Effect of polyelectrolyte on the barrier efficacy of layer-by-layer nanoclay coatings

The development of effective barrier materials is becoming increasingly important, particularly as microelectronic devices and food supplies must be protected for extended periods of time from atmospheric gases and water vapor. One of the most effective, facile, eco-friendly, and inexpensive strategies introduced in this spirit is the sequential buildup of layer-by-layer (LBL) surface coatings. This technology relies on the repeated, alternating deposition of impermeable nanoclay platelets possessing a large diameter-to-thickness aspect ratio and a polyelectrolyte adhesive. Previous studies have focused extensively on the use of polycations for this purpose since they are attracted by the negative charges inherently present on the face of natural nanoclays, such as montmorillonite (MMT). In this work, we compare the barrier properties of LBL coatings prepared with a common polycation and a polyester-based polyanion, which selectively interacts with the positive charges that accumulate on the edges of nanoclay platelets. Deposition of these coatings on a hydrophobic styrenic copolymer is reported here to promote dramatic reductions in the measured permeabilities of oxygen and carbon dioxide. This study, which systematically explores the dependence of single-gas permeability on factors such as MMT suspension concentration, bilayer (BL) coating number and temperature, aims to expand the understanding of LBL coatings by also elucidating morphological considerations.