Specific effects of the counterion type and concentration on the construction and morphology of polycation/azo dye multilayers

The growth and properties of the polycation/azo dye multilayer thin films as a function of specific effects of the counterion (Cl−, Br−, SO42−), and the counterion concentration on the polycation conformation, the pure dye being always adsorbed from salt-free aqueous solution, have been investigated. A strong polycation containing 95 mol% of N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the backbone and the azo dye Direct Red 80 were used as building blocks. An almost linear increase of the absorbance at 558 nm and of the layer pair thickness, measured by spectroscopic ellipsometry in wet state, with the increase of the layer pair number, were observed for all electrolytes. The specific effects of counterion type and concentration have been manifested in the amount of the dye adsorbed on each polycation layer, the thickness of the layer pair, and the surface morphology.