Conductometric studies of the interaction of CI Reactive Orange 16 with cationic alkyltrimethylammonium bromide surfactants

The interactions between an anionic dye, C.I. Reactive Orange 16 (RO16) and the cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (CTAB) were studied using a conductometric method. The specific conductance of dye-surfactant mixtures was measured at five different temperatures. The equilibrium constants and other thermodynamic functions for the process of dye-surfactant ion pair formation were calculated on the basis of two theoretical models. The results showed that an increase in temperature reduces the tendency for ion pair formation as equilibrium constants decrease with increasing temperature. According to results, the surfactant which contained the longer hydrophobic chain had a stronger tendency to associate with the dye and the equilibrium constants were considerably higher than those measured for the surfactant with the shorter hydrophobic chain. These results indicate that short range, non-electrostatic interactions have a significant influence on dye-surfactant ion pair formation as well as long range electrostatic forces. (c) 2005 Elsevier Ltd. All rights reserved.