  The organization of nano-particles inside grafted polymer layers is governed
by the interplay of polymer-induced entropic interactions and the action of
externally applied fields. Earlier work had shown that strong external forces
can drive the formation of colloidal structures in polymer brushes. Here we
show that external fields are not essential to obtain such colloidal patterns:
we report Monte Carlo and Molecular dynamics simulations that demonstrate that
ordered structures can be achieved by compressing a `sandwich' of two grafted
polymer layers, or by squeezing a coated nanotube, with nano-particles in
between. We show that the pattern formation can be efficiently controlled by
the applied pressure, while the characteristic length--scale, i.e. the typical
width of the patterns, is sensitive to the length of the polymers. Based on the
results of the simulations, we derive an approximate equation of state for
nano-sandwiches.
