Solubilization Enhancing Effect of A-B-Type Silicone Surfactants in Microemulsions

We report a solubilization enhancing effect of A-B-type silicone surfactants in microemulsions. The effect of added long-chain silicone surfactants, Si25C3EO51.6 (extended length≈21.8 nm) and Si14C3EO15.8 (extended length≈8.5 nm) on the solubilization capacity of C12EO5 (extended length≈3 nm)/water/dodecane microemulsion was investigated at the hydrophile-lipophile balance temperature at which a microemulsion (surfactant) phase containing equal weights of oil and water touches the three-phase body. The addition of silicone surfactants exhibits an enormous increase of the swelling of the middle phase primarily with an associated increase in the structural length scale of the microemulsion. The solubilization power increases with increasing x2 (mole fraction of silicone surfactants to the total surfactant) and going through a maximum it decreases, since a lamellar liquid crystal introduces in the multiphase region at low surfactant concentrations. The solubilization capacity reaches at the maximum to an almost equal level for different x2 values, 0.02 for Si25C3EO51.6 and 0.09 for Si14C3EO15.8. The solubilization power of the lamellar phase shows a similar trend with lower magnitude.