More than a quarter of a century ago, Bangham et al. 1 showed that phospholipids dispersed in water formed closed, multibilayer aggregates capable of separating an internal compartment from the bulk solution. As bilayers are relatively impermeable to many ions and nonelectrolytes, it became simple to create small domains of different composition within such a bilayer aggregate or li-posome and mimic many of the properties that nature has designed into cells and organelles. 2'5 As a result, there has been greateffort devoted to using liposomes as model membranes2 and, more re-cently, as drug delivery systems3 and microreactors for specialized chemistry. 4 Vesicles, 6 which are single-bilayer closed shells that encapsulate an aqueous interior, have become the preferred structure for use in most applications. 2, 3, 7 While vesicles often form spontaneously in vivo, they have only rarely been observed to form in vitro without the input of considerable mechanical energy or elaborate chemical treatments. 7 Hence, a variety of methods have been developed to create unilamellar vesicles, ie single-bilayer compartments, with sizes ranging from about 20 nm to more than 20 pm. 6'1