Stepwise assembly of ultrathin poly(vinyl alcohol) films on a gold substrate by repetitive adsorption/drying processes

Ultrathin poly(vinyl alcohol) (PVA) films were fabricated on a gold substrate by a repetitive process based on physical adsorption from aqueous solution in the presence of NaCl and subsequent drying. A quartz crystal microbalance (QCM) was used to analyze the assembled amount quantitatively. The assembled amount increased with increasing NaCl concentration and solution temperature, indicating the adsorption possibly occurred due to the hydrophobic effect. Reflection absorption spectroscopy (RAS) measurement showed that hydroxyl groups in assembled PVA formed hydrogen bonds. The assembled amount was also increased with increasing PVA concentration and molecular weight. Atomic force microscopy (AFM) revealed that the mean roughness for an ultrathin PVA film was 2.5 nm, which was comparable to 1.8 nm for a bare QCM surface. The fabrication process was applied to other polymers and to alternating assemblies between PVA and the polymers. We demonstrated a novel approach for easy fabrication of ultrathin films of noncharged polymers possessing inter- and/or intramolecular assembly properties in the dried state.