“…Urea increases the cmc of amphiphiles, and the effects are generally greater on cationic than on anionic amphiphiles, but they are also observed with nonionic amphiphiles, e.g., C 12 E 6 8 and zwitterionic amphiphiles 7b. Added urea increases the dissociation degree (α) of ionic surfactants, and this increase is accompanied by a loss of counterion selectivity by the micellar interface in cationic, cetyltrimethylammonium halide (CTAX, X = Cl, Br), anionic, methyl dodecyl sulfate (MeDS, Me = Tl, Na), zwitterionic hexadecyldimethylammoniumpropane sulfonate (HPS) micelles, and also cationic vesicles. , Added urea, as expected, also decreases micellar aggregation numbers . The effect of added urea on ionic micelles is consistent with urea-enhanced stabilization of free ions (hindering of ion pair formation).…”