Study On The Aqueous Two-phase Systems Of Surfactant Mixtures

Six cationic surfactants of quaternary ammonium salt type with different N-alkyl chains and head groups,N-dodecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide,N-dodecyl-N,N-di(2-hydroxyehtyl)-N-methyl ammonium bromide, N-tetradecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide,N-tetradecyl-N, N-di(2-hydroxyehtyl)-N-methyl ammonium bromide,N-cetyl-N-(2-hydroxyethyl)-N, N-dimethyl ammonium bromide and N-cetyl-N,N-di(2-hydroxyehtyl)-N-methyl ammonium bromide,have been synthesized and characterized by using IR,NMR and elemental analysis(EA).The phase diagrams of these cationic surfactants or N-dodecyl-N,N,N-trimethylammonium bromide(DTAB) and N-cetyl-N,N,N-trimethyl ammonium bromide(CTAB)mixed with sodium dodecyl sulfate(SDS) have been investigated.The influences of the length of carbon chain of cationic surfactants,the number of hydrophilic groups and the additive salts on the aqueous two-phase systems(ATPS) have been discussed.Furthermore,the phase inversion phenomena in N-dodecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide and N-dodecyl-N, N-di(2-hydroxyehtyl)-N-methyl ammonium bromide mixed with SDS were observed,respectively.The effects of temperature and the total concentration of surfactants on the ATPS have also been investigated by the UV-Vis spectroscopy.From the phase diagrams of the aqueous cationic and anionic surfactant mixtures, it can be observed that the values of critical micelle concentration of cationic surfactants reduce and the formation of micelles becomes easier.With the increase of chain length or the number of hydrophilic group of cationic surfactants,it also makes the formation of ATPS require more amounts of cationic surfactants.The locations of the ATPS with excess cationic surfactants shift to the higher content of cationic surfactant.The locations of the ATPS with excess anionic surfactants show almost unchanged and it indicated that the changes of cationic surfactants have little impact on the regions ATPS with excess anionic surfactants.From the results of the influences of salts on the ATPS,it can be seen that with the increase of ion radius,the electrostatic attraction and electrostatic repulsion are weakened and the widths of ATPS regions enlarged.The movement velocities of anionic ions of the added salts minimize and the ions can be easily absorbed.It requires more amounts of surfactant ions to balance the ions of the added salt and the ATPSs shift to the higher content of excess surfactant.From the observations of the phase inversion phenomena in both N-dodecyl-N-(2-hydroxyethyl)-N,N-dimethyl ammonium bromide and N-dodecyl-N, N-di(2-hydroxyehtyl)-N-methyl ammonium bromide mixed with SDS,with the temperature rising,the surfactant micelles change from a densed aggregation state to that with little micelles.The structure of the phase ATPS becomes loose and the phase inversion appeares.The increase of total concentration of surfactant makes an greater impact on the change of the micelle state of surfactants and the temperature of the phase inversion decreases.