Control of Nanoscale Structures of Amphiphilic Self-Assembly by Physical Factors

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(1) Reversible micelle - vesicle transition by changing pH.On protonation of oleyldimethylamine oxides to the degree of 0.5 (the half protonated state), vesicles are formed spontaneously from long fibrous micelles and this change occurs reversibly by changing the pH of the medium. The viscoelastic behavior changes from the Maxwell type characteristic to entangled network of long fibrous micelles to the gel like behavior. The conversion is rather fast and it seems to take place within 2 hours. It takes much longer time (about 14 days), however, for the viscoelastic properties of the vesicle suspension to recover to approximately the same level. The conversion most likely proceeds not in a transition like but in a continuous way.(2) Change of the structures of the films of tetradecyldimethylamine oxides (C14DMAO) at solid/solution interface.2-1. Mica/solution interfaces, hemimicelles or cylinders are formed at nonionic state while bilayers are formed at half- and full-protonated states.2-2. Graphite/solution interfaces. Hemimicelles are formed irrespective of the degrees of protonation.(3) Lamella and vesicle formation of C14DMAO by naphthalene sulfonate (NphS) counterions. This result is not trivial because most surfactant cations with a C16 tail form long fibrous micelles (the packing parameter p close to 0.5). In this study the surfactant cations with a C14 tail form lamella (p close to unity).3-1. The fttll-protonated species form lamella phase on addition of NphS and this separated lamella phase can be dispersed as lamella drops or onions at high temperatures.3-2. The half-protonated species form vesicles on addition of NphS and their charges are reversed as the binding of NphS increases.