1. Dynamic Tension Reduction for Adsorption from a Micellar Solution
The Direct Adsorption of Micelles to a Clean Air/Water Interface
Charles Maldarelli, Department of Chemical Engineering, City College of New York
We present evidence that surfactant aggregates can adsorb directly onto a clean air/water interface, and that this adsorption can explain the ultrafast reductions in tension which are observed when surfactant adsorbs from a micellar solution to a clean interface. A hydrophobic dye, Nile Red, is used to track the surfactant transport and the surfactant CH3(CH2)13(OCH2CH2)6OH which forms approximately spherical micelles is used.
In bulk micellar solutions with dissolved Nile red, the dye partitions into the micelle interior. Measurements of the dynamic tension reduction for adsorption to a clean interface from these solutions show a large initial decrease in tension relative to the tension reduction fpr micellar solutions without Nile Red. Micelles directly adsorbing to the interface release Nile Red which inserts into the monolayer, increases the surface pressure and accounts for this large decrease in tension. At later times, the dye desorbs off of the surface back into the micelles and the tension rises before decreasing to equilibrium.
Dynamic Tension Reduction for Adsorption from a Micellar Solution
Adsorption from micellar solution without dye
Tension (dyne/cm)
Desorption of Nile Red
Adsorption from micellar solution with dye