Effect of Antifoaming Agents on the Micellar Stability and Foamability of Sodium Dodecyl Sulfate Solutions

The effect of antifoaming agents on the foamability of sodium dodecyl sulfate (SDS) solutions was investigated and correlated with their effect on the micellar relaxation time τ2. The slow micellar relaxation time τ2 of SDS micelles, which is directly related to micellar stability, was determined by the pressure-jump method in the presence of the antifoaming agents 2-ethylhexanol (EH), tributyl phosphate (TBP), and tetrabutylammonium chloride (TBAC). Pressure-jump studies show an increase in τ2 up to a critical concentration of the antifoaming agent. Further addition of antifoaming agent results in a decrease in τ2. Such behavior has been observed for all three antifoaming additives. The increase in τ2 is attributed to the stabilization of SDS micelles by the additives, which essentially minimizes the repulsion between headgroups of SDS molecules at the micellar surface or at the interface. The antifoaming efficiency of EH, TBP, and TBAC was tested by simply generating the foam by the shaking method. The results of antifoaming experiments showed a strong correlation with the micellar relaxation time τ2.