Polyelectrolyte Adsorption onto a Surface-Confined Surfactant

Abstract

Using sodium dodecyl sulfate (SDS) as a surfactant and poly(diallyldimethylammonium chloride) (PDDA) as a polyelectrolyte, we formed a surfactant−polymer complex on a model surface of a positively charged 2-aminoethanethiol (cysteamine) self-assembled monolayer on gold. The complex formation is achieved by first SDS adsorption on cysteamine and subsequent adsorption of PDDA on the preformed SDS layer. Successful deposition of the PDDA layer on SDS without noticeable surfactant desorption shows that the complex formation is a fast process. The presence of SDS−PDDA complex on a cysteamine-modified gold substrate was observed by surface plasmon resonance (SPR) and Fourier transformed infrared spectroscopy. The thicknesses obtained from the SPR data were 1.5 nm for SDS and 1.1 nm for PDDA. Concentrations of SDS and PDDA in the parent solutions necessary to yield the complex upon adsorption were determined.