

Layer-by-layer nanocomposite thin films consisting of polyelectrolytes and high-aspect-ratio nanoclays are known to exhibit outstanding oxygen barrier performance. They also provide additional desirable properties such as environmentally benign processing, substrate conformity, mechanical ductility, and optical transparency. Despite these advantages, layer-by-layer (LbL) deposited nanocomposites suffer from extreme water sensitivity, leading to dramatically increased oxygen transmission under humid conditions, as well as poor water vapor barrier performance. Past research has demonstrated the tendency of ultrahigh-aspect-ratio nanoplatelets to deposit imperfectly, forming defect sites that act as permeation highways and result in worsened barrier performance relative to predictions. In this work, a second, lower-aspect-ratio nanoplatelet, laponite, is incorporated after the deposition of high-aspect-ratio (the ratio of diameter to thickness) vermiculite, in combination with cationic polyethylenimine, in order to fill defect sites, increasing permeation tortuosity and film density to improve the water vapor barrier and humid oxygen barrier. The resulting “trilayer” assemblies display a 36% reduction in water vapor transmission and more than double the oxygen barrier retention at 100% relative humidity relative to control “bilayer” films that do not include the smaller laponite clay. This study demonstrates a simple yet powerful pathway for improved water resistance of LbL-assembled nanocomposite barriers by incorporating nanoplatelets of multiple aspect ratios.