Janus micelles at the air/water interface

Janus micelles-asymmetric star block copolymers resulting from cross-linkin g of the polybutadiene middle blocks of polystyrene-block-polybutadiene-blo ck-poly(methyl methacrylate) triblock copolymersand the corresponding non-c ross-linked ABC triblock copolymer precursors form monolayers on a water su rface. Analysis of the lateral pressure/area isotherms and scanning force m icroscopy images of monolayers spread from dilute chloroform solutions reve al a lateral structure: In monolayers of both polymers, one observes elevat ed nanometer-sized domains separated by flat regions. However, the monolaye rs made from the two copolymers differ in morphology and size of the observ ed domains. Janus micelle monolayers are predominantly composed of arrays o f circular domains with height of 16-18 nm and diameter of 70-80 nm, while the monolayers of the precursor triblock copolymer are mainly composed of s ignificantly smaller elongated domains of approximately 3 nm height, 40 mn width, and nonuniform length. The formation of domains and the shape of the lateral pressure/area isotherms are in accordance with the assumption that the poly(methyl methacrylate) chains spread out on the water surface, whil e the hydrophobic polystyrene and polybutadiene chains dewet from the water surface. Differences in domain morphology are probably due to the differen t chain architectures of the two polymers but may as well be influenced by the preaggregation in the spreading solvent.