Studies on the Interaction of Surface Films with Solute in Solution. II. Sorption of Dye on the Built-up Film of Stearic Acid and Barium Stearate

Abstract

Abstract The amounts of dyes sorbed on the built-up films of stearic acid and of barium stearate were measured, under varying pH of the dye solutions into which the films were immersed. It has been observed in general that the amount of sorption was greater when the molecular weight of dye became greater. Nonionic attraction such as van der Waals’ force, which is considered to be a cause of interaction between dye molecules themselves, and aggregate formation among them may also be responsible for the interaction between dye and built-up film. Such an interaction may be favored by the decreasing ionic charges of the same sign existing on dye molecule and film. Acid dyes proved to be increasingly sorbed with decreasing pH until the aggregates of dye grew so large that they fell from the interface as a precipitate. The difference in detailed behaviors for sorption of several acid dyes could be explained by the difference in the strength of repulsive force of dye ions, suppressing the attraction, as well as of van der Waals force which was considered to be largely affected by molecular weight. In the case of basic dyes, ionic attraction is additionally taken into account to explain their sorption on the film of stearic acid. This has been suggested by the correlation between the degree of ionization and sorbed amount of chrysoidine, and supported by the fact that the built-up film of barium stearate took up less crystal violet than that of stearic acid did. In the case of the sorption of amphoteric dyes, a maximum was observed in general in a pH range which is roughly in agreement with an isoelectric region of dye. Tentative explanations have been made for this phenomenon, taking account of a change in the dissolved state of dyes.