ATR Study of the Ionizing Characteristics of 4-Heptadecyl-7-hydroxycoumarin in Cast Monolayer Films

Abstract

UV ATR spectroscopy has been used to investigate the pH titration characteristics of cast monolayer films of 4-heptadecyl-7-hydroxycoumarin. At high charge densities (>8 μC/cm2) the pH titration characteristics of the ionizing surface film resemble the profile generated from simple Gouy-Chapman (GC) theory. At low charge densities (<8 μC/cm2) significant deviation from GC theory is observed—minima in the measured pKa vs. surface charge density plots were obtained. Titrations conducted on monolayers which had been cast under a variety of conditions produced virtually identical results, implying that titration minima were not due to peculiarities in the physical character of the cast film. We ..