Layer-by-Layer Assembly of Multifunctional Thin Films - Overview
Texas A&M University, US
Keywords: layer-by-layer assembly, nanoparticles, polymers, conductive films, barrier films
Abstract:A variety of thin, functional coatings can be produced using layer-by-layer (LbL) assembly. Thin films, typically < 1µm thick, are created by alternately exposing a substrate to positively- and negatively-charged molecules or particles in water. This deposition process is repeated until the desired number of “bilayers” (or cationic-anionic pairs) is achieved. Several functionalities (electrically conductive films made with carbon black [or PEDOT] and oxygen barrier films made with clay) are described here. Coatings made from poly(acrylic acid) and polyethylenimine stabilized carbon black are able to achieve a sheet resistance of 500 ohm/square with a thickness of 5.4 mm. Even greater conductivity and transparency is achieved when poly(ethylene dioxythiophene), doped with poly(styrene sulfonate), is used in place of carbon black. These PEDOT-based assemblies can be protected from UV degradation by layering in UV absorbers such as TiO2 nanoparticles. Coatings of sodium montmorrilonite clay and cationic polyacrylamide, that are less than 600 nm thick, have been produced with an oxygen transmission rate below 0.005 cm3/m2 day. These thin, transparent composites are a good candidate for foil replacement in food packaging and flexible electronics packaging. Some intial results and future work using this clay-polymer nano brick wall structure as a flame retardant coating for foam will also be mentioned.