Effects of Surfactants and Various Additives on the Fluorescence Behavior of Fluorescent Whitening Agents

Abstract

The effects of surfactants and a variety of additives on the fluorescent behavior of four fluorescent whitening agents were investigated at 20°C. The used surfactants were two cationic (HDPC, HDAB), two anionic (SDBS, SDS), and a non-ionic ones (B-35). The main additives were alkylpyridinium salts, alkylammonium salts, and cyanoolefins. The surfactants had a remarkable influence on the fluorescence intensity and the maximum fluorescence wave length. In general, the intensity increased sharply with an increase in concentration above cmc, regardless of the ionic properties of the surfactant micelles. However, in the HDAB solution, the intensity for some anionic fluorescent agents decreased first with an increase in concentration of HDAB, and then increased with an increase in concentration above cmc, and in HDPC solutions the intensity for all fluorescent agents only decreased monotonously. It was found that these rather complicating changes in fluorescence intensity depended on the extent of electrostatic, and hydrophobic interactions of the fluorescent agents with micelles as well as the ionic properties of the surfactants. In addition, disappearance of the fluorescence intensity due to HDPC was discussed in terms of the energy transfer from the fluorescent agents to HDPC in the favorable molecular arrangement. Concerning additives, pyridinium salts always decreased the intensity. This observation also supported the above interpretation.