Adsorption behaviors of methyl orange to alternate polyion films as studied by in-situ absorption and second harmonic generation measurements

In-situ second harmonic generation (SHG) and total reflection absorption techniques were applied to the studies of the adsorption process of methyl orange at the polyion layer formed on the surface of a glass prism. In the case of poly(diallyldimethyl ammnoium chloride) (PDDA), adsorption isotherms obtained from the both techniques were well fitted to the Langmuir model, implying the same degree of noncentrosymmetric alignment during the adsorption process. As to poly(allylamine)hydrochloride (PAH), on the other hand, the both data resulted in different adsorption profiles; the Langmuir model was used for the absorption data, while the Brunauer–Emmett–Teller (BET) model for the SHG results.