The difficulty of mixing chemically incompatible substances-in particular macromolecules and colloidal particles-is a canonical problem limiting advances in fields ranging from health care to materials engineering(1-4). Although the self-assembly of chemically different moieties has been demonstrated in coordination complexes, supramolecular structures, and colloidal lattices among other systems(5-18), the mechanisms of mixing largely rely on specific interfacing of chemically, physically or geometrically complementary objects. Here, by taking advantage of the steric repulsion between brush-like polymers tethered to surface-active species, we obtained long-range arrays of perfectly mixed macromolecules with a variety of polymer architectures and a wide range of chemistries without the need of encoding specific complementarity. The net repulsion arises from the significant increase in the conformational entropy of the brush-like polymers with increasing distance between adjacent macromolecules at fluid interfaces. This entropic-templating assembly strategy enables long-range patterning of thin films on sub-100 nm length scales.