|153. Xu, H.; Erhardt, R.; Abetz, V.; Müller, A.H.E.; Goedel, W.: Janus micelles at the air/water interface, Langmuir 17, 6787 (2001)|
Janus micelles-asymmetric star block copolymers resulting from cross-linking of the polybutadiene middle blocks of polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymers-and the corresponding non-cross-linked ABC triblock copolymer precursors form monolayers on a water surface. Analysis of the lateral pressure/area isotherms and scanning force microscopy images of monolayers spread from dilute chloroform solutions reveal a lateral structure: In monolayers of both polymers, one observes elevated nanometer-sized domains separated by flat regions. However, the monolayers made from the two copolymers differ in morphology and size of the observed domains. Janus micelle monolayers are predominantly composed of arrays of 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 significantly smaller elongated domains of approximately 3 nm height, 40 nm 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, while the hydrophobic polystyrene and polybutadiene chains dewet from the water surface. Differences in domain morphology are probably due to the different chain architectures of the two polymers but may as well be influenced by the preaggregation in the spreading solvent.