| Details: |
Oppositely charged surfactant poly-electrolyte aqueous solutions exhibit spontaneous complex formation. These solutions show lowering of surface tension at low surfactant concentrations, even for non-surface active poly-electrolytes. There is bulk aggregate formation at Critical Aggregation Concentration (CAC) and micelle formation at the Critical Micellar Concentration (CMC) of the surfactant.
We studied the surface rheology of aqueous solutions of anionic poly-electrolytes (poly-acrylamide sulfonate (PAMPS) with a flexible backbone and xanthan with a rigid backbone) and a cationic surfactant dodecyl trimethyl ammonium bromide (DTAB). Surface elasticity and viscosity of the solutions exhibit a maximum at surfactant concentrations lower than DTAB solutions. Foaming and foam-stability are expected to depend on these coefficients. However, the solutions with xanthan show very poor foaming compared to those with PAMPS. This might depend on the adsorption kinetics of the solutions. At small compression expansion cycles, layers with both polymers appear insoluble. However, for large compression, the layers with xanthan remain insoluble while those with PAMPS become partially soluble. Does this difference lead to the large differences in foaming of the polymers at small surfactant concentrations?
These properties are being used to form microcapsules of different active materials. The uses of these microcapsules are many and varied, from medicines to perfume advertisements.
The presentation will end with a small introduction of my recent work on biological surfactants, which is in a very nascent stage. |