Thin polymer films as sacrificial layers for easier cleaning

Abstract

We propose a new approach for the removal of fouling agents from an interface. The interface is pre-coated with a polymer layer of a few nanometers thick that can be removed by a simple trigger such as a change in pH or salt concentration. When fouling agents adsorb on the interface, they can be removed by simply desorbing (sacrificing) the polymer coating. We show a proof of principle of this concept on the basis of two different types of sacrificial layers. The first system consists of a silica surface that is pre-coated with a polyelectrolyte multilayer of poly(allyl amine) hydrochloride (PAH) and poly(acrylic acid) PAA. The outer layer of the polyelectrolyte multilayer is the positively charged PAH and on top of that silica particles are adsorbed. We investigated the release of silica particles upon a pH drop (leading to desorption of the multilayer) as a function of the number of polyelectrolyte layers in the multilayer. Four layers are already enough to significantly enhance desorption of the silica particles (70% removal). With fourteen layers (total adsorbed amount of polymer approximately 6 mg/m 2) the silica particles are completely removed. The second system consists of a weak poly(acrylic acid) (PAA) brush, coated with an extra layer of PAA. At low pH the polyelectrolytes are uncharged, and the double polyelectrolyte layer is stable. However, when the pH is increased, the polyelectrolytes become charged and the extra PAA layer is removed, including any attached fouling agents. For this system, we show proof of principle of the sacrificial layer approach by measuring the hydrodynamic force necessary to remove PS particles (radius 3 μm) from a PAA brush. We show that the hydrodynamic force for removal is two orders of magnitude lower for the sacrificial layer system (PAA brush plus extra layer of PS-PAA), than for the PAA brush alone.