Dynamics of surfactant-rich phase separation from solutions containing non-ionic and zwitterionic surfactants

Cloud point technique was used to study the recovery of crystal violet from surfactant aqueous solutions containing oxyethylated methyl dodecanoate and cocamidopropyl betaine. The dynamics of the surfactant-rich phase separation was also studied. It was found that the separations of the surfactant-rich phases were not complete. The aqueous phases still contained globules of the surfactant-rich phases. The diameter of the surfactant globules in the bulk of the aqueous phase varied up to 700 μm. Formation of “layered” globules, composed of small globules deposited on large ones was also observed. The separation of the surfactant-rich phase depended upon the content of betaine and improved with an increased content of zwitterionic surfactant. The time needed to form large globules decreased significantly when betaine was added as the second surfactant. The interface was not stable and could be easily destroyed. Addition of betaine caused a significant (4 to 5-fold) reduction in the heterogeneity of the aqueous phase. The measurement of the greyness and image processing was less sensitive than spectrophotometric determination. Moreover, the measurement of phase greyness caused an overestimation of the separation and predicted too high recoveries of the dye. The addition of betaine increased the transfer of the dye to the surfactant-rich phase. Under the considered conditions, about 90% of the dye could be recovered from the aqueous solution.