Thin films of amphiphilic polyelectrolytes. Soft materials characterized by Kelvin probe force microscopy

Hydrophobically modified amphiphilic polyelectrolyte films derived from poly (maleic anhydride-alt-styrene) containing hydrophobic aryl-alkyl type side chains such as phenyl-ethyl, phenyl-butyl, naphthyl-ethyl and naphthyl-butyl were studied by Kelvin probe force microscopy. These films were adsorbed from polyelectrolyte solutions at 0.001 mol/L and 0.1 mol/L NaCl onto silicon wafers modified with 3-aminopropyltrimethoxysilane. At high ionic strength, the work function was dependent on the hydrophobic character of the side chain. At low ionic strength this behavior was determined by the spacer group in the side chain. The fractal analysis of the films indicated self-affinity surfaces whereas the fractal dimensions of the surface topography follow a similar trend as the electronic work function with the ionic strength. This behavior can be explained by the increasing hydrophobic character of the side chain with naphthyl moieties. Relationship between the molecular structure and the fractal dimensions with the work function of the adsorbed polyelectrolytes was found.