Aggregation behavior of betaine-amphiphiles in the presence of polyvinylpyrrolidone

The aggregation behavior of zwitterionic surfactant dodecylbetaine (C12BE) with and without polyvinylpyrrolidone (PVP) has been investigated by means of surface tension and steady-state fluorescence techniques. It shows that addition of PVP results in a decrease in the aggregation number of C12BE micelle and “hydrophobic index” (I1/I3) of the probe (pyrene and pyrene-1-carboxaldehyde). PVP molecules are responsible for the phenomena: they bind to the surface of the micelle and prevent the rapid exchange of amphiphiles between micelles and water phase. There are two transition points in the plot of surface tension vs. concentration of C12BE in the presence of PVP. The results indicate that the association takes place between PVP and C12BE when the C12BE concentration is above a critical aggregation concentration (CAC).