A re-examination of the use of 7,7,8,8-tetracyanoquinodimethane (TCNQ) in determining the critical micelle concentrations

Summary A detailed re-examination of the use of TCNQ in ] determining the critical micelle concentration (c. m. c.'s) of aqueous and reversed micelles was carried out. The mechanism of the interaction of TCNQ with ionic and non-ionic detergents was investigated in order to delineate the origin of the production of the dye anion-radical. In several cases, the formation of the latter species can be eliminated, or kept to a minimum, if highly purified detergents and solvents were used. Under these conditions, the neutral TCNQ visible absorption band should be used in the c.m.c. determination. The origin of the formation of the TCNQ anion-radical has been traced to the presence of difficulty removable impurities in the anionic and/or non-ionic surfactants, and to the reaction of the dye with the counter-ion of the positive micelles.