Formation and characterization of self-assembled films of thiol-derivatized poly(dimethylsiloxane) on gold

Poly(dimethylsiloxane) (PDMS) copolymers containing propanethiol side chain "stickers" for forming self-assembled films on gold surfaces have been studied by various experimental techniques including ellipsometry, contact angle measurements, FT-IR, angle-dependent XPS, and ToF-SIMS. The results show that the thiol-containing side chains do not all chemisorb to the gold surfaces. In addition, the concentration of these sticker units was found to have a dominant effect on the polymer film thickness, the surface wetting properties, and the orientation of the PDMS backbone. Ab initio calculations reveal that the IR-active PDMS Si-O stretching bands can be used as indications of chain orientation, and a comparison of the calculated spectra with grazing incidence reflection IR data shows that the self-assembled PDMS backbone is predominantly aligned parallel to the surface, plausibly as a result of the chemisorption.