Interactions of sulforhodamine B or ethyl eosin (as the anionic dye) with cetylpyridinium bromide (as a cationic surfactant) have been investigated by visible spectroscopy in aqueous solution. The object of research is the association between an anion of dye and of cationic surfactant in aqueous solutions and its features. Computer simulation of these interactions was carried out with the use of AM1 and PM3 semi-empirical methods. A new spectrophotometric method was developed for determination of critical micelle concentration of cationic surfactants.

Interactions of sulforhodamine B or ethyl eosin (as the anionic dye) with cetylpyridinium bromide (as a cationic surfactant) have been investigated by visible spectroscopy in aqueous solution. The object of research is the association between an anion of dye and of cationic surfactant in aqueous solutions and its features. Computer simulation of these interactions was carried out with the use of AM1 and PM3 semi-empirical methods. A new spectrophotometric method was developed for determination of critical micelle concentration of cationic surfactants.

The association of cationic dye (pinacyanol, PC) with anionic dyes (ethyleosin, EE, or rhodamine 200 C, R200C), and also the interaction “dye+surfactant” has been investigated in aqueous solutions by visible spectroscopy and computer simulation. Cetylpyridinium bromide (CPB), sodium dodecylsulfate (SDS) and triton X-100 (TX) were used as cationic, anionic and non-ionic surfactants respectively. The formation of “dye+surfactant” associates takes place at low dye concentrations (≥10‑6 M) and concentrations of surfactant, which are much smaller than the critical micelle concentrations (CMC). In contrast, similar concentrations (10‑6 – 10‑4 M) of small cations of tetramethylammonium or tetraethylammonium have no noticeable effect on the absorption spectra of the dye in the “dye+tetraalkylammonium salt” systems; it indicates the absence of formation of new compound between the dye and salt. The standard enthalpy of formation of “dye+dye” or “dye+surfactant” associates has been determined by AM1 and PM3 semiempirical methods. The computer simulation confirms that the formation of these associates is energetically beneficial.