Langmuir, Vol.24, No.21, 12340-12346, 2008
Toroid Morphology by ABC-Type Amphiphilic Rod-Coil Molecules at the Air-Water Interface
The interfacial and aggregation behavior of the ABC-type amphiphilic molecules with semirigid dumbbell-shaped core and variable length of hydrophobic branched tails (R=(CH2)(n)CH3 with n = 5 (1), 9 (2), 13 (3)) were investigated. At low surface pressure, smooth, uniform monolayers were formed at the air-water interface by molecules I and 2, whereas for molecule 3 unique 2D toroid aggregates have been formed. These aggregates were relatively stable within a range of surface pressure and spreading solution concentration. Upon compression, the 2D toroid aggregates collapsed into large, round 3D aggregates. Finally, the choice of spreading solvent has a great influence on aggregation formation into 2D or 3D micelles as a result of the variable balance of the hydrophobic interactions of branched tails and the pi-pi stacking interaction between aromatic segments.