Simultaneous Effects of Ionic Surfactant and Salt on Drop- Interface Coalescence

In this research, effect of simultaneous presence of ionic surfactant and salt on drop- interface coalescence time in the system of water (d) / toluene(c) was studied. Sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) as anionic and cationic surfactants were used. Sodium chloride (NaCl) and magnesium sulfate were used as salts. At first the system of water and toluene were examined separately with SDS+NaCl, SDS+MgSO4, CTAB+NaCl and CTAB+MgSO4. It was observed that drop size increased for system with SDS+NaCl and SDS+MgSO4 in contrary to system with CTAB+NaCl and CTAB+MgSO4 with respect to pure system of water and toluene. Partial coalescencetimes were increased for all system. In overall, this increase of coalescence time was more obvious for system with CTAB which was accompanied with reduction in drop size. For the case of mixed surfactants with single salt it was observed that partial coalescence was suppressed in system with (SDS+CTAB)+MgSO4 compared to the case of NaCl. On the other hand, drop size was decreased and total coalescence was time increased. It may be due to difference between anions and cations of two salts. For the case of both mixed surfactants and salts, drop size and coalescence time was decreased.