Dependence of the aggregation mode of two bidentate azo dyes in polycation/dye multilayers on the dye structure and the polycation conformation

Abstract

In this paper we report the growth particularities of some polycation/azo dye multilayers built up by the alternate adsorption of one polycation with quaternary ammonium salt groups in the backbone (95 mol % of N,N-dimethyl-2-hydroxypropyleneammonium chloride repeat units) (PCA5) and two bidentate azo dyes which differ from each other only by the position of sulfonic groups, Crocein scarlet MOO (CSMOO) and Ponceau SS (PSS). The multilayer build up was monitored by UV—vis spectroscopy. The polycation/azo dye binding mode in the multilayer depended on both the dye structure and the polycation conformation. H-aggregation was suggested for CSMOO, PCA5 being adsorbed from both saltless aqueous solution and 0.2 M low-molecular-weight salt (NaCl and Na2SO4) aqueous solution, while for PSS H-aggregation seemed to occur only when PCA5 was adsorbed from saltless aqueous solution. J-aggregation of PSS on the surface was suggested when PCA5 was adsorbed from 0.2 M Na2SO4 aqueous solution. The aggregation mode of the dye in the multilayer was correlated with the PCA5/dye interaction mode in the aqueous solution. Electrokinetic measurements were used to verify the dependence of the driving force for the PCA5/azo dye multilayer growth and the multilayer stability on the dye structure.