Deposition of ultrathin polymeric multilayers down to the Ångström level

Abstract

Polymer layers on surfaces have a high relevance in both academic and technical systems. Deposition of polymers on surfaces is either spontaneous or can be achieved unselectively by evaporation of the solvent. Here we report the regioselective deposition of ultrathin polymer films from aqueous solution by local mechanical energy input. We demonstrate that water soluble polymers can be literally nailed – or, rather, ironed – onto a silicon wafer surface by the mechanical impact of an atomic force microscope (AFM) tip. Each layer has a controllable height from 10 nm down to a few Ångströms. Moreover, we demonstrate that it is possible to stack multiple layers of equally charged polycarboxylate chains and their counterions, in contrast to the alternating deposition of anionic and cationic polymers by the well-known layer-by-layer (LBL) technique. Although the polymer used in this study is water-soluble, the layers do not re-dissolve again. As a tentative explanation, we suggest that the longevity of the multilayers must be caused by chemisorption in combination with an unfavorable entropy penalty upon dissolution of the polymers fixed to the surface.