COALESCENCE OF AIR BUBBLES IN AQUEOUS SOLUTIONS OF IONIC SURFACTANTS IN PRESENCE OF INORGANIC SALT

This work presents a study on adsorption characteristics of two anionic (SDS and SDBS) and one cationic (CTAB) surfactants at air–water interface in presence of inorganic salt (NaCl). Coalescence of air bubbles in these solutions is studied by measuring the rest time of air bubbles at flat air–water interface. Significant effects of salt on surface tension and coalescence are observed. Surface tension is reduced in presence of salt and rest time is increased. The stochastic model developed earlier by Ghosh and Juvekar (2002; Chem Eng Res Des, 80: 715–728) fits the rest time distributions very well. A comparison of seven film-drainage models with the mean values of these distributions is presented. It is observed that these models, within the limitations of the simplifying assumptions behind their development, can not predict the values of rest time accurately.