C12mimBr Ionic Liquid/SDS Vesicle Formation and Use As Template for the Synthesis of Hollow Silica Spheres

The phase behavior of an aqueous catanionic surfactant system, composed of a long-chain imidazolium ionic liquid 1-dodecyl-3-methylimidazolium bromide (C(12)mimBr) and sodium dodecyl sulfate (SDS), is described. The phase diagram of the catanionic system was determined by electrical conductivity measurements and the formation of vesicles in a birefringent L(alpha) phase characterized by transmission electron microscopy (TEM) and freeze-fracture transmission electron microscopy (FF-TEM). Rheological measurements were used to characterize the macroscopic properties of the birefringent L(alpha) phase. Both electrostatic and hydrophobic interactions contribute to the vesicle formation in the catanionic system. Compared to the DTAB/SDS aqueous solution, differences between the imidazolium and trimethylammonium headgroups geometric packing and charge density induce the different phase behavior in each system. Silica hollow spheres, with diameters 30-60 nm and a wall thickness of 8-10 nm, were prepared by using the vesicles as the templates. The hollow silica spheres were characterized by TEM, scanning electron microscopy (SEM), and nitrogen adsorption-desorption. The results suggest additional application for ionic liquid based vesicles to be used as templates for the synthesis of hollow inorganic materials.