Properties of 4-octadecyloxy-1-naphthoic acid in micellar solutions and in monolayer films adsorbed onto silica attenuated total reflectance plates

Abstract

The pH titration characteristics of 4-octadecyloxy-1-naphthoic acid (ONA) in micellar solution and in monolayer films adsorbed onto silica plates have been studied by convential UV absorption and fluorescence methods and by attenuated total reflectance spectroscopy. In micellar solution interfacial potentials were determined and compared with another lipoidal potential probe, 7-hydroxy-4-heptadecylcoumarin. Titration curves of ONA in adsorbed mixed monolayer films showed markedly different characteristics from those in micellar systems. Large hysteresis effects and very high pKa values were observed. The results have been analyzed in terms of ONA aggregate formation and the surface movement ..