AFM Study On Interfacial Aggregates Of Bolaform Amphiphiles

Surfactants may form micellar structures in aqueous solution, and uponadsorption at liquid/solid interface, they can form surface micelles. However,these surface micelles are not stable enough against drying process. In order toobtain stable surface micelles, in this thesis, we introduced rigid mesogenic groupand flexible spacers into bolaform amphiphles and investigated their surfaceaggregation behaviors by atomic force microscopy (AFM). we investigated factors to govern the aggregation behaviors of bolaformamphiphiles bearing azobenzene groups at the liquid/solid interface systematically.The bolaform amphiphile with shorter spacers presents diversified aggregatemorphologies at the solution/solid interface with changing of solutionconcentration: it forms loosely packed wormlike surface micelles at lowerconcentration; and then with the increase of the solution concentration, thewormlike surface micelles gradually convert into rodlike micelles in short-rangeorder and further into globular aggregates. Keeping the same bolaform amphiphileat a constant concentration(1.0×10-4 mol/L), sodium salicylate (NaSal) withdifferent concentration was added to study the effect of NaSal on the formation ofsurface micelles at the solution/mica interface. AFM observations show that the 22004 吉林大学硕士学位论文 林奥雷interfacial aggregates have obviously been changed by addition of NaSal. It wasfound that when a proper concentration of NaSal was added, the bolaformamphiphile with short spacer can form ordered stripe structure which is stableenough against drying. While, the bolaform amphiphile with longer spacers canform straight stripe structures at the interface, and they are stable against dryingprocess even without addition of electrolytes. Our research indicates that themorphology of interfacial aggregates can be adjusted by changing the chemicalstructure of bolaform amphiphiles as well as environmental conditions.Interestingly, surface micelles which are stable against drying process can beobtained through enhancing intermolecular interaction, and this may provide anew route for fabricating surface nanopatterning materials..