  Designable media can control properties of nanocomposite materials by
spatially organizing nanoparticles. Here we theoretically study particle
organization by ultrathin polymer films of grafted chains (``brushes'').
Polymer-soluble nanoparticles smaller than a brush-determined threshold
disperse in the film to a depth scaling inversely with particle volume. In the
polymer-insoluble case, aggregation is directed: provided particles are
non-wetting at the film surface, the brush stabilizes the dispersion and
selects its final morphology of giant elongated aggregates with a
brush-selected width.
