Spreading amphiphilic diblock copolymers on a two-dimensional liquid interface has been observed to produce nanoscale features via self-assembly. Here, we develop a model that incorporates the effects of polymer entanglement and surface diffusion in polymer blends to quantitatively predict the size of experimentally observed structures. Simulations show that different polymers in the blend cooperate to self-assemble into nanoscale features of varying sizes. Characteristic nanoscopic dimensions can be tuned by adjusting two easily controllable macroscopic quantities: the blend composition and the initial surface concentration. Theoretical predictions are in agreement with experimentally measured feature dimensions. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 136-143, 2011