Nanoprotective Layer-by-Layer Coatings with Epoxy Components for Enhancing Abrasion Resistance: Toward Robust Multimaterial Nanoscale Films

Abstract

Layer-by-Layer (LbL) assembled films offer many interesting applications (<i>e.g.</i>, in the field of nanoplasmonics), but are often mechanically feeble. The preparation of nanoprotective films of an oligomeric novolac epoxy resin with poly(ethyleneimine) using covalent LbL-assembly is described. The film growth is linear, and the thickness increment per layer pair is easily controlled by varying the polymer concentration and/or the adsorption times. The abrasion resistance of such cross-linked films was tested using a conventional rubbing machine and found to be greatly enhanced in comparison to that of classic LbL-films that are mostly assembled through electrostatic interactions. These robust LbL-films are then used to mechanically protect LbL-films that would completely be removed by a few rubbing cycles in the absence of a protective coating. A 45 nm thick LbL-film composed of gold nanoparticles and poly(allylamine hydrochloride) was chosen as an especially weak example for a functional multilayer system. The critical thickness for the protective LbL-coatings on top of the weak multilayer was determined to be about 6 layer pairs corresponding to about only 10 nm. At this thickness, the whole film withstands at least 25 abrasion cycles with a reduction of the total thickness of only about 2%