Directing Silver Nanoparticles into Colloid-Surfactant Lyotropic Lamellar Systems

We introduce hybrid systems composed of silver nanoparticles and ordered lamellar phases of the water/ SDS/hexanol/dodecane system. Silver colloids are selectively directed either to the aqueous layer or to the organic layer for the same basic system and are confined within the lamellae. In the case of hydrophobic particles, some penetration into the hydrophobic region of the surfactant layer is noted. The composites are investigated by SAXS and UV-visible absorption spectroscopy. The evolution of the periodicity was studied in detail, varying the different parameters of the phase diagram. It was found that the incorporation of silver colloids does not noticeably disturb the basic smectic structure, except that the interlamellar spacing changes. With the colloid in the aqueous region or in the organic region, the stability region of the Lα phase is modified only slightly compared to that when the colloids are absent. The formation and the stability of the hybrid systems are explained by a delicate balance of electrostatic repulsive, VDW attractive, and Helfrich long-range repulsive forces.