Interactions between some anionic dyes and cationic surfactants with different alkyl chain length studied by the method of continuous variations

Abstract

The method of continuous variations was used to investigate the interactions of anionic dyes C.I. Acid Orange 7 (AO7) and C.I. Acid Red 88 (AR88) with cationic surfactants: N-cetylpyridinium chloride (CPCl), N-dodecylpyridinium chloride (DPCl), N-decylpyridinium chloride (DecPCl) and octadecyltrimethylammonium bromide (OTMABr) in aqueous submicellar solutions. With the increasing alkyl chain length of surfactants and with increasing number of benzene rings of dyes, the interactions become stronger, which shows the importance of hydrophobic forces. Electrostatic interactions also play an important role, as shown by the effect of KCl on the binding process. Two methods for determining the formation constants, Schaeppi–Treadwell's and Schwarzenbach's methods, are described in this paper.