Ultrathin self-assembled polymeric films on solid surfaces. III. Influence of acrylate dithioalkyl side chain length on polymeric monolayer formation on gold

Abstract

Self-assembled films of acrylate polymers containing dithioalkyl side chains of varying lengths have been fabricated on gold substrates by adsorption from dilute organic solution. Anchoring alkyl side chain types studied include lipoate (n=4), pentyl dithioundecanoate (n=10), pentyl dithiopalmitate (n=15), and pentyl dithiotricosonate (n=22), where n represents the number of methylene units in the longer arm of the asymmetric disulfide side chain. Comprehensive characterization of polymer monolayers by x-ray photoelectron spectroscopy and reflection Fourier transform infrared spectroscopy showed improved order for structural assemblies of C11 (n=10) side chain polymer monolayers, over shorter and longer side chain polymer analogs, due to a higher percentage of bound thiolate anchors. Monolayer thicknesses range from 20 to 40 Å, primarily depending on side chain length and density along the polymer backbone. Cyclic voltammetry on gold electrodes shows that longer side chain polymer monolayers possess more structural defects resulting from considerable disorder in the films. Despite the less organized structural features for these polymer monolayers, their selective adsorption onto gold via specific side chain terminal disulfide anchors on microlithographed substrate patterns creates well-resolved surface-modified microstructures comparable to those from monomeric analogs, as shown by scanning Auger mapping.