| Abstract
| - This is a study of 10 asymmetric gemini surfactants that self-assemble into vesicles which, inturn, self-assemble into gels. The geminis have the following general structure: long-chain/phosphate/2-carbon spacer/quaternary nitrogen/short-chain. Dynamic light scattering and transmission electronmicroscopy (TEM) demonstrate that in dilute aqueous systems these compounds self-assemble into vesicles.The vesicles are cohesive as proven by cryo-high resolution electron microscopy (cryo-HRSEM) imagesthat reveal a “pearls on a string” morphology. These strings of vesicles create a complex network thatrigidifies the water. The one gemini in the study that does not form a gel is also the only vesicle systemthat, according to cryo-HRSEM and TEM, assembles into clumps rather than chains. It is proposed thatthe vesicles are cohesive owing to protrusion of short chains from the vesicle surfaces, thereby creatinghydrophobic “patches” whose intervesicular overlap supersedes the normal membrane/membrane repulsiveforces. Analogous geminis having two long chains, neither of which are thought capable of departing fromtheir bilayers, also form vesicles, but they are noncohesive (as expected from the model). Rheologicalexperiments carried out on the gels show that gelation is mechanically reversible. Thus, if an applied torquebreaks a string, the string can rapidly mend itself as long as the temperature exceeds its calorimetricallydetermined Tm value. Gel strength, as manifested by the yield stress of the soft material, was shown to beparticularly sensitive to the structure of the gemini. All three individual components of the systems (geminis,vesicles, and gels) have widespread practical applications.
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