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

Layer-by-Layer (LbL) assembled films offer many interesting applications (e.g., 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%.