Ordered Vesicles at the Silicon-Water Interface
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The purpose of this article is to examine the stable, ordered near-surface phase of dichain cationic surfactants, which has been recently reported, and to determine whether this phase can be unambiguously assigned as a vesicular phase. Such a phase would be a remarkable example of an aligned near-surface phase, extending hundreds of nanometers into solution, which exists in equilibrium with the bulk aqueous phase, and may explain the superspreading characteristics of these surfactants, providing a reservoir of surfactant near the surface.
These surfactants are also widely used as fabric softeners and are the subjects of keen interest for pharmaceutical applications. They have been shown to form vesicles in dilute solutions. This is particularly significant as it extends the range of standard vesicle-forming compounds beyond phospholipids, long the gold standard of the field. Furthermore, the vesicles formed by these cationic surfactants are generally smaller than those formed from phospholipids, ranging from as small as 30 nm. These cationic vesicles are the subjects of biomedical research, where they are highly regarded as effective gene transfer agents in gene therapy. Part of the success of this technique depends on the interaction between the cationic vesicle–DNA complex and the target cell membrane, which enables the DNA to cross undegraded, and thus it is of interest to know how the surfactant vesicles behave near a surface.