Layer-By-Layer Approach for Obtaining Highly Oriented Kaolin Platelets on Surfaces

The low cost and high aspect ratio of kaolin has garnered attention toward its application as an oxygen barrier coating. The challenge associated with achieving oxygen barrier properties is, however, obtaining aligned kaolin platelets. We report a simple layer-by-layer (LBL) approach for obtaining highly oriented kaolin films on glass, silicon, and 304 steel substrates. The process involves sequential deposition of the substrates into suspensions containing cationic and anionic kaolin particulates. The cationic kaolin suspensions were generated by a slow addition of a dilute kaolin suspension into a highly concentrated solution of polydiallydimethylammonium chloride cationic polymer. This led to a stable suspension of kaolin particles with equal particle size but opposite sign of the zeta potential to that of the "as received" kaolin particles, which are inherently slightly anionic. To generate an anionic suspension of kaolin particles with enhanced anionic charge, the "as received" anionic kaolin particles were added to a solution containing sodium polyacrylate. This produced a kaolin suspension with a larger negative zeta potential and particle size comparable in magnitude to those of the cationic kaolin suspension. It is shown that this LBL approach provides a means of achieving controlled amounts of highly oriented kaolin particles deposited on various substrates. Analysis using SEM, IR spectroscopy, and X-ray diffraction (2θ scans and rocking curves) provided evidence of the kaolin platelets lying parallel to the various substrates.