Layer -by -layer assembly of clay-filled polymer nanocomposite thin films

Abstract

A variety of functional thin films can be produced using the layer-by-layer\nassembly technique. In this work, assemblies of anionic clay and cationic polymer were\nstudied with regard to film growth and gas barrier properties. A simple, yet flexible\nrobotic dipping system, for the preparation of these thin films, was built. The robot\nalternately dips a substrate into aqueous mixtures with rinsing and drying in between.\nThin films of sodium montmorillonite clay and cationic polymer were grown and studied\non poly(ethylene terephthalate) film or a silicon wafer. After 30 clay polymer bilayers\nwere deposited, the resulting transparent film had an oxygen transmission rate (OTR)\nbelow 0.005 cm3/m2/day/atm. This low OTR, which is unprecedented for a clay-filled\npolymer composite, is believed to be due to a ?brick wall? nanostructure comprised of\ncompletely exfoliated clay bricks in polymeric ?mortar?. The growth of polymer and clay\nassemblies is then shown to be controlled by altering the pH of polyethylenimine (PEI).\nGrowth, oxygen permeability, and mechanical behavior of clay-PEI assemblies were\nstudied as a function of pH in an effort to tailor the behavior of these thin films. Thicker\ndeposition at high pH resulted in reduced oxygen permeability and lower modulus, which\nhighlights the tailorability of this system.