Studies on the Interaction of Surface Films with Solute in Solution. III. Effect of Dissolved Dyes upon the Monolayer of Octadecylamine

Abstract

Abstract The interaction between octadecylamine in monolayer and various dyes in aqueous substrate under varying pH was studied. Such a basic dye as chrysodine or crystal violet remarkably expanded the monolayer when pH of the solution was in a certain range on alkaline side. This has been attributed to the interactions between the molecules of dye themselves and that between dye and octadecylamine. Thus, it is mainly dipolar and van der Waals’ attraction, which was considered to be overshadowed by ionic repulsion when substrate pH was in the other region. Additional possibility of ion-dipole attraction due to the remaining charge of the monolayer was discussed in connection with the ionizations of octadecylamine and basic dyes. In contrast with this, the monolayer expanded remarkably when it was spread on an acidic solution of acid dye. The behavior could be accounted for by the sum of ionic, dipolar and van der Waals’ attraction. The possibility of the formation of colloidal aggregate of dye with which octadecylamine interacts has been discussed, in connection with the effect of metal ion in the substrate upon the monolayer of stearic acid.