Aggregation of azo dye Orange I induced by polyethylene glycol in aqueous solution

The aggregation behavior of azo dye Orange I by the addition of polyethylene glycol (PEG) in aqueous solution has been studied by means of UV–vis spectroscopy. The spectroscopic results show that J-aggregates of Orange I are formed in presence of high volume fraction of PEG with low molecular weight (200, 400 and 600), evidenced by large red shifts of the absorption band. The degree of aggregation strongly depends on the PEG molecular weight and concentration, as well as the ionic strength of the solutions. The effects of cationic surfactant cetyltrimethylammonium bromide (CTAB), nonionic surfactant polyoxyethylene (20) sorbitan monolaurate (Tween 20) and a series of water-miscible organic co-solvents on the absorption spectrum of Orange I are also investigated. The mechanism of the aggregation is discussed in terms of the noncovalent intermolecular interactions.