The interfacial properties of diblock copolymers are of particular importance to their application as solution-based surfactants. We have studied the ultrathin film or monolayer properties of a series of AB diblock copolymers using Langmuir film balance, Langmuir–Blodgett and microscopy (transmission electron and atomic force techniques). Previous studies have established that AB diblocks spontaneously self-assemble at the air/water interface to yield highly definèd, nanometre-sized aggregates which we refer to as surface micelles. We report two new aspects of 2D self assembly. (i) A highly ordered two-dimensional foam or honeycomb is observed in the Langmuir–Blodgett films of polystyrene-b-poly(sodium acrylate)(PS-b-PANa) and polystrene-b-poly(sodium methacrylate)(PS-b-PMANa) block copolymers. The cell areas of these nanofoams are remarkably small, ranging from 100 to 5000 nm2. (ii) Changes in the morphology of a surface micelle (circle, ribbon, plane) can be effected by adding homoPS to the diblock film. Transitions, paralleling those seen in the melt, occur as the homoPS partitions into the surface micelle.