Higher order self-assembly of mixed surfactant systems

Surfactants self-assemble into liquid crystal phases, e.g., hexagonal and lamellar phases, in aqueous solution. Phase formation depends on the type and concentration of surfactant and relative ratios of different species. The thrust of this research has been to exploit these variables to increase the versatility of the systems (by higher order self-assembly) for direct application. We have developed a novel encapsulated vesicular aggregate by self-assembly that can potentially function as a drug delivery system. Freeze-fracture (FF-TEM) and cryo-transmission electron microscopy were used for characterization.;Biological cells divide functions between a variety of membranes; outer membranes regulate permeation, diffusion, and recognition while internal membranes encapsulate necessary solutes and perform specific processes. To mimic this compartmentalization, self-assembled biomimetic structures such as vesicles are under intense scrutiny. Vesicle bilayers can control permeation of molecules and create an interior environment significantly different than the surrounding. We have developed a model cell, or "vesosome," by progressive self-assembly of molecules and molecular aggregates. Vesosomes are made by encapsulating tethered vesicle aggregates with an outer membrane. Loading vesicle bilayers with a few ligand molecules enables vesicles to self-assemble into tethered vesicle aggregates upon addition of receptor molecules, which bind the ligand and crosslink the vesicles. Aggregate size is controlled by manipulating the ionic strength of the solution (charged vesicles) or ligand-receptor ratio (uncharged vesicles), or by mechanical extrusion. Tasks can be divided among a variety of membrane enclosures. Interior vesicles encapsulate solutes while outer membranes regulate permeation or recognition; this "division of labor" resembles that of biological cells.;Nanostructured zeolites are prevalent throughout chemistry as catalysts and sorption media. Our studies indicate nanophase formation is driven by self-assembly of silicate and cationic surfactant species. Silicate polyanions assemble several surfactant cations into a neutral complex resembling a multi-tailed surfactant able to form hexagonal and rippled lamellar phases. FF-TEM indicated (1) the ratio of silicate to surfactant controlled the final phase morphology and (2) the lamellar ripple phase wavelength and bilayer spacing and hexagonal rod spacing are set by the length of surfactant molecules.